"""
Database connection and session management.
Uses async SQLAlchemy with asyncpg driver for PostgreSQL,
or aiosqlite for local/free-tier deployment.
"""

import uuid
import os

from sqlalchemy import CHAR, text
from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine, async_sessionmaker
from sqlalchemy.orm import DeclarativeBase
from sqlalchemy.types import TypeDecorator

from app.config import get_settings


class GUID(TypeDecorator):
    """
    Platform-independent GUID type.
    Uses PostgreSQL's UUID type when available, otherwise uses CHAR(32) for SQLite.
    """
    impl = CHAR
    cache_ok = True

    def load_dialect_impl(self, dialect):
        if dialect.name == 'postgresql':
            from sqlalchemy.dialects.postgresql import UUID as PG_UUID
            return dialect.type_descriptor(PG_UUID(as_uuid=True))
        else:
            return dialect.type_descriptor(CHAR(32))

    def process_bind_param(self, value, dialect):
        if value is None:
            return value
        elif dialect.name == 'postgresql':
            return value
        else:
            if isinstance(value, uuid.UUID):
                return value.hex
            else:
                return uuid.UUID(value).hex

    def process_result_value(self, value, dialect):
        if value is None:
            return value
        elif dialect.name == 'postgresql':
            return value
        else:
            if isinstance(value, uuid.UUID):
                return value
            return uuid.UUID(value)

settings = get_settings()

# Determine database URL - fallback to SQLite if no PostgreSQL configured
_db_url = settings.database_url

if not _db_url or _db_url == "":
    # Use SQLite as fallback (works without external DB)
    _db_dir = os.path.join(os.path.dirname(os.path.dirname(__file__)), "data")
    os.makedirs(_db_dir, exist_ok=True)
    _db_url = f"sqlite+aiosqlite:///{_db_dir}/fairrelay.db"
    _is_sqlite = True
else:
    _is_sqlite = False

# Create async engine with appropriate settings
if _is_sqlite:
    engine = create_async_engine(
        _db_url,
        echo=settings.debug,
        future=True,
        connect_args={"check_same_thread": False},
    )
else:
    engine = create_async_engine(
        _db_url,
        echo=settings.debug,
        future=True,
        pool_size=20,
        max_overflow=10,
        pool_recycle=3600,
        pool_pre_ping=True,
    )

# Session factory
async_session_maker = async_sessionmaker(
    engine,
    class_=AsyncSession,
    expire_on_commit=False,
)


class Base(DeclarativeBase):
    """Base class for all SQLAlchemy models."""
    pass


async def get_db() -> AsyncSession:
    """
    Dependency that provides a database session.
    Yields a session and ensures it's closed after use.
    """
    async with async_session_maker() as session:
        try:
            yield session
            await session.commit()
        except Exception:
            await session.rollback()
            raise
        finally:
            await session.close()


async def check_db_health() -> bool:
    """Check database connectivity by running a simple query."""
    try:
        async with engine.connect() as conn:
            await conn.execute(text("SELECT 1"))
        return True
    except Exception:
        return False


async def init_db() -> None:
    """Initialize database tables."""
    async with engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)