"""Async SQLAlchemy engine lifecycle management.

Initializes at Gateway startup, provides session factory for
repositories, disposes at shutdown.

When database.backend="memory", init_engine is a no-op and
get_session_factory() returns None. Repositories must check for
None and fall back to in-memory implementations.
"""

from __future__ import annotations

import logging

from sqlalchemy.ext.asyncio import AsyncEngine, AsyncSession, async_sessionmaker, create_async_engine

logger = logging.getLogger(__name__)

_engine: AsyncEngine | None = None
_session_factory: async_sessionmaker[AsyncSession] | None = None


async def init_engine(
    backend: str,
    *,
    url: str = "",
    echo: bool = False,
    pool_size: int = 5,
    sqlite_dir: str = "",
) -> None:
    """Create the async engine and session factory, then auto-create tables.

    Args:
        backend: "memory", "sqlite", or "postgres".
        url: SQLAlchemy async URL (for sqlite/postgres).
        echo: Echo SQL to log.
        pool_size: Postgres connection pool size.
        sqlite_dir: Directory to create for SQLite (ensured to exist).
    """
    global _engine, _session_factory

    if backend == "memory":
        logger.info("Persistence backend=memory -- ORM engine not initialized")
        return

    if backend == "postgres":
        try:
            import asyncpg  # noqa: F401
        except ImportError:
            raise ImportError("database.backend is set to 'postgres' but asyncpg is not installed.\nInstall it with:\n    uv sync --extra postgres\nOr switch to backend: sqlite in config.yaml for single-node deployment.") from None

    if backend == "sqlite":
        import os

        os.makedirs(sqlite_dir or ".", exist_ok=True)
        _engine = create_async_engine(url, echo=echo)
    elif backend == "postgres":
        _engine = create_async_engine(
            url,
            echo=echo,
            pool_size=pool_size,
            pool_pre_ping=True,
        )
    else:
        raise ValueError(f"Unknown persistence backend: {backend!r}")

    _session_factory = async_sessionmaker(_engine, expire_on_commit=False)

    # Auto-create tables (dev convenience). Production should use Alembic.
    from deerflow.persistence.base import Base

    # Import all models so Base.metadata discovers them.
    # When no models exist yet (scaffolding phase), this is a no-op.
    try:
        import deerflow.persistence.models  # noqa: F401
    except ImportError:
        pass

    async with _engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)

    logger.info("Persistence engine initialized: backend=%s", backend)


async def init_engine_from_config(config) -> None:
    """Convenience: init engine from a DatabaseConfig object."""
    if config.backend == "memory":
        await init_engine("memory")
        return
    await init_engine(
        backend=config.backend,
        url=config.app_sqlalchemy_url,
        echo=config.echo_sql,
        pool_size=config.pool_size,
        sqlite_dir=config.sqlite_dir if config.backend == "sqlite" else "",
    )


def get_session_factory() -> async_sessionmaker[AsyncSession] | None:
    """Return the async session factory, or None if backend=memory."""
    return _session_factory


def get_engine() -> AsyncEngine | None:
    """Return the async engine, or None if not initialized."""
    return _engine


async def close_engine() -> None:
    """Dispose the engine, release all connections."""
    global _engine, _session_factory
    if _engine is not None:
        await _engine.dispose()
        logger.info("Persistence engine closed")
    _engine = None
    _session_factory = None