"""Reacts to an admin editing a PlaceSettings row (grid size) by:

1. Rebuilding that event's Redis canvas from history at the (possibly new)
   dimensions - a resize invalidates the old Redis bytes (wrong length,
   wrong meaning), so this keeps Redis self-healing instead of relying on
   the admin remembering to click "Resync canvas from DB" after every
   resize.
2. Pushing the new size to that event's already-connected clients. Unlike
   the clock app, place has no periodic heartbeat broadcast to piggyback
   this onto, so it's broadcast explicitly here instead.
"""

from asgiref.sync import async_to_sync
from channels.layers import get_channel_layer
from django.db.models.signals import post_save
from django.dispatch import receiver

from .broadcast import place_group
from .canvas import rebuild_canvas_from_history
from .models import PlaceSettings


@receiver(post_save, sender=PlaceSettings)
def on_settings_saved(sender, instance, **kwargs):
    rebuild_canvas_from_history(instance.event, instance.width, instance.height)

    channel_layer = get_channel_layer()
    if channel_layer is None:
        return
    async_to_sync(channel_layer.group_send)(
        place_group(instance.event.path),
        {
            "type": "settings_changed",
            "width": instance.width,
            "height": instance.height,
        },
    )