from contextlib import asynccontextmanager

from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware
from fastapi.responses import JSONResponse
from sqlalchemy import text
from sqlalchemy.exc import IntegrityError, OperationalError, ProgrammingError
from sqlalchemy.orm.exc import StaleDataError

from app.api.routes import chat, documents, health, knowledge, sources
from app.core.config import settings
from app.db.session import engine


def create_app(db_engine=engine) -> FastAPI:
    @asynccontextmanager
    async def lifespan(app: FastAPI):
        try:
            with db_engine.connect() as connection:
                revision = connection.scalar(text("SELECT version_num FROM alembic_version"))
                if revision != "0002_catalog":
                    raise RuntimeError(
                        "数据库版本不匹配，请先在 backend 目录执行 alembic upgrade head"
                    )
        except ProgrammingError as exc:
            raise RuntimeError(
                "数据库尚未初始化，请先在 backend 目录执行 alembic upgrade head"
            ) from exc
        try:
            yield
        finally:
            db_engine.dispose()

    app = FastAPI(title=settings.app_name, version="0.2.0", lifespan=lifespan)
    app.add_middleware(
        CORSMiddleware,
        allow_origins=settings.cors_origin_list,
        allow_credentials=True,
        allow_methods=["*"],
        allow_headers=["*"],
    )
    for router in (health.router, chat.router, knowledge.router, sources.router, documents.router):
        app.include_router(router, prefix=settings.api_prefix)

    @app.exception_handler(StaleDataError)
    async def stale_data_handler(request, exc):
        return JSONResponse(status_code=409, content={"detail": "记录已更新，请刷新后重试"})

    @app.exception_handler(IntegrityError)
    async def integrity_handler(request, exc):
        return JSONResponse(status_code=409, content={"detail": "数据关联或约束冲突"})

    @app.exception_handler(OperationalError)
    async def database_unavailable_handler(request, exc):
        return JSONResponse(status_code=503, content={"detail": "数据库暂不可用"})

    @app.get("/")
    def root():
        return {"message": "Nalati Tourism QA API", "docs": "/docs"}

    return app


app = create_app()