Adds invoice pdf download

Author: marcortola

src/Api/Api.php

@@ -117,10 +117,14 @@ private function createJsonBody(array $parameters): ?string
      * @return mixed
      * @throws DomainException
      */
-    protected function handleResponse(ResponseInterface $response, string $class)
+    protected function handleResponse(ResponseInterface $response, ?string $class = null)
     {
         $this->handleErrors($response);
 
+        if (null === $class) {
+            return $response->getBody()->__toString();
+        }
+
         $response = $this->hydrator->hydrate($response, $class);
 
         if ($response instanceof Collection) {

src/Api/InvoiceApi.php

@@ -21,6 +21,18 @@ public function invoice(int $id): Invoice
         return $this->handleResponse($response, InvoiceFactory::class);
     }
 
+    /**
+     * @see https://apidocs.cuentica.com/versions/latest_release/#customer-id
+     * @throws DomainException
+     * @throws ClientExceptionInterface
+     */
+    public function pdf(int $id): string
+    {
+        $response = $this->httpGet('/invoice/'.$id.'/pdf');
+
+        return $this->handleResponse($response);
+    }
+
     /**
      * @see https://apidocs.cuentica.com/versions/latest_release/#customer
      * @throws DomainException