"""A single response shape for every error the API returns.

    {"detail": "...", "code": "...", "errors": {"field": ["..."]}}

`errors` is only present for validation failures. The SPA reads `code` to
branch (e.g. `registration_required`) and `detail` to show a message.
"""

from rest_framework import exceptions
from rest_framework.views import exception_handler as drf_exception_handler


def exception_handler(exc, context):
    response = drf_exception_handler(exc, context)
    if response is None:
        return None

    code = getattr(exc, "default_code", "error")
    data = response.data

    if isinstance(exc, exceptions.ValidationError):
        detail = "The submitted data was invalid."
        if isinstance(data, dict):
            non_field = data.get("detail") or data.get("non_field_errors")
            if non_field:
                detail = non_field[0] if isinstance(non_field, list) else str(non_field)
        response.data = {"detail": str(detail), "code": code, "errors": data}
        return response

    detail = data.get("detail") if isinstance(data, dict) else data
    response.data = {"detail": str(detail), "code": code}
    return response