from django.db.models.signals import post_save, post_delete, m2m_changed
from django.dispatch import receiver
from .models import Control, Risk, ResidualRisk, AuditLog, Incident
from .utils import model_diff

@receiver(post_save, sender=Control)
def update_residual_risk_on_control_change(sender, instance, **kwargs):
  """
  Whenever a control is saved, check if the related risk has a residual risk.
  If a control is completed or verified, flag the residual risk for review.
  """

  risk = instance.risk

  # Ensure residual risk exists
  residual, created = ResidualRisk.objects.get_or_create(risk=risk)

  # If a control is marked as completed or verified, we mark residual risk for review
  if instance.status in ["completed", "verified"]:
      residual.review_required = True
      residual.save()


@receiver(post_save, sender=Risk)
def log_risk_save(sender, instance, created, **kwargs):
    if created:
        AuditLog.objects.create(
            user=getattr(instance, "_changed_by", None),
            action="create",
            model="Risk",
            object_id=instance.pk,
            changes={f.name: {"old": None, "new": getattr(instance, f.name)} for f in instance._meta.fields},
        )
    else:
        old = Risk.objects.get(pk=instance.pk)
        changes = model_diff(old, instance)

        if changes:
            AuditLog.objects.create(
                user=getattr(instance, "_changed_by", None),
                action="update",
                model="Risk",
                object_id=instance.pk,
                changes=changes,
            )

@receiver(post_delete, sender=Risk)
def log_risk_delete(sender, instance, **kwargs):
    """
    Signal that runs after a Risk is deleted.
    """
    AuditLog.objects.create(
        user=getattr(instance, "_changed_by", None),
        action="delete",
        model="Risk",
        object_id=instance.pk,
        changes=None, # no fields to track on deletion
    )


@receiver(post_save, sender=Control)
def log_control_save(sender, instance, created, **kwargs):
    if created:
        AuditLog.objects.create(
            user=getattr(instance, "_changed_by", None),
            action="create",
            model="Control",
            object_id=instance.pk,
            changes={f.name: {"old": None, "new": getattr(instance, f.name)} for f in instance._meta.fields},
        )
    else:
        old = Control.objects.get(pk=instance.pk)
        changes = model_diff(old, instance)

        if changes:
            AuditLog.objects.create(
                user=getattr(instance, "_changed_by", None),
                action="update",
                model="Control",
                object_id=instance.pk,
                changes=changes,
            )

@receiver(post_delete, sender=Control)
def log_control_delete(sender, instance, **kwargs):
    AuditLog.objects.create(
        user=getattr(instance, "_changed_by", None),
        action="delete",
        model="Control",
        object_id=instance.pk,
        changes=None,
    )


@receiver(post_save, sender=ResidualRisk)
def log_residual_save(sender, instance, created, **kwargs):
    if created:
        AuditLog.objects.create(
            user=getattr(instance, "_changed_by", None),
            action="create",
            model="ResidualRisk",
            object_id=instance.pk,
            changes={f.name: {"old": None, "new": getattr(instance, f.name)} for f in instance._meta.fields},
        )
    else:
        old = ResidualRisk.objects.get(pk=instance.pk)
        changes = model_diff(old, instance)

        if changes:
            AuditLog.objects.create(
                user=getattr(instance, "_changed_by", None),
                action="update",
                model="ResidualRisk",
                object_id=instance.pk,
                changes=changes,
            )

@receiver(post_delete, sender=ResidualRisk)
def log_residual_delete(sender, instance, **kwargs):
    AuditLog.objects.create(
        user=getattr(instance, "_changed_by", None),
        action="delete",
        model="ResidualRisk",
        object_id=instance.pk,
        changes=None,
    )


@receiver(post_save, sender=Incident)
def log_incident_save(sender, instance, created, **kwargs):
    if created:
        AuditLog.objects.create(
            user=getattr(instance, "_changed_by", None),
            action="create",
            model="Incident",
            object_id=instance.pk,
            changes={f.name: {"old": None, "new": getattr(instance, f.name)} for f in instance._meta.fields},
        )
    else:
        old = Incident.objects.get(pk=instance.pk)
        changes = model_diff(old, instance)

        if changes:
            AuditLog.objects.create(
                user=getattr(instance, "_changed_by", None),
                action="update",
                model="Incident",
                object_id=instance.pk,
                changes=changes,
            )

@receiver(m2m_changed, sender=Incident.related_risks.through)
def log_incident_risks_change(sender, instance, action, reverse, model, pk_set, **kwargs):
    if action in ["post_add", "post_remove", "post_clear"]:
        AuditLog.objects.create(
            user=getattr(instance, "_changed_by", None),
            action="update",
            model="Incident",
            object_id=instance.pk,
            changes={"related_risks": {"action": action, "ids": list(pk_set)}},
        )

@receiver(post_delete, sender=Incident)
def log_incident_delete(sender, instance, **kwargs):
    AuditLog.objects.create(
        user=getattr(instance, "_changed_by", None),
        action="delete",
        model="Incident",
        object_id=instance.pk,
        changes=None,
    )