Updating sqlite implementation

internal/store/sqlite/sqlite.go

@@ -74,7 +74,43 @@ func (s *SQLiteStore) Close() error {
 }
 
 func (s *SQLiteStore) SaveNote(ctx context.Context, note models.Note) (models.Note, error) {
-	return models.Note{}, fmt.Errorf("not implemented")
+	tx, err := s.getWriteTransaction(ctx)
+	if err != nil {
+		return models.Note{}, err
+	}
+	defer tx.Rollback()
+
+	if note.ID == 0 {
+		result, err := tx.ExecContext(ctx, `
+			INSERT INTO notes (content, last_update) VALUES (?, ?);
+		`, note.Content, note.LastUpdate)
+		if err != nil {
+			return models.Note{}, fmt.Errorf("failed to insert note: %w", err)
+		}
+		id, err := result.LastInsertId()
+		if err != nil {
+			return models.Note{}, fmt.Errorf("failed to get last insert ID: %w", err)
+		}
+		note.ID = int(id)
+	} else {
+		_, err := s.scanNote(tx.QueryRowContext(ctx, `
+			SELECT id, content, last_update FROM notes WHERE id = ?;
+		`, note.ID))
+		if err != nil {
+			return models.Note{}, fmt.Errorf("cannot update note not found: %w", err)
+		}
+		_, err = tx.ExecContext(ctx, `
+			UPDATE notes SET content = ?, last_update = ? WHERE id = ?;
+		`, note.Content, note.LastUpdate, note.ID)
+		if err != nil {
+			return models.Note{}, fmt.Errorf("failed to update note: %w", err)
+		}
+	}
+
+	if err := tx.Commit(); err != nil {
+		return models.Note{}, fmt.Errorf("failed to commit transaction: %w", err)
+	}
+	return note, nil
 }
 
 func (s *SQLiteStore) validateSchema(ctx context.Context) error {
@@ -87,3 +123,20 @@ func (s *SQLiteStore) validateSchema(ctx context.Context) error {
 	`, nil)
 	return err
 }
+
+func (s *SQLiteStore) getWriteTransaction(ctx context.Context) (*sql.Tx, error) {
+	tx, err := s.write.BeginTx(ctx, nil)
+	if err != nil {
+		return nil, fmt.Errorf("failed to begin transaction: %w", err)
+	}
+	return tx, nil
+}
+
+func (s *SQLiteStore) scanNote(results *sql.Row) (models.Note, error) {
+	var note models.Note
+	err := results.Scan(&note.ID, &note.Content, &note.LastUpdate)
+	if err != nil {
+		return models.Note{}, fmt.Errorf("failed to scan note: %w", err)
+	}
+	return note, nil
+}