from rest_framework import serializers
from .models import Skill, UserSkill
from .utils import proficiency_to_level


class SkillSerializer(serializers.ModelSerializer):
    class Meta:
        model = Skill
        fields = ['id', 'skill_name', 'category', 'description', 'difficulty_level']


class UserSkillSerializer(serializers.ModelSerializer):
    skill = SkillSerializer(read_only=True)

    class Meta:
        model = UserSkill
        fields = ['id', 'skill', 'proficiency', 'user_level', 'updated_at']


class UserSkillCreateUpdateSerializer(serializers.Serializer):
    skill_id = serializers.IntegerField()
    proficiency = serializers.IntegerField()

    def validate_proficiency(self, value):
        if not 0 <= value <= 100:
            raise serializers.ValidationError("Proficiency must be between 0 and 100.")
        return value

    def validate_skill_id(self, value):
        if not Skill.objects.filter(id=value).exists():
            raise serializers.ValidationError("Skill with this ID does not exist.")
        return value

    def create(self, validated_data):
        skill_id = validated_data['skill_id']
        proficiency = validated_data['proficiency']
        user = self.context['request'].user
        user_level = proficiency_to_level(proficiency)

        user_skill, _ = UserSkill.objects.update_or_create(
            user=user,
            skill_id=skill_id,
            defaults={'proficiency': proficiency, 'user_level': user_level}
        )
        return user_skill

    def update(self, instance, validated_data):
        # skill_id is immutable on update — a UserSkill binds a user to a
        # specific skill; reassigning it would corrupt that identity.
        proficiency = validated_data.get('proficiency', instance.proficiency)
        instance.proficiency = proficiency
        instance.user_level = proficiency_to_level(proficiency)
        instance.save()
        return instance