src/app/core/exceptions.py

"""Custom application exceptions and FastAPI exception handlers."""

from __future__ import annotations

from fastapi import FastAPI, Request, status
from fastapi.responses import JSONResponse

from app.core.logging import get_logger

logger = get_logger(__name__)


class AppException(Exception):
    """Base class for all expected, handled application errors."""

    status_code: int = status.HTTP_400_BAD_REQUEST
    detail: str = "Application error"

    def __init__(self, detail: str | None = None) -> None:
        if detail is not None:
            self.detail = detail
        super().__init__(self.detail)


class NotFoundError(AppException):
    status_code = status.HTTP_404_NOT_FOUND
    detail = "Resource not found"


class ConflictError(AppException):
    status_code = status.HTTP_409_CONFLICT
    detail = "Resource already exists"


class AuthenticationError(AppException):
    status_code = status.HTTP_401_UNAUTHORIZED
    detail = "Could not validate credentials"


class AuthorizationError(AppException):
    status_code = status.HTTP_403_FORBIDDEN
    detail = "Not enough permissions"


class ValidationError(AppException):
    status_code = status.HTTP_422_UNPROCESSABLE_ENTITY
    detail = "Validation failed"


class ServiceUnavailableError(AppException):
    status_code = status.HTTP_503_SERVICE_UNAVAILABLE
    detail = "Service temporarily unavailable"


def register_exception_handlers(app: FastAPI) -> None:
    @app.exception_handler(AppException)
    async def _app_exception_handler(request: Request, exc: AppException) -> JSONResponse:
        if exc.status_code >= 500:
            logger.error("app_exception", detail=exc.detail, path=request.url.path)
        return JSONResponse(
            status_code=exc.status_code,
            content={"detail": exc.detail},
        )

    @app.exception_handler(Exception)
    async def _unhandled_exception_handler(request: Request, exc: Exception) -> JSONResponse:
        logger.exception("unhandled_exception", path=request.url.path)
        return JSONResponse(
            status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
            content={"detail": "Internal server error"},
        )