from django.db.models.signals import m2m_changed
from django.dispatch import receiver
from .models import Card

@receiver(m2m_changed, sender=Card.decks.through)
def update_card_style(sender, instance, action, **kwargs):
    if action == "post_add":
        decks = instance.decks.all()
        num_decks = decks.count()
        if num_decks == 1:
            instance.style = "background-color: " + decks.first().hex_color + ";"
        elif num_decks >= 2:
            hex_colors = [deck.hex_color for deck in decks]
            instance.style = f"background: linear-gradient(to right, {', '.join(hex_colors)});"
        else:
            instance.style = "background: linear-gradient(to right, #AAAAAA, #AAAAAA, #AAAAAA);"
        instance.save(update_fields=["style"])