"""PM error envelope — same contract as the ERP: {"error": {code, message, field}}."""
from fastapi import FastAPI, Request
from fastapi.responses import JSONResponse


class AppError(Exception):
    status_code = 400
    code = "BAD_REQUEST"

    def __init__(self, message: str, field: str | None = None, code: str | None = None):
        super().__init__(message)
        self.message = message
        self.field = field
        if code:
            self.code = code

    @property
    def body(self) -> dict:
        error = {"code": self.code, "message": self.message}
        if self.field is not None:
            error["field"] = self.field
        return {"error": error}


class AuthError(AppError):
    status_code, code = 401, "UNAUTHORIZED"


class ValidationError(AppError):
    status_code, code = 400, "VALIDATION_ERROR"


class ForbiddenError(AppError):
    status_code, code = 403, "FORBIDDEN"


class NotFoundError(AppError):
    status_code, code = 404, "NOT_FOUND"


class ConflictError(AppError):
    status_code, code = 409, "CONFLICT"


class UpstreamError(AppError):
    """Upstream service unreachable / errored."""
    status_code, code = 503, "UPSTREAM_UNAVAILABLE"


def install_error_handlers(app: FastAPI) -> None:
    @app.exception_handler(AppError)
    async def _app_error(_: Request, exc: AppError) -> JSONResponse:
        return JSONResponse(status_code=exc.status_code, content=exc.body)