from collections.abc import Callable

from fastapi import FastAPI, Request, Response

app = FastAPI()


@app.middleware("http")
async def custom_header_middleware(request: Request, call_next: Callable) -> Response:
    response = await call_next(request)
    response.headers["X-Custom-Header"] = "Hello, World!"
    return response


@app.get("/")
async def read_root() -> dict[str, str]:
    return {"message": "Hello, World!"}


@app.get("/test")
async def test() -> dict[str, str]:
    raise Exception("Test exception")
    return {"message": "Test"}


if __name__ == "__main__":
    import uvicorn

    uvicorn.run(app, host="0.0.0.0", port=8000)

@app.middleware("http")
async def custom_header_middleware(request: Request, call_next: Callable) -> Response:
    try:
        response = await call_next(request)
    except Exception:
        response = Response(content="Internal Server Error", status_code=500)
    response.headers["X-Custom-Header"] = "Hello, World!"
    return response

@app.exception_handler(Exception)
async def exception_handler(request: Request, exc: Exception) -> Response:
    response = Response(content="Internal Server Error", status_code=500)
    response.headers["X-Custom-Header"] = "Hello, World!"
    return response

def custom_header_middleware(app: ASGIApp) -> ASGIApp:
    async def asgi(scope: Scope, receive: Receive, send: Send) -> None:
        if scope.get("type") != "http":
            await app(scope, receive, send)
            return

        async def send_wrapper(message: Message) -> None:
            if message.get("type") == "http.response.start":
                headers: list[tuple[bytes, bytes]] = list(message.get("headers", []))
                headers.append((b"x-custom-header", b"Hello, World!"))
                message["headers"] = headers
            await send(message)

        await app(scope, receive, send_wrapper)

    return asgi


app: ASGIApp = custom_header_middleware(app)