feat(purchases): fresh purchases implementation

app/Domains/Purchases/Http/Resources/ExpenseCategoryResource.php

@@ -0,0 +1,48 @@
+<?php
+
+namespace App\Domains\Purchases\Http\Resources;
+
+use App\Domains\Accounts\Http\Resources\CompanyResource;
+use Illuminate\Http\Request;
+use Illuminate\Http\Resources\Json\JsonResource;
+
+/**
+ * A spending bucket as the admin API publishes it.
+ *
+ * A category owns very little: a label, an optional blurb, and the company it
+ * belongs to. The two remaining fields are worked out at read time rather than
+ * stored -- `amount` totals every expense filed under the category, and the
+ * creation date is rendered through the owning company's date format. Each is
+ * a trip to the database per serialised row, so a page of categories pays for
+ * them once per row.
+ *
+ * The owning company is published only when the relation resolves, and that is
+ * asked of the database every time rather than read off whatever the caller
+ * eager loaded -- another query per row. This is the payload's established
+ * shape and is kept deliberately.
+ */
+class ExpenseCategoryResource extends JsonResource
+{
+    /**
+     * Transform the resource into an array.
+     *
+     * @param  Request  $request
+     */
+    public function toArray($request): array
+    {
+        $category = $this->resource;
+
+        return [
+            'id' => $category->id,
+            'name' => $category->name,
+            'description' => $category->description,
+            'company_id' => $category->company_id,
+            'amount' => $category->amount,
+            'formatted_created_at' => $category->formattedCreatedAt,
+            'company' => $this->when(
+                $category->company()->exists(),
+                fn () => new CompanyResource($category->company)
+            ),
+        ];
+    }
+}