Add checkout sessions and webhook event type constants

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/Id/Resources/AppCheckoutSession.php

@@ -0,0 +1,97 @@
+<?php
+
+namespace Anikeen\Id\Resources;
+
+use Anikeen\Id\Concerns\IsCheckoutSession;
+use Anikeen\Id\Exceptions\ApiException;
+use Anikeen\Id\Support\AppRequest;
+use JsonSerializable;
+
+/**
+ * A checkout session created with the app's own token, see AppCheckoutSessions.
+ *
+ * @property string $id
+ * @property string $user_id
+ * @property ?string $oauth_client_id
+ * @property string $status open, completed, cancelled or expired
+ * @property ?string $return_url
+ * @property ?object $metadata
+ * @property ?string $confirmation_url
+ * @property list<string> $subscription_ids
+ * @property list<object> $subscriptions
+ * @property ?string $expires_at
+ * @property ?string $completed_at
+ * @property ?string $cancelled_at
+ * @property ?string $created_at
+ */
+class AppCheckoutSession implements JsonSerializable
+{
+    use IsCheckoutSession;
+
+    public const STATUS_OPEN = 'open';
+    public const STATUS_COMPLETED = 'completed';
+    public const STATUS_CANCELLED = 'cancelled';
+    public const STATUS_EXPIRED = 'expired';
+
+    public function __construct(protected object $data)
+    {
+    }
+
+    public function __get(string $name): mixed
+    {
+        return $this->data->{$name} ?? null;
+    }
+
+    public function __isset(string $name): bool
+    {
+        return isset($this->data->{$name});
+    }
+
+    /**
+     * The session's subscriptions (drafts until the user confirms).
+     *
+     * @return list<AppSubscription>
+     */
+    public function subscriptions(): array
+    {
+        return array_map(fn (object $subscription) => new AppSubscription($subscription), array_values((array) ($this->data->subscriptions ?? [])));
+    }
+
+    /**
+     * Withdraw an open session (e.g. the cart changed): it and its drafts are cancelled.
+     *
+     * @throws ApiException 409 "checkout_session_completed", "checkout_session_cancelled", "checkout_session_expired"
+     */
+    public function cancel(): self
+    {
+        return $this->send('POST', '/cancel');
+    }
+
+    /**
+     * @throws ApiException
+     */
+    public function refresh(): self
+    {
+        return $this->send('GET', '');
+    }
+
+    public function toArray(): array
+    {
+        return (array) $this->data;
+    }
+
+    public function jsonSerialize(): array
+    {
+        return $this->toArray();
+    }
+
+    /**
+     * @throws ApiException
+     */
+    private function send(string $method, string $action): self
+    {
+        $this->data = AppRequest::send($method, sprintf('v1/client/checkout-sessions/%s%s', $this->id, $action))->data;
+
+        return $this;
+    }
+}