diff --git a/actions-web.php b/actions-web.php
index 0dd8e60..fb4ae50 100644
--- a/actions-web.php
+++ b/actions-web.php
@@ -682,14 +682,14 @@ function getcouponlist()
 
 function generatecoupons($multiplier)
 {
-    global $db, $credit;
+    global $db, $credit, $codeGenerator;
     if (iscreditenabled() == false) {
         return;
     }
     // if credit system disabled, exit
     $requiredcredit = $credit['min'] + $credit['rent'] + $credit['longrental'];
     $value = $requiredcredit * $multiplier;
-    $codes = generatecodes(10, 6);
+    $codes = $codeGenerator->generate(10, 6);
     foreach ($codes as $code) {
         $result = $db->query("INSERT IGNORE INTO coupons SET coupon='" . $code . "',value='" . $value . "',status='0'");
     }
diff --git a/common.php b/common.php
index f96fa0d..782a099 100644
--- a/common.php
+++ b/common.php
@@ -1,5 +1,7 @@
 <?php
 
+use BikeShare\Credit\CodeGenerator\CodeGenerator;
+use BikeShare\Credit\CodeGenerator\CodeGeneratorInterface;
 use BikeShare\Mail\DebugMailSender;
 use BikeShare\Mail\MailSenderInterface;
 use BikeShare\Mail\PHPMailerMailSender;
@@ -52,6 +54,11 @@
     $db
 );
 
+/**
+ * @var CodeGeneratorInterface $codeGenerator
+ */
+$codeGenerator = new CodeGenerator();
+
 
 function error($message)
 {
@@ -61,19 +68,6 @@ function error($message)
 }
 
 
-function generatecodes($numcodes,$codelength,$wastage=25)
-{
-   // exclude problem chars: B8G6I1l0OQDS5Z2
-   // acceptable characters:
-   $goodchars='ACEFHJKMNPRTUVWXY4937';
-   // build array allowing for possible wastage through duplicate values
-   for ($i=0;$i<=$numcodes+$wastage+1;$i++)
-      {
-      $codes[]=substr(str_shuffle($goodchars),0,$codelength);
-      }
-   return array_slice($codes,0,($numcodes+1));
-}
-
 function getprivileges($userid)
 {
    global $db;
diff --git a/src/Credit/CodeGenerator/CodeGenerator.php b/src/Credit/CodeGenerator/CodeGenerator.php
new file mode 100644
index 0000000..f1487b4
--- /dev/null
+++ b/src/Credit/CodeGenerator/CodeGenerator.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace BikeShare\Credit\CodeGenerator;
+
+class CodeGenerator implements CodeGeneratorInterface
+{
+    // exclude problem chars: B8G6I1l0OQDS5Z2
+    private $acceptableChars = 'ACEFHJKMNPRTUVWXY4937';
+
+    public function generate($count, $length, $wastage = 25)
+    {
+        // build array allowing for possible wastage through duplicate values
+        for ($i = 0; $i <= $count + $wastage + 1; $i++) {
+            $codes[] = substr(str_shuffle($this->acceptableChars), 0, $length);
+        }
+
+        return array_slice($codes, 0, ($count));
+    }
+}
diff --git a/src/Credit/CodeGenerator/CodeGeneratorInterface.php b/src/Credit/CodeGenerator/CodeGeneratorInterface.php
new file mode 100644
index 0000000..cd2cf13
--- /dev/null
+++ b/src/Credit/CodeGenerator/CodeGeneratorInterface.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace BikeShare\Credit\CodeGenerator;
+
+interface CodeGeneratorInterface
+{
+    public function generate($count, $length, $wastage);
+}
diff --git a/tests/Credit/CodeGenerator/CodeGeneratorTest.php b/tests/Credit/CodeGenerator/CodeGeneratorTest.php
new file mode 100644
index 0000000..e49e6c2
--- /dev/null
+++ b/tests/Credit/CodeGenerator/CodeGeneratorTest.php
@@ -0,0 +1,26 @@
+<?php
+
+namespace Test\BikeShare\Credit\CodeGenerator;
+
+use BikeShare\Credit\CodeGenerator\CodeGenerator;
+use PHPUnit\Framework\TestCase;
+
+class CodeGeneratorTest extends TestCase
+{
+    private $acceptableChars = 'ACEFHJKMNPRTUVWXY4937';
+
+    public function testGenerate()
+    {
+        $count = 10;
+        $length = 8;
+        $wastage = 25;
+
+        $codeGenerator = new CodeGenerator();
+        $codes = $codeGenerator->generate($count, $length, $wastage);
+        $this->assertCount($count, $codes);
+        foreach ($codes as $code) {
+            $this->assertEquals($length, strlen($code));
+            $this->assertRegExp('/^[' . $this->acceptableChars . ']{' . $length . '}$/', $code);
+        }
+    }
+}