feat(purchase): add expiration time calculations to PurchaseResource and implement related tests

app/Domains/Purchase/Resources/PurchaseResource.php

@@ -17,6 +17,8 @@ class PurchaseResource extends JsonResource
      */
     public function toArray(Request $request): array
     {
+        $serverTime = now();
+        $expiresAt = $this->stockReservation?->expires_at;
         $items = $this->resource->relationLoaded('items')
             ? $this->resource->getRelation('items')
             : collect();
@@ -48,7 +50,11 @@ class PurchaseResource extends JsonResource
             'created_at' => $this->created_at,
             'status' => $this->status,
             'payment_method' => $this->payment_method,
-            'expires_at' => $this->stockReservation?->expires_at,
+            'expires_at' => $expiresAt,
+            'expires_in_seconds' => $expiresAt === null
+                ? null
+                : max(0, $expiresAt->getTimestamp() - $serverTime->getTimestamp()),
+            'server_time' => $serverTime,
             'dni' => $this->dni,
             'transfer_payer_dni' => $this->transfer_payer_dni,
             'telefono' => $this->telefono,

tests/Unit/Purchase/PurchaseResourceTest.php

@@ -0,0 +1,69 @@
+<?php
+
+namespace Tests\Unit\Purchase;
+
+use App\Domains\Catalog\Models\StockReservation;
+use App\Domains\Purchase\Models\Purchase;
+use App\Domains\Purchase\Resources\PurchaseResource;
+use Illuminate\Http\Request;
+use Illuminate\Support\Carbon;
+use Tests\TestCase;
+
+class PurchaseResourceTest extends TestCase
+{
+    public function test_it_exposes_the_remaining_checkout_time_using_the_server_clock(): void
+    {
+        $now = now()->startOfSecond();
+        $this->travelTo($now);
+        $expiresAt = $now->copy()->addMinutes(12);
+
+        $resource = $this->resourceFor(Purchase::STATUS_PENDING_PAYMENT, $expiresAt);
+
+        $this->assertTrue($expiresAt->equalTo($resource['expires_at']));
+        $this->assertSame(720, $resource['expires_in_seconds']);
+        $this->assertTrue($now->equalTo($resource['server_time']));
+
+        $this->travelBack();
+    }
+
+    public function test_it_clamps_an_overdue_checkout_to_zero_seconds(): void
+    {
+        $now = now()->startOfSecond();
+        $this->travelTo($now);
+
+        $resource = $this->resourceFor(
+            Purchase::STATUS_CREATED,
+            $now->copy()->subSecond(),
+        );
+
+        $this->assertSame(0, $resource['expires_in_seconds']);
+
+        $this->travelBack();
+    }
+
+    public function test_it_exposes_null_expiration_after_the_purchase_enters_review(): void
+    {
+        $resource = $this->resourceFor(
+            Purchase::STATUS_IN_REVIEW,
+            null,
+        );
+
+        $this->assertNull($resource['expires_at']);
+        $this->assertNull($resource['expires_in_seconds']);
+    }
+
+    /** @return array<string, mixed> */
+    private function resourceFor(string $status, ?Carbon $expiresAt): array
+    {
+        $purchase = (new Purchase)->forceFill([
+            'status' => $status,
+            'total' => '0.00',
+        ]);
+        $purchase->setRelation('stockReservation', (new StockReservation)->forceFill([
+            'status' => StockReservation::STATUS_ACTIVE,
+            'expires_at' => $expiresAt,
+        ]));
+
+        return (new PurchaseResource($purchase))->toArray(Request::create('/'));
+    }
+}