{
   "user":{
      "id":6,
      "vouchers":[
         {
            "id":2,
            "affects":"subscription_items",
            "type":"percentage",
            "value":"20",
            "pivot":{
               "user_id":6,
               "voucher_id":2,
               "duration":4,
               "created_at":"2015-04-26 20:44:46",
               "updated_at":"2015-04-26 20:49:05"
            }
         },
         {
            "id":3,
            "code":"giftbox",
            "affects":"giftboxes",
            "type":"percentage",
            "value":"25",
            "pivot":{
               "user_id":6,
               "voucher_id":3,
               "duration":1,
               "created_at":"2015-04-26 21:25:15",
               "updated_at":"2015-04-26 21:25:15"
            }
         }
      ]
   },
}

private function vouchers_that_affect($list)
{
    /*
     * If there is no user, abort
     */
    if( ! $this->user ) return false;
    return array_where($this->user->vouchers, function($key, $voucher) use ($list)
    {
        return
            /*
             * Where they effect the right thing, they
             * haven't already been used too many times.
             */
            in_array($voucher->affects, $list)
            && $voucher->pivot->duration > 0;
    });
}

$this->giftbox_vouchers = $this->vouchers_that_affect(['giftboxes', 'giftbox_additional_items']);
$this->subscription_vouchers = $this->vouchers_that_affect(['subscription_items', 'additional_items', 'subscription_base_price']);

"subscription_vouchers":[
   {
      "id":2,
      "code":"subscription",
      "affects":"subscription_items",
      "type":"percentage",
      "value":"20",
      "pivot":{
         "user_id":6,
         "voucher_id":2,
         "duration":4,
         "created_at":"2015-04-26 20:44:46",
         "updated_at":"2015-04-26 20:49:05"
      }
   }
],
"giftbox_vouchers":{
   "1":{
      "id":3,
      "code":"giftbox",
      "affects":"giftboxes",
      "type":"percentage",
      "value":"25",
      "pivot":{
         "user_id":6,
         "voucher_id":3,
         "duration":1,
         "created_at":"2015-04-26 21:25:15",
         "updated_at":"2015-04-26 21:25:15"
      }
   }
},

"subscription_vouchers":[
   {
      "id":2,
   }
],
"giftbox_vouchers":{
   "1":{
      "id":3,
   }
},