from typing import AsyncGenerator
from sqlalchemy.ext.asyncio import create_async_engine, async_sessionmaker, AsyncSession
from sqlalchemy.orm import declarative_base
from backend.app.core.config import settings
from backend.app.core.logger import logger

# Build engine with appropriate connect_args depending on SQLite or PostgreSQL
connect_args = {}
engine_kwargs = {"echo": False, "future": True}

if settings.DATABASE_URL.startswith("sqlite"):
    connect_args["check_same_thread"] = False
else:
    engine_kwargs.update({
        "pool_size": 10,
        "max_overflow": 20,
        "pool_pre_ping": True,
    })

engine = create_async_engine(
    settings.DATABASE_URL,
    connect_args=connect_args,
    **engine_kwargs,
)

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

Base = declarative_base()


async def get_db() -> AsyncGenerator[AsyncSession, None]:
    async with AsyncSessionLocal() as session:
        try:
            yield session
        except Exception as ex:
            await session.rollback()
            logger.error(f"Database session error: {ex}")
            raise
        finally:
            await session.close()


async def init_db() -> None:
    """Initialize database tables for development/testing."""
    async with engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)
    logger.info("Database schema initialized.")