from django.db import transaction
from rest_framework import serializers

from apps.accounts.serializers import UserSerializer
from apps.library.models import LibraryItem
from apps.library.serializers import LibraryItemSerializer

from .models import Comment, Moment, MomentItem, Reaction


class MomentItemSerializer(serializers.ModelSerializer):
    library_item = LibraryItemSerializer(read_only=True)

    class Meta:
        model = MomentItem
        fields = ["id", "library_item", "order"]


class CommentSerializer(serializers.ModelSerializer):
    author = UserSerializer(read_only=True)

    class Meta:
        model = Comment
        fields = ["id", "moment", "author", "parent", "body", "created_at"]
        read_only_fields = ["id", "moment", "author", "created_at"]

    def validate_parent(self, value):
        if value is None:
            return value
        if value.parent_id is not None:
            raise serializers.ValidationError("Cannot reply to a reply; reply to the original comment instead.")
        moment = self.context.get("moment")
        if moment is not None and value.moment_id != moment.id:
            raise serializers.ValidationError("Reply must target a comment on the same Moment.")
        return value


class ReactionSerializer(serializers.ModelSerializer):
    user = UserSerializer(read_only=True)

    class Meta:
        model = Reaction
        fields = ["id", "moment", "user", "reaction_type", "created_at"]
        read_only_fields = ["id", "moment", "user", "created_at"]


class MomentSerializer(serializers.ModelSerializer):
    owner = UserSerializer(read_only=True)
    items = MomentItemSerializer(many=True, read_only=True)
    library_item_ids = serializers.PrimaryKeyRelatedField(
        queryset=LibraryItem.objects.all(), many=True, write_only=True, source="library_items", required=False
    )
    comment_count = serializers.IntegerField(source="comments.count", read_only=True)
    reaction_count = serializers.IntegerField(source="reactions.count", read_only=True)
    viewer_reaction_id = serializers.SerializerMethodField()

    class Meta:
        model = Moment
        fields = [
            "id", "owner", "caption", "location", "audience", "items",
            "library_item_ids", "comment_count", "reaction_count", "viewer_reaction_id",
            "created_at", "updated_at",
        ]
        read_only_fields = [
            "id", "owner", "items", "comment_count", "reaction_count", "viewer_reaction_id",
            "created_at", "updated_at",
        ]

    def get_viewer_reaction_id(self, obj):
        request = self.context.get("request")
        if not request or not request.user.is_authenticated:
            return None
        # obj.reactions is prefetched by the view, so this doesn't re-query per moment.
        reaction = next((r for r in obj.reactions.all() if r.user_id == request.user.id), None)
        return reaction.id if reaction else None

    def validate_library_item_ids(self, library_items):
        request = self.context["request"]
        seen_ids = set()
        for item in library_items:
            if item.owner_id != request.user.id:
                raise serializers.ValidationError("Can only share items from your own library.")
            if item.id in seen_ids:
                raise serializers.ValidationError("The same photo was selected more than once.")
            seen_ids.add(item.id)
        return library_items

    def validate(self, attrs):
        library_items = attrs.get("library_items", [])
        caption = attrs.get("caption", "")
        if not library_items and not caption.strip():
            raise serializers.ValidationError("A Moment needs a caption or at least one photo.")
        return attrs

    def create(self, validated_data):
        library_items = validated_data.pop("library_items", [])
        validated_data["owner"] = self.context["request"].user
        with transaction.atomic():
            moment = Moment.objects.create(**validated_data)
            MomentItem.objects.bulk_create(
                [MomentItem(moment=moment, library_item=item, order=i) for i, item in enumerate(library_items)]
            )
        return moment