from django.contrib.auth.models import User
from rest_framework import serializers

from .models import Event, EventParticipation


class ParticipationSerializer(serializers.Serializer):
    """Serializer for EventParticipation that handles username lookup."""

    event = serializers.PrimaryKeyRelatedField(queryset=Event.objects.all())
    user = serializers.CharField()
    status = serializers.CharField(required=False)
    comment = serializers.CharField(required=False, allow_blank=True)

    def to_representation(self, instance):
        """Serialize an EventParticipation instance."""
        return {
            "event": instance.event.pk,
            "user": instance.user.username,
            "status": instance.status,
            "comment": instance.comment,
        }

    def validate_user(self, value):
        """Look up user by username (case-insensitive)."""
        try:
            return User.objects.get(username__iexact=value)
        except User.DoesNotExist:
            raise serializers.ValidationError(f"User '{value}' does not exist")

    def create(self, validated_data):
        """Create or update EventParticipation based on event and user."""
        event = validated_data.get("event")
        user = validated_data.get("user")

        # Only include fields that were actually present in the request,
        # so a status-only update doesn't wipe the comment (and vice versa).
        defaults = {}
        if "status" in validated_data:
            defaults["status"] = validated_data["status"]
        if "comment" in validated_data:
            defaults["comment"] = validated_data["comment"]

        participation, created = EventParticipation.objects.update_or_create(
            event=event,
            user=user,
            defaults=defaults,
        )

        return participation

    def update(self, instance, validated_data):
        instance.status = validated_data.get("status", instance.status)
        instance.comment = validated_data.get("comment", instance.comment)
        instance.save()
        return instance