feat: added fts5 backend

sqlite.go

@@ -184,6 +184,68 @@ func (s *sqliteStore) tombstone(ctx context.Context, publicID int64, version int
 	return id, nil
 }
 
+func (s *sqliteStore) indexFTS(ctx context.Context, id int64, note string) error {
+	_, err := s.db.ExecContext(ctx,
+		`INSERT INTO flashcard_fts(rowid, note) VALUES (?, ?)`,
+		id, note,
+	)
+	if err != nil {
+		return fmt.Errorf("index fts: %w", err)
+	}
+	return nil
+}
+
+func (s *sqliteStore) deleteFTS(ctx context.Context, id int64) error {
+	_, err := s.db.ExecContext(ctx,
+		`DELETE FROM flashcard_fts WHERE rowid = ?`,
+		id,
+	)
+	if err != nil {
+		return fmt.Errorf("delete fts: %w", err)
+	}
+	return nil
+}
+
+func (s *sqliteStore) searchFTS(ctx context.Context, query string, limit uint64) ([]searchResult, error) {
+	if limit == 0 {
+		limit = 5
+	}
+
+	rows, err := s.db.QueryContext(ctx,
+		`SELECT rowid, rank FROM flashcard_fts WHERE note MATCH ? ORDER BY rank LIMIT ?`,
+		query, limit,
+	)
+	if err != nil {
+		return nil, fmt.Errorf("fts query: %w", err)
+	}
+	defer rows.Close()
+
+	var results []searchResult
+	for rows.Next() {
+		var id int64
+		var rank float64
+		if err := rows.Scan(&id, &rank); err != nil {
+			return nil, fmt.Errorf("scan: %w", err)
+		}
+		entry, err := s.getByID(ctx, id)
+		if err != nil {
+			return nil, fmt.Errorf("get entry: %w", err)
+		}
+		if entry == nil {
+			continue
+		}
+		results = append(results, searchResult{
+			Entry: *entry,
+			Score: float32(-rank),
+		})
+	}
+	if err := rows.Err(); err != nil {
+		return nil, fmt.Errorf("rows: %w", err)
+	}
+
+	return results, nil
+}
+
 func (s *sqliteStore) close() error {
 	return s.db.Close()
 }