from django.db import models, transaction
from django.db.models.signals import post_save
from django.dispatch import receiver
from django.core.mail import send_mail
from django.conf import settings
 
@receiver(post_save, sender='orders.Order')
def order_created_handler(sender, instance, created, **kwargs):
    if not created:
        return
 
    with transaction.atomic(savepoint=True):
        order = instance
        order.status = 'confirmed'
        order.save(update_fields=['status', 'updated_at'])
 
        for item in order.items.select_related('product'):
            product = item.product
            product.stock -= item.quantity
            if product.stock < 0:
                raise ValueError(f'Insufficient stock for {product.name}')
            product.save(update_fields=['stock'])
 
        send_mail(
            subject=f'Order #{order.id} Confirmed',
            message=f'Your order has been confirmed and is being processed.',
            from_email=settings.DEFAULT_FROM_EMAIL,
            recipient_list=[order.customer.email],
            fail_silently=False,
        )