from rest_framework import serializers
from .models import Coaster


class CoasterSerializer(serializers.ModelSerializer):
    creator_username = serializers.ReadOnlyField(source='creator.username')
    rating_avg = serializers.SerializerMethodField()
    rating_count = serializers.SerializerMethodField()
    user_rating = serializers.SerializerMethodField()

    class Meta:
        model = Coaster
        fields = [
            'id', 'creator_username', 'challenge', 'name',
            'anchors', 'acceleration_strips',
            'rating_avg', 'rating_count', 'user_rating',
            'created_at', 'updated_at',
        ]
        read_only_fields = ['id', 'creator_username', 'created_at', 'updated_at']

    def get_rating_avg(self, obj):
        ratings = list(obj.ratings.values_list('rating', flat=True))
        if not ratings:
            return None
        return round(sum(ratings) / len(ratings), 2)

    def get_rating_count(self, obj):
        return obj.ratings.count()

    def get_user_rating(self, obj):
        request = self.context.get('request')
        if not request or not request.user.is_authenticated:
            return None
        rating = obj.ratings.filter(user=request.user).first()
        return rating.rating if rating else None