Update last_subscribed_at on a change

[MAILPOET-1993]

lib/Models/Subscriber.php

@@ -412,6 +412,11 @@ class Subscriber extends Model {
       $new_status = $subscriber->status;
     }
 
+    // Update last_subscribed_at when status changes to subscribed
+    if ($old_status !== self::STATUS_SUBSCRIBED && $subscriber->status === self::STATUS_SUBSCRIBED) {
+      $subscriber->set('last_subscribed_at', WPFunctions::get()->currentTime('mysql'));
+    }
+
     if ($subscriber->save()) {
       if (!empty($custom_fields)) {
         $subscriber->saveCustomFields($custom_fields);

tests/integration/Models/SubscriberTest.php

@@ -129,6 +129,35 @@ class SubscriberTest extends \MailPoetTest {
     expect($subscriber_updated->status)->equals(Subscriber::STATUS_SUBSCRIBED);
   }
 
+  function testItUpdateLastSubscribedAtCorrectly() {
+    $subscriber = Subscriber::where('email', $this->test_data['email'])->findOne();
+    $subscriber->status = Subscriber::STATUS_UNCONFIRMED;
+    $subscriber->last_subscribed_at = null;
+    $subscriber->save();
+    $subscriber_updated = Subscriber::where('email', $this->test_data['email'])
+      ->findOne();
+    expect($subscriber_updated->last_subscribed_at)->null();
+
+    // Change to subscribed updates last_updated_at
+    $subscriber->status = Subscriber::STATUS_SUBSCRIBED;
+    $subscriber->save();
+    $subscriber_updated = Subscriber::where('email', $this->test_data['email'])
+      ->findOne();
+    $last_subscribed_at = new Carbon($subscriber_updated->last_updated_at);
+    expect($last_subscribed_at)->lessThan((new Carbon())->addSeconds(2));
+    expect($last_subscribed_at)->greaterThan((new Carbon())->subSeconds(2));
+
+    // Change to other status keeps last_updated_at
+    $last_subscribed_at = (new Carbon())->subHour();
+    $subscriber->last_subscribed_at = $last_subscribed_at;
+    $subscriber->save();
+    $subscriber->status = Subscriber::STATUS_INACTIVE;
+    $subscriber->save();
+    $subscriber_updated = Subscriber::where('email', $this->test_data['email'])
+      ->findOne();
+    expect($subscriber_updated->last_subscribed_at)->equals($last_subscribed_at->toDateTimeString());
+  }
+
   function testItHasSearchFilter() {
     $subscriber = Subscriber::filter('search', 'john')
       ->findOne();