app_factory.py

import os.path
import tomllib
from contextlib import asynccontextmanager
from typing import Callable, Awaitable

from fastapi import FastAPI, Request
from fastapi.middleware.cors import CORSMiddleware
from fastapi.responses import JSONResponse, Response

from common import project_root
from common.exception import CommonException


async def exception_handler(_: Request, e: Exception) -> Response:
    if isinstance(e, CommonException):
        return JSONResponse(
            status_code=e.code, content={"code": e.code, "error": e.error}
        )
    return JSONResponse(
        status_code=500,
        content={"code": 500, "error": CommonException.parse_exception(e)},
    )


def app_factory(
    startup_funcs: list[Callable[..., Awaitable]] | None = None,
    shutdown_funcs: list[Callable[..., Awaitable]] | None = None,
    version: str | None = None,
    patch_funcs: list[Callable[[FastAPI], None]] | None = None,
) -> FastAPI:
    @asynccontextmanager
    async def lifespan(fastapi: FastAPI):
        for startup_func in startup_funcs or []:
            await startup_func(fastapi)
        yield
        for shutdown_func in shutdown_funcs or []:
            await shutdown_func(fastapi)

    project_file: str = "pyproject.toml"
    if version is None and os.path.exists(project_root.path(project_file)):
        with project_root.open(project_file, "rb") as f:
            version = tomllib.load(f)["project"]["version"]

    app = FastAPI(lifespan=lifespan, version=version)

    for patch_func in patch_funcs or []:
        patch_func(app)

    app.add_middleware(
        CORSMiddleware,  # noqa
        allow_origins=["*"],
        allow_credentials=True,
        allow_methods=["*"],
        allow_headers=["*"],
    )

    app.add_exception_handler(Exception, exception_handler)

    return app