from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession, async_sessionmaker
from sqlalchemy.orm import declarative_base
from sqlalchemy import TypeDecorator, CHAR
from sqlalchemy.dialects.postgresql import UUID as PG_UUID
import uuid
from app.config import settings

# Custom UUID type for MySQL compatibility
class GUID(TypeDecorator):
    """Platform-independent GUID type.
    Uses PostgreSQL's UUID type, otherwise uses CHAR(36), storing as stringified hex values.
    """
    impl = CHAR
    cache_ok = True

    def load_dialect_impl(self, dialect):
        if dialect.name == 'postgresql':
            return dialect.type_descriptor(PG_UUID())
        else:
            return dialect.type_descriptor(CHAR(36))

    def process_bind_param(self, value, dialect):
        if value is None:
            return value
        elif dialect.name == 'postgresql':
            return str(value)
        else:
            if not isinstance(value, uuid.UUID):
                return str(uuid.UUID(value))
            else:
                return str(value)

    def process_result_value(self, value, dialect):
        if value is None:
            return value
        else:
            if not isinstance(value, uuid.UUID):
                value = uuid.UUID(value)
            return value

# Create async engine
engine = create_async_engine(
    settings.DATABASE_URL,
    echo=settings.DATABASE_ECHO,
    pool_pre_ping=True,
    pool_recycle=3600,
    pool_size=10,
    max_overflow=20,
)

# Create async session factory
AsyncSessionLocal = async_sessionmaker(
    engine,
    class_=AsyncSession,
    expire_on_commit=False,
    autocommit=False,
    autoflush=False,
)

# Create declarative base
Base = declarative_base()

# Dependency to get DB session
async def get_db():
    async with AsyncSessionLocal() as session:
        try:
            yield session
        finally:
            await session.close()

# Initialize database
async def init_db():
    async with engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)