From 6dc2ccbb55c0ab53c8ab954f9ab2b9804cd2d7e2 Mon Sep 17 00:00:00 2001
From: Yisroel Baum <yisroel.d.baum@gmail.com>
Date: Thu, 20 Aug 2026 08:21:15 +0300
Subject: [PATCH] spread heavy workload days

---
 .../Schedule/EvenDistributionScheduler.php    | 106 +++++++++++-------
 .../CreateSchedule/CreateSchedule.php         |  12 --
 2 files changed, 65 insertions(+), 53 deletions(-)

diff --git a/backend/app/Schedule/EvenDistributionScheduler.php b/backend/app/Schedule/EvenDistributionScheduler.php
index 5030655..3cdb919 100644
--- a/backend/app/Schedule/EvenDistributionScheduler.php
+++ b/backend/app/Schedule/EvenDistributionScheduler.php
@@ -18,15 +18,7 @@ class EvenDistributionScheduler
         $differenceInDays = $startDate->diff($targetDate)->days;
         $dayCount = $differenceInDays + 1;
 
-        if ($workloadPlacement === WorkloadPlacement::Spread) {
-            return $this->sparseDates(
-                assignmentCount: $assignmentCount,
-                dayCount: $dayCount,
-                startDate: $startDate,
-            );
-        }
-
-        return $this->groupedDates(
+        return $this->distributedDates(
             assignmentCount: $assignmentCount,
             dayCount: $dayCount,
             startDate: $startDate,
@@ -37,33 +29,7 @@ class EvenDistributionScheduler
     /**
      * @return list<DateTimeImmutable>
      */
-    private function sparseDates(
-        int $assignmentCount,
-        int $dayCount,
-        DateTimeImmutable $startDate,
-    ): array {
-        if ($assignmentCount === 1) {
-            return [$startDate];
-        }
-
-        $dates = [];
-        for ($assignmentIndex = 0;
-            $assignmentIndex < $assignmentCount;
-            $assignmentIndex++
-        ) {
-            $scaledIndex = $assignmentIndex * ($dayCount - 1)
-                / ($assignmentCount - 1);
-            $dayIndex = (int) floor($scaledIndex + 0.5);
-            $dates[] = $startDate->modify("+{$dayIndex} days");
-        }
-
-        return $dates;
-    }
-
-    /**
-     * @return list<DateTimeImmutable>
-     */
-    private function groupedDates(
+    private function distributedDates(
         int $assignmentCount,
         int $dayCount,
         DateTimeImmutable $startDate,
@@ -71,19 +37,18 @@ class EvenDistributionScheduler
     ): array {
         $assignmentsPerDay = intdiv($assignmentCount, $dayCount);
         $remainderDayCount = $assignmentCount % $dayCount;
-        $remainderBlockStart = $this->remainderBlockStart(
+        $remainderDayIndexes = $this->remainderDayIndexes(
+            assignmentsPerDay: $assignmentsPerDay,
             dayCount: $dayCount,
             remainderDayCount: $remainderDayCount,
             workloadPlacement: $workloadPlacement,
         );
+        $remainderDays = array_fill_keys($remainderDayIndexes, true);
         $dates = [];
 
         for ($dayIndex = 0; $dayIndex < $dayCount; $dayIndex++) {
             $assignmentCountForDay = $assignmentsPerDay;
-            if (
-                $dayIndex >= $remainderBlockStart
-                && $dayIndex < $remainderBlockStart + $remainderDayCount
-            ) {
+            if (isset($remainderDays[$dayIndex])) {
                 $assignmentCountForDay++;
             }
 
@@ -96,6 +61,65 @@ class EvenDistributionScheduler
         return $dates;
     }
 
+    /**
+     * @return list<int>
+     */
+    private function remainderDayIndexes(
+        int $assignmentsPerDay,
+        int $dayCount,
+        int $remainderDayCount,
+        WorkloadPlacement $workloadPlacement,
+    ): array {
+        if ($remainderDayCount === 0) {
+            return [];
+        }
+
+        if ($workloadPlacement === WorkloadPlacement::Spread) {
+            return $this->spreadRemainderDayIndexes(
+                assignmentsPerDay: $assignmentsPerDay,
+                dayCount: $dayCount,
+                remainderDayCount: $remainderDayCount,
+            );
+        }
+
+        $blockStart = $this->remainderBlockStart(
+            dayCount: $dayCount,
+            remainderDayCount: $remainderDayCount,
+            workloadPlacement: $workloadPlacement,
+        );
+
+        return range($blockStart, $blockStart + $remainderDayCount - 1);
+    }
+
+    /**
+     * @return list<int>
+     */
+    private function spreadRemainderDayIndexes(
+        int $assignmentsPerDay,
+        int $dayCount,
+        int $remainderDayCount,
+    ): array {
+        if ($remainderDayCount === 1) {
+            if ($assignmentsPerDay === 0) {
+                return [0];
+            }
+
+            return [intdiv($dayCount - 1, 2)];
+        }
+
+        $dayIndexes = [];
+        for ($remainderIndex = 0;
+            $remainderIndex < $remainderDayCount;
+            $remainderIndex++
+        ) {
+            $scaledIndex = $remainderIndex * ($dayCount - 1)
+                / ($remainderDayCount - 1);
+            $dayIndexes[] = (int) floor($scaledIndex + 0.5);
+        }
+
+        return $dayIndexes;
+    }
+
     private function remainderBlockStart(
         int $dayCount,
         int $remainderDayCount,
diff --git a/backend/app/Schedule/UseCases/CreateSchedule/CreateSchedule.php b/backend/app/Schedule/UseCases/CreateSchedule/CreateSchedule.php
index e131aa4..fe9392a 100644
--- a/backend/app/Schedule/UseCases/CreateSchedule/CreateSchedule.php
+++ b/backend/app/Schedule/UseCases/CreateSchedule/CreateSchedule.php
@@ -248,9 +248,6 @@ class CreateSchedule
         return $workloadPlacement;
     }
 
-    /**
-     * @throws BadRequestException
-     */
     private function resolvedWorkloadPlacement(
         ?WorkloadPlacement $requestedWorkloadPlacement,
         int $assignmentCount,
@@ -267,15 +264,6 @@ class CreateSchedule
                 : WorkloadPlacement::Middle;
         }
 
-        if (
-            $requestedWorkloadPlacement === WorkloadPlacement::Spread
-            && ! $isSparse
-        ) {
-            throw new BadRequestException(
-                'spread placement requires fewer assignments than days',
-            );
-        }
-
         return $requestedWorkloadPlacement;
     }
 }