# history_tracking/mixins.py


class HistoricalChangeMixin:
    @property
    def diff_against_previous(self):
        prev_record = self.prev_record
        if not prev_record:
            return {}

        changes = {}
        for field in self.__dict__:
            if field not in [
                "history_date",
                "history_id",
                "history_type",
                "history_user_id",
            ] and not field.startswith("_"):
                old_value = getattr(prev_record, field)
                new_value = getattr(self, field)
                if old_value != new_value:
                    changes[field] = {"old": old_value, "new": new_value}
        return changes