"""跨 app 账目守护信号。

CreditReservation.task 是 OneToOneField(on_delete=CASCADE):AITask 被硬删(用户删项目
→ AITask.project CASCADE 级联删任务、或直接删任务)时,预留行会被一并删掉。若该预留
还处于 ACTIVE,account.reserved_balance 里冻结的份额就永远退不回来 —— 这是资金审计
I2「冻结不平」的根因(ZWQ-Test / 演示团队实测漂移 ¥10 / ¥30,且随测试删项目持续增长)。

修法:在 AITask 删除前(pre_delete,级联删除同样触发)把仍 ACTIVE 的预留正常走
release_credit 释放 —— 退还冻结、落 RELEASE 流水,然后再让级联删掉预留行。
release_credit 自带行锁 + 幂等(非 ACTIVE 直接返回),并发安全。
"""
from django.db.models.signals import pre_delete
from django.dispatch import receiver


@receiver(pre_delete, sender="ai.AITask", dispatch_uid="billing.release_reservation_before_task_delete")
def release_reservation_before_task_delete(sender, instance, **kwargs):
    from apps.billing.models import CreditReservation
    from apps.billing.services.ledger import release_credit

    reservation = CreditReservation.objects.filter(
        task=instance, status=CreditReservation.Status.ACTIVE
    ).first()
    if reservation is not None:
        release_credit(reservation=reservation, reason="任务删除,释放未结预留")