feat(ai): integrate local Ollama AI for in-context sentence translation and caching (Task 13)

app/database.py

@@ -1,5 +1,6 @@
 import sqlite3
 import contextlib
+import hashlib
 from pathlib import Path
 from typing import Generator
 from app import config
@@ -186,6 +187,21 @@ def _migrate(conn: sqlite3.Connection):
     """)
     conn.execute("CREATE INDEX IF NOT EXISTS idx_offline_dict_term ON offline_dictionary(term COLLATE NOCASE);")
 
+    # Ensure sentence_translations table exists
+    conn.execute("""
+    CREATE TABLE IF NOT EXISTS sentence_translations (
+        id INTEGER PRIMARY KEY AUTOINCREMENT,
+        sentence_hash TEXT NOT NULL,
+        original_text TEXT NOT NULL,
+        translated_text TEXT NOT NULL,
+        target_word TEXT DEFAULT '',
+        word_meaning TEXT DEFAULT '',
+        source TEXT DEFAULT 'local_llm',
+        created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+    );
+    """)
+    conn.execute("CREATE INDEX IF NOT EXISTS idx_sentence_trans_hash ON sentence_translations(sentence_hash);")
+
     # Auto-seed offline dictionary if empty
     _seed_offline_dictionary(conn)
 
@@ -333,6 +349,59 @@ def init_db():
             pos TEXT DEFAULT ''
         );
         CREATE INDEX IF NOT EXISTS idx_offline_dict_term ON offline_dictionary(term COLLATE NOCASE);
+
+        CREATE TABLE IF NOT EXISTS sentence_translations (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            sentence_hash TEXT NOT NULL,
+            original_text TEXT NOT NULL,
+            translated_text TEXT NOT NULL,
+            target_word TEXT DEFAULT '',
+            word_meaning TEXT DEFAULT '',
+            source TEXT DEFAULT 'local_llm',
+            created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+        );
+        CREATE INDEX IF NOT EXISTS idx_sentence_trans_hash ON sentence_translations(sentence_hash);
         """)
         # Apply migrations for pre-existing databases
         _migrate(conn)
+
+
+def compute_sentence_hash(sentence: str, target_word: str = "") -> str:
+    norm = f"{sentence.strip().lower()}||{target_word.strip().lower()}"
+    return hashlib.sha256(norm.encode("utf-8")).hexdigest()
+
+
+def get_cached_sentence_translation(sentence: str, target_word: str = "") -> dict | None:
+    s_hash = compute_sentence_hash(sentence, target_word)
+    with get_db() as conn:
+        row = conn.execute(
+            """
+            SELECT original_text, translated_text, target_word, word_meaning, source, created_at
+            FROM sentence_translations
+            WHERE sentence_hash = ?
+            ORDER BY id DESC LIMIT 1
+            """,
+            (s_hash,),
+        ).fetchone()
+        if row:
+            return dict(row)
+    return None
+
+
+def save_sentence_translation(
+    sentence: str,
+    translated_text: str,
+    target_word: str = "",
+    word_meaning: str = "",
+    source: str = "local_llm",
+) -> None:
+    s_hash = compute_sentence_hash(sentence, target_word)
+    with get_db() as conn:
+        conn.execute(
+            """
+            INSERT INTO sentence_translations (sentence_hash, original_text, translated_text, target_word, word_meaning, source)
+            VALUES (?, ?, ?, ?, ?, ?)
+            """,
+            (s_hash, sentence.strip(), translated_text.strip(), target_word.strip(), word_meaning.strip(), source),
+        )
+