feat: implement webhook setup call parsing and response handling

docs/Webhooks.md

@@ -96,9 +96,11 @@ Verification is performed against the **raw request body bytes**. JSON that is p
 ```php
 use Vatly\API\Exceptions\InvalidSignatureException;
 use Vatly\API\Webhooks\Webhook;
+use Vatly\API\Webhooks\WebhookSetupCallPayload;
+use Vatly\API\Webhooks\WebhookSignatureValidator;
 
 $payload   = file_get_contents('php://input');
-$signature = $_SERVER['HTTP_VATLY_SIGNATURE'] ?? '';
+$signature = $_SERVER[WebhookSignatureValidator::SIGNATURE_HEADER_NAME] ?? '';
 $secret    = getenv('VATLY_WEBHOOK_SECRET');
 
 try {
@@ -108,8 +110,13 @@ try {
     exit('Invalid signature');
 }
 
+if ($event instanceof WebhookSetupCallPayload) {
+    http_response_code(200);
+    exit;
+}
+
 // Dedupe with Vatly-Event-Id (stable across retry attempts).
-$eventId = $_SERVER['HTTP_VATLY_EVENT_ID'] ?? $event->id;
+$eventId = $_SERVER[WebhookSignatureValidator::EVENT_ID_HEADER_NAME] ?? $event->id;
 if (alreadyProcessed($eventId)) {
     http_response_code(200);
     exit;
@@ -126,6 +133,8 @@ markProcessed($eventId);
 http_response_code(200);
 ```
 
+When a webhook endpoint is registered, Vatly sends a signed setup call with `{"message":"Setup call","testmode":true}`. `Webhook::parse()` returns a `WebhookSetupCallPayload` for this body so receivers can acknowledge it without running normal event handling.
+
 `Webhook::parse()` throws `Vatly\API\Exceptions\InvalidSignatureException` when the signature header is malformed, the timestamp is outside the tolerance window, or the HMAC does not match. It throws `InvalidArgumentException` when the body is not valid JSON or is missing required fields.
 
 ### Replay-window tolerance

src/API/Webhooks/Webhook.php

@@ -35,6 +35,10 @@ public static function parse(string $payload, string $signature, string $secret)
             );
         }
 
+        if (self::isSetupCall($decoded)) {
+            return new WebhookSetupCallPayload($decoded->message, $decoded->testmode);
+        }
+
         foreach (['id', 'resource', 'eventName', 'entityType', 'entityId', 'createdAt', 'testmode'] as $field) {
             if (! isset($decoded->{$field})) {
                 throw new \InvalidArgumentException(
@@ -61,4 +65,15 @@ public static function parse(string $payload, string $signature, string $secret)
             $object,
         );
     }
+
+    private static function isSetupCall($decoded): bool
+    {
+        if (! is_object($decoded)) {
+            return false;
+        }
+
+        return isset($decoded->message, $decoded->testmode)
+            && is_bool($decoded->testmode)
+            && ! isset($decoded->id);
+    }
 }

src/API/Webhooks/WebhookSetupCallPayload.php

@@ -0,0 +1,32 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Vatly\API\Webhooks;
+
+/**
+ * Represents the setup verification call sent when a webhook endpoint is registered.
+ */
+class WebhookSetupCallPayload extends WebhookPayload
+{
+    public const RESOURCE = 'webhook_setup_call';
+    public const EVENT_NAME = 'webhook.setup';
+
+    public string $message;
+
+    public function __construct(string $message, bool $testmode)
+    {
+        parent::__construct(
+            '',
+            self::RESOURCE,
+            self::EVENT_NAME,
+            'webhook',
+            '',
+            $testmode,
+            '',
+            null,
+        );
+
+        $this->message = $message;
+    }
+}

tests/Webhooks/WebhookTest.php

@@ -9,6 +9,7 @@
 use Vatly\API\Exceptions\InvalidSignatureException;
 use Vatly\API\Webhooks\Webhook;
 use Vatly\API\Webhooks\WebhookPayload;
+use Vatly\API\Webhooks\WebhookSetupCallPayload;
 
 class WebhookTest extends TestCase
 {
@@ -78,6 +79,24 @@ public function test_it_parses_a_webhook_without_object(): void
         $this->assertNull($event->object);
     }
 
+    public function test_it_parses_the_webhook_setup_call(): void
+    {
+        $payload = json_encode([
+            'message' => 'Setup call',
+            'testmode' => true,
+        ]);
+        $signature = $this->sign($payload);
+
+        $event = Webhook::parse($payload, $signature, $this->secret);
+
+        $this->assertInstanceOf(WebhookSetupCallPayload::class, $event);
+        $this->assertSame('Setup call', $event->message);
+        $this->assertSame(WebhookSetupCallPayload::RESOURCE, $event->resource);
+        $this->assertSame(WebhookSetupCallPayload::EVENT_NAME, $event->eventName);
+        $this->assertTrue($event->testmode);
+        $this->assertNull($event->object);
+    }
+
     public function test_it_throws_for_invalid_signature(): void
     {
         $this->expectException(InvalidSignatureException::class);