UX: Show loading spinner when loading categories

This change ensures loading spinners are displayed when more categories
or subcategories are being loaded in the modal used for editing the
list of categories in the sidebar.

app/assets/javascripts/discourse/app/components/sidebar/edit-navigation-menu/categories-modal.gjs

@@ -6,7 +6,7 @@ import { action } from "@ember/object";
 import didInsert from "@ember/render-modifiers/modifiers/did-insert";
 import { service } from "@ember/service";
 import { TrackedSet } from "@ember-compat/tracked-built-ins";
-import { eq, gt, has } from "truth-helpers";
+import { eq, gt, has, not, or } from "truth-helpers";
 import DButton from "discourse/components/d-button";
 import EditNavigationMenuModal from "discourse/components/sidebar/edit-navigation-menu/modal";
 import borderColor from "discourse/helpers/border-color";
@@ -70,41 +70,6 @@ function splitWhere(elements, f) {
   }, []);
 }
 
-// categories must be topologically sorted so that the parents appear before
-// the children
-function findPartialCategories(categories) {
-  const categoriesById = new Map(
-    categories.map((category) => [category.id, category])
-  );
-  const subcategoryCounts = new Map();
-  const subcategoryCountsRecursive = new Map();
-  const partialCategoryInfos = new Map();
-
-  for (const category of categories.slice().reverse()) {
-    const count = subcategoryCounts.get(category.parent_category_id) || 0;
-    subcategoryCounts.set(category.parent_category_id, count + 1);
-
-    const recursiveCount =
-      subcategoryCountsRecursive.get(category.parent_category_id) || 0;
-
-    subcategoryCountsRecursive.set(
-      category.parent_category_id,
-      recursiveCount + (subcategoryCountsRecursive.get(category.id) || 0) + 1
-    );
-  }
-
-  for (const [id, count] of subcategoryCounts) {
-    if (count === 5 && categoriesById.has(id)) {
-      partialCategoryInfos.set(id, {
-        level: categoriesById.get(id).level + 1,
-        offset: subcategoryCountsRecursive.get(id),
-      });
-    }
-  }
-
-  return partialCategoryInfos;
-}
-
 export default class SidebarEditNavigationMenuCategoriesModal extends Component {
   @service currentUser;
   @service site;
@@ -116,13 +81,14 @@ export default class SidebarEditNavigationMenuCategoriesModal extends Component
   selectedCategoryIds = new TrackedSet([
     ...this.currentUser.sidebar_category_ids,
   ]);
+  @tracked loadAnotherPage = false;
+  @tracked loadingSubcategories = new TrackedSet();
   selectedFilter = "";
   selectedMode = "everything";
   loadedFilter;
   loadedMode;
   loadedPage;
   saving = false;
-  loadAnotherPage = false;
   unseenCategoryIdsChanged = false;
   observer = new IntersectionObserver(
     ([entry]) => {
@@ -143,6 +109,20 @@ export default class SidebarEditNavigationMenuCategoriesModal extends Component
   }
 
   recomputeGroupings() {
+    const categoriesById = new Map();
+    const categoriesCountByParentId = new Map();
+
+    this.fetchedCategories.forEach((category) => {
+      categoriesById.set(category.id, category);
+
+      if (category.parent_category_id !== undefined) {
+        categoriesCountByParentId.set(
+          category.parent_category_id,
+          (categoriesCountByParentId.get(category.parent_category_id) || 0) + 1
+        );
+      }
+    });
+
     const categoriesWithShowMores = this.fetchedCategories.flatMap((el, i) => {
       const result = [{ type: "category", category: el }];
 
@@ -156,20 +136,21 @@ export default class SidebarEditNavigationMenuCategoriesModal extends Component
       if (
         !nextIsSibling &&
         !nextIsChild &&
-        this.partialCategoryInfos.has(elParentID)
+        elParentID &&
+        categoriesCountByParentId.get(elParentID) <
+          categoriesById.get(elParentID).subcategory_count
       ) {
-        const { level, offset } = this.partialCategoryInfos.get(elParentID);
-
         result.push({
           type: "show-more",
           id: elParentID,
-          level,
-          offset,
+          level: el.level,
+          offset: categoriesCountByParentId.get(elParentID),
+          loading: false,
         });
       }
 
       return result;
-    }, []);
+    });
 
     this.fetchedCategoriesGroupings = splitWhere(
       categoriesWithShowMores,
@@ -180,7 +161,6 @@ export default class SidebarEditNavigationMenuCategoriesModal extends Component
 
   setFetchedCategories(categories) {
     this.fetchedCategories = categories;
-    this.partialCategoryInfos = findPartialCategories(categories);
     this.recomputeGroupings();
   }
 
@@ -199,18 +179,10 @@ export default class SidebarEditNavigationMenuCategoriesModal extends Component
       categories = [...this.fetchedCategories.slice(index), ...categories];
     }
 
-    this.partialCategoryInfos = new Map([
-      ...this.partialCategoryInfos,
-      ...findPartialCategories(categories),
-    ]);
-
     this.recomputeGroupings();
   }
 
-  substituteInFetchedCategories(id, subcategories, offset) {
-    this.partialCategoryInfos.delete(id);
-    this.recomputeGroupings();
-
+  substituteInFetchedCategories(id, subcategories) {
     if (subcategories.length !== 0) {
       const index =
         this.fetchedCategories.findLastIndex(
@@ -222,18 +194,10 @@ export default class SidebarEditNavigationMenuCategoriesModal extends Component
         ...subcategories,
         ...this.fetchedCategories.slice(index),
       ];
-
-      this.partialCategoryInfos = new Map([
-        ...this.partialCategoryInfos,
-        ...findPartialCategories(subcategories),
-      ]);
-
-      this.partialCategoryInfos.set(id, {
-        offset: offset + subcategories.length,
-      });
-
-      this.recomputeGroupings();
     }
+
+    this.recomputeGroupings();
+    this.loadingSubcategories.delete(id);
   }
 
   @action
@@ -296,7 +260,7 @@ export default class SidebarEditNavigationMenuCategoriesModal extends Component
           opts
         );
 
-        this.substituteInFetchedCategories(id, subcategories, offset);
+        this.substituteInFetchedCategories(id, subcategories);
       }
     } else {
       // The shown categories are stale, refresh everything
@@ -327,6 +291,7 @@ export default class SidebarEditNavigationMenuCategoriesModal extends Component
 
   @action
   async loadSubcategories(id, offset) {
+    this.loadingSubcategories.add(id);
     this.subcategoryLoadList.push({ id, offset });
     this.debouncedSendRequest();
   }
@@ -428,11 +393,7 @@ export default class SidebarEditNavigationMenuCategoriesModal extends Component
       class="sidebar__edit-navigation-menu__categories-modal"
     >
       <form class="sidebar-categories-form">
-        {{#if this.initialLoad}}
-          <div class="sidebar-categories-form__loading">
-            {{loadingSpinner size="small"}}
-          </div>
-        {{else}}
+        {{#if (not this.initialLoad)}}
           {{#each this.fetchedCategoriesGroupings as |categories|}}
             <div
               style={{borderColor (get categories "0.category.color") "left"}}
@@ -491,11 +452,19 @@ export default class SidebarEditNavigationMenuCategoriesModal extends Component
                     <label class="sidebar-categories-form__category-label">
                       <div class="sidebar-categories-form__category-wrapper">
                         <div class="sidebar-categories-form__category-badge">
-                          <DButton
-                            @label="sidebar.categories_form_modal.show_more"
-                            @action={{fn this.loadSubcategories c.id c.offset}}
-                            class="btn-flat"
-                          />
+                          {{#if (has this.loadingSubcategories c.id)}}
+                            {{loadingSpinner size="small"}}
+                          {{else}}
+                            <DButton
+                              @label="sidebar.categories_form_modal.show_more"
+                              @action={{fn
+                                this.loadSubcategories
+                                c.id
+                                c.offset
+                              }}
+                              class="btn-flat"
+                            />
+                          {{/if}}
                         </div>
                       </div>
                     </label>
@@ -509,6 +478,11 @@ export default class SidebarEditNavigationMenuCategoriesModal extends Component
             </div>
           {{/each}}
         {{/if}}
+        {{#if (or this.initialLoad this.loadAnotherPage)}}
+          <div class="sidebar-categories-form__loading">
+            {{loadingSpinner}}
+          </div>
+        {{/if}}
       </form>
     </EditNavigationMenuModal>
   </template>