// =======================================================================
// Notes Application - Reader & Bookshelf Module (Native ES Module)
// =======================================================================

import { api } from './api.js';
import { escapeHtml, escapeRegex, slugify, showToast, playAudio } from './ui.js';
import { getAllCards, fetchCards } from './dictionary.js';

// Reader State & Appearance Settings
const DEFAULT_READER_SETTINGS = {
    fontSize: 18,
    fontFamily: 'serif',
    lineHeight: 1.65,
    marginWidth: 'normal',
    theme: 'dark',
    textAlign: 'left',
    flowMode: 'chapters',      // 'chapters' | 'continuous'
    autoLoadNext: true         // boolean: seamlessly load next chapter on scroll
};

let readerSettings = { ...DEFAULT_READER_SETTINGS };
let currentBook = null;
let currentChapterIndex = 0;
const loadedChaptersSet = new Set();
let isAppendingChapter = false;
let isHighlightEnabled = false;
let popupCurrentData = null;
let readerScrollSaveTimer = null;
let popupScrollRaf = null;

let isZenMode = false;
let zenHudIdleTimer = null;

export function getIsZenMode() {
    return isZenMode;
}

export function getCurrentBook() {
    return currentBook;
}

export function getCurrentChapterIndex() {
    return currentChapterIndex;
}

// -----------------------------------------------------------------------
// Bookshelf Actions & Rendering
// -----------------------------------------------------------------------
function createBookCard(b) {
    const card = document.createElement('div');
    const isRfc = (b.source_type === 'rfc');
    const isWiki = (b.source_type === 'wikipedia');
    if (isWiki) card.className = 'book-card wiki-card';
    else if (isRfc) card.className = 'book-card rfc-card';
    else card.className = 'book-card';

    const totalCh = Math.max(1, b.chapters_count || 1);
    const chIndex = Math.max(0, Math.min(totalCh - 1, b.current_chapter || 0));
    const pos = (typeof b.current_position === 'number') ? Math.max(0, Math.min(1.0, b.current_position)) : 0.0;

    const progressFraction = (chIndex + pos) / totalCh;
    const totalPct = Math.min(100, Math.max(0, Math.round(progressFraction * 100)));
    const chPct = Math.min(100, Math.max(0, Math.round(pos * 100)));

    const progressLabels = totalCh === 1
        ? `<span>1 глава • ${totalPct}%</span><span>${totalPct}%</span>`
        : `<span>Глава ${chIndex + 1} из ${totalCh} (${chPct}%)</span><span>${totalPct}%</span>`;

    let coverHtml = '';
    if (b.cover_url) {
        coverHtml = `<div class="book-cover-img-wrap"><img src="${escapeHtml(b.cover_url)}" class="book-cover-img" alt="Cover" loading="lazy" onerror="this.parentElement.innerHTML='<div class=\\\'book-cover-icon ${isWiki ? 'wiki-cover-icon' : (isRfc ? 'rfc-cover-icon' : '')}\\\'>${isWiki ? '🌐' : (isRfc ? '📜' : '📄')}</div>';"/></div>`;
    } else {
        let coverIcon = '📄';
        if (b.source_type === 'epub') coverIcon = '📕';
        else if (b.source_type === 'pdf') coverIcon = '📑';
        else if (isRfc) coverIcon = '📜';
        else if (isWiki) coverIcon = '🌐';
        const coverIconClass = isWiki ? 'wiki-cover-icon' : (isRfc ? 'rfc-cover-icon' : '');
        coverHtml = `<div class="book-cover-icon ${coverIconClass}">${coverIcon}</div>`;
    }

    let badgeClass = 'badge-format';
    if (isWiki) badgeClass = 'badge-format badge-wiki';
    else if (isRfc) badgeClass = 'badge-format badge-rfc';

    const readMinutes = Math.max(1, Math.round((b.total_words || 800) / 180));
    const timeBadge = (b.total_words && b.total_words > 0)
        ? `<span class="badge-time" title="Примерное время чтения: ~${readMinutes} минут">⏱️ ~${readMinutes} мин</span>`
        : '';
    const progressFillClass = isWiki ? 'wiki-progress-fill' : (isRfc ? 'rfc-progress-fill' : '');

    const authorDisplay = b.author || (isWiki ? 'Wikipedia' : (isRfc ? 'IETF' : 'Неизвестный автор'));
    const sourceLabel = isWiki ? 'WIKIPEDIA' : (isRfc ? 'RFC' : (b.source_type || 'text').toUpperCase());

    card.innerHTML = `
        <div>
            <div class="book-card-top">
                ${coverHtml}
                <div class="book-card-info">
                    <h4 class="book-card-title" title="${escapeHtml(b.title)}">${escapeHtml(b.title)}</h4>
                    <p class="book-card-author">${escapeHtml(authorDisplay)}</p>
                    <div class="book-card-badges">
                        <span class="${badgeClass}">${escapeHtml(sourceLabel)}</span>
                        ${timeBadge}
                        <span class="badge-words">${b.total_words ? b.total_words.toLocaleString() + ' слов' : ''}</span>
                    </div>
                </div>
            </div>
            <div class="book-progress-wrap">
                <div class="book-progress-labels">
                    ${progressLabels}
                </div>
                <div class="book-progress-bar-bg">
                    <div class="book-progress-bar-fill ${progressFillClass}" style="width: ${totalPct}%"></div>
                </div>
            </div>
        </div>
        <div class="book-card-actions">
            <button class="btn btn-primary btn-sm read-book-btn" data-id="${b.id}">📖 Читать</button>
            <button class="btn btn-outline btn-xs train-book-btn" data-title="${escapeHtml(b.title)}" title="Тренировать слова из этой книги">🎓 Слова книги</button>
            <button class="icon-btn delete-book-btn" data-id="${b.id}" title="Удалить из библиотеки">🗑️</button>
        </div>
    `;

    card.querySelector('.read-book-btn').addEventListener('click', () => {
        window.location.hash = `#reader/book/${b.id}`;
    });
    card.querySelector('.train-book-btn').addEventListener('click', () => {
        const bookTag = slugify(b.title);
        window.location.hash = `#srs/${encodeURIComponent(bookTag)}`;
    });
    card.querySelector('.delete-book-btn').addEventListener('click', async () => {
        const typeName = isWiki ? 'статью Википедии' : (isRfc ? 'спецификацию' : 'книгу');
        if (confirm(`Удалить ${typeName} "${b.title}" из библиотеки?`)) {
            await api.books.delete(b.id);
            loadBookshelf();
        }
    });

    return card;
}

export async function loadBookshelf() {
    if (isZenMode) toggleZenMode(false);
    const bookshelfContainer = document.getElementById('bookshelf-container');
    const readerInterface = document.getElementById('reader-interface');
    const bookshelfGrid = document.getElementById('bookshelf-grid');
    const bookshelfEmpty = document.getElementById('bookshelf-empty');
    const rfcGrid = document.getElementById('rfc-grid');
    const rfcEmptyState = document.getElementById('rfc-empty-state');
    const wikiGrid = document.getElementById('wiki-grid');
    const wikiEmptyState = document.getElementById('wiki-empty-state');

    if (!bookshelfContainer) return;
    if (!window.location.hash.includes('/book/')) {
        bookshelfContainer.classList.remove('hidden');
        if (readerInterface) readerInterface.classList.add('hidden');
    }
    if (bookshelfGrid) bookshelfGrid.innerHTML = '';
    if (rfcGrid) rfcGrid.innerHTML = '';
    if (wikiGrid) wikiGrid.innerHTML = '';
    if (bookshelfEmpty) bookshelfEmpty.classList.add('hidden');
    if (rfcEmptyState) rfcEmptyState.classList.add('hidden');
    if (wikiEmptyState) wikiEmptyState.classList.add('hidden');

    try {
        const books = await api.books.getAll();
        renderBookshelf(books || []);
    } catch (e) {
        console.error('Error loading bookshelf:', e);
    }
}

export function renderBookshelf(books) {
    const bookshelfGrid = document.getElementById('bookshelf-grid');
    const bookshelfEmpty = document.getElementById('bookshelf-empty');
    const rfcGrid = document.getElementById('rfc-grid');
    const rfcEmptyState = document.getElementById('rfc-empty-state');
    const wikiGrid = document.getElementById('wiki-grid');
    const wikiEmptyState = document.getElementById('wiki-empty-state');

    if (bookshelfGrid) bookshelfGrid.innerHTML = '';
    if (rfcGrid) rfcGrid.innerHTML = '';
    if (wikiGrid) wikiGrid.innerHTML = '';

    const generalBooks = (books || []).filter(b => b.source_type !== 'rfc' && b.source_type !== 'wikipedia');
    const rfcBooks = (books || []).filter(b => b.source_type === 'rfc');
    const wikiBooks = (books || []).filter(b => b.source_type === 'wikipedia');

    if (bookshelfEmpty) {
        bookshelfEmpty.classList.toggle('hidden', generalBooks.length > 0);
    }
    if (bookshelfGrid) {
        generalBooks.forEach(b => {
            bookshelfGrid.appendChild(createBookCard(b));
        });
    }

    if (wikiEmptyState) {
        wikiEmptyState.classList.toggle('hidden', wikiBooks.length > 0);
    }
    if (wikiGrid) {
        wikiBooks.forEach(b => {
            wikiGrid.appendChild(createBookCard(b));
        });
    }

    if (rfcEmptyState) {
        rfcEmptyState.classList.toggle('hidden', rfcBooks.length > 0);
    }
    if (rfcGrid) {
        rfcBooks.forEach(b => {
            rfcGrid.appendChild(createBookCard(b));
        });
    }
}

// -----------------------------------------------------------------------
// Open Book & Render Chapters
// -----------------------------------------------------------------------
export async function openBook(bookId, specificChapterIdx = null, updateHash = true) {
    if (!bookId) return;

    const readerView = document.getElementById('reader-view');
    const dictionaryView = document.getElementById('dictionary-view');
    const srsView = document.getElementById('srs-view');
    const bookshelfContainer = document.getElementById('bookshelf-container');
    const readerInterface = document.getElementById('reader-interface');
    const readerBookTitle = document.getElementById('reader-book-title');
    const readerBookAuthor = document.getElementById('reader-book-author');
    const readerChapterSelect = document.getElementById('reader-chapter-select');
    const readerPrevChBtn = document.getElementById('reader-prev-ch-btn');
    const readerNextChBtn = document.getElementById('reader-next-ch-btn');
    const readerContentBody = document.getElementById('reader-content-body');

    if (readerView) readerView.classList.remove('hidden');
    if (dictionaryView) dictionaryView.classList.add('hidden');
    if (srsView) srsView.classList.add('hidden');
    if (bookshelfContainer) bookshelfContainer.classList.add('hidden');
    if (readerInterface) readerInterface.classList.remove('hidden');

    // Update mobile navigation tabs
    const navItems = document.querySelectorAll('.mobile-tab-btn');
    navItems.forEach(btn => {
        btn.classList.toggle('active', btn.dataset.tab === 'reader');
    });

    if (currentBook && currentBook.id === bookId) {
        if (specificChapterIdx !== null && specificChapterIdx !== undefined && !isNaN(specificChapterIdx)) {
            if (specificChapterIdx !== currentChapterIndex) {
                currentChapterIndex = specificChapterIdx;
                if (readerChapterSelect) readerChapterSelect.value = currentChapterIndex;
                updateChapterSelectIcons();
                if (readerPrevChBtn) readerPrevChBtn.disabled = currentChapterIndex <= 0;
                if (readerNextChBtn) readerNextChBtn.disabled = currentChapterIndex >= currentBook.chapters.length - 1;

                if (readerSettings.flowMode === 'continuous') {
                    const target = document.getElementById(`chapter-anchor-${specificChapterIdx}`)
                                   || (readerContentBody && readerContentBody.querySelector(`[data-chapter-idx="${specificChapterIdx}"]`));
                    if (target) {
                        scrollToElement(target, true);
                    } else {
                        renderContinuousBook(specificChapterIdx);
                    }
                } else {
                    renderChapter(specificChapterIdx, null, null, null);
                }
            }
        }
        if (updateHash) {
            const desiredHash = `#reader/book/${bookId}/ch/${currentChapterIndex}`;
            if (window.location.hash !== desiredHash) {
                history.replaceState(null, '', desiredHash);
            }
        }
        return;
    }

    try {
        if (readerBookTitle) readerBookTitle.textContent = 'Загрузка книги...';
        const bookData = await api.books.get(bookId);
        currentBook = bookData;

        // Load saved reading position from localStorage or server
        let targetChapter = currentBook.current_chapter || 0;
        let targetScrollTop = null;
        let targetFraction = currentBook.current_position || 0;
        let targetAnchorIdx = null;

        try {
            const raw = localStorage.getItem(`notes_book_${bookId}_pos`);
            if (raw) {
                const parsed = JSON.parse(raw);
                if (parsed && typeof parsed.chapter === 'number') {
                    targetChapter = parsed.chapter;
                    targetScrollTop = parsed.scrollTop;
                    targetFraction = parsed.fraction;
                    targetAnchorIdx = parsed.anchorIdx;
                }
            }
        } catch (e) {}

        if (specificChapterIdx !== null && specificChapterIdx !== undefined && !isNaN(specificChapterIdx)) {
            targetChapter = specificChapterIdx;
            if (specificChapterIdx !== (currentBook.current_chapter || 0)) {
                targetScrollTop = 0;
                targetFraction = 0;
                targetAnchorIdx = 0;
            }
        }

        currentChapterIndex = Math.max(0, Math.min(targetChapter, (currentBook.chapters ? currentBook.chapters.length - 1 : 0)));

        if (readerBookTitle) readerBookTitle.textContent = currentBook.title;
        if (readerBookAuthor) readerBookAuthor.textContent = currentBook.author || '';

        // Populate chapter selector with visual status markers
        if (readerChapterSelect) {
            readerChapterSelect.innerHTML = '';
            const chapters = currentBook.chapters || [];
            chapters.forEach((ch, idx) => {
                const opt = document.createElement('option');
                opt.value = idx;
                const statusIcon = idx < currentChapterIndex ? '✔ ' : (idx === currentChapterIndex ? '▶ ' : '○ ');
                opt.textContent = `${statusIcon}${ch.title || `Глава ${idx + 1}`}`;
                readerChapterSelect.appendChild(opt);
            });
        }

        applyReaderSettings();

        try {
            localStorage.setItem('notes_active_book_id', bookId);
            localStorage.setItem('notes_active_view', 'reader-view');
        } catch (e) {}

        if (updateHash) {
            const desiredHash = `#reader/book/${bookId}/ch/${currentChapterIndex}`;
            if (window.location.hash !== desiredHash) {
                history.replaceState(null, '', desiredHash);
            }
        }

        renderChapter(currentChapterIndex, targetScrollTop, targetFraction, targetAnchorIdx);
    } catch (e) {
        console.error('Error opening book:', e);
        alert('Не удалось открыть книгу');
        window.location.hash = '#reader';
    }
}

export function buildChapterDOM(chapterIdx, knownWordsMap, isContinuous = false) {
    if (!currentBook || !currentBook.chapters) return document.createDocumentFragment();
    const chapter = currentBook.chapters[chapterIdx] || { title: '', content: '' };
    const frag = document.createDocumentFragment();

    if (chapterIdx > 0 || isContinuous) {
        const divider = document.createElement('div');
        divider.className = 'reader-chapter-divider';
        divider.id = `chapter-anchor-${chapterIdx}`;
        divider.setAttribute('data-chapter-idx', chapterIdx.toString());

        const badge = document.createElement('span');
        badge.className = 'divider-badge';
        badge.textContent = `Глава ${chapterIdx + 1} из ${currentBook.chapters.length}`;

        const titleEl = document.createElement('h2');
        titleEl.className = 'divider-title';
        titleEl.textContent = chapter.title || `Глава ${chapterIdx + 1}`;

        divider.appendChild(badge);
        divider.appendChild(titleEl);
        frag.appendChild(divider);
    } else {
        const h = document.createElement('h2');
        h.textContent = chapter.title || `Глава 1`;
        h.setAttribute('data-block-idx', '0');
        h.setAttribute('data-chapter-idx', '0');
        h.id = `chapter-anchor-0`;
        frag.appendChild(h);
    }

    const blocks = parseContentBlocks(chapter.content);

    blocks.forEach((block, blockIdx) => {
        const domIdx = blockIdx + 1;
        let blockEl = null;

        if (block.type === 'code') {
            blockEl = document.createElement('div');
            blockEl.className = 'reader-code-block';

            const header = document.createElement('div');
            header.className = 'reader-code-header';

            const langSpan = document.createElement('span');
            langSpan.className = 'reader-code-lang';
            langSpan.textContent = block.lang || 'code';

            const copyBtn = document.createElement('button');
            copyBtn.className = 'reader-copy-code-btn';
            copyBtn.type = 'button';
            copyBtn.innerHTML = '📋 Копировать';
            copyBtn.onclick = async (e) => {
                e.stopPropagation();
                try {
                    await navigator.clipboard.writeText(block.code);
                    copyBtn.innerHTML = '✅ Скопировано!';
                    setTimeout(() => { copyBtn.innerHTML = '📋 Копировать'; }, 2000);
                } catch (err) {
                    console.error('Copy failed:', err);
                }
            };

            header.appendChild(langSpan);
            header.appendChild(copyBtn);

            const pre = document.createElement('pre');
            const codeEl = document.createElement('code');
            if (block.lang) codeEl.className = `language-${block.lang}`;
            codeEl.textContent = block.code;
            pre.appendChild(codeEl);

            blockEl.appendChild(header);
            blockEl.appendChild(pre);
        } else if (block.type === 'figure') {
            blockEl = document.createElement('figure');
            blockEl.className = 'reader-figure';

            const img = document.createElement('img');
            img.className = 'reader-figure-img';
            img.src = block.src;
            img.alt = block.alt || '';
            img.loading = 'lazy';
            img.onerror = () => { blockEl.style.display = 'none'; };
            blockEl.appendChild(img);

            if (block.caption) {
                const figcaption = document.createElement('figcaption');
                figcaption.className = 'reader-figcaption';
                renderInteractiveSpans(figcaption, block.caption, block.caption, knownWordsMap);
                blockEl.appendChild(figcaption);
            }
        } else if (block.type === 'table') {
            blockEl = document.createElement('div');
            blockEl.className = 'reader-table-wrap';
            const table = document.createElement('table');
            table.className = 'reader-table';

            if (block.headers && block.headers.length > 0) {
                const thead = document.createElement('thead');
                const headerTr = document.createElement('tr');
                block.headers.forEach((hText, colIdx) => {
                    const th = document.createElement('th');
                    if (block.alignments && block.alignments[colIdx]) {
                        th.style.textAlign = block.alignments[colIdx];
                    }
                    renderInteractiveSpans(th, hText, hText, knownWordsMap);
                    headerTr.appendChild(th);
                });
                thead.appendChild(headerTr);
                table.appendChild(thead);
            }

            if (block.rows && block.rows.length > 0) {
                const tbody = document.createElement('tbody');
                block.rows.forEach(row => {
                    const tr = document.createElement('tr');
                    row.forEach((cellText, colIdx) => {
                        const td = document.createElement('td');
                        if (block.alignments && block.alignments[colIdx]) {
                            td.style.textAlign = block.alignments[colIdx];
                        }
                        renderInteractiveSpans(td, cellText, cellText, knownWordsMap);
                        tr.appendChild(td);
                    });
                    tbody.appendChild(tr);
                });
                table.appendChild(tbody);
            }
            blockEl.appendChild(table);
        } else if (block.type === 'heading') {
            const tag = `h${Math.min(4, Math.max(1, block.level || 2))}`;
            blockEl = document.createElement(tag);
            if (block.align) blockEl.style.textAlign = block.align;
            renderInteractiveSpans(blockEl, block.text, block.text, knownWordsMap);
        } else if (block.type === 'blockquote') {
            blockEl = document.createElement('blockquote');
            renderInteractiveSpans(blockEl, block.text, block.text, knownWordsMap);
        } else if (block.type === 'ul' || block.type === 'ol') {
            blockEl = document.createElement(block.type);
            block.items.forEach(itemText => {
                const li = document.createElement('li');
                renderInteractiveSpans(li, itemText, itemText, knownWordsMap);
                blockEl.appendChild(li);
            });
        } else if (block.type === 'hr') {
            blockEl = document.createElement('hr');
        } else {
            blockEl = document.createElement('p');
            if (block.align) {
                blockEl.style.textAlign = block.align;
                blockEl.classList.add('text-center');
            }
            renderInteractiveSpans(blockEl, block.text, block.text, knownWordsMap);
        }

        if (blockEl) {
            blockEl.setAttribute('data-block-idx', domIdx.toString());
            blockEl.setAttribute('data-chapter-idx', chapterIdx.toString());
            frag.appendChild(blockEl);
        }
    });

    return frag;
}

export function buildChapterFooterDOM(chapterIdx) {
    if (!currentBook || !currentBook.chapters) return null;
    const totalCh = currentBook.chapters.length;
    const isLastChapter = (chapterIdx >= totalCh - 1);

    const footer = document.createElement('div');
    footer.className = 'reader-chapter-footer';
    footer.id = `reader-chapter-footer-${chapterIdx}`;
    footer.setAttribute('data-footer-for-ch', chapterIdx.toString());

    if (isLastChapter) {
        footer.classList.add('reader-book-finished');
        footer.innerHTML = `
            <div class="chapter-footer-status">
                <span class="status-check">🎉</span>
                <strong style="color: var(--primary); font-size: 16px;">Книга прочитана!</strong>
            </div>
            <p class="chapter-footer-hint">Поздравляем! Вы завершили чтение «${escapeHtml(currentBook.title)}».</p>
            <div class="chapter-footer-nav">
                <button type="button" class="btn btn-trainer btn-sm reader-footer-nav-btn" id="footer-train-btn-${chapterIdx}">
                    🎓 Тренировать слова книги
                </button>
                <button type="button" class="btn btn-outline btn-sm reader-footer-nav-btn" id="footer-shelf-btn-${chapterIdx}">
                    📚 К библиотеке
                </button>
            </div>
        `;
        const trainBtn = footer.querySelector(`#footer-train-btn-${chapterIdx}`);
        if (trainBtn) {
            trainBtn.onclick = () => {
                const tag = slugify(currentBook.title);
                window.location.hash = `#srs/${encodeURIComponent(tag)}`;
            };
        }
        const shelfBtn = footer.querySelector(`#footer-shelf-btn-${chapterIdx}`);
        if (shelfBtn) {
            shelfBtn.onclick = () => {
                window.location.hash = '#reader';
            };
        }
        return footer;
    }

    const nextCh = chapterIdx + 1;
    const nextTitle = currentBook.chapters[nextCh]?.title || `Глава ${nextCh + 1}`;

    footer.innerHTML = `
        <div class="chapter-footer-status">
            <span class="status-check">✔</span>
            <span>Глава ${chapterIdx + 1} завершена</span>
        </div>
        <div class="chapter-footer-nav">
            ${chapterIdx > 0 ? `
            <button type="button" class="btn btn-outline btn-sm reader-footer-nav-btn prev" id="footer-prev-btn-${chapterIdx}">
                ◀ Назад
            </button>` : ''}
            <button type="button" class="btn btn-primary btn-sm reader-footer-nav-btn next" id="footer-next-btn-${chapterIdx}">
                Следующая: ${escapeHtml(nextTitle)} ▶
            </button>
        </div>
        <div class="chapter-footer-hint">
            ${readerSettings.flowMode === 'chapters' && readerSettings.autoLoadNext
                ? '⚡ Автоподгрузка включена: следующая глава подгрузится автоматически при скролле вниз'
                : '💡 Нажмите кнопку выше для перехода к следующей главе'}
        </div>
    `;

    const nextBtn = footer.querySelector(`#footer-next-btn-${chapterIdx}`);
    if (nextBtn) {
        nextBtn.onclick = () => {
            if (readerSettings.flowMode === 'continuous') {
                const target = document.getElementById(`chapter-anchor-${nextCh}`);
                if (target) scrollToElement(target, true);
            } else if (readerSettings.autoLoadNext) {
                appendNextChapter(nextCh, true);
            } else {
                window.location.hash = `#reader/book/${currentBook.id}/ch/${nextCh}`;
            }
        };
    }

    const prevBtn = footer.querySelector(`#footer-prev-btn-${chapterIdx}`);
    if (prevBtn) {
        prevBtn.onclick = () => {
            window.location.hash = `#reader/book/${currentBook.id}/ch/${chapterIdx - 1}`;
        };
    }

    return footer;
}

export function scrollToElement(targetEl, smooth = true) {
    const readerScrollArea = document.getElementById('reader-scroll-area');
    if (!targetEl || !readerScrollArea) return;
    const containerTop = readerScrollArea.getBoundingClientRect().top;
    const elTop = targetEl.getBoundingClientRect().top;
    const targetScroll = readerScrollArea.scrollTop + (elTop - containerTop - 10);
    readerScrollArea.scrollTo({
        top: Math.max(0, targetScroll),
        behavior: smooth ? 'smooth' : 'auto'
    });
}

export function updateChapterSelectIcons() {
    const readerChapterSelect = document.getElementById('reader-chapter-select');
    if (!readerChapterSelect || !readerChapterSelect.options || !currentBook || !currentBook.chapters) return;
    for (let i = 0; i < readerChapterSelect.options.length; i++) {
        const rawTitle = currentBook.chapters[i]?.title || `Глава ${i + 1}`;
        const icon = i < currentChapterIndex ? '✔ ' : (i === currentChapterIndex ? '▶ ' : '○ ');
        readerChapterSelect.options[i].textContent = `${icon}${rawTitle}`;
    }
}

export function appendNextChapter(nextCh, smoothScroll = false) {
    if (!currentBook || !currentBook.chapters || nextCh >= currentBook.chapters.length) return;
    const readerContentBody = document.getElementById('reader-content-body');
    const readerPrevChBtn = document.getElementById('reader-prev-ch-btn');
    const readerNextChBtn = document.getElementById('reader-next-ch-btn');

    if (!readerContentBody) return;

    if (loadedChaptersSet.has(nextCh)) {
        if (smoothScroll) {
            const target = document.getElementById(`chapter-anchor-${nextCh}`);
            if (target) scrollToElement(target, true);
        }
        return;
    }

    const oldFooter = readerContentBody.querySelector(`.reader-chapter-footer[data-footer-for-ch="${nextCh - 1}"]`);
    if (oldFooter) {
        oldFooter.remove();
    }

    const knownWordsMap = new Map();
    const allCards = getAllCards() || [];
    allCards.forEach(c => {
        if (c.term) knownWordsMap.set(c.term.trim().toLowerCase(), c);
    });

    const chFrag = buildChapterDOM(nextCh, knownWordsMap, true);
    readerContentBody.appendChild(chFrag);

    const newFooter = buildChapterFooterDOM(nextCh);
    if (newFooter) {
        readerContentBody.appendChild(newFooter);
    }

    loadedChaptersSet.add(nextCh);

    if (readerPrevChBtn) readerPrevChBtn.disabled = false;
    if (readerNextChBtn) readerNextChBtn.disabled = nextCh >= currentBook.chapters.length - 1;

    if (smoothScroll) {
        const anchor = document.getElementById(`chapter-anchor-${nextCh}`);
        if (anchor) {
            scrollToElement(anchor, true);
        }
    }
}

export function renderContinuousBook(targetChapter = 0, restoreScrollTop = null, restoreFraction = null, restoreAnchorIdx = null) {
    if (!currentBook || !currentBook.chapters) return;

    const readerChapterSelect = document.getElementById('reader-chapter-select');
    const readerPrevChBtn = document.getElementById('reader-prev-ch-btn');
    const readerNextChBtn = document.getElementById('reader-next-ch-btn');
    const readerContentBody = document.getElementById('reader-content-body');
    const readerScrollArea = document.getElementById('reader-scroll-area');

    currentChapterIndex = Math.max(0, Math.min(targetChapter, currentBook.chapters.length - 1));
    if (readerChapterSelect) readerChapterSelect.value = currentChapterIndex;

    updateChapterSelectIcons();

    if (readerPrevChBtn) readerPrevChBtn.disabled = currentChapterIndex <= 0;
    if (readerNextChBtn) readerNextChBtn.disabled = currentChapterIndex >= currentBook.chapters.length - 1;

    if (!readerContentBody) return;
    readerContentBody.innerHTML = '';
    loadedChaptersSet.clear();

    const knownWordsMap = new Map();
    const allCards = getAllCards() || [];
    allCards.forEach(c => {
        if (c.term) knownWordsMap.set(c.term.trim().toLowerCase(), c);
    });

    const totalChapters = currentBook.chapters.length;
    const docFrag = document.createDocumentFragment();

    for (let ch = 0; ch < totalChapters; ch++) {
        loadedChaptersSet.add(ch);
        const chFrag = buildChapterDOM(ch, knownWordsMap, ch > 0);
        docFrag.appendChild(chFrag);
    }

    const finishFooter = buildChapterFooterDOM(totalChapters - 1);
    if (finishFooter) {
        docFrag.appendChild(finishFooter);
    }

    readerContentBody.appendChild(docFrag);

    // Apply scroll: either restored from storage/arguments or to target chapter anchor
    if (restoreScrollTop !== null || restoreFraction !== null || restoreAnchorIdx !== null) {
        applyScroll(restoreAnchorIdx, restoreScrollTop, restoreFraction, currentChapterIndex);
    } else if (currentChapterIndex > 0) {
        requestAnimationFrame(() => {
            const targetAnchor = document.getElementById(`chapter-anchor-${currentChapterIndex}`);
            if (targetAnchor) {
                scrollToElement(targetAnchor, false);
            }
            updateReaderProgressBar();
        });
    } else {
        if (readerScrollArea) readerScrollArea.scrollTop = 0;
        updateReaderProgressBar();
    }

    const posToSave = (restoreFraction !== null && restoreFraction > 0) ? restoreFraction : 0;
    api.books.saveProgress(currentBook.id, { current_chapter: currentChapterIndex, current_position: posToSave })
        .catch(err => console.log('Progress save error:', err));
}

export function renderChapter(index, restoreScrollTop = null, restoreFraction = null, restoreAnchorIdx = null) {
    if (!currentBook || !currentBook.chapters) return;

    if (readerSettings.flowMode === 'continuous') {
        renderContinuousBook(index, restoreScrollTop, restoreFraction, restoreAnchorIdx);
        return;
    }

    const readerChapterSelect = document.getElementById('reader-chapter-select');
    const readerPrevChBtn = document.getElementById('reader-prev-ch-btn');
    const readerNextChBtn = document.getElementById('reader-next-ch-btn');
    const readerContentBody = document.getElementById('reader-content-body');

    currentChapterIndex = Math.max(0, Math.min(index, currentBook.chapters.length - 1));
    if (readerChapterSelect) readerChapterSelect.value = currentChapterIndex;

    updateChapterSelectIcons();

    if (readerPrevChBtn) readerPrevChBtn.disabled = currentChapterIndex <= 0;
    if (readerNextChBtn) readerNextChBtn.disabled = currentChapterIndex >= currentBook.chapters.length - 1;

    if (!readerContentBody) return;
    readerContentBody.innerHTML = '';
    loadedChaptersSet.clear();
    loadedChaptersSet.add(currentChapterIndex);

    const knownWordsMap = new Map();
    const allCards = getAllCards() || [];
    allCards.forEach(c => {
        if (c.term) knownWordsMap.set(c.term.trim().toLowerCase(), c);
    });

    const chFrag = buildChapterDOM(currentChapterIndex, knownWordsMap, false);
    readerContentBody.appendChild(chFrag);

    const footer = buildChapterFooterDOM(currentChapterIndex);
    if (footer) {
        readerContentBody.appendChild(footer);
    }

    applyScroll(restoreAnchorIdx, restoreScrollTop, restoreFraction, currentChapterIndex);

    // Save progress to server
    const posToSave = (restoreFraction !== null && restoreFraction > 0) ? restoreFraction : 0;
    api.books.saveProgress(currentBook.id, { current_chapter: currentChapterIndex, current_position: posToSave })
        .catch(err => console.log('Progress save error:', err));
}

export function applyScroll(restoreAnchorIdx = null, restoreScrollTop = null, restoreFraction = null, chIdx = 0) {
    const readerScrollArea = document.getElementById('reader-scroll-area');
    const readerContentBody = document.getElementById('reader-content-body');
    if (!readerScrollArea) return;

    function doScroll() {
        if (restoreAnchorIdx !== null && restoreAnchorIdx !== undefined) {
            const el = (readerContentBody && readerContentBody.querySelector(`[data-chapter-idx="${chIdx}"][data-block-idx="${restoreAnchorIdx}"]`))
                       || (readerContentBody && readerContentBody.querySelector(`[data-block-idx="${restoreAnchorIdx}"]`));
            if (el) {
                const containerTop = readerScrollArea.getBoundingClientRect().top;
                const elTop = el.getBoundingClientRect().top;
                readerScrollArea.scrollTop += (elTop - containerTop - 10);
                updateReaderProgressBar();
                return;
            }
        }
        if (restoreScrollTop !== null && restoreScrollTop > 0) {
            readerScrollArea.scrollTop = restoreScrollTop;
        } else if (restoreFraction !== null && restoreFraction > 0) {
            const maxScroll = Math.max(0, readerScrollArea.scrollHeight - readerScrollArea.clientHeight);
            readerScrollArea.scrollTop = Math.round(maxScroll * restoreFraction);
        } else if (chIdx > 0) {
            const anchor = document.getElementById(`chapter-anchor-${chIdx}`);
            if (anchor) {
                const containerTop = readerScrollArea.getBoundingClientRect().top;
                const elTop = anchor.getBoundingClientRect().top;
                readerScrollArea.scrollTop += (elTop - containerTop - 10);
            } else {
                readerScrollArea.scrollTop = 0;
            }
        } else {
            readerScrollArea.scrollTop = 0;
        }
        updateReaderProgressBar();
    }

    requestAnimationFrame(() => {
        doScroll();
        setTimeout(doScroll, 100);
    });
}

// -----------------------------------------------------------------------
// Content Block Parsing & Interactive Spans
// -----------------------------------------------------------------------
export function parseContentBlocks(content) {
    if (!content) return [];
    const lines = content.replace(/\r\n/g, '\n').replace(/\r/g, '\n').split('\n');
    const blocks = [];

    let i = 0;
    while (i < lines.length) {
        const line = lines[i];
        const trimmed = line.trim();

        // 1. Fenced Code Block: ```lang ... ```
        if (trimmed.startsWith('```')) {
            const lang = trimmed.slice(3).trim() || 'code';
            const codeLines = [];
            i++;
            while (i < lines.length && !lines[i].trim().startsWith('```')) {
                codeLines.push(lines[i]);
                i++;
            }
            if (i < lines.length && lines[i].trim().startsWith('```')) {
                i++; // skip closing ```
            }
            blocks.push({
                type: 'code',
                lang: lang,
                code: codeLines.join('\n')
            });
            continue;
        }

        // 2. Empty line
        if (!trimmed) {
            i++;
            continue;
        }

        // 2a. HTML Figure Block: <figure ...> ... </figure>
        if (/^<figure\b/i.test(trimmed)) {
            const figLines = [];
            while (i < lines.length) {
                figLines.push(lines[i]);
                if (/<\/figure>/i.test(lines[i])) {
                    i++;
                    break;
                }
                i++;
            }
            const figHtml = figLines.join('\n');
            const imgMatch = figHtml.match(/<img\b([^>]*)>/i);
            let src = '';
            let alt = '';
            if (imgMatch) {
                const srcM = imgMatch[1].match(/src=["']([^"']+)["']/i);
                const altM = imgMatch[1].match(/alt=["']([^"']*)["']/i);
                if (srcM) src = srcM[1];
                if (altM) alt = altM[1];
            }
            let caption = '';
            const capMatch = figHtml.match(/<figcaption\b[^>]*>([\s\S]*?)<\/figcaption>/i);
            if (capMatch) {
                caption = capMatch[1].replace(/<[^>]+>/g, ' ').replace(/\s+/g, ' ').trim();
            }
            if (src) {
                blocks.push({
                    type: 'figure',
                    src: src,
                    alt: alt,
                    caption: caption
                });
                continue;
            }
        }

        // 2b. HTML Data Table: <div class="reader-table-wrap"><table ...> or <table ...>
        if (/^(?:<div[^>]*class=["'][^"']*reader-table-wrap[^"']*["'][^>]*>\s*)?<table\b/i.test(trimmed)) {
            const tableLines = [];
            while (i < lines.length) {
                tableLines.push(lines[i]);
                if (/<\/table>(?:\s*<\/div>)?/i.test(lines[i])) {
                    i++;
                    break;
                }
                i++;
            }
            const fullTableHtml = tableLines.join('\n');
            const tpl = document.createElement('template');
            tpl.innerHTML = fullTableHtml;
            const tableEl = tpl.content.querySelector('table');
            if (tableEl) {
                const headers = [];
                const ths = tableEl.querySelectorAll('thead th, tr:first-child th');
                ths.forEach(th => headers.push(th.textContent.trim()));

                const rows = [];
                const trs = tableEl.querySelectorAll('tbody tr, tr');
                trs.forEach((tr) => {
                    const tds = tr.querySelectorAll('td');
                    if (tds.length > 0) {
                        const rowCells = [];
                        tds.forEach(td => rowCells.push(td.textContent.trim()));
                        rows.push(rowCells);
                    }
                });

                if (headers.length > 0 || rows.length > 0) {
                    blocks.push({
                        type: 'table',
                        headers: headers,
                        alignments: headers.map(() => 'left'),
                        rows: rows
                    });
                    continue;
                }
            }
        }

        // 3. Markdown Table: lines starting with | and ending with |
        if (trimmed.startsWith('|') && trimmed.endsWith('|')) {
            const tableLines = [];
            while (i < lines.length && lines[i].trim().startsWith('|')) {
                tableLines.push(lines[i].trim());
                i++;
            }
            if (tableLines.length >= 2) {
                const splitRow = (rowStr) => {
                    const inner = rowStr.replace(/^\|/, '').replace(/\|$/, '');
                    return inner.split(/(?<!\\)\|/).map(c => c.trim().replace(/\\\|/g, '|'));
                };
                const headers = splitRow(tableLines[0]);
                const alignRow = splitRow(tableLines[1]);
                const alignments = alignRow.map(col => {
                    const tc = col.trim();
                    if (tc.startsWith(':') && tc.endsWith(':')) return 'center';
                    if (tc.endsWith(':')) return 'right';
                    return 'left';
                });
                const rows = [];
                for (let r = 2; r < tableLines.length; r++) {
                    rows.push(splitRow(tableLines[r]));
                }
                blocks.push({
                    type: 'table',
                    headers: headers,
                    alignments: alignments,
                    rows: rows
                });
                continue;
            }
        }

        // 4. Markdown Headings: #, ##, ###, ####, #####, ######
        const headingMatch = line.match(/^(\#{1,6})\s+(.+)$/);
        if (headingMatch) {
            blocks.push({
                type: 'heading',
                level: Math.min(6, Math.max(1, headingMatch[1].length)),
                text: headingMatch[2].trim()
            });
            i++;
            continue;
        }

        // HTML Heading: <h1...>...</h1>
        const htmlHeadingMatch = line.match(/^<h([1-6])([^>]*)>(.*?)<\/h\1>/i);
        if (htmlHeadingMatch) {
            const level = parseInt(htmlHeadingMatch[1], 10);
            const attrs = htmlHeadingMatch[2] || '';
            const hText = htmlHeadingMatch[3].trim();
            const align = /align=["']?center["']?/i.test(attrs) ? 'center' : '';
            blocks.push({
                type: 'heading',
                level: level,
                text: hText,
                align: align
            });
            i++;
            continue;
        }

        // 5. Horizontal Rule: --- or *** or ___ or <hr>
        if (/^(\-{3,}|\*{3,}|\_{3,})$/.test(trimmed) || trimmed === '<hr>' || trimmed === '<hr/>' || trimmed === '<hr />') {
            blocks.push({ type: 'hr' });
            i++;
            continue;
        }

        // 6. Blockquote: > ...
        if (trimmed.startsWith('>')) {
            const quoteLines = [];
            while (i < lines.length && lines[i].trim().startsWith('>')) {
                quoteLines.push(lines[i].trim().replace(/^>\s?/, ''));
                i++;
            }
            blocks.push({
                type: 'blockquote',
                text: quoteLines.join(' ')
            });
            continue;
        }

        // 7. Unordered List: - item or * item or + item
        if (/^[-*+]\s+/.test(trimmed)) {
            const listItems = [];
            while (i < lines.length && /^[-*+]\s+/.test(lines[i].trim())) {
                listItems.push(lines[i].trim().replace(/^[-*+]\s+/, ''));
                i++;
            }
            blocks.push({
                type: 'ul',
                items: listItems
            });
            continue;
        }

        // 8. Ordered List: 1. item
        if (/^\d+\.\s+/.test(trimmed)) {
            const listItems = [];
            while (i < lines.length && /^\d+\.\s+/.test(lines[i].trim())) {
                listItems.push(lines[i].trim().replace(/^\d+\.\s+/, ''));
                i++;
            }
            blocks.push({
                type: 'ol',
                items: listItems
            });
            continue;
        }

        // 9. Centered HTML block (<p align="center"> or <div align="center">)
        if (/^<(?:p|div)[^>]*align=["']?center["']?[^>]*>/i.test(trimmed)) {
            const htmlLines = [];
            while (i < lines.length) {
                const cur = lines[i];
                htmlLines.push(cur.trim());
                if (/<\/(?:p|div)>/i.test(cur)) {
                    i++;
                    break;
                }
                i++;
            }
            blocks.push({
                type: 'paragraph',
                text: htmlLines.join(' '),
                align: 'center'
            });
            continue;
        }

        // 10. Regular paragraph: gather lines until next block marker or empty line
        const paraLines = [];
        while (i < lines.length) {
            const cur = lines[i];
            const curTrim = cur.trim();
            if (!curTrim) break;
            if (curTrim.startsWith('```') ||
                /^#{1,6}\s+/.test(curTrim) ||
                /^<h[1-6][^>]*>/i.test(curTrim) ||
                (curTrim.startsWith('|') && curTrim.endsWith('|')) ||
                curTrim.startsWith('>') ||
                /^[-*+]\s+/.test(curTrim) ||
                /^\d+\.\s+/.test(curTrim) ||
                /^(\-{3,}|\*{3,}|\_{3,})$/.test(curTrim) ||
                /^<figure\b/i.test(curTrim) ||
                /^<table\b/i.test(curTrim) ||
                curTrim.includes('reader-table-wrap') ||
                /^<(?:p|div)[^>]*align=["']?center/i.test(curTrim)) {
                break;
            }
            paraLines.push(curTrim);
            i++;
        }
        if (paraLines.length > 0) {
            blocks.push({
                type: 'paragraph',
                text: paraLines.join(' ')
            });
        }
    }

    return blocks;
}

export function renderInteractiveSpans(container, text, contextText, knownWordsMap) {
    if (!text) return;

    let processed = text
        .replace(/&middot;/g, '·')
        .replace(/&bull;/g, '•')
        .replace(/&mdash;/g, '—')
        .replace(/&ndash;/g, '–');

    processed = processed.replace(/^<p[^>]*>/i, '').replace(/<\/p>$/i, '');
    processed = processed.replace(/<\/?(?:picture|source)[^>]*>/gi, '');

    // Convert Markdown inline patterns into HTML
    processed = processed.replace(/!\[([^\]]*)\]\(([^)]+)\)/g, '<img src="$2" alt="$1">');
    processed = processed.replace(/\[([^\]]+)\]\(([^)]+)\)/g, '<a href="$2">$1</a>');
    processed = processed.replace(/`([^`]+)`/g, '<code class="reader-inline-code">$1</code>');
    processed = processed.replace(/\*\*([^*]+)\*\*/g, '<strong>$1</strong>');
    processed = processed.replace(/__([^_]+)__/g, '<strong>$1</strong>');
    processed = processed.replace(/(?<!\*)\*([^*]+)\*(?!\*)/g, '<em>$1</em>');
    processed = processed.replace(/(?<!_)_([^_]+)_(?!_)/g, '<em>$1</em>');

    const tpl = document.createElement('template');
    tpl.innerHTML = processed;

    function transformDOMNode(node) {
        if (node.nodeType === Node.TEXT_NODE) {
            const raw = node.textContent;
            if (!raw) return document.createTextNode('');
            const frag = document.createDocumentFragment();
            const tokens = raw.split(/([A-Za-z0-9'-]+)/);
            for (const token of tokens) {
                const isWord = /^[A-Za-z0-9'-]+$/.test(token) && token.replace(/[^A-Za-z0-9]/g, '').length >= 1;
                if (isWord) {
                    const span = document.createElement('span');
                    span.className = 'reader-word';
                    span.dataset.word = token;
                    span.dataset.context = contextText || raw;
                    span.textContent = token;

                    const lower = token.toLowerCase();
                    if (knownWordsMap && knownWordsMap.has(lower)) {
                        const card = knownWordsMap.get(lower);
                        span.classList.add(card.srs_state === 'mastered' ? 'status-mastered' : 'status-learning');
                    }
                    if (isHighlightEnabled) {
                        span.classList.add('highlight-enabled');
                    }

                    frag.appendChild(span);
                } else {
                    frag.appendChild(document.createTextNode(token));
                }
            }
            return frag;
        }

        if (node.nodeType === Node.ELEMENT_NODE) {
            const tag = node.tagName.toLowerCase();

            if (tag === 'code' || tag === 'pre') {
                const codeEl = document.createElement('code');
                codeEl.className = 'reader-inline-code';
                codeEl.textContent = node.textContent;
                return codeEl;
            }

            if (tag === 'img') {
                const img = document.createElement('img');
                img.className = 'reader-img';
                img.src = node.getAttribute('src') || '';
                img.alt = node.getAttribute('alt') || '';
                if (node.getAttribute('width')) img.setAttribute('width', node.getAttribute('width'));
                if (node.getAttribute('height')) img.setAttribute('height', node.getAttribute('height'));
                img.addEventListener('error', () => {
                    img.style.display = 'none';
                });
                return img;
            }

            if (tag === 'a') {
                const a = document.createElement('a');
                a.className = 'reader-link';
                a.href = node.getAttribute('href') || '#';
                a.target = '_blank';
                a.rel = 'noopener noreferrer';
                Array.from(node.childNodes).forEach(child => {
                    a.appendChild(transformDOMNode(child));
                });
                return a;
            }

            if (tag === 'br') {
                return document.createElement('br');
            }

            if (tag === 'strong' || tag === 'b') {
                const strong = document.createElement('strong');
                Array.from(node.childNodes).forEach(child => {
                    strong.appendChild(transformDOMNode(child));
                });
                return strong;
            }

            if (tag === 'em' || tag === 'i') {
                const em = document.createElement('em');
                Array.from(node.childNodes).forEach(child => {
                    em.appendChild(transformDOMNode(child));
                });
                return em;
            }

            if (tag === 'sub' || tag === 'sup') {
                const el = document.createElement(tag);
                Array.from(node.childNodes).forEach(child => {
                    el.appendChild(transformDOMNode(child));
                });
                return el;
            }

            const containerEl = document.createElement(tag === 'p' ? 'span' : tag);
            if (node.hasAttribute('style')) {
                containerEl.setAttribute('style', node.getAttribute('style'));
            }
            Array.from(node.childNodes).forEach(child => {
                containerEl.appendChild(transformDOMNode(child));
            });
            return containerEl;
        }

        return document.createTextNode('');
    }

    Array.from(tpl.content.childNodes).forEach(childNode => {
        container.appendChild(transformDOMNode(childNode));
    });
}

export function robustSentenceSplit(text) {
    if (!text) return [];
    let s = text;

    // Step 1: Protect decimal numbers (e.g. 3.14, 1.5)
    s = s.replace(/(\d+)\.(\d+)/g, '$1§DOT§$2');

    // Step 2: Protect acronyms with dots like U.S., U.K., e.g., i.e., a.m., p.m., Ph.D.
    s = s.replace(/\b((?:[A-Za-z]\.){2,})/g, (m) => m.replace(/\./g, '§DOT§'));

    // Step 3: Protect single-letter initials like 'John F. Kennedy', 'J. K. Rowling'
    s = s.replace(/\b([A-Za-z])\.(?=\s+[A-Za-z0-9"“'‘«—])/g, '$1§DOT§');

    // Step 4: Protect common honorifics, titles, and abbreviations
    const abbrPattern = /\b(Mr|Mrs|Ms|Miss|Dr|Prof|Rev|Hon|Capt|Col|Gen|Lt|Cmdr|Sgt|Cpl|Pvt|Maj|Adm|Gov|Sen|Rep|Pres|Sec|Treas|Insp|Det|Supt|Messrs|Mmes|St|Mt|Ft|etc|vs|v|Jr|Sr|approx|app|apt|dept|univ|assn|assoc|bldg|co|corp|inc|ltd|est|misc|al|ibid|op|cit|ed|eds|trans|vol|vols|no|nos|sec|secs|ch|chs|fig|figs|p|pp|ave|blvd|rd|st|ct|ln|dr|hwy|jan|feb|mar|apr|jun|jul|aug|sep|sept|oct|nov|dec)\./gi;
    s = s.replace(abbrPattern, '$1§DOT§');

    // Step 5: Protect ellipsis (... or ....)
    s = s.replace(/\.{2,}/g, (m) => '§ELLIPSIS§' + '§DOT§'.repeat(m.length));

    // Step 6: Protect any period followed by lowercase letter (e.g. 'word. otherword')
    s = s.replace(/\.([\'"”’»)]*\s+[a-zа-яё])/g, '§DOT§$1');

    // Step 7: Split on sentence terminators [.!?] followed by whitespace and uppercase/number/quote/start of dialog
    const marked = s.replace(/([.!?]['"”’»)]*)(\s+)(?=[A-Z0-9"“'‘«—]|$)/g, '$1§SEP§');

    return marked.split('§SEP§')
        .map(part => part.replace(/§DOT§/g, '.').replace(/§ELLIPSIS§/g, '').trim())
        .filter(Boolean);
}

export function extractContextSentence(fullText, word) {
    if (!fullText) return '';
    const sentences = robustSentenceSplit(fullText);
    const cleanWord = (word || '').trim();
    if (cleanWord) {
        const escaped = escapeRegex(cleanWord);
        const wordRe = new RegExp(`(?:^|\\W)${escaped}(?:$|\\W)`, 'i');
        for (const s of sentences) {
            if (wordRe.test(s)) {
                return s.replace(/\s+/g, ' ').trim();
            }
        }
    }
    return sentences.length > 0 ? sentences[0].replace(/\s+/g, ' ').trim() : fullText.slice(0, 160).trim();
}

// -----------------------------------------------------------------------
// Interactive Word Popup
// -----------------------------------------------------------------------
export function positionWordPopup(targetElement) {
    const readerWordPopup = document.getElementById('reader-word-popup');
    if (!targetElement || !readerWordPopup) return;
    if (window.innerWidth <= 768) {
        readerWordPopup.style.top = '';
        readerWordPopup.style.left = '';
        readerWordPopup.style.right = '';
        readerWordPopup.style.bottom = '';
        readerWordPopup.style.width = '';
        return;
    }
    const rect = targetElement.getBoundingClientRect();
    const popupWidth = (readerWordPopup.offsetWidth && readerWordPopup.offsetWidth >= 280 && readerWordPopup.offsetWidth <= 380)
        ? readerWordPopup.offsetWidth
        : 340;
    const popupHeight = readerWordPopup.offsetHeight || 220;
    const viewportWidth = window.innerWidth;
    const viewportHeight = window.innerHeight;

    let left = rect.left + (rect.width / 2) - (popupWidth / 2);
    if (left + popupWidth > viewportWidth - 16) {
        left = viewportWidth - popupWidth - 16;
    }
    if (left < 16) {
        left = 16;
    }

    const minTop = isZenMode ? 16 : 65;
    let top = rect.bottom + 8;
    if (top + popupHeight > viewportHeight - 16) {
        if (rect.top - popupHeight - 8 >= minTop || rect.top > viewportHeight / 2) {
            top = Math.max(minTop, rect.top - popupHeight - 8);
        }
    }

    readerWordPopup.style.top = `${Math.round(top)}px`;
    readerWordPopup.style.left = `${Math.round(left)}px`;
    readerWordPopup.style.right = 'auto';
    readerWordPopup.style.bottom = 'auto';
    readerWordPopup.style.width = `${popupWidth}px`;
}

export async function openWordPopup(term, contextSentence, targetElement, paragraphContext = '') {
    const readerWordPopup = document.getElementById('reader-word-popup');
    const readerSettingsPanel = document.getElementById('reader-settings-panel');
    const popupTerm = document.getElementById('popup-term');
    const popupPhonetic = document.getElementById('popup-phonetic');
    const popupTranslation = document.getElementById('popup-translation');
    const popupContext = document.getElementById('popup-context');
    const popupLoading = document.getElementById('popup-loading');
    const popupContent = document.getElementById('popup-content');
    const popupInLibrary = document.getElementById('popup-in-library');
    const popupSaveBtn = document.getElementById('popup-save-btn');
    const popupSavedBadge = document.getElementById('popup-saved-badge');
    const popupAddContextBtn = document.getElementById('popup-add-context-btn');
    const popupAudioBtn = document.getElementById('popup-audio-btn');

    const cleanTerm = (term || '').replace(/^['"“«`\s\-_.,;:!?()[\]{}]+|['"”»`\s\-_.,;:!?()[\]{}]+$/g, '').trim();
    if (!cleanTerm || !readerWordPopup) return;
    if (readerSettingsPanel) readerSettingsPanel.classList.add('hidden');

    const lowerClean = cleanTerm.toLowerCase();
    const allCards = getAllCards() || [];
    const existingCard = allCards.find(c => c.term && c.term.trim().toLowerCase() === lowerClean);

    popupCurrentData = {
        term: cleanTerm,
        contextSentence: contextSentence,
        paragraphContext: paragraphContext,
        targetElement: targetElement,
        existingCard: existingCard,
    };

    if (popupTerm) popupTerm.textContent = cleanTerm;
    if (popupPhonetic) popupPhonetic.textContent = '';
    if (popupTranslation) popupTranslation.textContent = '';
    if (popupContext) popupContext.textContent = contextSentence ? `“${contextSentence}”` : '';
    if (popupLoading) popupLoading.classList.remove('hidden');
    if (popupContent) popupContent.classList.add('hidden');

    const popupTranslateSentenceBtn = document.getElementById('popup-translate-sentence-btn');
    const popupAiSourceBadge = document.getElementById('popup-ai-source-badge');
    const popupSentenceLoading = document.getElementById('popup-sentence-loading');
    const popupSentenceTranslationWrap = document.getElementById('popup-sentence-translation-wrap');
    const popupSentenceRu = document.getElementById('popup-sentence-ru');
    const popupContextMeaningWrap = document.getElementById('popup-context-meaning-wrap');
    const popupContextMeaningVal = document.getElementById('popup-context-meaning-val');
    const popupSentenceAiBar = document.querySelector('.popup-sentence-ai-bar');

    const popupPhrasalCard = document.getElementById('popup-phrasal-card');
    const popupPhrasalTerm = document.getElementById('popup-phrasal-term');
    const popupPhrasalRaw = document.getElementById('popup-phrasal-raw');
    const popupPhrasalTranslation = document.getElementById('popup-phrasal-translation');
    const popupPhrasalLibraryBadge = document.getElementById('popup-phrasal-library-badge');
    const popupSwitchPhrasalBtn = document.getElementById('popup-switch-phrasal-btn');

    if (popupPhrasalCard) popupPhrasalCard.classList.add('hidden');
    popupCurrentData.phrasalVerb = null;
    popupCurrentData.isPhrasalMode = false;

    if (popupSentenceLoading) popupSentenceLoading.classList.add('hidden');
    if (popupSentenceTranslationWrap) popupSentenceTranslationWrap.classList.add('hidden');
    if (popupSentenceRu) popupSentenceRu.textContent = '';
    if (popupContextMeaningWrap) popupContextMeaningWrap.classList.add('hidden');
    if (popupContextMeaningVal) popupContextMeaningVal.textContent = '';
    if (popupAiSourceBadge) popupAiSourceBadge.classList.add('hidden');
    if (popupTranslateSentenceBtn) {
        popupTranslateSentenceBtn.disabled = false;
        popupTranslateSentenceBtn.textContent = '🌐 Перевести предложение';
        if (popupSentenceAiBar) popupSentenceAiBar.classList.toggle('hidden', !contextSentence);
    }

    if (popupInLibrary) {
        popupInLibrary.classList.toggle('hidden', !existingCard);
    }

    if (existingCard) {
        if (popupSaveBtn) popupSaveBtn.classList.add('hidden');
        if (popupSavedBadge) {
            popupSavedBadge.classList.remove('hidden');
            popupSavedBadge.textContent = '⭐ Слово уже в библиотеке';
        }
        if (popupAddContextBtn) {
            if (contextSentence && (!existingCard.context_sentence || !existingCard.context_sentence.includes(contextSentence))) {
                popupAddContextBtn.classList.remove('hidden');
            } else {
                popupAddContextBtn.classList.add('hidden');
            }
        }
    } else {
        if (popupSavedBadge) popupSavedBadge.classList.add('hidden');
        if (popupSaveBtn) {
            popupSaveBtn.classList.remove('hidden');
            popupSaveBtn.disabled = false;
        }
        if (popupAddContextBtn) popupAddContextBtn.classList.add('hidden');
    }

    readerWordPopup.classList.remove('hidden');
    positionWordPopup(targetElement);

    try {
        const data = await api.lookup.search(cleanTerm, contextSentence);
        popupCurrentData.lookup = data;

        // Phrasal verb detection
        if (data.phrasal_verb) {
            const pv = data.phrasal_verb;
            popupCurrentData.phrasalVerb = pv;
            if (popupPhrasalCard) {
                popupPhrasalCard.classList.remove('hidden');
                if (popupPhrasalTerm) popupPhrasalTerm.textContent = pv.term;
                if (popupPhrasalRaw) popupPhrasalRaw.textContent = `(в тексте: «${pv.raw}»)`;
                if (popupPhrasalTranslation) popupPhrasalTranslation.textContent = pv.translation;
                if (popupPhrasalLibraryBadge) popupPhrasalLibraryBadge.classList.toggle('hidden', !pv.in_library);
                if (popupSwitchPhrasalBtn) {
                    popupSwitchPhrasalBtn.textContent = `🔗 Переключить на «${pv.term}»`;
                }
            }
        } else {
            if (popupPhrasalCard) popupPhrasalCard.classList.add('hidden');
        }

        const trans = data.translation || data.translation_ru || (data.translations_list && data.translations_list.length > 0 ? data.translations_list.join(', ') : '');
        if (popupPhonetic) popupPhonetic.textContent = data.phonetic || '';
        if (popupTranslation) popupTranslation.textContent = trans || 'Перевод не найден';
        if (popupLoading) popupLoading.classList.add('hidden');
        if (popupContent) popupContent.classList.remove('hidden');
        if (popupAudioBtn) {
            popupAudioBtn.classList.remove('hidden');
            popupAudioBtn.style.display = 'inline-flex';
        }
        popupCurrentData.audioUrl = data.audio_url || '';

        const inLib = Boolean(data.in_library || existingCard);
        const libCard = data.library_card || existingCard;
        if (inLib) {
            popupCurrentData.existingCard = libCard;
            if (popupInLibrary) popupInLibrary.classList.remove('hidden');
            if (popupSaveBtn) popupSaveBtn.classList.add('hidden');
            if (popupSavedBadge) {
                popupSavedBadge.classList.remove('hidden');
                popupSavedBadge.textContent = '⭐ Слово уже в библиотеке';
            }
            if (popupAddContextBtn) {
                if (contextSentence && libCard && (!libCard.context_sentence || !libCard.context_sentence.includes(contextSentence))) {
                    popupAddContextBtn.classList.remove('hidden');
                } else {
                    popupAddContextBtn.classList.add('hidden');
                }
            }
        } else {
            if (popupInLibrary) popupInLibrary.classList.add('hidden');
            if (popupSaveBtn) popupSaveBtn.classList.remove('hidden');
            if (popupSavedBadge) popupSavedBadge.classList.add('hidden');
            if (popupAddContextBtn) popupAddContextBtn.classList.add('hidden');
        }

        positionWordPopup(targetElement);
    } catch (e) {
        console.error('Popup lookup error:', e);
        if (popupTranslation) popupTranslation.textContent = 'Сетевая ошибка';
        if (popupLoading) popupLoading.classList.add('hidden');
        if (popupContent) popupContent.classList.remove('hidden');
        positionWordPopup(targetElement);
    }
}

export async function handleWordClick(word, paragraphText, targetElement) {
    const sentence = extractContextSentence(paragraphText, word);
    openWordPopup(word, sentence, targetElement, paragraphText);
}

function updatePopupPositionOnScroll() {
    const readerWordPopup = document.getElementById('reader-word-popup');
    if (!readerWordPopup || readerWordPopup.classList.contains('hidden')) return;
    if (window.innerWidth <= 768) return;
    if (!popupCurrentData || !popupCurrentData.targetElement || !popupCurrentData.targetElement.isConnected) {
        readerWordPopup.classList.add('hidden');
        return;
    }
    const rect = popupCurrentData.targetElement.getBoundingClientRect();
    const headerOffset = 65;
    if (rect.bottom < headerOffset || rect.top > window.innerHeight) {
        readerWordPopup.classList.add('hidden');
        return;
    }
    positionWordPopup(popupCurrentData.targetElement);
}

function schedulePopupUpdate() {
    const readerWordPopup = document.getElementById('reader-word-popup');
    if (!readerWordPopup || readerWordPopup.classList.contains('hidden')) return;
    if (popupScrollRaf) return;
    popupScrollRaf = requestAnimationFrame(() => {
        popupScrollRaf = null;
        updatePopupPositionOnScroll();
    });
}

// -----------------------------------------------------------------------
// Scroll Position Tracking & Metrics
// -----------------------------------------------------------------------
export function getReaderScrollMetrics() {
    const readerScrollArea = document.getElementById('reader-scroll-area');
    if (!readerScrollArea) return { scrollTop: 0, maxScroll: 0, pct: 0, fraction: 0 };
    const scrollTop = readerScrollArea.scrollTop;
    const maxScroll = Math.max(0, readerScrollArea.scrollHeight - readerScrollArea.clientHeight);
    const fraction = maxScroll > 0 ? Math.min(1.0, Math.max(0, scrollTop / maxScroll)) : 0;
    const pct = Math.min(100, Math.max(0, Math.round(fraction * 100)));
    return { scrollTop, maxScroll, pct, fraction };
}

export function getActiveAnchorIndex() {
    const readerScrollArea = document.getElementById('reader-scroll-area');
    const readerContentBody = document.getElementById('reader-content-body');
    if (!readerScrollArea || !readerContentBody) return null;
    const blocks = readerContentBody.querySelectorAll('[data-block-idx]');
    if (!blocks || blocks.length === 0) return null;
    const containerTop = readerScrollArea.getBoundingClientRect().top;
    for (let el of blocks) {
        const rect = el.getBoundingClientRect();
        if (rect.bottom >= containerTop + 10) {
            return parseInt(el.getAttribute('data-block-idx'), 10);
        }
    }
    return 0;
}

export function getActiveVisibleChapter() {
    const readerScrollArea = document.getElementById('reader-scroll-area');
    const readerContentBody = document.getElementById('reader-content-body');
    if (!readerScrollArea || !readerContentBody) return currentChapterIndex;
    const anchors = readerContentBody.querySelectorAll('[id^="chapter-anchor-"]');
    if (!anchors || anchors.length === 0) return currentChapterIndex;

    const containerTop = readerScrollArea.getBoundingClientRect().top;
    let activeIdx = 0;

    for (let el of anchors) {
        const rect = el.getBoundingClientRect();
        if (rect.top <= containerTop + 140) {
            const ch = parseInt(el.getAttribute('data-chapter-idx'), 10);
            if (!isNaN(ch)) activeIdx = ch;
        } else {
            break;
        }
    }
    return activeIdx;
}

export function updateReaderProgressBar() {
    const readerChapterProgressFill = document.getElementById('reader-chapter-progress-fill');
    const readerScrollPctBadge = document.getElementById('reader-scroll-pct-badge');
    const { pct, fraction } = getReaderScrollMetrics();

    if (readerSettings.flowMode === 'continuous') {
        if (readerChapterProgressFill) {
            readerChapterProgressFill.style.width = `${pct}%`;
        }
        if (readerScrollPctBadge) {
            readerScrollPctBadge.textContent = `${pct}%`;
            const totalCh = currentBook && currentBook.chapters ? currentBook.chapters.length : 1;
            readerScrollPctBadge.title = `Вся книга: ${pct}% • Глава ${currentChapterIndex + 1} из ${totalCh}`;
        }
        return;
    }

    if (readerChapterProgressFill) {
        readerChapterProgressFill.style.width = `${pct}%`;
    }

    if (currentBook) {
        const totalCh = Math.max(1, (currentBook.chapters ? currentBook.chapters.length : 1));
        const overallFraction = (currentChapterIndex + fraction) / totalCh;
        const totalPct = Math.min(100, Math.max(0, Math.round(overallFraction * 100)));

        if (readerScrollPctBadge) {
            readerScrollPctBadge.textContent = `${pct}%`;
            readerScrollPctBadge.title = `Глава ${currentChapterIndex + 1}/${totalCh}: ${pct}% • Вся книга: ${totalPct}%`;
        }
    } else if (readerScrollPctBadge) {
        readerScrollPctBadge.textContent = `${pct}%`;
    }

    // Update Zen HUD elements if present
    const zenHudTitle = document.getElementById('zen-hud-title');
    const zenHudChapter = document.getElementById('zen-hud-chapter');
    const zenHudProgress = document.getElementById('zen-hud-progress');

    if (zenHudTitle && currentBook) {
        zenHudTitle.textContent = currentBook.title || 'Книга';
        zenHudTitle.title = currentBook.title || 'Книга';
    }
    if (zenHudChapter && currentBook && currentBook.chapters) {
        const totalCh = currentBook.chapters.length;
        const ch = currentBook.chapters[currentChapterIndex];
        const chTitle = ch ? (ch.title || `Глава ${currentChapterIndex + 1}`) : `Глава ${currentChapterIndex + 1}`;
        zenHudChapter.textContent = totalCh > 1 ? `Гл. ${currentChapterIndex + 1}/${totalCh}` : chTitle;
        zenHudChapter.title = chTitle;
    }
    if (zenHudProgress) {
        zenHudProgress.textContent = `${pct}%`;
    }
}

export function handleReaderScroll() {
    const readerScrollArea = document.getElementById('reader-scroll-area');
    const readerChapterSelect = document.getElementById('reader-chapter-select');
    const readerPrevChBtn = document.getElementById('reader-prev-ch-btn');
    const readerNextChBtn = document.getElementById('reader-next-ch-btn');

    if (!currentBook || !readerScrollArea) return;
    updateReaderProgressBar();

    // 1. Detect active visible chapter in continuous or multi-chapter view
    if (readerSettings.flowMode === 'continuous' || loadedChaptersSet.size > 1) {
        const activeCh = getActiveVisibleChapter();
        if (activeCh !== null && activeCh !== undefined && activeCh !== currentChapterIndex) {
            currentChapterIndex = activeCh;
            if (readerChapterSelect) readerChapterSelect.value = currentChapterIndex;
            updateChapterSelectIcons();
            if (readerPrevChBtn) readerPrevChBtn.disabled = currentChapterIndex <= 0;
            if (readerNextChBtn) readerNextChBtn.disabled = currentChapterIndex >= currentBook.chapters.length - 1;

            const desiredHash = `#reader/book/${currentBook.id}/ch/${currentChapterIndex}`;
            if (window.location.hash !== desiredHash) {
                history.replaceState(null, '', desiredHash);
            }
        }
    }

    // 2. Infinite scroll: auto-append next chapter in chapters mode with autoload
    if (readerSettings.flowMode === 'chapters' && readerSettings.autoLoadNext && !isAppendingChapter) {
        const distanceToBottom = readerScrollArea.scrollHeight - (readerScrollArea.scrollTop + readerScrollArea.clientHeight);
        if (distanceToBottom < 700) {
            const loadedArr = Array.from(loadedChaptersSet);
            const highestCh = loadedArr.length > 0 ? Math.max(...loadedArr) : currentChapterIndex;
            if (currentBook && currentBook.chapters && highestCh < currentBook.chapters.length - 1) {
                isAppendingChapter = true;
                appendNextChapter(highestCh + 1, false);
                setTimeout(() => { isAppendingChapter = false; }, 200);
            }
        }
    }

    const { scrollTop, fraction } = getReaderScrollMetrics();
    const anchorIdx = getActiveAnchorIndex();

    // 3. Instant local persistence
    try {
        const key = `notes_book_${currentBook.id}_pos`;
        localStorage.setItem(key, JSON.stringify({
            chapter: currentChapterIndex,
            scrollTop: scrollTop,
            fraction: fraction,
            anchorIdx: anchorIdx,
            savedAt: Date.now()
        }));
        localStorage.setItem('notes_active_book_id', currentBook.id);
        localStorage.setItem('notes_active_view', 'reader-view');
    } catch (e) {}

    // 4. Debounced server sync (every 800ms)
    clearTimeout(readerScrollSaveTimer);
    readerScrollSaveTimer = setTimeout(() => {
        if (!currentBook) return;
        api.books.saveProgress(currentBook.id, { current_chapter: currentChapterIndex, current_position: fraction })
            .catch(err => console.log('Progress save error:', err));
    }, 800);
}

// -----------------------------------------------------------------------
// Reader Appearance & Settings
// -----------------------------------------------------------------------
export function loadSavedReaderSettings() {
    try {
        const saved = localStorage.getItem('notes_reader_settings');
        if (saved) {
            readerSettings = Object.assign({}, DEFAULT_READER_SETTINGS, JSON.parse(saved));
        }
    } catch (e) {}
}

export function saveReaderSettings() {
    try {
        localStorage.setItem('notes_reader_settings', JSON.stringify(readerSettings));
    } catch (e) {}
}

export function applyReaderSettings() {
    const readerScrollArea = document.getElementById('reader-scroll-area');
    const settingFontSizeVal = document.getElementById('setting-font-size-val');
    const readerContentBody = document.getElementById('reader-content-body');
    if (!readerScrollArea) return;

    const anchorIdx = getActiveAnchorIndex();

    // 1. Font size
    readerScrollArea.style.setProperty('--reader-font-size', `${readerSettings.fontSize}px`);
    if (settingFontSizeVal) settingFontSizeVal.textContent = `${readerSettings.fontSize} px`;

    // 2. Line height
    readerScrollArea.style.setProperty('--reader-line-height', readerSettings.lineHeight);

    // 3. Theme
    readerScrollArea.classList.remove('reader-theme-dark', 'reader-theme-sepia', 'reader-theme-light', 'reader-theme-oled');
    readerScrollArea.classList.add(`reader-theme-${readerSettings.theme}`);

    // 4. Font family
    readerScrollArea.classList.remove('reader-font-sans', 'reader-font-serif', 'reader-font-mono');
    readerScrollArea.classList.add(`reader-font-${readerSettings.fontFamily}`);

    // 5. Margin width
    readerScrollArea.classList.remove('reader-margins-narrow', 'reader-margins-normal', 'reader-margins-wide');
    readerScrollArea.classList.add(`reader-margins-${readerSettings.marginWidth}`);

    // 6. Text align
    readerScrollArea.classList.remove('reader-align-left', 'reader-align-justify');
    readerScrollArea.classList.add(`reader-align-${readerSettings.textAlign}`);

    updateReaderSettingsUI();

    // Re-anchor scroll position after font/layout change
    if (anchorIdx !== null && anchorIdx !== undefined && readerContentBody) {
        requestAnimationFrame(() => {
            const el = readerContentBody.querySelector(`[data-block-idx="${anchorIdx}"]`);
            if (el) {
                const containerTop = readerScrollArea.getBoundingClientRect().top;
                const elTop = el.getBoundingClientRect().top;
                readerScrollArea.scrollTop += (elTop - containerTop - 10);
            }
        });
    }
}

export function updateReaderSettingsUI() {
    const readerSettingsPanel = document.getElementById('reader-settings-panel');
    const settingFontSizeVal = document.getElementById('setting-font-size-val');
    const readerFontFamilyGroup = document.getElementById('reader-font-family-group');
    const readerLineHeightGroup = document.getElementById('reader-line-height-group');
    const readerMarginsGroup = document.getElementById('reader-margins-group');
    const readerThemeGroup = document.getElementById('reader-theme-group');
    const readerAlignGroup = document.getElementById('reader-align-group');
    const readerModeGroup = document.getElementById('reader-mode-group');
    const readerAutoloadGroup = document.getElementById('reader-autoload-group');
    const settingAutoloadRow = document.getElementById('setting-autoload-row');

    if (!readerSettingsPanel) return;

    if (settingFontSizeVal) settingFontSizeVal.textContent = `${readerSettings.fontSize} px`;

    if (readerFontFamilyGroup) {
        readerFontFamilyGroup.querySelectorAll('.seg-btn').forEach(btn => {
            btn.classList.toggle('active', btn.dataset.font === readerSettings.fontFamily);
        });
    }

    if (readerLineHeightGroup) {
        readerLineHeightGroup.querySelectorAll('.seg-btn').forEach(btn => {
            btn.classList.toggle('active', Math.abs(parseFloat(btn.dataset.lh) - parseFloat(readerSettings.lineHeight)) < 0.05);
        });
    }

    if (readerMarginsGroup) {
        readerMarginsGroup.querySelectorAll('.seg-btn').forEach(btn => {
            btn.classList.toggle('active', btn.dataset.margin === readerSettings.marginWidth);
        });
    }

    if (readerThemeGroup) {
        readerThemeGroup.querySelectorAll('.theme-chip').forEach(btn => {
            btn.classList.toggle('active', btn.dataset.theme === readerSettings.theme);
        });
    }

    if (readerAlignGroup) {
        readerAlignGroup.querySelectorAll('.seg-btn').forEach(btn => {
            btn.classList.toggle('active', btn.dataset.align === readerSettings.textAlign);
        });
    }

    if (readerModeGroup) {
        readerModeGroup.querySelectorAll('.seg-btn').forEach(btn => {
            btn.classList.toggle('active', btn.dataset.flow === readerSettings.flowMode);
        });
    }

    if (settingAutoloadRow) {
        settingAutoloadRow.style.display = (readerSettings.flowMode === 'chapters') ? '' : 'none';
    }

    if (readerAutoloadGroup) {
        readerAutoloadGroup.querySelectorAll('.seg-btn').forEach(btn => {
            btn.classList.toggle('active', (btn.dataset.autoload === 'true') === readerSettings.autoLoadNext);
        });
    }
}

export function positionSettingsPanel() {
    const readerSettingsPanel = document.getElementById('reader-settings-panel');
    const readerSettingsBtn = document.getElementById('reader-settings-btn');
    if (!readerSettingsPanel || !readerSettingsBtn) return;
    if (window.innerWidth <= 768) {
        readerSettingsPanel.style.top = '';
        readerSettingsPanel.style.left = '';
        readerSettingsPanel.style.right = '';
        readerSettingsPanel.style.maxHeight = '';
        return;
    }
    const rect = readerSettingsBtn.getBoundingClientRect();
    const panelWidth = 330;
    const viewportWidth = window.innerWidth;
    const viewportHeight = window.innerHeight;

    let left = rect.right - panelWidth;
    if (left < 16) left = 16;
    if (left + panelWidth > viewportWidth - 16) {
        left = viewportWidth - panelWidth - 16;
    }

    const top = Math.round(rect.bottom + 8);
    const maxH = Math.max(260, viewportHeight - top - 16);

    readerSettingsPanel.style.top = `${top}px`;
    readerSettingsPanel.style.left = `${Math.round(left)}px`;
    readerSettingsPanel.style.right = 'auto';
    readerSettingsPanel.style.maxHeight = `${maxH}px`;
}

// -----------------------------------------------------------------------
// Zen Focus Mode
// -----------------------------------------------------------------------
export function wakeZenHud() {
    if (!isZenMode) return;
    const hud = document.getElementById('reader-zen-hud');
    if (!hud) return;
    hud.classList.remove('hud-idle');
    if (zenHudIdleTimer) {
        clearTimeout(zenHudIdleTimer);
    }
    zenHudIdleTimer = setTimeout(() => {
        if (isZenMode && hud) {
            hud.classList.add('hud-idle');
        }
    }, 3000);
}

export function toggleZenMode(forceState = null) {
    const newState = (forceState !== null) ? Boolean(forceState) : !isZenMode;
    if (isZenMode === newState) return;
    isZenMode = newState;

    const hud = document.getElementById('reader-zen-hud');
    const zenBtn = document.getElementById('reader-zen-btn');
    const readerSettingsPanel = document.getElementById('reader-settings-panel');

    if (isZenMode) {
        document.body.classList.add('zen-mode-active');
        if (zenBtn) zenBtn.classList.add('active');
        if (readerSettingsPanel) readerSettingsPanel.classList.add('hidden');
        if (hud) {
            hud.classList.remove('hidden');
            hud.classList.remove('hud-idle');
            wakeZenHud();
        }
        if (!document.fullscreenElement && document.documentElement.requestFullscreen) {
            document.documentElement.requestFullscreen().catch(() => {});
        }
    } else {
        document.body.classList.remove('zen-mode-active');
        if (zenBtn) zenBtn.classList.remove('active');
        if (hud) {
            hud.classList.add('hidden');
            hud.classList.remove('hud-idle');
        }
        if (zenHudIdleTimer) {
            clearTimeout(zenHudIdleTimer);
            zenHudIdleTimer = null;
        }
        if (document.fullscreenElement && document.exitFullscreen) {
            document.exitFullscreen().catch(() => {});
        }
    }
}

// -----------------------------------------------------------------------
// Reader Module Initialization
// -----------------------------------------------------------------------
export function initReader() {
    loadSavedReaderSettings();
    applyReaderSettings();

    const readerSettingsBtn = document.getElementById('reader-settings-btn');
    const readerSettingsPanel = document.getElementById('reader-settings-panel');
    const readerSettingsCloseBtn = document.getElementById('reader-settings-close-btn');
    const readerWordPopup = document.getElementById('reader-word-popup');
    const settingFontDecBtn = document.getElementById('setting-font-dec-btn');
    const settingFontIncBtn = document.getElementById('setting-font-inc-btn');
    const readerFontFamilyGroup = document.getElementById('reader-font-family-group');
    const readerLineHeightGroup = document.getElementById('reader-line-height-group');
    const readerMarginsGroup = document.getElementById('reader-margins-group');
    const readerThemeGroup = document.getElementById('reader-theme-group');
    const readerAlignGroup = document.getElementById('reader-align-group');
    const readerModeGroup = document.getElementById('reader-mode-group');
    const readerAutoloadGroup = document.getElementById('reader-autoload-group');

    const readerContentBody = document.getElementById('reader-content-body');
    const readerScrollArea = document.getElementById('reader-scroll-area');
    const readerChapterSelect = document.getElementById('reader-chapter-select');
    const readerPrevChBtn = document.getElementById('reader-prev-ch-btn');
    const readerNextChBtn = document.getElementById('reader-next-ch-btn');
    const readerBackBtn = document.getElementById('reader-back-btn');
    const readerToggleHighlightBtn = document.getElementById('reader-toggle-highlight-btn');
    const readerTrainBtn = document.getElementById('reader-train-btn');
    const readerZenBtn = document.getElementById('reader-zen-btn');
    const zenHudExitBtn = document.getElementById('zen-hud-exit-btn');

    if (readerZenBtn) {
        readerZenBtn.addEventListener('click', (e) => {
            e.stopPropagation();
            toggleZenMode();
        });
    }

    if (zenHudExitBtn) {
        zenHudExitBtn.addEventListener('click', (e) => {
            e.stopPropagation();
            toggleZenMode(false);
        });
    }

    // Wake HUD on user activity during zen mode
    ['mousemove', 'touchstart', 'scroll'].forEach(evt => {
        window.addEventListener(evt, () => {
            if (isZenMode) wakeZenHud();
        }, { passive: true });
    });

    // Keyboard shortcut for Zen Mode (F / f / а / А) and exit on Escape
    document.addEventListener('keydown', (e) => {
        const tag = (e.target && e.target.tagName) ? e.target.tagName.toLowerCase() : '';
        if (tag === 'input' || tag === 'textarea' || (e.target && e.target.isContentEditable)) {
            return;
        }

        const readerView = document.getElementById('reader-view');
        const readerInterface = document.getElementById('reader-interface');
        const isReaderActive = readerView && !readerView.classList.contains('hidden') &&
                               readerInterface && !readerInterface.classList.contains('hidden');

        if (!isReaderActive) return;

        if (e.key === 'Escape' && isZenMode) {
            e.preventDefault();
            toggleZenMode(false);
            return;
        }

        if ((e.key === 'f' || e.key === 'F' || e.key === 'а' || e.key === 'А') && !e.ctrlKey && !e.metaKey && !e.altKey) {
            e.preventDefault();
            toggleZenMode();
        }
    });

    // Native fullscreen sync
    document.addEventListener('fullscreenchange', () => {
        if (!document.fullscreenElement && isZenMode) {
            toggleZenMode(false);
        }
    });

    const popupCloseBtn = document.getElementById('popup-close-btn');
    const popupSaveBtn = document.getElementById('popup-save-btn');
    const popupSavedBadge = document.getElementById('popup-saved-badge');
    const popupInLibrary = document.getElementById('popup-in-library');
    const popupAddContextBtn = document.getElementById('popup-add-context-btn');
    const popupTranslation = document.getElementById('popup-translation');

    const addTextBtn = document.getElementById('add-text-btn');
    const addBookModal = document.getElementById('add-book-modal');
    const closeAddBookModalBtn = document.getElementById('close-add-book-modal-btn');
    const cancelAddBookBtn = document.getElementById('cancel-add-book-btn');
    const addBookForm = document.getElementById('add-book-form');
    const bookTitleInput = document.getElementById('book-title-input');
    const bookAuthorInput = document.getElementById('book-author-input');
    const bookContentInput = document.getElementById('book-content-input');
    const bookFileInput = document.getElementById('book-file-input');

    // Settings panel triggers
    if (readerSettingsBtn) {
        readerSettingsBtn.addEventListener('click', (e) => {
            e.stopPropagation();
            if (readerWordPopup) readerWordPopup.classList.add('hidden');
            if (readerSettingsPanel) {
                const isHidden = readerSettingsPanel.classList.contains('hidden');
                readerSettingsPanel.classList.toggle('hidden', !isHidden);
                if (isHidden) {
                    updateReaderSettingsUI();
                    positionSettingsPanel();
                }
            }
        });
    }

    if (readerSettingsCloseBtn) {
        readerSettingsCloseBtn.addEventListener('click', () => {
            if (readerSettingsPanel) readerSettingsPanel.classList.add('hidden');
        });
    }

    if (settingFontDecBtn) {
        settingFontDecBtn.addEventListener('click', () => {
            if (readerSettings.fontSize > 13) {
                readerSettings.fontSize -= 1;
                applyReaderSettings();
                saveReaderSettings();
            }
        });
    }

    if (settingFontIncBtn) {
        settingFontIncBtn.addEventListener('click', () => {
            if (readerSettings.fontSize < 34) {
                readerSettings.fontSize += 1;
                applyReaderSettings();
                saveReaderSettings();
            }
        });
    }

    if (readerFontFamilyGroup) {
        readerFontFamilyGroup.addEventListener('click', (e) => {
            const btn = e.target.closest('.seg-btn');
            if (btn && btn.dataset.font) {
                readerSettings.fontFamily = btn.dataset.font;
                applyReaderSettings();
                saveReaderSettings();
            }
        });
    }

    if (readerLineHeightGroup) {
        readerLineHeightGroup.addEventListener('click', (e) => {
            const btn = e.target.closest('.seg-btn');
            if (btn && btn.dataset.lh) {
                readerSettings.lineHeight = parseFloat(btn.dataset.lh);
                applyReaderSettings();
                saveReaderSettings();
            }
        });
    }

    if (readerMarginsGroup) {
        readerMarginsGroup.addEventListener('click', (e) => {
            const btn = e.target.closest('.seg-btn');
            if (btn && btn.dataset.margin) {
                readerSettings.marginWidth = btn.dataset.margin;
                applyReaderSettings();
                saveReaderSettings();
            }
        });
    }

    if (readerThemeGroup) {
        readerThemeGroup.addEventListener('click', (e) => {
            const btn = e.target.closest('.theme-chip');
            if (btn && btn.dataset.theme) {
                readerSettings.theme = btn.dataset.theme;
                applyReaderSettings();
                saveReaderSettings();
            }
        });
    }

    if (readerAlignGroup) {
        readerAlignGroup.addEventListener('click', (e) => {
            const btn = e.target.closest('.seg-btn');
            if (btn && btn.dataset.align) {
                readerSettings.textAlign = btn.dataset.align;
                applyReaderSettings();
                saveReaderSettings();
            }
        });
    }

    if (readerModeGroup) {
        readerModeGroup.addEventListener('click', (e) => {
            const btn = e.target.closest('.seg-btn');
            if (btn && btn.dataset.flow) {
                if (readerSettings.flowMode !== btn.dataset.flow) {
                    readerSettings.flowMode = btn.dataset.flow;
                    saveReaderSettings();
                    updateReaderSettingsUI();
                    if (currentBook) {
                        if (readerSettings.flowMode === 'continuous') {
                            renderContinuousBook(currentChapterIndex);
                        } else {
                            renderChapter(currentChapterIndex);
                        }
                    }
                }
            }
        });
    }

    if (readerAutoloadGroup) {
        readerAutoloadGroup.addEventListener('click', (e) => {
            const btn = e.target.closest('.seg-btn');
            if (btn && btn.dataset.autoload !== undefined) {
                readerSettings.autoLoadNext = (btn.dataset.autoload === 'true');
                saveReaderSettings();
                updateReaderSettingsUI();
                const footerHint = readerContentBody ? readerContentBody.querySelector('.chapter-footer-hint') : null;
                if (footerHint) {
                    footerHint.textContent = (readerSettings.flowMode === 'chapters' && readerSettings.autoLoadNext)
                        ? '⚡ Автоподгрузка включена: следующая глава подгрузится автоматически при скролле вниз'
                        : '💡 Нажмите кнопку выше для перехода к следующей главе';
                }
            }
        });
    }

    document.addEventListener('click', (e) => {
        if (readerSettingsPanel && !readerSettingsPanel.classList.contains('hidden')) {
            if (!readerSettingsPanel.contains(e.target) && e.target !== readerSettingsBtn && !readerSettingsBtn.contains(e.target)) {
                readerSettingsPanel.classList.add('hidden');
            }
        }
    });

    window.addEventListener('resize', () => {
        if (readerSettingsPanel && !readerSettingsPanel.classList.contains('hidden')) {
            positionSettingsPanel();
        }
    }, { passive: true });

    window.addEventListener('scroll', () => {
        if (readerSettingsPanel && !readerSettingsPanel.classList.contains('hidden') && window.innerWidth > 768) {
            positionSettingsPanel();
        }
    }, { passive: true });

    // Word clicking & highlighting
    if (readerContentBody) {
        readerContentBody.addEventListener('click', (e) => {
            const wordSpan = e.target.closest('.reader-word');
            if (wordSpan) {
                e.stopPropagation();
                const word = wordSpan.dataset.word;
                const context = wordSpan.dataset.context || wordSpan.closest('p, div, li, td, th, blockquote, figcaption')?.textContent || word;
                handleWordClick(word, context, wordSpan);
            }
        });

        // Phrase/chunk selection in reader
        readerContentBody.addEventListener('mouseup', () => {
            const sel = window.getSelection();
            const text = sel.toString().trim();
            if (text && text.split(/\s+/).length >= 2 && text.length <= 80) {
                const range = sel.getRangeAt(0);
                const rect = range.getBoundingClientRect();
                openWordPopup(text, text, {
                    getBoundingClientRect: () => rect,
                });
            }
        });
    }

    if (readerToggleHighlightBtn) {
        readerToggleHighlightBtn.addEventListener('click', () => {
            isHighlightEnabled = !isHighlightEnabled;
            readerToggleHighlightBtn.classList.toggle('btn-primary', isHighlightEnabled);
            if (readerContentBody) {
                readerContentBody.querySelectorAll('.reader-word').forEach(w => {
                    w.classList.toggle('highlight-enabled', isHighlightEnabled);
                });
            }
        });
    }

    if (readerTrainBtn) {
        readerTrainBtn.addEventListener('click', () => {
            if (currentBook) {
                const bookTag = slugify(currentBook.title);
                window.location.hash = `#srs/${encodeURIComponent(bookTag)}`;
            }
        });
    }

    // Popup actions
    if (popupCloseBtn) {
        popupCloseBtn.addEventListener('click', () => {
            if (readerWordPopup) readerWordPopup.classList.add('hidden');
        });
    }

    document.addEventListener('click', (e) => {
        if (readerWordPopup && !readerWordPopup.contains(e.target) && !e.target.classList.contains('reader-word')) {
            readerWordPopup.classList.add('hidden');
        }
    });

    window.addEventListener('scroll', schedulePopupUpdate, { passive: true, capture: true });
    window.addEventListener('resize', schedulePopupUpdate, { passive: true });

    const popupAudioBtn = document.getElementById('popup-audio-btn');
    const popupAudioSentenceBtn = document.getElementById('popup-audio-sentence-btn');
    const popupAudioRuBtn = document.getElementById('popup-audio-ru-btn');
    const popupTranslateSentenceBtn = document.getElementById('popup-translate-sentence-btn');
    const popupUseContextMeaningBtn = document.getElementById('popup-use-context-meaning-btn');
    const popupSentenceLoading = document.getElementById('popup-sentence-loading');
    const popupSentenceTranslationWrap = document.getElementById('popup-sentence-translation-wrap');
    const popupSentenceRu = document.getElementById('popup-sentence-ru');
    const popupContextMeaningWrap = document.getElementById('popup-context-meaning-wrap');
    const popupContextMeaningVal = document.getElementById('popup-context-meaning-val');
    const popupAiSourceBadge = document.getElementById('popup-ai-source-badge');

    if (popupAudioBtn) {
        popupAudioBtn.addEventListener('click', (e) => {
            e.stopPropagation();
            if (!popupCurrentData || !popupCurrentData.term) return;
            const term = popupCurrentData.term;
            const url = popupCurrentData.audioUrl || `/api/tts?text=${encodeURIComponent(term)}&lang=en`;
            playAudio(url);
        });
    }

    if (popupAudioSentenceBtn) {
        popupAudioSentenceBtn.addEventListener('click', (e) => {
            e.stopPropagation();
            if (!popupCurrentData || !popupCurrentData.contextSentence) return;
            const sentence = popupCurrentData.contextSentence;
            const url = `/api/tts?text=${encodeURIComponent(sentence)}&lang=en`;
            playAudio(url);
        });
    }

    if (popupAudioRuBtn) {
        popupAudioRuBtn.addEventListener('click', (e) => {
            e.stopPropagation();
            const ruText = (popupSentenceRu && popupSentenceRu.textContent || '').trim();
            if (!ruText || ruText.startsWith('(') || ruText.startsWith('Ошибка')) return;
            const url = `/api/tts?text=${encodeURIComponent(ruText)}&lang=ru`;
            playAudio(url);
        });
    }

    if (popupTranslateSentenceBtn) {
        popupTranslateSentenceBtn.addEventListener('click', async (e) => {
            e.stopPropagation();
            if (!popupCurrentData || !popupCurrentData.contextSentence) return;
            const ctxSentence = popupCurrentData.contextSentence;
            const term = popupCurrentData.term;

            popupTranslateSentenceBtn.disabled = true;
            if (popupSentenceLoading) popupSentenceLoading.classList.remove('hidden');
            if (popupSentenceTranslationWrap) popupSentenceTranslationWrap.classList.add('hidden');
            if (popupContextMeaningWrap) popupContextMeaningWrap.classList.add('hidden');

            try {
                const res = await api.lookup.translateSentence(ctxSentence, term, popupCurrentData.paragraphContext || '');
                if (popupSentenceLoading) popupSentenceLoading.classList.add('hidden');
                if (popupSentenceTranslationWrap) popupSentenceTranslationWrap.classList.remove('hidden');

                if (popupSentenceRu) {
                    popupSentenceRu.textContent = res.sentence_ru || 'Перевод не получен';
                }

                if (res.word_meaning && res.word_meaning.trim()) {
                    popupCurrentData.contextMeaning = res.word_meaning.trim();
                    if (popupContextMeaningWrap) popupContextMeaningWrap.classList.remove('hidden');
                    if (popupContextMeaningVal) popupContextMeaningVal.textContent = res.word_meaning.trim();
                } else {
                    if (popupContextMeaningWrap) popupContextMeaningWrap.classList.add('hidden');
                }

                if (popupAiSourceBadge) {
                    popupAiSourceBadge.classList.remove('hidden');
                    popupAiSourceBadge.textContent = res.cached ? '⚡ Кеш (0.01ms)' : '⚡ Local AI (Qwen)';
                    popupAiSourceBadge.title = res.source || '';
                }

                positionWordPopup(popupCurrentData.targetElement);
            } catch (err) {
                console.error('Sentence translation error:', err);
                if (popupSentenceLoading) popupSentenceLoading.classList.add('hidden');
                if (popupSentenceTranslationWrap) popupSentenceTranslationWrap.classList.remove('hidden');
                if (popupSentenceRu) popupSentenceRu.textContent = 'Ошибка связи с локальным ИИ';
            } finally {
                popupTranslateSentenceBtn.disabled = false;
            }
        });
    }

    if (popupUseContextMeaningBtn) {
        popupUseContextMeaningBtn.addEventListener('click', (e) => {
            e.stopPropagation();
            if (!popupCurrentData || !popupCurrentData.contextMeaning) return;
            const meaning = popupCurrentData.contextMeaning;
            if (popupTranslation) popupTranslation.textContent = meaning;
            if (popupCurrentData.lookup) {
                popupCurrentData.lookup.translation = meaning;
            }
            popupUseContextMeaningBtn.textContent = '✓ Вставлено!';
            setTimeout(() => {
                if (popupUseContextMeaningBtn) popupUseContextMeaningBtn.textContent = 'Вставить в карточку';
            }, 1800);
        });
    }

    const popupSwitchPhrasalBtn = document.getElementById('popup-switch-phrasal-btn');
    if (popupSwitchPhrasalBtn) {
        popupSwitchPhrasalBtn.addEventListener('click', (e) => {
            e.stopPropagation();
            if (!popupCurrentData || !popupCurrentData.phrasalVerb) return;
            const pv = popupCurrentData.phrasalVerb;

            if (!popupCurrentData.isPhrasalMode) {
                // Switch to phrasal verb mode
                popupCurrentData.isPhrasalMode = true;
                if (popupTerm) popupTerm.textContent = pv.term;
                if (popupTranslation) popupTranslation.textContent = pv.translation;
                if (popupPhonetic) popupPhonetic.textContent = '';

                const inLib = Boolean(pv.in_library);
                if (popupInLibrary) popupInLibrary.classList.toggle('hidden', !inLib);
                if (popupSaveBtn) {
                    popupSaveBtn.classList.toggle('hidden', inLib);
                    popupSaveBtn.textContent = `💾 Сохранить «${pv.term}» в словарь`;
                }
                if (popupSavedBadge) {
                    popupSavedBadge.classList.toggle('hidden', !inLib);
                    popupSavedBadge.textContent = '⭐ Фразовый глагол уже в библиотеке';
                }
                if (popupAddContextBtn) popupAddContextBtn.classList.add('hidden');
                popupSwitchPhrasalBtn.textContent = `↩️ Вернуться к «${popupCurrentData.term}»`;
            } else {
                // Revert back to single word
                popupCurrentData.isPhrasalMode = false;
                const origTrans = popupCurrentData.lookup ? (popupCurrentData.lookup.translation || popupCurrentData.lookup.translation_ru || '') : '';

                if (popupTerm) popupTerm.textContent = popupCurrentData.term;
                if (popupTranslation) popupTranslation.textContent = origTrans;
                if (popupPhonetic) popupPhonetic.textContent = popupCurrentData.lookup?.phonetic || '';

                const inLib = Boolean(popupCurrentData.lookup?.in_library || popupCurrentData.existingCard);
                if (popupInLibrary) popupInLibrary.classList.toggle('hidden', !inLib);
                if (popupSaveBtn) {
                    popupSaveBtn.classList.toggle('hidden', inLib);
                    popupSaveBtn.textContent = '💾 Добавить в словарь';
                }
                if (popupSavedBadge) {
                    popupSavedBadge.classList.toggle('hidden', !inLib);
                    popupSavedBadge.textContent = '⭐ Слово уже в библиотеке';
                }
                popupSwitchPhrasalBtn.textContent = `🔗 Переключить на «${pv.term}»`;
            }
            positionWordPopup(popupCurrentData.targetElement);
        });
    }

    if (popupSaveBtn) {
        popupSaveBtn.addEventListener('click', async () => {
            if (!popupCurrentData) return;
            const d = popupCurrentData;
            const lookup = d.lookup || {};
            const bookTag = currentBook ? slugify(currentBook.title) : 'reader';
            const isPv = Boolean(d.isPhrasalMode && d.phrasalVerb);
            const termToSave = isPv ? d.phrasalVerb.term : d.term;
            const transToSave = isPv
                ? d.phrasalVerb.translation
                : (lookup.translation || lookup.translation_ru || (popupTranslation ? popupTranslation.textContent : ''));
            const collectionToSave = isPv ? 'Фразовые глаголы & Идиомы' : 'Книги & Сериалы';
            const tagsToSave = isPv ? `${bookTag}, phrasal-verbs, reader` : `${bookTag}, reader`;

            const payload = {
                term: termToSave,
                translation: transToSave,
                context_sentence: d.contextSentence || '',
                phonetic: isPv ? '' : (lookup.phonetic || ''),
                audio_url: isPv ? '' : (lookup.audio_url || ''),
                part_of_speech: isPv ? 'verb phrase' : (lookup.part_of_speech || ''),
                definition_en: lookup.definition_en || '',
                collection: collectionToSave,
                tags: tagsToSave,
                notes: currentBook ? `Из книги: ${currentBook.title}` : '',
            };

            try {
                const resp = await api.cards.create(payload);
                if (resp.ok) {
                    const resData = await resp.json();
                    popupSaveBtn.classList.add('hidden');
                    if (popupSavedBadge) {
                        popupSavedBadge.classList.remove('hidden');
                        popupSavedBadge.textContent = resData.already_exists ? '⭐ Уже есть в библиотеке' : '✅ Сохранено в словарь!';
                    }
                    if (popupInLibrary) popupInLibrary.classList.remove('hidden');
                    if (popupAddContextBtn) popupAddContextBtn.classList.add('hidden');

                    if (d.targetElement) {
                        d.targetElement.classList.add('status-learning');
                        if (isHighlightEnabled) d.targetElement.classList.add('highlight-enabled');
                    }

                    await fetchCards();
                } else {
                    alert('Не удалось сохранить слово');
                }
            } catch (e) {
                console.error('Save card from reader error:', e);
            }
        });
    }

    if (popupAddContextBtn) {
        popupAddContextBtn.addEventListener('click', async () => {
            if (!popupCurrentData) return;
            const d = popupCurrentData;
            const lookup = d.lookup || {};
            const bookTag = currentBook ? slugify(currentBook.title) : 'reader';
            const payload = {
                term: d.term,
                translation: lookup.translation || lookup.translation_ru || (popupTranslation ? popupTranslation.textContent : ''),
                context_sentence: d.contextSentence || '',
                phonetic: lookup.phonetic || '',
                audio_url: lookup.audio_url || '',
                part_of_speech: lookup.part_of_speech || '',
                definition_en: lookup.definition_en || '',
                collection: 'Книги & Сериалы',
                tags: `${bookTag}, reader`,
                notes: currentBook ? `Из книги: ${currentBook.title}` : '',
            };

            popupAddContextBtn.disabled = true;
            popupAddContextBtn.textContent = 'Сохраняем...';

            try {
                const resp = await api.cards.create(payload);
                if (resp.ok) {
                    popupAddContextBtn.classList.add('hidden');
                    if (popupSavedBadge) {
                        popupSavedBadge.textContent = '✅ Цитата прикреплена к карточке!';
                        popupSavedBadge.classList.remove('hidden');
                    }
                    await fetchCards();
                } else {
                    alert('Не удалось обновить контекст');
                }
            } catch (e) {
                console.error('Add context error:', e);
            } finally {
                popupAddContextBtn.disabled = false;
                popupAddContextBtn.textContent = '+ Добавить эту цитату к карточке';
            }
        });
    }

    // Chapter Navigation & Reader Toolbar
    if (readerChapterSelect) {
        readerChapterSelect.addEventListener('change', () => {
            const ch = parseInt(readerChapterSelect.value, 10);
            if (!currentBook) return;

            if (readerSettings.flowMode === 'continuous') {
                currentChapterIndex = ch;
                updateChapterSelectIcons();
                if (readerPrevChBtn) readerPrevChBtn.disabled = currentChapterIndex <= 0;
                if (readerNextChBtn) readerNextChBtn.disabled = currentChapterIndex >= currentBook.chapters.length - 1;

                const target = document.getElementById(`chapter-anchor-${ch}`)
                               || (readerContentBody && readerContentBody.querySelector(`[data-chapter-idx="${ch}"]`));
                if (target) {
                    scrollToElement(target, true);
                } else {
                    renderContinuousBook(ch);
                }

                const desiredHash = `#reader/book/${currentBook.id}/ch/${ch}`;
                if (window.location.hash !== desiredHash) {
                    history.replaceState(null, '', desiredHash);
                }
                return;
            }

            window.location.hash = `#reader/book/${currentBook.id}/ch/${ch}`;
        });
    }

    if (readerPrevChBtn) {
        readerPrevChBtn.addEventListener('click', () => {
            if (currentBook && currentChapterIndex > 0) {
                const prev = currentChapterIndex - 1;
                if (readerSettings.flowMode === 'continuous') {
                    currentChapterIndex = prev;
                    if (readerChapterSelect) readerChapterSelect.value = prev;
                    updateChapterSelectIcons();
                    readerPrevChBtn.disabled = currentChapterIndex <= 0;
                    if (readerNextChBtn) readerNextChBtn.disabled = currentChapterIndex >= currentBook.chapters.length - 1;

                    const target = document.getElementById(`chapter-anchor-${prev}`)
                                   || (readerContentBody && readerContentBody.querySelector(`[data-chapter-idx="${prev}"]`));
                    if (target) {
                        scrollToElement(target, true);
                    } else {
                        renderContinuousBook(prev);
                    }

                    const desiredHash = `#reader/book/${currentBook.id}/ch/${prev}`;
                    if (window.location.hash !== desiredHash) {
                        history.replaceState(null, '', desiredHash);
                    }
                    return;
                }
                window.location.hash = `#reader/book/${currentBook.id}/ch/${prev}`;
            }
        });
    }

    if (readerNextChBtn) {
        readerNextChBtn.addEventListener('click', () => {
            if (currentBook && currentBook.chapters && currentChapterIndex < currentBook.chapters.length - 1) {
                const next = currentChapterIndex + 1;
                if (readerSettings.flowMode === 'continuous') {
                    currentChapterIndex = next;
                    if (readerChapterSelect) readerChapterSelect.value = next;
                    updateChapterSelectIcons();
                    if (readerPrevChBtn) readerPrevChBtn.disabled = currentChapterIndex <= 0;
                    readerNextChBtn.disabled = currentChapterIndex >= currentBook.chapters.length - 1;

                    const target = document.getElementById(`chapter-anchor-${next}`)
                                   || (readerContentBody && readerContentBody.querySelector(`[data-chapter-idx="${next}"]`));
                    if (target) {
                        scrollToElement(target, true);
                    } else {
                        renderContinuousBook(next);
                    }

                    const desiredHash = `#reader/book/${currentBook.id}/ch/${next}`;
                    if (window.location.hash !== desiredHash) {
                        history.replaceState(null, '', desiredHash);
                    }
                    return;
                }
                if (readerSettings.flowMode === 'chapters' && readerSettings.autoLoadNext) {
                    appendNextChapter(next, true);
                } else {
                    window.location.hash = `#reader/book/${currentBook.id}/ch/${next}`;
                }
            }
        });
    }

    if (readerBackBtn) {
        readerBackBtn.addEventListener('click', () => {
            if (isZenMode) toggleZenMode(false);
            window.location.hash = '#reader';
        });
    }

    if (readerScrollArea) {
        readerScrollArea.addEventListener('scroll', handleReaderScroll, { passive: true });
    }

    window.addEventListener('beforeunload', () => {
        if (currentBook && readerScrollArea) {
            const { scrollTop, fraction } = getReaderScrollMetrics();
            const anchorIdx = getActiveAnchorIndex();
            try {
                localStorage.setItem(`notes_book_${currentBook.id}_pos`, JSON.stringify({
                    chapter: currentChapterIndex,
                    scrollTop: scrollTop,
                    fraction: fraction,
                    anchorIdx: anchorIdx,
                    savedAt: Date.now()
                }));
                localStorage.setItem('notes_active_book_id', currentBook.id);
            } catch (e) {}
            if (navigator.sendBeacon) {
                const blob = new Blob([JSON.stringify({ current_chapter: currentChapterIndex, current_position: fraction })], { type: 'application/json' });
                navigator.sendBeacon(`/api/books/${currentBook.id}/progress`, blob);
            }
        }
    });

    // Bookshelf Add/Upload Actions
    if (addTextBtn && addBookModal && addBookForm) {
        addTextBtn.addEventListener('click', () => {
            addBookForm.reset();
            addBookModal.classList.remove('hidden');
        });
    }

    if (closeAddBookModalBtn && addBookModal) {
        closeAddBookModalBtn.addEventListener('click', () => addBookModal.classList.add('hidden'));
    }
    if (cancelAddBookBtn && addBookModal) {
        cancelAddBookBtn.addEventListener('click', () => addBookModal.classList.add('hidden'));
    }

    if (addBookForm) {
        addBookForm.addEventListener('submit', async (e) => {
            e.preventDefault();
            const title = bookTitleInput ? bookTitleInput.value.trim() : '';
            const author = bookAuthorInput ? bookAuthorInput.value.trim() : '';
            const content = bookContentInput ? bookContentInput.value.trim() : '';

            if (!title || !content) return;

            try {
                const resp = await api.books.createManual({
                    title: title,
                    author: author,
                    content: content,
                    source_type: 'text',
                });

                if (resp.ok) {
                    const book = await resp.json();
                    if (addBookModal) addBookModal.classList.add('hidden');
                    window.location.hash = `#reader/book/${book.id}`;
                } else {
                    alert('Ошибка при сохранении книги');
                }
            } catch (err) {
                console.error('Book create error:', err);
            }
        });
    }

    if (bookFileInput) {
        bookFileInput.addEventListener('change', async () => {
            const file = bookFileInput.files[0];
            if (!file) return;

            const formData = new FormData();
            formData.append('file', file);

            try {
                const resp = await api.books.uploadFile(formData);

                if (resp.ok) {
                    const book = await resp.json();
                    bookFileInput.value = '';
                    window.location.hash = `#reader/book/${book.id}`;
                } else {
                    let errMsg = 'Не удалось обработать файл';
                    try {
                        const errData = await resp.json();
                        errMsg = errData.detail || errMsg;
                    } catch (_) {
                        if (resp.status === 413) {
                            errMsg = 'Файл слишком большой (превышен лимит размера в Nginx)';
                        } else {
                            errMsg = `Код ответа сервера: HTTP ${resp.status}`;
                        }
                    }
                    alert(`Ошибка загрузки: ${errMsg}`);
                }
            } catch (e) {
                console.error('File upload error:', e);
                alert('Ошибка сети или соединение прервано при загрузке файла');
            }
        });
    }

    // RFC Fetching & Presets
    const rfcFetchForm = document.getElementById('rfc-fetch-form');
    const rfcInput = document.getElementById('rfc-input');
    const rfcFetchBtn = document.getElementById('rfc-fetch-btn');
    const rfcFetchStatus = document.getElementById('rfc-fetch-status');
    const rfcPresetChips = document.querySelectorAll('.rfc-preset-chip');

    async function handleRfcFetch(query) {
        if (!query) return;
        query = query.trim();
        if (!query) return;

        if (rfcFetchBtn) rfcFetchBtn.disabled = true;
        if (rfcInput) rfcInput.disabled = true;
        if (rfcFetchStatus) {
            rfcFetchStatus.className = 'rfc-fetch-status rfc-status-loading';
            rfcFetchStatus.innerHTML = `<span>⏳ Загрузка и разбор спецификации RFC...</span>`;
            rfcFetchStatus.classList.remove('hidden');
        }

        try {
            const book = await api.books.fetchRfc(query);
            if (rfcFetchStatus) {
                rfcFetchStatus.className = 'rfc-fetch-status rfc-status-success';
                rfcFetchStatus.innerHTML = `<span>✅ ${escapeHtml(book.title)} успешно добавлен!</span>`;
            }
            showToast(book.already_existed ? `Открываем ${book.title}` : `RFC спецификация загружена!`);
            if (rfcInput) rfcInput.value = '';
            setTimeout(() => {
                if (rfcFetchStatus) rfcFetchStatus.classList.add('hidden');
                window.location.hash = `#reader/book/${book.id}`;
            }, 400);
        } catch (err) {
            console.error('RFC fetch error:', err);
            if (rfcFetchStatus) {
                rfcFetchStatus.className = 'rfc-fetch-status rfc-status-error';
                rfcFetchStatus.innerHTML = `<span>❌ Ошибка: ${escapeHtml(err.message || 'Не удалось загрузить RFC')}</span>`;
                rfcFetchStatus.classList.remove('hidden');
            }
            showToast(err.message || 'Ошибка загрузки RFC', 4000);
        } finally {
            if (rfcFetchBtn) rfcFetchBtn.disabled = false;
            if (rfcInput) {
                rfcInput.disabled = false;
                rfcInput.focus();
            }
        }
    }

    if (rfcFetchForm) {
        rfcFetchForm.addEventListener('submit', (e) => {
            e.preventDefault();
            const val = rfcInput ? rfcInput.value : '';
            handleRfcFetch(val);
        });
    }

    if (rfcPresetChips && rfcPresetChips.length > 0) {
        rfcPresetChips.forEach(chip => {
            chip.addEventListener('click', () => {
                const rfcVal = chip.dataset.rfc;
                if (rfcInput) rfcInput.value = rfcVal;
                handleRfcFetch(rfcVal);
            });
        });
    }

    // -----------------------------------------------------------------------
    // Wikipedia Autonomous Import & Settings
    // -----------------------------------------------------------------------
    const WIKI_SETTINGS_KEY = 'notes_wiki_settings';
    const wikiReadBtn = document.getElementById('wiki-read-btn');
    const wikiSettingsBtn = document.getElementById('wiki-settings-btn');
    const wikiSettingsModal = document.getElementById('wiki-settings-modal');
    const wikiSettingsCloseBtn = document.getElementById('wiki-settings-close-btn');
    const wikiSettingsSaveBtn = document.getElementById('wiki-settings-save-btn');
    const wikiFetchStatus = document.getElementById('wiki-fetch-status');
    const wikiCustomForm = document.getElementById('wiki-custom-form');
    const wikiCustomInput = document.getElementById('wiki-custom-input');
    const wikiCustomFetchBtn = document.getElementById('wiki-custom-fetch-btn');

    const wikiActiveLangBadge = document.getElementById('wiki-active-lang-badge');
    const wikiActiveTimeBadge = document.getElementById('wiki-active-time-badge');
    const wikiActiveTopicBadge = document.getElementById('wiki-active-topic-badge');

    const TOPIC_LABELS = {
        'random': '🎲 Любая тема',
        'science': '🚀 Наука и космос',
        'tech': '💻 Технологии и IT',
        'history': '🏛️ История',
        'nature': '🌿 Природа',
        'psychology': '🧠 Психология',
        'featured': '⭐ Статья дня'
    };

    const TIME_LABELS = {
        '5': '⏱️ ~5 мин',
        '10-15': '⏱️ ~10-15 мин',
        '20+': '⏱️ 20+ мин',
        'any': '⏱️ Любой объем'
    };

    function getStoredWikiSettings() {
        try {
            const raw = localStorage.getItem(WIKI_SETTINGS_KEY);
            if (raw) {
                const parsed = JSON.parse(raw);
                if (parsed && typeof parsed === 'object') {
                    return {
                        lang: parsed.lang || 'simple',
                        time_budget: parsed.time_budget || '10-15',
                        topic: parsed.topic || 'random'
                    };
                }
            }
        } catch (_) {}
        return { lang: 'simple', time_budget: '10-15', topic: 'random' };
    }

    function saveStoredWikiSettings(settings) {
        try {
            localStorage.setItem(WIKI_SETTINGS_KEY, JSON.stringify(settings));
        } catch (_) {}
        updateWikiUIBadges(settings);
    }

    function updateWikiUIBadges(settings) {
        if (wikiActiveLangBadge) {
            wikiActiveLangBadge.textContent = settings.lang === 'en' ? 'Standard English (B2–C1)' : 'Simple English (A2–B1)';
        }
        if (wikiActiveTimeBadge) {
            wikiActiveTimeBadge.textContent = TIME_LABELS[settings.time_budget] || '⏱️ ~10-15 мин';
        }
        if (wikiActiveTopicBadge) {
            wikiActiveTopicBadge.textContent = TOPIC_LABELS[settings.topic] || '🎲 Любая тема';
        }
    }

    function syncWikiModalInputs(settings) {
        const langRadios = document.querySelectorAll('input[name="wiki-lang"]');
        langRadios.forEach(r => {
            r.checked = (r.value === settings.lang);
        });
        const timeRadios = document.querySelectorAll('input[name="wiki-time"]');
        timeRadios.forEach(r => {
            r.checked = (r.value === settings.time_budget);
        });
        const topicSelect = document.getElementById('wiki-topic-select');
        if (topicSelect) {
            topicSelect.value = settings.topic || 'random';
        }
    }

    function readWikiModalInputs() {
        const langRadio = document.querySelector('input[name="wiki-lang"]:checked');
        const timeRadio = document.querySelector('input[name="wiki-time"]:checked');
        const topicSelect = document.getElementById('wiki-topic-select');

        return {
            lang: langRadio ? langRadio.value : 'simple',
            time_budget: timeRadio ? timeRadio.value : '10-15',
            topic: topicSelect ? topicSelect.value : 'random'
        };
    }

    const currentWikiSettings = getStoredWikiSettings();
    updateWikiUIBadges(currentWikiSettings);

    if (wikiSettingsBtn && wikiSettingsModal) {
        wikiSettingsBtn.addEventListener('click', () => {
            syncWikiModalInputs(getStoredWikiSettings());
            wikiSettingsModal.classList.remove('hidden');
        });
    }

    if (wikiSettingsCloseBtn && wikiSettingsModal) {
        wikiSettingsCloseBtn.addEventListener('click', () => {
            wikiSettingsModal.classList.add('hidden');
        });
    }

    if (wikiSettingsModal) {
        wikiSettingsModal.addEventListener('click', (e) => {
            if (e.target === wikiSettingsModal) {
                wikiSettingsModal.classList.add('hidden');
            }
        });
    }

    if (wikiSettingsSaveBtn && wikiSettingsModal) {
        wikiSettingsSaveBtn.addEventListener('click', () => {
            const newSettings = readWikiModalInputs();
            saveStoredWikiSettings(newSettings);
            wikiSettingsModal.classList.add('hidden');
            showToast('Настройки статей Википедии сохранены!');
        });
    }

    async function handleWikiFetch(params) {
        const isCustom = Boolean(params.query);
        const activeBtn = isCustom ? wikiCustomFetchBtn : wikiReadBtn;

        if (activeBtn) activeBtn.disabled = true;
        if (wikiReadBtn) wikiReadBtn.disabled = true;
        if (wikiCustomInput) wikiCustomInput.disabled = true;

        if (wikiFetchStatus) {
            wikiFetchStatus.className = 'wiki-fetch-status wiki-status-loading';
            wikiFetchStatus.innerHTML = `<span>⏳ ${isCustom ? 'Загрузка статьи по запросу...' : 'Подбираем и загружаем статью из Википедии...'}</span>`;
            wikiFetchStatus.classList.remove('hidden');
        }

        try {
            const book = await api.books.fetchWikipedia(params);
            if (wikiFetchStatus) {
                wikiFetchStatus.className = 'wiki-fetch-status wiki-status-success';
                const estMin = Math.max(1, Math.round((book.total_words || 800) / 180));
                wikiFetchStatus.innerHTML = `<span>✅ Статья «${escapeHtml(book.title)}» сохранена (~${estMin} мин, ${book.total_words ? book.total_words.toLocaleString() : ''} слов)!</span>`;
            }
            showToast(book.already_existed ? `Открываем ${book.title}` : `Статья Википедии сохранена офлайн!`);
            if (wikiCustomInput) wikiCustomInput.value = '';
            await loadBookshelf();
            setTimeout(() => {
                if (wikiFetchStatus) wikiFetchStatus.classList.add('hidden');
                if (wikiSettingsModal) wikiSettingsModal.classList.add('hidden');
                window.location.hash = `#reader/book/${book.id}`;
            }, 500);
        } catch (err) {
            console.error('Wikipedia fetch error:', err);
            if (wikiFetchStatus) {
                wikiFetchStatus.className = 'wiki-fetch-status wiki-status-error';
                wikiFetchStatus.innerHTML = `<span>❌ Ошибка: ${escapeHtml(err.message || 'Не удалось загрузить статью')}</span>`;
                wikiFetchStatus.classList.remove('hidden');
            }
            showToast(err.message || 'Ошибка загрузки статьи Wikipedia', 4000);
        } finally {
            if (activeBtn) activeBtn.disabled = false;
            if (wikiReadBtn) wikiReadBtn.disabled = false;
            if (wikiCustomInput) wikiCustomInput.disabled = false;
        }
    }

    if (wikiReadBtn) {
        wikiReadBtn.addEventListener('click', () => {
            const currentSettings = getStoredWikiSettings();
            handleWikiFetch({
                query: '',
                lang: currentSettings.lang,
                time_budget: currentSettings.time_budget,
                topic: currentSettings.topic,
                force: false
            });
        });
    }

    if (wikiCustomForm) {
        wikiCustomForm.addEventListener('submit', (e) => {
            e.preventDefault();
            const val = wikiCustomInput ? wikiCustomInput.value.trim() : '';
            if (!val) return;
            const currentSettings = getStoredWikiSettings();
            handleWikiFetch({
                query: val,
                lang: currentSettings.lang,
                time_budget: currentSettings.time_budget,
                topic: currentSettings.topic,
                force: false
            });
        });
    }
}