class EventSerializer(serializers.ModelSerializer):
    started_at = serializers.DateTimeField(source='event.started_at', required=False)
    ended_at = serializers.DateTimeField(source='event.ended_at', required=False,)

    class Meta:
        model = EventLang
        fields = ('event', 'title', 'id', 'lang_code', 'description', 'agenda', 'ended_at', 'started_at')
        extra_kwargs = {'event': {'required': False}}

    def create(self, validated_data):
        event = validated_data.pop('event', None)
        if event:
            validated_data['event'] = self._get_or_create_event(event)
        return super().create(validated_data)

    def update(self, instance, validated_data):
        event = validated_data.pop('event', None)
        if event:
            Event.objects.filter(id=instance.event_id).update(**event)
        return super().update(instance, validated_data)

    @staticmethod
    def _get_or_create_event(event):
        if isinstance(event, Event):
            return event
        return Event.objects.create(**event)