[feat:] reordering courses if they are of the same sport and are not weighted equally

MainWindow.axaml.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
+using System.Threading.Tasks;
 using Avalonia.Controls;
 using Avalonia.Input;
 using Avalonia.Interactivity;
@@ -59,14 +60,14 @@ public partial class MainWindow : Window
         }
     }
 
-    private void ChangeStudentCourse(Sport targetSport)
+    private async void ChangeStudentCourse(Sport targetSport)
     {
         if (LbResult.SelectedItem is not ResultEntry selectedEntry)
             return;
 
         try
         {
-            if (ApplyStudentCourseChange(selectedEntry.Student, selectedEntry.Semester, targetSport))
+            if (await ApplyStudentCourseChange(selectedEntry.Student, selectedEntry.Semester, targetSport))
             {
                 CourseCrafter.ReloadResult();
                 RefreshResultView();
@@ -79,7 +80,7 @@ public partial class MainWindow : Window
         }
     }
 
-    private bool ApplyStudentCourseChange(Student student, int semester, Sport targetSport)
+    private async Task<bool> ApplyStudentCourseChange(Student student, int semester, Sport targetSport)
     {
         if (semester < 1 || semester > 4)
             return false;
@@ -92,14 +93,24 @@ public partial class MainWindow : Window
             .Where(course => course.Instance.Students.Contains(student.ID))
             .ToList();
 
-        CourseCrafter.CourseInstance? targetCourse = currentCourses
-            .FirstOrDefault(course => course.Instance.Sport.Name == targetSport.Name)
-            .Instance;
+        string? oldSportName = currentCourses
+            .Select(course => course.Instance.Sport.Name)
+            .FirstOrDefault();
 
-        if (targetCourse == null)
+        var existingTargetCourses = semesterCourses
+            .Where(course => course.Instance.Sport.Name == targetSport.Name)
+            .ToList();
+
+        CourseCrafter.CourseInstance? targetCourse = existingTargetCourses
+            .Where(course => !course.Instance.Students.Contains(student.ID) &&
+                             course.Instance.Students.Count < course.Instance.Sport.MaxStudents)
+            .OrderBy(course => course.Instance.Students.Count)
+            .Select(course => course.Instance)
+            .FirstOrDefault();
+
+        if (targetCourse == null && existingTargetCourses.Any())
         {
-            targetCourse = semesterCourses
-                .Where(course => course.Instance.Sport.Name == targetSport.Name)
+            targetCourse = existingTargetCourses
                 .OrderBy(course => course.Instance.Students.Count)
                 .Select(course => course.Instance)
                 .FirstOrDefault();
@@ -140,9 +151,87 @@ public partial class MainWindow : Window
             changed = true;
         }
 
+        if (changed && !string.IsNullOrEmpty(oldSportName) &&
+            IsRebalanceNeededForSportSemester(oldSportName, semester))
+        {
+            var result = await MessageBox.Show(this,
+                $"Der Kursplan für {oldSportName} im {semester}. Semester ist nach der Änderung unausgeglichen. Soll die alte Sportart umverteilt werden?",
+                "Umverteilung der alten Sportart", MessageBoxButton.YesNo);
+
+            if (result == MessageBoxResult.Yes)
+                BalanceSportSemester(oldSportName, semester);
+        }
+
         return changed;
     }
 
+    private bool IsRebalanceNeededForSportSemester(string sportName, int semester)
+    {
+        var courses = CourseCrafter.GeneratedCourses
+            .Where(course => course.Semester == semester && course.Instance.Sport.Name == sportName)
+            .ToList();
+
+        if (courses.Count <= 1)
+            return false;
+
+        var ordered = courses
+            .OrderBy(course => course.Instance.Students.Count)
+            .ToList();
+
+        int minCount = ordered.First().Instance.Students.Count;
+        int maxCount = ordered.Last().Instance.Students.Count;
+        if (maxCount - minCount <= 1)
+            return false;
+
+        if (ordered.Last().Instance.Students.Count - 1 < GetEffectiveMinStudents(ordered.Last().Instance.Sport, semester))
+            return false;
+
+        if (ordered.First().Instance.Students.Count >= ordered.First().Instance.Sport.MaxStudents)
+            return false;
+
+        return true;
+    }
+
+    private void BalanceSportSemester(string sportName, int semester)
+    {
+        bool changed;
+        do
+        {
+            changed = false;
+
+            var courses = CourseCrafter.GeneratedCourses
+                .Where(course => course.Semester == semester && course.Instance.Sport.Name == sportName)
+                .OrderBy(course => course.Instance.Students.Count)
+                .ToList();
+
+            if (courses.Count <= 1)
+                break;
+
+            var target = courses.First();
+            var source = courses.Last();
+
+            if (source.Instance.Students.Count <= target.Instance.Students.Count + 1)
+                break;
+
+            if (source.Instance.Students.Count - 1 < GetEffectiveMinStudents(source.Instance.Sport, semester))
+                break;
+
+            if (target.Instance.Students.Count >= target.Instance.Sport.MaxStudents)
+                break;
+
+            var studentId = source.Instance.Students[^1];
+            source.Instance.Students.RemoveAt(source.Instance.Students.Count - 1);
+            target.Instance.Students.Add(studentId);
+            changed = true;
+        } while (changed);
+    }
+
+    private int GetEffectiveMinStudents(Sport sport, int semester)
+    {
+        int reduction = (semester >= 3) ? 2 : 0;
+        return Math.Max(1, sport.MinStudents - reduction);
+    }
+
     private async void MnuExpSettings_OnClick(object? sender, RoutedEventArgs e)
     {
         await ExportConfigurationAsync();

crafter.cs

@@ -383,6 +383,8 @@ public class CourseCrafter
         }
     }
 
+    BalanceCoursesBetweenSameSportAndSemester();
+
     // ---------------------------------------------------------------------------
     // Lokale Hilfsfunktionen
     // ---------------------------------------------------------------------------
@@ -406,6 +408,54 @@ public class CourseCrafter
         return true;
     }
 
+    void BalanceCoursesBetweenSameSportAndSemester()
+    {
+        bool changed;
+        do
+        {
+            changed = false;
+            var groups = GeneratedCourses
+                .GroupBy(c => (c.Semester, c.Instance.Sport.Name))
+                .Where(g => g.Count() > 1);
+
+            foreach (var group in groups)
+            {
+                var courses = group
+                    .OrderBy(c => c.Instance.Students.Count)
+                    .ToList();
+
+                for (int sourceIndex = courses.Count - 1; sourceIndex > 0; sourceIndex--)
+                {
+                    var sourceCourse = courses[sourceIndex];
+                    for (int targetIndex = 0; targetIndex < sourceIndex; targetIndex++)
+                    {
+                        var targetCourse = courses[targetIndex];
+                        if (sourceCourse.Instance.Students.Count <= targetCourse.Instance.Students.Count + 1)
+                            break;
+
+                        if (targetCourse.Instance.Students.Count >= targetCourse.Instance.Sport.MaxStudents)
+                            continue;
+
+                        if (sourceCourse.Instance.Students.Count - 1 < getEffectiveMinStudents(sourceCourse.Instance.Sport, sourceCourse.Semester))
+                            continue;
+
+                        var studentId = sourceCourse.Instance.Students[^1];
+                        sourceCourse.Instance.Students.RemoveAt(sourceCourse.Instance.Students.Count - 1);
+                        targetCourse.Instance.Students.Add(studentId);
+                        changed = true;
+                        break;
+                    }
+
+                    if (changed)
+                        break;
+                }
+
+                if (changed)
+                    break;
+            }
+        } while (changed);
+    }
+
     bool requestExit()
     {
         globalCount++;