From 3f07acfbd527d9aae05e49f26cdaa6a78f3c433a Mon Sep 17 00:00:00 2001
From: "Andreas (@xAndy) Zimmermann" <xandy@hackerspace-bamberg.de>
Date: Sat, 13 May 2023 16:25:33 +0200
Subject: [PATCH] fair shift distribution, no overlapping shifts

---
 shiftregister/fallback/models.py | 49 ++++++++++++++++++++++++++++----
 1 file changed, 43 insertions(+), 6 deletions(-)

diff --git a/shiftregister/fallback/models.py b/shiftregister/fallback/models.py
index c4bbf40..9d2e0a4 100644
--- a/shiftregister/fallback/models.py
+++ b/shiftregister/fallback/models.py
@@ -1,6 +1,8 @@
 from shiftregister.importer.models import *
 from django.db.models import Max, Sum
-from django.db.models import Count, Exists, OuterRef, Subquery, Func
+from django.db.models import Count, Exists, OuterRef, ExpressionWrapper
+from django.db.models.lookups import LessThan
+from django.db.models.fields import DateTimeField
 import math
 
 night_shift_query = Q(start_at__hour__gte=21) | Q(start_at__hour__lte=10)
@@ -49,10 +51,35 @@ class TeamMember(models.Model):
         print(
             f"total:{total_slot_count} max:{max_shifts_per_member} calc:{shifts_per_member} chosen:{shift_count} calc:{active_team_members*shift_count} free `before:{free_slot_count} {self.name}"
         )
+        blocked_times = []
+        for shift in self.fallback_shifts.all():
+            blocked_times.append(
+                Q(start_at__gte=(shift.start_at + shift.duration))
+                | Q(end_at__lte=shift.start_at)
+            )
         # easy part: enough free shifts for everyone:
-        shifts = free_bucket.order_by("?")[:shift_count]
-        for shift in shifts:
+        assigned_shift_count = 0
+        for _ in range(shift_count):
+            shift = (
+                free_bucket.annotate(
+                    end_at=ExpressionWrapper(
+                        F("start_at") + F("duration"),
+                        output_field=models.DateTimeField(),
+                    )
+                )
+                .filter(*blocked_times)
+                .order_by("?")
+                .first()
+            )
+            if not shift:
+                break
             self.fallback_shifts.add(shift)
+            assigned_shift_count += 1
+            blocked_times.append(
+                Q(start_at__gte=(shift.start_at + shift.duration))
+                | Q(end_at__lte=shift.start_at)
+            )
+            # blocked_times.append(Q(start_at__gte=(shift.start_at+shift.duration)) | LessThan(F('start_at')+F('duration'), shift.start_at, output_field=DateTimeField()))
 
         # there is a chance that even if qota*teammembers team members are activatet, there are still unasigned shifts
         # this happens if there are shifts with multiple people left, as we can not assign multiple slots for
@@ -61,7 +88,7 @@ class TeamMember(models.Model):
 
         # if len(shifts) >= (shift_count - 1):
         #    return
-        shifts_needed = shift_count - len(shifts)
+        shifts_needed = shift_count - assigned_shift_count
         # this is not done very often so we can do this kinda inefficient but readable and maintainable:
         # for each missing shift, get the team member who has the most shifts in our bucket and take one of them at random
         # but also take care to not take any slots for shifts we already have...
@@ -93,14 +120,20 @@ class TeamMember(models.Model):
             for member in sorted_members:
                 # now get all their assignments in the relevant bucket but exclude the ones where we already have a slot in the same shift...
                 assignment = (
-                    FallbackAssignment.objects.filter(
-                        team_member_id=member.id, shift_id__in=canidate_shift_ids
+                    FallbackAssignment.objects.annotate(
+                        start_at=F("shift__start_at"),
+                        end_at=ExpressionWrapper(
+                            F("shift__start_at") + F("shift__duration"),
+                            output_field=models.DateTimeField(),
+                        ),
                     )
+                    .filter(team_member_id=member.id, shift_id__in=canidate_shift_ids)
                     .exclude(
                         shift_id__in=FallbackAssignment.objects.filter(
                             team_member_id=self.pk
                         ).values("shift_id")
                     )
+                    .filter(*blocked_times)
                     .order_by("?")
                     .first()
                 )
@@ -110,6 +143,10 @@ class TeamMember(models.Model):
                 print("could not find any matching assignments to take away")
                 return
             shifts_needed -= 1
+            blocked_times.append(
+                Q(start_at__gte=(assignment.shift.start_at + assignment.shift.duration))
+                | Q(end_at__lte=assignment.shift.start_at)
+            )
             self.fallback_shifts.add(assignment.shift)
             assignment.delete()