from collections.abc import Mapping

from fastapi import FastAPI, Request
from fastapi.exceptions import RequestValidationError
from fastapi.responses import JSONResponse
from starlette.exceptions import HTTPException as StarletteHTTPException

PROBLEM_JSON = "application/problem+json"


class AppError(Exception):
    def __init__(
        self,
        status: int,
        title: str,
        detail: str,
        headers: Mapping[str, str] | None = None,
    ) -> None:
        super().__init__(detail)
        self.status = status
        self.title = title
        self.detail = detail
        self.headers = headers


def problem(
    status: int,
    title: str,
    detail: str | None = None,
    headers: Mapping[str, str] | None = None,
) -> JSONResponse:
    body: dict[str, object] = {"type": "about:blank", "title": title, "status": status}
    if detail:
        body["detail"] = detail
    return JSONResponse(
        status_code=status,
        content=body,
        media_type=PROBLEM_JSON,
        headers=dict(headers) if headers else None,
    )


def register_error_handlers(app: FastAPI) -> None:
    @app.exception_handler(AppError)
    async def _app_error(_: Request, exc: AppError) -> JSONResponse:
        return problem(exc.status, exc.title, exc.detail, exc.headers)

    @app.exception_handler(RequestValidationError)
    async def _validation(_: Request, exc: RequestValidationError) -> JSONResponse:
        errors = exc.errors()
        return problem(422, "Validation error", str(errors[0]["msg"]) if errors else None)

    @app.exception_handler(StarletteHTTPException)
    async def _http(_: Request, exc: StarletteHTTPException) -> JSONResponse:
        return problem(exc.status_code, str(exc.detail), headers=exc.headers)