Some more fixes to forum handling

app/Providers/ForumServiceProvider.php

@@ -4,8 +4,11 @@ declare(strict_types=1);
 
 namespace App\Providers;
 
+use App\Support\Forum\CategoryTreeBuilder;
 use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Support\Facades\View;
 use Illuminate\Support\ServiceProvider;
+use TeamTeaTime\Forum\Models\Category;
 use TeamTeaTime\Forum\Models\Post;
 
 class ForumServiceProvider extends ServiceProvider
@@ -27,5 +30,29 @@ class ForumServiceProvider extends ServiceProvider
         Post::addGlobalScope('withAuthorRole', function (Builder $builder) {
             $builder->with(['author.role']);
         });
+
+        $categoryTreeBuilder = $this->app->make(CategoryTreeBuilder::class);
+
+        View::composer('forum::category.index', function ($view) use ($categoryTreeBuilder): void {
+            $view->with('categories', $categoryTreeBuilder->buildAccessibleTo(request()->user()));
+        });
+
+        View::composer('forum::category.manage', function ($view) use ($categoryTreeBuilder): void {
+            $categories = Category::defaultOrder()->get();
+            $tree = $categoryTreeBuilder->build($categories);
+            $categoryTreeBuilder->hideManageColumns($tree);
+
+            $view->with('categories', $tree);
+        });
+
+        View::composer('forum::thread.show', function ($view) use ($categoryTreeBuilder): void {
+            $data = $view->getData();
+
+            if (! empty($data['categories'])) {
+                return;
+            }
+
+            $view->with('categories', $categoryTreeBuilder->buildThreadDestinations());
+        });
     }
 }

app/Support/Forum/CategoryTreeBuilder.php

@@ -0,0 +1,107 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Support\Forum;
+
+use Illuminate\Database\Eloquent\Collection as EloquentCollection;
+use TeamTeaTime\Forum\Models\Category;
+use TeamTeaTime\Forum\Support\Access\CategoryAccess;
+
+final class CategoryTreeBuilder
+{
+    /**
+     * @param  EloquentCollection<int, Category>  $categories
+     * @return EloquentCollection<int, Category>
+     */
+    public function build(EloquentCollection $categories): EloquentCollection
+    {
+        if ($categories->isEmpty()) {
+            return new EloquentCollection;
+        }
+
+        $rootParentId = $this->resolveRootParentId($categories);
+        $categories->linkNodes();
+
+        /** @var EloquentCollection<int, Category> $tree */
+        $tree = $categories
+            ->filter(static fn (Category $category): bool => $category->getParentId() === $rootParentId)
+            ->values();
+
+        return $this->removeParentRelationships($tree);
+    }
+
+    /**
+     * @return EloquentCollection<int, Category>
+     */
+    public function buildAccessibleTo(mixed $user): EloquentCollection
+    {
+        return $this->build(CategoryAccess::getFilteredTreeFor($user));
+    }
+
+    /**
+     * @return EloquentCollection<int, Category>
+     */
+    public function buildThreadDestinations(): EloquentCollection
+    {
+        return $this->build(Category::query()->threadDestinations()->get());
+    }
+
+    /**
+     * @param  EloquentCollection<int, Category>  $categories
+     */
+    public function hideManageColumns(EloquentCollection $categories): void
+    {
+        $categories->each(function (Category $category): void {
+            $category->makeHidden(['_lft', '_rgt', 'thread_count', 'post_count']);
+
+            if ($category->relationLoaded('children') && $category->children->isNotEmpty()) {
+                /** @var EloquentCollection<int, Category> $children */
+                $children = $category->children;
+                $this->hideManageColumns($children);
+            }
+        });
+    }
+
+    /**
+     * @param  EloquentCollection<int, Category>  $categories
+     */
+    private function resolveRootParentId(EloquentCollection $categories): int|string|null
+    {
+        $rootParentId = null;
+        $lowestLeft = null;
+
+        foreach ($categories as $category) {
+            $left = $category->getLft();
+
+            if ($lowestLeft === null || ($left !== null && $left < $lowestLeft)) {
+                $lowestLeft = $left;
+                $rootParentId = $category->getParentId();
+            }
+        }
+
+        return $rootParentId;
+    }
+
+    /**
+     * @param  EloquentCollection<int, Category>  $categories
+     * @return EloquentCollection<int, Category>
+     */
+    private function removeParentRelationships(EloquentCollection $categories): EloquentCollection
+    {
+        $categories->each(function (Category $category): void {
+            $category->setRelation('parent', null);
+
+            if (! $category->relationLoaded('children')) {
+                return;
+            }
+
+            /** @var EloquentCollection<int, Category> $children */
+            $children = $category->children;
+
+            $category->setRelation('children', $this->removeParentRelationships($children));
+        });
+
+        return $categories;
+    }
+}