from django.utils.timezone import now
from .models import AuditLog, Risk, Notification

def model_diff(old, new, fields=None):
    """
    Compare two model instances and return a dict of changed fields.
    - old: previous model instance (from DB)
    - new: updated model instance (unsaved)
    - fields: optional list of fields to check
    """
    changes = {}
    opts = new._meta

    if fields is None:
        fields = [f.name for f in opts.fields]

    for field_name in fields:
        old_value = getattr(old, field_name, None)
        new_value = getattr(new, field_name, None)

        if old_value != new_value:
            changes[field_name] = {"old": old_value, "new": new_value}

    return changes

def check_risk_followups():
    """
    Check if follow ups need attention and create notifications.
    Ensures no duplicate notifications per risk per day
    """
    today = now().date()
    risks = Risk.objects.filter(follow_up__lte=today)

    for risk in risks:
        if risk.owner:
            notification, created = Notification.objects.get_or_create(
                user=risk.owner,
                message=f"Follow-up required for risk: {risk.title}",
                defaults={"read": False, "sent": False},
            )

            if created:
                AuditLog.objects.create(
                    user=None,  # system action
                    action="create",
                    model="Notification",
                    object_id=notification.pk,
                    changes={"message": notification.message, "user": risk.owner.username},
                )