Send messages on shift changes

shiftregister/app/apps.py

@@ -4,3 +4,6 @@ from django.apps import AppConfig
 class AppConfig(AppConfig):
     default_auto_field = "django.db.models.BigAutoField"
     name = "shiftregister.app"
+
+    def ready(self):
+        from . import signals

shiftregister/app/signals.py

@@ -0,0 +1,39 @@
+from django.db.models.signals import pre_save
+from django.dispatch import receiver
+from django.shortcuts import reverse
+from django.template import Context, Template
+from .models import Message, Shift
+
+
+@receiver(pre_save, dispatch_uid="notify_shift_changed")
+def notify_shift_changed(sender, **kwargs):
+    if issubclass(sender, Shift):
+        instance = kwargs["instance"]
+        try:
+            prev = Shift.objects.get(pk=instance.id)
+        except Shift.DoesNotExist:
+            return
+
+        if (
+            prev.room == instance.room
+            and prev.start_at == instance.start_at
+            and prev.duration == instance.duration
+            and prev.deleted == instance.deleted
+        ):
+            return
+
+        message = f"Eine deiner kontakt-Schichten hat sich geändert: https://kontakt.rocks{reverse('shift', kwargs={'shiftid': instance.id})}"
+        if instance.deleted:
+            template = Template(
+                'Deine kontakt-Schicht "{{ room }}" am {{ start_at|date:"l" }} um {{ start_at|date:"H:i" }} Uhr entfällt.'
+            )
+            message = template.render(
+                Context({"room": prev.room, "start_at": prev.start_at})
+            )
+
+        Message.objects.bulk_create(
+            (
+                Message(text=message, to=reg.helper)
+                for reg in instance.shiftregistration_set.all()
+            )
+        )

shiftregister/metrics/views.py

@@ -3,10 +3,20 @@ from shiftregister.app.models import Helper
 
 
 def metrics(request):
-    response = HttpResponse("\n".join((f"shiftregister_{name} {value}" for name, value in (
+    response = HttpResponse(
+        "\n".join(
+            (
+                f"shiftregister_{name} {value}"
+                for name, value in (
                     ("helpers_total", Helper.objects.count()),
-        ("helpers_confirmed_total", Helper.objects.filter(number_validated=True).count()),
+                    (
-    ))))
+                        "helpers_confirmed_total",
+                        Helper.objects.filter(number_validated=True).count(),
+                    ),
+                )
+            )
+        )
+    )
     response.headers["Content-Type"] = "text/plain"
 
     return response