Adds refund transaction functionality

src/Gateway.php

@@ -135,6 +135,33 @@ protected function process(Transaction $transaction)
         return Processor::process($transaction);
     }
 
+    /**
+     * @param \CraigPaul\Moneris\Transaction|string $transaction
+     * @param string|null $order
+     *
+     * @return \CraigPaul\Moneris\Response
+     */
+    public function refund($transaction, string $order = null, $amount = null)
+    {
+        if ($transaction instanceof Transaction) {
+            $order = $transaction->order();
+            $amount = $amount ?? $transaction->amount();
+            $transaction = $transaction->number();
+        }
+
+        $params = [
+            'type' => 'refund',
+            'crypt_type' => Crypt::SSL_ENABLED_MERCHANT,
+            'amount' => $amount,
+            'txn_number' => $transaction,
+            'order_id' => $order,
+        ];
+
+        $transaction = $this->transaction($params);
+
+        return $this->process($transaction);
+    }
+
     /**
      * Get or create a new Transaction instance.
      *

src/Transaction.php

@@ -54,6 +54,20 @@ public function __construct(Gateway $gateway, array $params = [])
         $this->params = $this->prepare($params);
     }
 
+    /**
+     * Retrieve the amount for the transaction. The is only available on certain transaction types.
+     *
+     * @return string|null
+     */
+    public function amount()
+    {
+        if (isset($this->params['amount'])) {
+            return $this->params['amount'];
+        }
+
+        return null;
+    }
+
     /**
      * Check that the required parameters have not been provided to the transaction.
      *
@@ -216,6 +230,12 @@ public function valid()
                     $errors[] = Validator::set($params, 'order_id') ? null : 'Order id not provided.';
                     $errors[] = Validator::set($params, 'txn_number') ? null : 'Transaction number not provided.';
 
+                    break;
+                case 'refund':
+                    $errors[] = Validator::set($params, 'amount') ? null : 'Amount not provided.';
+                    $errors[] = Validator::set($params, 'order_id') ? null : 'Order id not provided.';
+                    $errors[] = Validator::set($params, 'txn_number') ? null : 'Transaction number not provided.';
+
                     break;
                 default:
                     $errors[] = $params['type'].' is not a supported transaction type.';