"""Database engine, session management, and base model."""

from __future__ import annotations

import contextlib
import uuid
from collections.abc import AsyncGenerator
from datetime import datetime
from typing import Any  # noqa: F401

from sqlalchemy import DateTime, String, func, text  # noqa: F401
from sqlalchemy import event as sa_event  # noqa: F401
from sqlalchemy.dialects.postgresql import UUID as PGUUID
from sqlalchemy.ext.asyncio import (
    AsyncEngine,
    AsyncSession,
    async_sessionmaker,
    create_async_engine,
)
from sqlalchemy.orm import DeclarativeBase, Mapped, declared_attr, mapped_column

from app.config import get_settings


class Base(DeclarativeBase):
    """Declarative base with shared columns and tenant-scoping support."""

    @declared_attr.directive
    def __tablename__(self) -> str:
        return self.__name__.lower() + "s"


class SoftDeleteMixin:
    """Adds deleted_at column for soft-delete support."""

    deleted_at: Mapped[datetime | None] = mapped_column(
        DateTime(timezone=True), nullable=True, default=None
    )


class TimestampMixin:
    """Adds created_at and updated_at timestamps."""

    created_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True), nullable=False, server_default=func.now()
    )
    updated_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True), nullable=False, server_default=func.now(), onupdate=func.now()
    )


class TenantMixin(TimestampMixin, SoftDeleteMixin):
    """Adds tenant_id column and enables ORM-level auto-filtering."""

    tenant_id: Mapped[uuid.UUID] = mapped_column(PGUUID(as_uuid=True), nullable=False, index=True)


# Global engine and session factory
_engine: AsyncEngine | None = None
_session_factory: async_sessionmaker[AsyncSession] | None = None


def get_engine() -> AsyncEngine:
    """Get or create the global async engine."""
    global _engine
    if _engine is None:
        settings = get_settings()
        _engine = create_async_engine(
            settings.database_url,
            pool_size=settings.db_pool_size,
            max_overflow=settings.db_max_overflow,
            echo=settings.db_echo,
        )
    return _engine


def get_session_factory() -> async_sessionmaker[AsyncSession]:
    """Get or create the global session factory."""
    global _session_factory
    if _session_factory is None:
        _session_factory = async_sessionmaker(
            bind=get_engine(),
            expire_on_commit=False,
            class_=AsyncSession,
        )
    return _session_factory


async def get_db() -> AsyncGenerator[AsyncSession, None]:
    """FastAPI dependency: yield an async database session."""
    factory = get_session_factory()
    async with factory() as session:
        try:
            yield session
            await session.commit()
        except Exception:
            await session.rollback()
            raise


async def set_tenant_context(session: AsyncSession, tenant_id: uuid.UUID | str) -> None:
    """Set PostgreSQL session variable for RLS tenant context."""
    await session.execute(
        text("SELECT set_config('app.current_tenant_id', :tid, true)"),
        {"tid": str(tenant_id)},
    )


@contextlib.asynccontextmanager
async def create_db_session(
    tenant_id: uuid.UUID | str | None = None,
) -> AsyncGenerator[AsyncSession, None]:
    """Create a standalone session outside FastAPI (e.g. for tests/workers)."""
    factory = get_session_factory()
    async with factory() as session:
        if tenant_id is not None:
            await set_tenant_context(session, tenant_id)
        try:
            yield session
            await session.commit()
        except Exception:
            await session.rollback()
            raise


async def close_engine() -> None:
    """Dispose the global engine (for shutdown)."""
    global _engine, _session_factory
    if _engine is not None:
        await _engine.dispose()
        _engine = None
        _session_factory = None


def reset_engine_for_testing(engine: AsyncEngine) -> async_sessionmaker[AsyncSession]:
    """Replace the global engine with a test engine. Returns a session factory."""
    global _engine, _session_factory
    _engine = engine
    _session_factory = async_sessionmaker(bind=engine, expire_on_commit=False, class_=AsyncSession)
    return _session_factory