feat: allow single request scheduling

Until now the steering API client was expected to submit two requests.

1. The initial schedule request, with a `schedule` object
2. A second schedule request, with an additional `solutions` object

This `solutions` object was empty, if no conflicts arose from the
submitted schedule in the first place. But instead of just creating the
requested schedule if no conflicts were detected we still required that
second round-trip, introducing possible race conditions in the client,
if another successful scheduling request was made between requests.

From now on the steering API will create schedules if no conflicts have
been detected and will only require the client to submit solutions if
there really are conflicts to solve.

program/models.py

@@ -41,6 +41,12 @@ from steering.settings import (
 )
 
 
+class ScheduleConflictError(ValidationError):
+    def __init__(self, *args, conflicts=None, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.conflicts = conflicts
+
+
 class Type(models.Model):
     name = models.CharField(max_length=32)
     slug = models.SlugField(max_length=32, unique=True)
@@ -732,7 +738,7 @@ class Schedule(models.Model):
         """
 
         sdl = data["schedule"]
-        solutions = data["solutions"]
+        solutions = data.get("solutions", [])
 
         # Regenerate conflicts
         schedule = Schedule.instantiate_upcoming(sdl, show_pk, schedule_pk)
@@ -756,9 +762,10 @@ class Schedule(models.Model):
         )
 
         if len(solutions) != num_conflicts:
-            raise ValidationError(
+            raise ScheduleConflictError(
                 _("Numbers of conflicts and solutions don't match."),
                 code="one-solution-per-conflict",
+                conflicts=conflicts,
             )
 
         # Projected timeslots to create
@@ -963,7 +970,11 @@ class Schedule(models.Model):
             conflicts["notes"] = data.get("notes")
             conflicts["playlists"] = data.get("playlists")
 
-            return conflicts
+            raise ScheduleConflictError(
+                _("Not all conflicts have been resolved."),
+                code="unresolved-conflicts",
+                conflicts=conflicts,
+            )
 
         # Collect upcoming timeslots to delete which might still remain
         del_timeslots = TimeSlot.objects.filter(

program/views.py

@@ -42,6 +42,7 @@ from program.models import (
     MusicFocus,
     Note,
     Schedule,
+    ScheduleConflictError,
     Show,
     TimeSlot,
     Topic,
@@ -483,28 +484,17 @@ class APIScheduleViewSet(
         if show_pk is None or "schedule" not in request.data:
             return Response(status=status.HTTP_400_BAD_REQUEST)
 
-        # First create submit -> return projected timeslots and collisions
-        # TODO: Perhaps directly insert into database if no conflicts found
-        if "solutions" not in request.data:
+        try:
+            resolution = Schedule.resolve_conflicts(request.data, pk, show_pk)
+        except ScheduleConflictError as exc:
             # TODO: respond with status.HTTP_409_CONFLICT when the dashboard can handle it
-            return Response(
-                Schedule.make_conflicts(request.data["schedule"], pk, show_pk),
-            )
-
-        # Otherwise try to resolve
-        resolution = Schedule.resolve_conflicts(request.data, pk, show_pk)
+            return Response(exc.conflicts)
 
         if all(key in resolution for key in ["create", "update", "delete"]):
             # this is a dry-run
             return Response(resolution, status=status.HTTP_202_ACCEPTED)
 
-        # If resolution went well
-        if "projected" not in resolution:
-            return Response(resolution, status=status.HTTP_201_CREATED)
-
-        # Otherwise return conflicts
-        # TODO: respond with status.HTTP_409_CONFLICT when the dashboard can handle it
-        return Response(resolution)
+        return Response(resolution, status=status.HTTP_201_CREATED)
 
     def update(self, request, *args, **kwargs):
         """
@@ -540,26 +530,14 @@ class APIScheduleViewSet(
             serializer = ScheduleSerializer(schedule)
             return Response(serializer.data)
 
-        # First update submit -> return projected timeslots and collisions
-        if "solutions" not in request.data:
-            # TODO: respond with status.HTTP_409_CONFLICT when the dashboard can handle it
-            return Response(
-                Schedule.make_conflicts(
-                    request.data["schedule"], schedule.pk, schedule.show.pk
-                )
+        try:
+            resolution = Schedule.resolve_conflicts(
+                request.data, schedule.pk, schedule.show.pk
             )
+        except ScheduleConflictError as exc:
+            # TODO: respond with status.HTTP_409_CONFLICT when the dashboard can handle it
+            return Response(exc.conflicts)
 
-        # Otherwise try to resolve
-        resolution = Schedule.resolve_conflicts(
-            request.data, schedule.pk, schedule.show.pk
-        )
-
-        # If resolution went well
-        if "projected" not in resolution:
-            return Response(resolution)
-
-        # Otherwise return conflicts
-        # TODO: respond with status.HTTP_409_CONFLICT when the dashboard can handle it
         return Response(resolution)
 
     def destroy(self, request, *args, **kwargs):