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


class AppError(Exception):
    def __init__(self, message: str, status_code: int = 400, code: str = "app_error") -> None:
        self.message = message
        self.status_code = status_code
        self.code = code


class NotFoundError(AppError):
    def __init__(self, message: str = "Resource not found") -> None:
        super().__init__(message=message, status_code=404, code="not_found")


class LLMUnavailableError(AppError):
    def __init__(self, message: str = "LLM service is unavailable") -> None:
        super().__init__(message=message, status_code=503, code="llm_unavailable")


class ParseError(AppError):
    def __init__(self, message: str = "Unable to parse AI output") -> None:
        super().__init__(message=message, status_code=422, code="parse_error")


def error_payload(code: str, message: str, details: object | None = None) -> dict[str, object]:
    payload: dict[str, object] = {"error": {"code": code, "message": message}}
    if details is not None:
        payload["error"]["details"] = details
    return payload


def register_exception_handlers(app: FastAPI) -> None:
    @app.exception_handler(AppError)
    async def app_error_handler(_: Request, exc: AppError) -> ORJSONResponse:
        return ORJSONResponse(
            status_code=exc.status_code,
            content=error_payload(exc.code, exc.message),
        )

    @app.exception_handler(StarletteHTTPException)
    async def http_error_handler(_: Request, exc: StarletteHTTPException) -> ORJSONResponse:
        return ORJSONResponse(
            status_code=exc.status_code,
            content=error_payload("http_error", str(exc.detail)),
        )

    @app.exception_handler(RequestValidationError)
    async def validation_error_handler(_: Request, exc: RequestValidationError) -> ORJSONResponse:
        return ORJSONResponse(
            status_code=422,
            content=error_payload("validation_error", "Invalid request payload", exc.errors()),
        )