from contextlib import asynccontextmanager
from typing import AsyncGenerator

from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware
from sqlalchemy.ext.asyncio import AsyncEngine, create_async_engine

from app.config import settings
from app.api.v1.router import api_v1_router
from app.ws.handler import ws_router

engine: AsyncEngine | None = None


@asynccontextmanager
async def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
    """Manage application lifespan: set up and tear down DB engine."""
    global engine
    engine = create_async_engine(
        settings.DATABASE_URL,
        echo=False,
        pool_size=20,
        max_overflow=10,
        pool_pre_ping=True,
    )
    yield
    if engine is not None:
        await engine.dispose()
        engine = None


def create_app() -> FastAPI:
    """Application factory."""
    application = FastAPI(
        title="Amazon AI Transcreation Platform",
        description="Backend API for AI-powered marketing transcreation",
        version="1.0.0",
        lifespan=lifespan,
    )

    # CORS middleware (permissive for development)
    application.add_middleware(
        CORSMiddleware,
        allow_origins=["*"],
        allow_credentials=True,
        allow_methods=["*"],
        allow_headers=["*"],
    )

    # API routes
    application.include_router(api_v1_router)

    # WebSocket routes
    application.include_router(ws_router)

    @application.get("/health", tags=["health"])
    async def health_check() -> dict:
        return {"status": "healthy", "version": "1.0.0"}

    return application


app = create_app()