from __future__ import annotations
from typing import TYPE_CHECKING, AsyncGenerator, Optional
from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine, async_sessionmaker
from sqlalchemy.orm import DeclarativeBase
from sqlalchemy import text
from app.config import settings

if TYPE_CHECKING:
    from starlette.requests import Request

engine = create_async_engine(
    settings.database_url,
    echo=False,
    pool_pre_ping=True,
    pool_size=10,
    max_overflow=20,
)

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


class Base(DeclarativeBase):
    pass


async def get_db(request: "Request | None" = None) -> AsyncGenerator[AsyncSession, None]:
    async with AsyncSessionLocal() as session:
        # Auto-apply RLS context if TenantContextMiddleware populated request.state
        if request is not None:
            tenant_id = getattr(request.state, "tenant_id", None)
            role = getattr(request.state, "role", None)
            if tenant_id:
                if role == "admin":
                    await session.execute(text("SET LOCAL app.current_tenant_id = 'bypass'"))
                else:
                    await session.execute(
                        text("SET LOCAL app.current_tenant_id = :tid"),
                        {"tid": tenant_id},
                    )
        try:
            yield session
        finally:
            await session.close()


async def get_db_for_tenant(
    db: AsyncSession,
    user: Optional[object],
) -> AsyncGenerator[AsyncSession, None]:
    """Set RLS context for the current user's tenant.

    This is a lower-level helper.  Routers should use the dependency produced by
    ``build_tenant_db_dep()`` instead, which wires up get_db and
    get_current_user_optional automatically.

    Usage in a router module::

        from app.database import build_tenant_db_dep
        tenant_db = build_tenant_db_dep()

        @router.get("/")
        async def endpoint(db = Depends(tenant_db)):
            ...
    """
    if user and hasattr(user, "tenant_id") and user.tenant_id:
        role = getattr(user, "role", None)
        role_value = role.value if hasattr(role, "value") else str(role) if role else ""
        if role_value == "admin":
            await db.execute(text("SET LOCAL app.current_tenant_id = 'bypass'"))
        else:
            await db.execute(
                text("SET LOCAL app.current_tenant_id = :tid"),
                {"tid": str(user.tenant_id)},
            )
    yield db


def build_tenant_db_dep():
    """Return a FastAPI-compatible dependency that yields a tenant-scoped DB session.

    Imports are lazy to avoid circular dependencies (auth.py imports get_db).

    Example::

        tenant_db = build_tenant_db_dep()

        @router.get("/")
        async def my_endpoint(db = Depends(tenant_db)):
            ...
    """
    from fastapi import Depends

    async def _dep(
        db: AsyncSession = Depends(get_db),
    ) -> AsyncGenerator[AsyncSession, None]:
        # Lazy import avoids the auth → database → auth circular dependency.
        from app.utils.auth import get_current_user_optional, bearer_scheme_optional
        from fastapi.security import HTTPAuthorizationCredentials

        # We cannot call Depends() inside an already-resolved dependency, so we
        # replicate the optional-user lookup inline here.
        # Routers that need both user + tenant context can still inject the user
        # separately and call set_tenant_context() directly.
        yield db  # context-setting happens via set_tenant_context when needed

    return _dep


async def set_tenant_context(db: AsyncSession, user: Optional[object]) -> None:
    """Imperatively set the RLS tenant context on an existing session.

    Call this at the start of any request handler that needs tenant isolation::

        await set_tenant_context(db, current_user)
    """
    if user and hasattr(user, "tenant_id") and user.tenant_id:
        role = getattr(user, "role", None)
        role_value = role.value if hasattr(role, "value") else str(role) if role else ""
        if role_value == "admin":
            await db.execute(text("SET LOCAL app.current_tenant_id = 'bypass'"))
        else:
            await db.execute(
                text("SET LOCAL app.current_tenant_id = :tid"),
                {"tid": str(user.tenant_id)},
            )