from django.core.exceptions import ValidationError
from django.db.models.signals import m2m_changed
from django.dispatch import receiver
from .models import TradeOffer
from cards.models import Card

def check_trade_offer_rarity(instance):
    combined_cards = list(instance.have_cards.all()) + list(instance.want_cards.all())
    # Map rarities 6 (Super Rare) and 7 (Special Art Rare) to a single value (here, 6)
    rarities = {
        card.rarity_id if card.rarity_id not in (6, 7) else 6
        for card in combined_cards
    }
    if len(rarities) > 1:
        raise ValidationError("All cards in a trade offer must have the same rarity.")

@receiver(m2m_changed, sender=TradeOffer.have_cards.through)
def validate_have_cards_rarity(sender, instance, action, **kwargs):
    if action == "post_add":
        check_trade_offer_rarity(instance)

@receiver(m2m_changed, sender=TradeOffer.want_cards.through)
def validate_want_cards_rarity(sender, instance, action, **kwargs):
    if action == "post_add":
        check_trade_offer_rarity(instance)