from rest_framework import serializers

from apps.shelf_items.models import ShelfItem
from apps.books.models import Book
from apps.shelves.models import Shelf
from apps.shelves.serializers import ShelfSerializer
from apps.books.serializers import BookSerializer

class ShelfItemSerializer(serializers.ModelSerializer):
    shelf = ShelfSerializer(read_only=True)
    shelf_id = serializers.PrimaryKeyRelatedField(
        queryset=Shelf.objects.all(),
        source="shelf", 
        write_only=True
    )

    book = BookSerializer(read_only=True)
    book_id = serializers.PrimaryKeyRelatedField(
        queryset=Book.objects.all(),
        source="book", 
        write_only=True
    )

    class Meta:
        model = ShelfItem
        fields = [
            "id",
            "shelf",
            "shelf_id",
            "book",
            "book_id",
            "quantity"
        ]
        read_only_fields = ["id"]

    def __init__(self, instance=None, data=..., **kwargs):
        super().__init__(instance, data, **kwargs)

        request = self.context.get("request")        
        if request and request.user:
            self.fields["shelf_id"].queryset = Shelf.objects.filter(
                user=request.user
            )

            self.fields["book_id"].queryset = Book.objects.filter(
                user=request.user
            )

    def validate(self, attrs):
        attrs = super().validate(attrs)

        book = attrs.get("book")
        shelf = attrs.get("shelf")

        if book and shelf:
            qs = ShelfItem.objects.filter(
                book=book,
                shelf=shelf
            )
            
            if self.instance:
                qs = qs.exclude(pk=self.instance.pk)

            if qs.exists():
                raise serializers.ValidationError(
                    "This Book already exists in shelf!"
                )
                
            if book.user_id != shelf.user_id:
                raise serializers.ValidationError(
                    "Book and Shelf must be from the same user!"
                )
        
        return attrs