nimbusflow/backend/database/connection.py

# backend/database/connection.py
"""
Thin convenience layer over the builtin ``sqlite3`` module.

Why we need a wrapper
---------------------
* The repository (`repository.py`) expects the following public API:
      - ``execute``                – run an INSERT/UPDATE/DELETE.
      - ``fetchone`` / ``fetchall`` – run a SELECT and get the result(s).
      - ``lastrowid``              – primary‑key of the most recent INSERT.
      - ``close``                  – close the DB connection.
* A wrapper lets us:
      • Set a sensible ``row_factory`` (``sqlite3.Row``) so column names are
        accessible as ``row["ColumnName"]``.
      • Centralise ``commit``/``rollback`` handling.
      • Provide type hints and a context‑manager interface
        (``with DatabaseConnection(...):``) which is handy for tests.
* No external dependencies – everything stays pure‑Python/SQLite.

The implementation below is deliberately tiny: it only does what the
application needs while remaining easy to extend later (e.g. add
connection‑pooling or logging).
"""

from __future__ import annotations

import sqlite3
from pathlib import Path
from typing import Any, Iterable, Tuple, List, Optional, Union


class DatabaseConnection:
    """
    Simple wrapper around a SQLite connection.

    Core behaviour
    ---------------
    * ``row_factory`` is set to :class:`sqlite3.Row` – callers can use
      ``row["col_name"]`` or treat the row like a mapping.
    * All ``execute`` calls are automatically committed.
      If an exception bubbles out, the transaction is rolled back.
    * ``execute`` returns the cursor so callers can chain
      ``cursor.lastrowid`` if they need the autogenerated PK.
    * Implements the context‑manager protocol (``with ... as db:``).

    The public API matches what ``Repository`` expects:
        - execute(sql, params=None) → None
        - fetchone(sql, params=None) → Optional[sqlite3.Row]
        - fetchall(sql, params=None) → List[sqlite3.Row]
        - lastrowid → int
        - close()
    """

    # -----------------------------------------------------------------
    # Construction / context‑manager protocol
    # -----------------------------------------------------------------
    def __init__(
        self,
        db_path: Union[str, Path],
        *,
        timeout: float = 5.0,
        detect_types: int = sqlite3.PARSE_DECLTYPES | sqlite3.PARSE_COLNAMES,
    ) -> None:
        """
        Parameters
        ----------
        db_path
            Path to the SQLite file.  ``":memory:"`` works for tests.
        timeout
            Seconds to wait for a lock before raising ``sqlite3.OperationalError``.
        detect_types
            Enable type conversion (so DATE/DATETIME are returned as ``datetime``).
        """
        self._conn: sqlite3.Connection = sqlite3.connect(
            str(db_path), timeout=timeout, detect_types=detect_types
        )
        # ``Row`` makes column access dictionary‑like and preserves order.
        self._conn.row_factory = sqlite3.Row
        self._cursor: sqlite3.Cursor = self._conn.cursor()

    def __enter__(self) -> "DatabaseConnection":
        """Allow ``with DatabaseConnection(...) as db:`` usage."""
        return self

    def __exit__(self, exc_type, exc_val, exc_tb) -> Optional[bool]:
        """
        On normal exit commit the transaction, otherwise roll back.
        Returning ``False`` propagates any exception.
        """
        if exc_type is None:
            try:
                self._conn.commit()
            finally:
                self.close()
        else:
            # Something went wrong – roll back to keep the DB clean.
            self._conn.rollback()
            self.close()
        # ``None`` means “don’t suppress exceptions”
        return None

    # -----------------------------------------------------------------
    # Low‑level helpers used by the repository
    # -----------------------------------------------------------------
    @property
    def cursor(self) -> sqlite3.Cursor:
        """Expose the underlying cursor – rarely needed outside the repo."""
        return self._cursor

    @property
    def lastrowid(self) -> int:
        """PK of the most recent ``INSERT`` executed on this connection."""
        return self._cursor.lastrowid

    # -----------------------------------------------------------------
    # Public API – the four methods used throughout the code base
    # -----------------------------------------------------------------
    def execute(self, sql: str, params: Optional[Tuple[Any, ...]] = None) -> None:
        """
        Run an INSERT/UPDATE/DELETE statement and commit immediately.

        ``params`` may be ``None`` (no placeholders) or a tuple of values.
        """
        try:
            if params is None:
                self._cursor.execute(sql)
            else:
                self._cursor.execute(sql, params)
            self._conn.commit()
        except Exception:
            # Ensure we don’t leave the connection in a half‑committed state.
            self._conn.rollback()
            raise

    def fetchone(
        self, sql: str, params: Optional[Tuple[Any, ...]] = None
    ) -> Optional[sqlite3.Row]:
        """
        Execute a SELECT that returns at most one row.

        Returns ``None`` when the result set is empty.
        """
        if params is None:
            self._cursor.execute(sql)
        else:
            self._cursor.execute(sql, params)
        return self._cursor.fetchone()

    def fetchall(
        self, sql: str, params: Optional[Tuple[Any, ...]] = None
    ) -> List[sqlite3.Row]:
        """
        Execute a SELECT and return **all** rows as a list.

        The rows are ``sqlite3.Row`` instances, which behave like dicts.
        """
        if params is None:
            self._cursor.execute(sql)
        else:
            self._cursor.execute(sql, params)
        return self._cursor.fetchall()

    def close(self) -> None:
        """Close the underlying SQLite connection."""
        # ``cursor`` is automatically closed when the connection closes,
        # but we explicitly close it for clarity.
        try:
            self._cursor.close()
        finally:
            self._conn.close()