can create and drag and drop pages

Management.Web/Pages/Course/Module/ModuleItems/DroppablePage.razor.cs

@@ -0,0 +1,85 @@
+using Microsoft.AspNetCore.Components;
+
+namespace Management.Web.Course.Module.ModuleItems;
+public class DroppablePage : ComponentBase
+{
+  [Inject]
+  protected CoursePlanner planner { get; set; } = default!;
+
+  [Parameter, EditorRequired]
+  public LocalCoursePage Page { get; set; } = default!;
+  private void dropOnDate(DateTime dropDate)
+  {
+    if (planner.LocalCourse == null) return;
+    var currentModule = planner
+      .LocalCourse
+      .Modules
+      .First(m =>
+        m.Pages.Contains(Page)
+      ) ?? throw new Exception("in drop page callback, could not find module");
+
+
+    var defaultDueTimeDate = new DateTime(
+      year: dropDate.Year,
+      month: dropDate.Month,
+      day: dropDate.Day,
+      hour: planner.LocalCourse.Settings.DefaultDueTime.Hour,
+      minute: planner.LocalCourse.Settings.DefaultDueTime.Minute,
+      second: 0
+    );
+
+    var moduleWithUpdatedPage = currentModule with
+    {
+      Pages = currentModule.Pages.Select(p =>
+        p.Name != Page.Name // we are only changing the due date, so the name should be the same
+        ? p
+        : p with { DueAt = defaultDueTimeDate }
+      )
+    };
+    var updatedModules = planner.LocalCourse.Modules
+      .Select(m =>
+        m.Name == moduleWithUpdatedPage.Name
+          ? moduleWithUpdatedPage
+          : m
+      );
+    var newCourse = planner.LocalCourse with
+    {
+      Modules = updatedModules
+    };
+    planner.LocalCourse = newCourse;
+  }
+  private void dropOnModule(LocalModule module)
+  {
+    if (planner.LocalCourse == null) return;
+    var newModules = planner.LocalCourse.Modules.Select(m =>
+      m.Name != module.Name
+        ? m with
+        {
+          Pages = m.Pages.Where(p => p.Name != Page.Name).DistinctBy(p => p.Name)
+        }
+        : m with
+        {
+          Pages = m.Pages.Append(Page).DistinctBy(a => a.Name)
+        }
+    );
+
+    var newCourse = planner.LocalCourse with
+    {
+      Modules = newModules
+    };
+    planner.LocalCourse = newCourse;
+  }
+
+  protected void dropCallback(DateTime? dropDate, LocalModule? module)
+  {
+    if (module == null)
+    {
+      dropOnDate(dropDate ?? Page.DueAt);
+    }
+    else
+    {
+      dropOnModule(module);
+    }
+  }
+
+}