"""
Databaskonfiguration och session-hantering för LandveX Admin Backend.
Inkluderar tenant schema-isolering via PostgreSQL search_path.
"""
from contextlib import asynccontextmanager
from typing import AsyncGenerator, Optional

from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession, async_sessionmaker
from sqlalchemy.orm import declarative_base
from sqlalchemy import text

from app.config import get_settings

settings = get_settings()

# SQLite stödjer inte pool_size/max_overflow
if settings.DATABASE_URL.startswith("sqlite"):
    engine = create_async_engine(
        settings.DATABASE_URL,
        echo=settings.DEBUG,
        future=True,
    )
else:
    engine = create_async_engine(
        settings.DATABASE_URL,
        pool_size=settings.DATABASE_POOL_SIZE,
        max_overflow=settings.DATABASE_MAX_OVERFLOW,
        pool_pre_ping=True,
        echo=settings.DEBUG,
        future=True,
    )

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

Base = declarative_base()


async def get_db() -> AsyncSession:
    """Dependency för FastAPI-endpoints."""
    async with AsyncSessionLocal() as session:
        try:
            yield session
            await session.commit()
        except Exception:
            await session.rollback()
            raise
        finally:
            await session.close()


@asynccontextmanager
async def get_db_context() -> AsyncGenerator[AsyncSession, None]:
    """Context manager för databassessioner."""
    async with AsyncSessionLocal() as session:
        try:
            yield session
            await session.commit()
        except Exception:
            await session.rollback()
            raise
        finally:
            await session.close()


class TenantContext:
    """Context manager för tenant schema-isolering.

    Använder PostgreSQL search_path och application context
    för att säkerställa dataisolering mellan tenants.
    """

    def __init__(self, session: AsyncSession, tenant_schema: Optional[str] = None):
        self.session = session
        self.tenant_schema = tenant_schema or settings.DEFAULT_TENANT_SCHEMA

    async def __aenter__(self):
        """Sätt tenant context på databasanslutningen."""
        await self.session.execute(
            text(f'SET search_path TO "{self.tenant_schema}", public')
        )
        await self.session.execute(
            text("SELECT set_config('app.current_tenant', :tenant, true)"),
            {"tenant": self.tenant_schema}
        )
        return self

    async def __aexit__(self, exc_type, exc_val, exc_tb):
        """Återställ tenant context."""
        await self.session.execute(text('SET search_path TO public'))
        await self.session.execute(
            text("SELECT set_config('app.current_tenant', '', true)")
        )
        return False


async def set_tenant_schema(session: AsyncSession, tenant_schema: str) -> None:
    """Sätt tenant schema för aktuell session."""
    await session.execute(
        text(f'SET search_path TO "{tenant_schema}", public')
    )
    await session.execute(
        text("SELECT set_config('app.current_tenant', :tenant, true)"),
        {"tenant": tenant_schema}
    )


async def reset_tenant_schema(session: AsyncSession) -> None:
    """Återställ schema till default."""
    await session.execute(text('SET search_path TO public'))
    await session.execute(
        text("SELECT set_config('app.current_tenant', '', true)")
    )


async def create_tenant_schema(schema_name: str) -> None:
    """Skapa ett nytt schema för en tenant."""
    async with engine.begin() as conn:
        await conn.execute(text(f'CREATE SCHEMA IF NOT EXISTS "{schema_name}"'))
        await conn.execute(text(f'GRANT USAGE ON SCHEMA "{schema_name}" TO PUBLIC'))


async def drop_tenant_schema(schema_name: str) -> None:
    """Ta bort ett tenant schema."""
    async with engine.begin() as conn:
        await conn.execute(text(f'DROP SCHEMA IF EXISTS "{schema_name}" CASCADE'))


async def schema_exists(schema_name: str) -> bool:
    """Kolla om ett schema finns."""
    async with engine.connect() as conn:
        result = await conn.execute(
            text(
                "SELECT EXISTS(SELECT 1 FROM information_schema.schemata WHERE schema_name = :schema)"
            ),
            {"schema": schema_name}
        )
        return result.scalar()