"""数据库会话与引擎管理。"""

from __future__ import annotations

from collections.abc import AsyncGenerator

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

from .core.config import settings

DATABASE_URL = settings.database_url


def _is_sqlite() -> bool:
    return DATABASE_URL.lower().startswith("sqlite")


engine_kwargs = {
    "echo": settings.debug,
    "future": True,
    "pool_pre_ping": not _is_sqlite(),
}
if _is_sqlite():
    engine_kwargs["connect_args"] = {
        "timeout": 30,
        "check_same_thread": False,
    }
    engine_kwargs["poolclass"] = NullPool
if not _is_sqlite():
    engine_kwargs.update(
        {
            "pool_size": max(5, int(settings.db_pool_size)),
            "max_overflow": max(0, int(settings.db_max_overflow)),
            "pool_timeout": max(5, int(settings.db_pool_timeout)),
            "pool_recycle": max(60, int(settings.db_pool_recycle)),
            # 强制数据库会话时区为北京时间，确保 now()/CURRENT_TIMESTAMP 为 Asia/Shanghai。
            "connect_args": {"server_settings": {"timezone": "Asia/Shanghai"}},
        }
    )

engine: AsyncEngine = create_async_engine(
    DATABASE_URL,
    **engine_kwargs,
)

if _is_sqlite():
    @event.listens_for(engine.sync_engine, "connect")
    def _configure_sqlite_pragmas(dbapi_connection, _connection_record) -> None:  # pragma: no cover
        cursor = dbapi_connection.cursor()
        try:
            cursor.execute("PRAGMA journal_mode=WAL")
            cursor.execute("PRAGMA synchronous=NORMAL")
            cursor.execute("PRAGMA busy_timeout=30000")
        finally:
            cursor.close()

AsyncSessionLocal = async_sessionmaker(
    bind=engine,
    class_=AsyncSession,
    expire_on_commit=False,
    autoflush=False,
)


async def get_db() -> AsyncGenerator[AsyncSession, None]:
    """FastAPI 依赖：提供数据库会话。"""
    async with AsyncSessionLocal() as session:
        yield session