from django.db.models.signals import pre_save, post_save, pre_delete, post_delete, m2m_changed
from django.dispatch import receiver

from .models import DataAccess, ModelLog, ModelOperation, BaseModel, SideStoreModel
from django.contrib.auth import get_user_model
from django.utils import timezone

from channels.layers import get_channel_layer
from asgiref.sync import async_to_sync

from threading import Timer
from functools import partial

# Synchronization

User = get_user_model()

@receiver([pre_save, pre_delete])
def synchronization_prepare(sender, instance, created=False, **kwargs):

    # some classes are excluded in settings_app.py: SYNC_APPS
    if not isinstance(instance, BaseModel):
        return

    save_model_log_if_possible(instance, kwargs.get('signal'), created)

@receiver([post_save, post_delete])
def synchronization_notifications(sender, instance, created=False, **kwargs):
    """
    Signal handler that sends notifications through WebSocket channels when model instances are saved or deleted.
    The function creates a WebSocket group name for each affected user and sends a sync update message
    to all clients connected to that group.
    """

    # some classes are excluded in settings_app.py: SYNC_APPS
    if not isinstance(instance, BaseModel):
        return

    # print(f'*** signals {sender}')
    notify_impacted_users(instance, kwargs.get('signal'))

def notify_impacted_users(instance, signal):
    user_ids = set()
    # add impacted users
    if isinstance(instance, User):
        user_ids.add(instance.id)
    elif isinstance(instance, BaseModel):
        owner = instance.last_updated_by
        if owner:
            user_ids.add(owner.id)

    if isinstance(instance, BaseModel):
        if instance._users_to_notify is not None:
            user_ids.update(instance._users_to_notify)
        else:
            print('no users to notify')

    print(f'notify: {user_ids}')
    for user_id in user_ids:
        send_user_message(user_id)

def save_model_log_if_possible(instance, signal, created):
    user = instance.last_updated_by
    if user:
        if signal == post_save or signal == pre_save:
            if created:
                operation = ModelOperation.POST
            else:
                operation = ModelOperation.PUT
        else:
            operation = ModelOperation.DELETE

        model_name = instance.__class__.__name__
        store_id = None
        if isinstance(instance, SideStoreModel):
            store_id = instance.store_id

        if operation == ModelOperation.DELETE: # delete now unnecessary logs
            ModelLog.objects.filter(model_id=instance.id).delete()

        users = {user}
        data_access_list = related_data_access(instance)
        for data_access in data_access_list:
            users.add(data_access.owner)
            users.update(data_access.shared_with.all())
        if isinstance(instance, DataAccess):
            users.add(instance.owner)
            users.update(instance.shared_with.all())

        user_ids = [user.id for user in users]

        print(f'users to notify: {user_ids}')
        instance._users_to_notify = user_ids # save this for the post_save signal
        save_model_log(users, operation, model_name, instance.id, store_id)

    else:
        print('>>> Model Log could not be created because instance.last_updated_by is None')

def save_model_log(users, model_operation, model_name, model_id, store_id):
    now = timezone.now()
    existing_log = ModelLog.objects.filter(users__in=users, model_id=model_id, operation=model_operation).first()
    if existing_log:
        # print(f'update existing log {existing_log.users} ')
        existing_log.date = now
        existing_log.model_operation = model_operation
        existing_log.save()
        existing_log.users.set(users)
    else:
        model_log = ModelLog()
        model_log.operation = model_operation
        model_log.date = now
        model_log.model_name = model_name
        model_log.model_id = model_id
        model_log.store_id = store_id
        model_log.save()
        model_log.users.set(users)

def related_data_access(instance):
    related_instances = instance.related_instances()
    related_ids = [ri.id for ri in instance.related_instances()]
    related_ids.append(instance.id)
    return DataAccess.objects.filter(model_id__in=related_ids)

def delete_data_access_if_necessary(model_id):
    DataAccess.objects.filter(model_id=model_id).delete()

@receiver(m2m_changed, sender=DataAccess.shared_with.through)
def handle_shared_with_changes(sender, instance, action, pk_set, **kwargs):

    users = User.objects.filter(id__in=pk_set)

    if action == "post_add":
        instance.create_access_log(users, 'GRANT_ACCESS')
    elif action == "post_remove":
        instance.create_access_log(users, 'REVOKE_ACCESS')

    for user_id in pk_set:
        send_user_message(user_id)

def send_user_message(user_id):

    if not hasattr(send_user_message, '_buffer'):
        send_user_message._buffer = set()
        send_user_message._timer = None

    send_user_message._buffer.add(user_id)

    if send_user_message._timer:
        send_user_message._timer.cancel()

    def send_buffered_messages():
        channel_layer = get_channel_layer()
        for buffered_id in send_user_message._buffer:
            group_name = f"sync_{buffered_id}"
            print(f">>> send to group {group_name}")
            async_to_sync(channel_layer.group_send)(
                group_name, {"type": "sync.update", "message": "hello"}
            )
        send_user_message._buffer.clear()
        send_user_message._timer = None

    send_user_message._timer = Timer(0.1, send_buffered_messages)
    send_user_message._timer.start()

@receiver(pre_delete, sender=DataAccess)
def revoke_access_after_delete(sender, instance, **kwargs):
    instance.create_revoke_access_log()