
# Analysis of `database.py` vs. `database_improved.py`

This document provides a detailed comparison of the two database modules and presents a consolidated, improved version.

## `database.py` (The Original)

-   **Connection Handling**: Creates a new database connection for every single query (`execute_query`, `execute_single_query`). It uses a `with` statement, which ensures the connection is closed, but the overhead of establishing a connection (file I/O, parsing the database header, etc.) is incurred repeatedly.
-   **Row Factory**: Uses the default `sqlite3` row factory, which returns results as tuples. Accessing data requires using integer indices (e.g., `row[0]`, `row[1]`), which makes the code harder to read and more brittle to changes in the query's `SELECT` order.
-   **Error Handling**: Basic error handling is present, correctly identifying locked databases.
-   **Type Hinting**: Uses `tuple` for `params` and doesn't specify the return type of `execute_query` and `execute_single_query` in a detailed way.

## `database_improved.py` (The Challenger)

-   **Connection Handling**: Establishes a single, persistent connection when the `DatabaseConnection` object is initialized (`__init__`). This connection is reused for all subsequent queries, which is significantly more performant as the connection overhead is paid only once.
-   **Row Factory**: Sets `conn.row_factory = sqlite3.Row`. This is a major improvement. It causes the database to return rows that behave like dictionaries, allowing for column access by name (e.g., `row['title']`, `row['author']`). This makes the code that consumes the data much more readable and robust.
-   **Context Manager**: Implements `__enter__` and `__exit__` methods, allowing the `DatabaseConnection` object itself to be used as a context manager to ensure the connection is closed when the block is exited.
-   **Cursor Management**: Uses a `get_cursor` context manager to handle cursor creation and error handling for individual queries.
-   **Type Hinting**: More specific type hints are used, such as `List[sqlite3.Row]` and `Optional[sqlite3.Row]`, which improves code clarity.

## Verdict

**`database_improved.py` is unequivocally better.**

The two most significant advantages are:

1.  **Performance**: The persistent connection model avoids the high cost of reconnecting for every query. For an application that might run dozens of queries in a single command (especially with deduplication), this will result in a noticeable speed improvement.
2.  **Maintainability**: The use of `sqlite3.Row` is a huge win for code quality. Accessing data by column name (`row['id']`) instead of by index (`row[0]`) makes the code in other parts of the application (like the service and handler layers) much easier to write, read, and maintain. It also prevents bugs when the order of columns in a `SELECT` statement is changed.

The improved version is a clear winner and should be the standard for the project.

---

# Fully Updated and Consolidated `database.py`

Here is the recommended version of `database.py` that merges the best features of both files, adds more robust typing, and includes comprehensive docstrings.

```python
"""
Handles the connection to the Zotero SQLite database, providing a performant
and robust interface for executing queries.
"""

import sqlite3
import logging
from pathlib import Path
from typing import Optional, Any, List, Tuple, Iterable
from contextlib import contextmanager

logger = logging.getLogger(__name__)


class DatabaseError(Exception):
    """Custom exception for general database errors."""
    pass


class DatabaseLockedError(DatabaseError):
    """Custom exception for when the Zotero database is locked."""
    pass


class DatabaseConnection:
    """
    Manages a persistent, read-only connection to the Zotero SQLite database.

    This class is designed for performance by holding a single connection open
    for the lifetime of the object. It also uses sqlite3.Row as a row factory,
    allowing for dictionary-like access to columns.

    It can be used as a context manager to ensure the connection is closed:
    
    with DatabaseConnection(db_path) as db:
        db.execute_query(...)
    """
    
    def __init__(self, db_path: Path):
        """
        Initializes the database connection.

        Args:
            db_path: The absolute path to the zotero.sqlite file.
        """
        self.db_path = db_path
        self._connection: Optional[sqlite3.Connection] = None
        self._verify_database_exists()
        self._init_connection()
    
    def _verify_database_exists(self) -> None:
        """Verify that the database file exists on the filesystem."""
        if not self.db_path.exists():
            raise DatabaseError(f"Database not found at path: {self.db_path}")
        if not self.db_path.is_file():
            raise DatabaseError(f"Path is not a file: {self.db_path}")

    def _create_connection(self) -> sqlite3.Connection:
        """
        Creates a new read-only database connection with a Row factory.
        
        Returns:
            A new sqlite3.Connection object.
        """
        try:
            # Connect in read-only mode (uri=True is required for mode)
            conn = sqlite3.connect(f'file:{self.db_path}?mode=ro', uri=True)
            # Use the Row factory for dict-like access to results
            conn.row_factory = sqlite3.Row
            return conn
        except sqlite3.OperationalError as e:
            if "unable to open database file" in str(e):
                raise DatabaseError(f"Failed to open database file: {self.db_path}")
            raise

    def _init_connection(self) -> None:
        """Initializes the persistent connection and verifies its integrity."""
        try:
            self._connection = self._create_connection()
            # Perform a quick query to ensure it's a valid Zotero DB
            self.execute_single_query("SELECT name FROM sqlite_master WHERE type='table' AND name='items'")
            logger.debug(f"Successfully initialized database connection to {self.db_path}")
        except (sqlite3.OperationalError, sqlite3.DatabaseError) as e:
            if "database is locked" in str(e).lower():
                raise DatabaseLockedError("Zotero database is locked. Please close Zotero and try again.")
            raise DatabaseError(f"Failed to initialize or verify database: {e}")
        except Exception as e:
            logger.error(f"An unexpected error occurred during database initialization: {e}")
            raise

    @contextmanager
    def get_cursor(self) -> sqlite3.Cursor:
        """
        Provides a cursor from the persistent connection.

        This is a context manager that handles exceptions and ensures that
        the connection is alive.
        """
        if not self._connection:
            raise DatabaseError("Connection is not initialized. Cannot get cursor.")
        
        try:
            yield self._connection.cursor()
        except sqlite3.OperationalError as e:
            if "database is locked" in str(e).lower():
                raise DatabaseLockedError("Zotero database is locked during operation. Please close Zotero.")
            raise DatabaseError(f"A database operation failed: {e}")
        except Exception as e:
            raise DatabaseError(f"An unexpected error occurred while executing a query: {e}")

    def execute_query(self, query: str, params: Iterable[Any] = ()) -> List[sqlite3.Row]:
        """
        Execute a query that returns multiple rows.

        Args:
            query: The SQL query string to execute.
            params: A tuple or list of parameters to substitute into the query.

        Returns:
            A list of sqlite3.Row objects.
        """
        with self.get_cursor() as cursor:
            cursor.execute(query, params)
            return cursor.fetchall()

    def execute_single_query(self, query: str, params: Iterable[Any] = ()) -> Optional[sqlite3.Row]:
        """
        Execute a query that returns a single row.

        Args:
            query: The SQL query string to execute.
            params: A tuple or list of parameters to substitute into the query.

        Returns:
            A single sqlite3.Row object, or None if no results are found.
        """
        with self.get_cursor() as cursor:
            cursor.execute(query, params)
            return cursor.fetchone()

    def get_database_version(self) -> str:
        """
        Get the Zotero database schema version.

        Returns:
            The version string, or "unknown" if it cannot be retrieved.
        """
        try:
            result = self.execute_single_query("SELECT version FROM version WHERE schema = 'system'")
            return str(result['version']) if result else "unknown"
        except (DatabaseError, sqlite3.Error) as e:
            logger.warning(f"Could not read database version: {e}")
            return "unknown"

    def close(self) -> None:
        """Closes the database connection if it is open."""
        if self._connection:
            self._connection.close()
            self._connection = None
            logger.debug("Database connection closed.")

    def __enter__(self):
        """Enter the runtime context for the connection."""
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        """Exit the runtime context, ensuring the connection is closed."""
        self.close()

```
