add subscriber endpoint

src/Entities/Subscriber.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace D3\KlicktippPhpClient\Entities;
+
+use Doctrine\Common\Collections\ArrayCollection;
+
+class Subscriber extends ArrayCollection
+{
+    public function getId(): string
+    {
+        return $this->get('id');
+    }
+
+    public function isSubscribed(): bool
+    {
+        // ToDo: adjust request
+        return $this->get('isSubscribed');
+    }
+}

src/Resources/Subscriber.php

@@ -0,0 +1,59 @@
+<?php
+
+namespace D3\KlicktippPhpClient\Resources;
+
+use D3\KlicktippPhpClient\Entities\Subscriber as SubscriberEntity;
+use D3\KlicktippPhpClient\Exceptions\BaseException;
+use GuzzleHttp\Exception\GuzzleException;
+
+class Subscriber extends Model
+{
+    /**
+     * @throws BaseException|GuzzleException
+     */
+    public function index(): array
+    {
+        return $this->connection->requestAndParse(
+            'GET',
+            'subscriber',
+            [
+                'query' => $this->getQuery()
+            ]
+        );
+    }
+
+    /**
+     * @throws BaseException|GuzzleException
+     */
+    public function get(string $subscriberId): SubscriberEntity
+    {
+        $data = $this->connection->requestAndParse(
+            'GET',
+            'subscriber/'.urlencode(trim($subscriberId)),
+            [
+                'query' => $this->getQuery()
+            ]
+        );
+
+        return new SubscriberEntity($data);
+    }
+
+    /**
+     * @throws BaseException|GuzzleException
+     */
+    public function search(string $mailAddress): string
+    {
+        return current(
+            $this->connection->requestAndParse(
+                'POST',
+                'subscriber/search',
+                [
+                    'query' => $this->getQuery(),
+                    'form_params' => [
+                        'email' => trim($mailAddress)
+                    ]
+                ]
+            )
+        );
+    }
+}