Add migration for existing overlapping absences

aleksis/apps/kolego/migrations/0005_fix_overlapping_absences.py

+# Generated by Django 4.2.13 on 2024-07-16 11:01
+from datetime import datetime, time
+
+from django.db import migrations, models
+from django.db.models import Q
+
+
+def _run_forward(apps, schema_editor):
+    Absence = apps.get_model("kolego", "Absence")
+    for absence in Absence.objects.order_by("-datetime_start", "-date_start"):
+        # Convert dates of new event to datetimes in case dates are used
+        new_datetime_start = (
+            absence.datetime_start
+            if absence.datetime_start
+            else datetime.combine(absence.date_start, time.min)
+        ).astimezone(absence.timezone)
+        new_datetime_end = (
+            absence.datetime_end
+            if absence.datetime_end
+            else datetime.combine(absence.date_end, time.max)
+        ).astimezone(absence.timezone)
+
+        events_within = Absence.objects.filter(
+            person=absence.person,
+        ).filter(
+            Q(datetime_start__lte=new_datetime_end, datetime_end__gte=new_datetime_start)
+            | Q(date_start__lte=new_datetime_end.date(), date_end__gte=new_datetime_start.date())
+        )
+
+        for event_within in events_within:
+            event_within_datetime_start = (
+                event_within.datetime_start
+                if event_within.datetime_start
+                else datetime.combine(event_within.date_start, time.min)
+            )
+            event_within_datetime_end = (
+                event_within.datetime_end
+                if event_within.datetime_end
+                else datetime.combine(event_within.date_end, time.max)
+            )
+
+            # If overlapping absence has the same reason, just extend it
+            if event_within.reason == absence.reason:
+                event_within.datetime_start = min(new_datetime_start, event_within_datetime_start)
+                event_within.datetime_end = max(new_datetime_end, event_within_datetime_end)
+                event_within.save()
+            else:
+                if (
+                    new_datetime_start > event_within_datetime_start
+                    and new_datetime_end < event_within_datetime_end
+                ):
+                    # Cut existing event in two parts
+                    # First, cut end date of existing one
+                    event_within.datetime_end = new_datetime_start
+                    event_within.save()
+                    # Then, create new event based on existing one filling up the remaining time
+                    end_filler_event = event_within
+                    end_filler_event.pk = None
+                    end_filler_event.id = None
+                    end_filler_event.calendarevent_ptr_id = None
+                    end_filler_event.freebusy_ptr_id = None
+                    end_filler_event._state.adding = True
+                    end_filler_event.datetime_start = new_datetime_end
+                    end_filler_event.datetime_end = event_within_datetime_end
+
+                    end_filler_event.save()
+                elif (
+                    new_datetime_start <= event_within_datetime_start
+                    and new_datetime_end >= event_within_datetime_end
+                ):
+                    # Delete existing event
+                    event_within.delete()
+                elif (
+                    new_datetime_start > event_within_datetime_start
+                    and new_datetime_start < event_within_datetime_end
+                    and new_datetime_end >= event_within_datetime_end
+                ):
+                    # Cut end of existing event
+                    event_within.datetime_end = new_datetime_start
+                    event_within.save()
+                elif (
+                    new_datetime_start <= event_within_datetime_start
+                    and new_datetime_end < event_within_datetime_end
+                    and new_datetime_end > event_within_datetime_start
+                ):
+                    # Cut start of existing event
+                    event_within.datetime_start = new_datetime_end
+                    event_within.save()
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("kolego", "0004_absencereasontag_absencereason_tags"),
+    ]
+
+    operations = [migrations.RunPython(_run_forward)]