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

# ---------------------------------------------------------------------------
# General definitions
# ---------------------------------------------------------------------------

def serialize_value(value):
    if isinstance(value, Model):
        return value.pk  # oder str(value), wenn du mehr Infos willst
    if isinstance(value, (datetime, date)):
        return value.isoformat()
    return value

# ---------------------------------------------------------------------------
# Risks
# ---------------------------------------------------------------------------
@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": serialize_value(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:
            clean_changes = {
                field: {"old": serialize_value(vals["old"]), "new": serialize_value(vals["new"])}
                for field, vals in changes.items()
            }
            AuditLog.objects.create(
                user=getattr(instance, "_changed_by", None),
                action="update",
                model="Risk",
                object_id=instance.pk,
                changes=clean_changes,
            )

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

# ---------------------------------------------------------------------------
# Controls
# ---------------------------------------------------------------------------

@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": serialize_value(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:
            clean_changes = {
                field: {"old": serialize_value(vals["old"]), "new": serialize_value(vals["new"])}
                for field, vals in changes.items()
            }
            AuditLog.objects.create(
                user=getattr(instance, "_changed_by", None),
                action="update",
                model="Control",
                object_id=instance.pk,
                changes=clean_changes,
            )

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

@receiver(m2m_changed, sender=Control.risks.through)
def control_risks_changed(sender, instance, action, reverse, pk_set, **kwargs):
    if action in {"post_add", "post_remove", "post_clear"}:
        if action == "post_clear":
            affected_risks = instance.risks.all()
        elif pk_set:
            if reverse:
                from .models import Risk
                affected_risks = Risk.objects.filter(pk__in=pk_set)
            else:
                affected_risks = Risk.objects.filter(pk__in=pk_set)
        else:
            affected_risks = instance.risks.all()

        from .models import ResidualRisk
        for risk in affected_risks:
            residual, _ = ResidualRisk.objects.get_or_create(risk=risk)
            residual.review_required = True
            residual.save()

# ---------------------------------------------------------------------------
# Residual risks
# ---------------------------------------------------------------------------

@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": serialize_value(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:
            clean_changes = {
                field: {"old": serialize_value(vals["old"]), "new": serialize_value(vals["new"])}
                for field, vals in changes.items()
            }
            AuditLog.objects.create(
                user=getattr(instance, "_changed_by", None),
                action="update",
                model="ResidualRisk",
                object_id=instance.pk,
                changes=clean_changes,
            )

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

# ---------------------------------------------------------------------------
# Incidents
# ---------------------------------------------------------------------------

@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": serialize_value(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:
            clean_changes = {
                field: {"old": serialize_value(vals["old"]), "new": serialize_value(vals["new"])}
                for field, vals in changes.items()
            }
            AuditLog.objects.create(
                user=getattr(instance, "_changed_by", None),
                action="update",
                model="Incident",
                object_id=instance.pk,
                changes=clean_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"]:
        user = getattr(instance, "_changed_by", None) or get_current_user()
        AuditLog.objects.create(
            user=user,
            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):
    user = getattr(instance, "_changed_by", None) or get_current_user()
    AuditLog.objects.create(
        user=user,
        action="delete",
        model="Incident",
        object_id=instance.pk,
        changes=None,
    )