from collections.abc import AsyncIterator

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

from .settings import get_settings

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


def get_engine() -> AsyncEngine:
    global _engine, _sessionmaker
    if _engine is None:
        s = get_settings()
        # PH-016: explicit pool sizing. pool_pre_ping protects against stale
        # connections after PG restarts; pool_recycle bounds connection age.
        _engine = create_async_engine(
            s.database_url,
            pool_pre_ping=True,
            pool_size=s.db_pool_size,
            max_overflow=s.db_max_overflow,
            pool_timeout=s.db_pool_timeout_sec,
            pool_recycle=s.db_pool_recycle_sec,
            future=True,
        )
        _sessionmaker = async_sessionmaker(_engine, expire_on_commit=False)
    return _engine


def get_sessionmaker() -> async_sessionmaker[AsyncSession]:
    if _sessionmaker is None:
        get_engine()
    assert _sessionmaker is not None
    return _sessionmaker


async def dispose_engine() -> None:
    global _engine, _sessionmaker
    if _engine is not None:
        await _engine.dispose()
    _engine = None
    _sessionmaker = None


async def get_session() -> AsyncIterator[AsyncSession]:
    sm = get_sessionmaker()
    async with sm() as session:
        yield session