Update cart serialize and deserialization (#13)

* Use built in unserialization exceptions so that the nested deserialization happens in other code paths
* Added functions for nested serialization

src/Models/Cart/Item.php

@@ -1,7 +1,9 @@
 <?php
 namespace BoldApps\ShopifyToolkit\Models\Cart;
 
-class Item
+use BoldApps\ShopifyToolkit\Contracts\Serializeable;
+
+class Item implements Serializeable
 {
  /**
  * @var int

src/Services/Cart.php

@@ -9,6 +9,15 @@
 
 class Cart extends Base
 {
+ protected $unserializationExceptions = [
+ 'items' => 'unserializeItems',
+ 'variant_options' => 'unserializeOptions',
+ ];
+
+ protected $serializationExceptions = [
+ 'items' => 'serializeItems',
+ 'variantOptions' => 'serializeOptions',
+ ];
 
  /**
  * @return CartModel
@@ -18,7 +27,6 @@ public function get($cartToken, $password = null)
 
  $raw = $this->client->get('cart.json',[], $this->getCartCookie($cartToken), $password, true);
 
- $raw['items'] = $this->unserializeItems($raw['items']);
  $cart = $this->unserializeModel($raw, CartModel::class);
 
  return $cart;
@@ -96,6 +104,26 @@ private function getCartCookie($cartToken) {
  return [$cartCookie];
  }
 
+ /**
+ * @param $entities
+ *
+ * @return array|null
+ */
+ protected function serializeItems($entities)
+ {
+ if (null === $entities) {
+ return;
+ }
+
+ if ($entities instanceof Collection) {
+ return $entities->map(function ($entity) {
+ return $this->serializeModel($entity);
+ })->toArray();
+ }
+
+ return $entities;
+ }
+
  /**
  * @param array $data
  *
@@ -108,13 +136,32 @@ protected function unserializeItems($data)
  }
 
  $items = array_map(function ($item){
- $item['variant_options'] = $this->unserializeOptions($item['variant_options']);
  return $this->unserializeModel($item, CartItemModel::class);
  }, $data);
 
  return new Collection($items);
  }
 
+ /**
+ * @param $entities
+ *
+ * @return array|null
+ */
+ protected function serializeOptions($entities)
+ {
+ if (null === $entities) {
+ return;
+ }
+
+ if ($entities instanceof Collection) {
+ return $entities->map(function ($entity) {
+ return $this->serializeModel($entity);
+ })->toArray();
+ }
+
+ return $entities;
+ }
+
  /**
  * @param array $data
  *