Refactor sending methods to use error mappers

We want to add some logic to error handling.
This commit extracts error handling code from sending methods classes,
which already do a lot of other stuff, to error mappers which are responsible
for creating proper error object (MailerError). This error object is a replacement
for assoc. array which already had some special keys for certain usecases and
can not be properly type hinted.

[MAILPOET-1154]

lib/API/JSON/v1/Mailer.php

@@ -34,7 +34,7 @@ class Mailer extends APIEndpoint {
     if($result['response'] === false) {
       $error = sprintf(
         __('The email could not be sent: %s', 'mailpoet'),
-        $result['error_message']
+        $result['error']->getMessage()
       );
       return $this->errorResponse(array(APIError::BAD_REQUEST => $error));
     } else {

lib/Cron/Workers/SendingQueue/SendingQueue.php

@@ -5,6 +5,7 @@ use MailPoet\Cron\CronHelper;
 use MailPoet\Cron\Workers\SendingQueue\Tasks\Links;
 use MailPoet\Cron\Workers\SendingQueue\Tasks\Mailer as MailerTask;
 use MailPoet\Cron\Workers\SendingQueue\Tasks\Newsletter as NewsletterTask;
+use MailPoet\Mailer\MailerError;
 use MailPoet\Mailer\MailerLog;
 use MailPoet\Models\ScheduledTask as ScheduledTaskModel;
 use MailPoet\Models\StatisticsNewsletters as StatisticsNewslettersModel;
@@ -164,10 +165,12 @@ class SendingQueue {
     );
     // log error message and schedule retry/pause sending
     if($send_result['response'] === false) {
-      if(isset($send_result['retry_interval'])) {
-        MailerLog::processNonBlockingError($send_result['operation'], $send_result['error_message'], $send_result['retry_interval']);
+      $error = $send_result['error'];
+      assert($error instanceof MailerError);
+      if($error->getRetryInterval() !== null) {
+        MailerLog::processNonBlockingError($error->getOperation(), $error->getMessage(), $error->getRetryInterval());
       } else {
-        MailerLog::processError($send_result['operation'], $send_result['error_message']);
+        MailerLog::processError($error->getOperation(), $error->getMessage());
       }
     }
     // update processed/to process list

lib/Mailer/Mailer.php

@@ -1,6 +1,11 @@
 <?php
 namespace MailPoet\Mailer;
 
+use MailPoet\Mailer\Methods\ErrorMappers\AmazonSESMapper;
+use MailPoet\Mailer\Methods\ErrorMappers\MailPoetMapper;
+use MailPoet\Mailer\Methods\ErrorMappers\PHPMailMapper;
+use MailPoet\Mailer\Methods\ErrorMappers\SendGridMapper;
+use MailPoet\Mailer\Methods\ErrorMappers\SMTPMapper;
 use MailPoet\Models\Setting;
 
 if(!defined('ABSPATH')) exit;
@@ -42,28 +47,32 @@ class Mailer {
           $this->mailer_config['secret_key'],
           $this->sender,
           $this->reply_to,
-          $this->return_path
+          $this->return_path,
+          new AmazonSESMapper()
         );
         break;
       case self::METHOD_MAILPOET:
         $mailer_instance = new $this->mailer_config['class'](
           $this->mailer_config['mailpoet_api_key'],
           $this->sender,
-          $this->reply_to
+          $this->reply_to,
+          new MailPoetMapper()
         );
         break;
       case self::METHOD_SENDGRID:
         $mailer_instance = new $this->mailer_config['class'](
           $this->mailer_config['api_key'],
           $this->sender,
-          $this->reply_to
+          $this->reply_to,
+          new SendGridMapper()
         );
         break;
       case self::METHOD_PHPMAIL:
         $mailer_instance = new $this->mailer_config['class'](
           $this->sender,
           $this->reply_to,
-          $this->return_path
+          $this->return_path,
+          new PHPMailMapper()
         );
         break;
       case self::METHOD_SMTP:
@@ -76,7 +85,8 @@ class Mailer {
           $this->mailer_config['encryption'],
           $this->sender,
           $this->reply_to,
-          $this->return_path
+          $this->return_path,
+          new SMTPMapper()
         );
         break;
       default:
@@ -166,25 +176,16 @@ class Mailer {
     return sprintf('=?utf-8?B?%s?=', base64_encode($name));
   }
 
-  static function formatMailerConnectionErrorResult($error_message) {
-    return array(
+  static function formatMailerErrorResult(MailerError $error) {
+    return [
       'response' => false,
-      'operation' => 'connect',
-      'error_message' => $error_message
-    );
-  }
-
-  static function formatMailerSendErrorResult($error_message) {
-    return array(
-      'response' => false,
-      'operation' => 'send',
-      'error_message' => $error_message
-    );
+      'error' => $error,
+    ];
   }
 
   static function formatMailerSendSuccessResult() {
-    return array(
+    return [
       'response' => true
-    );
+    ];
   }
 }

lib/Mailer/MailerError.php

@@ -0,0 +1,63 @@
+<?php
+namespace MailPoet\Mailer;
+
+class MailerError {
+  const OPERATION_CONNECT = 'connect';
+  const OPERATION_SEND = 'send';
+
+  const LEVEL_HARD = 'hard';
+  const LEVEL_SOFT = 'soft';
+
+  /** @var string */
+  private $operation;
+
+  /** @var string */
+  private $level;
+
+  /** @var string|null */
+  private $message;
+
+  /** @var int|null */
+  private $retry_interval;
+
+  /**
+   * @param string $operation
+   * @param string $level
+   * @param null|string $message
+   * @param int|null $retry_interval
+   */
+  function __construct($operation, $level, $message = null, $retry_interval = null) {
+    $this->operation = $operation;
+    $this->level = $level;
+    $this->message = $message;
+    $this->retry_interval = $retry_interval;
+  }
+
+  /**
+   * @return string
+   */
+  function getOperation() {
+    return $this->operation;
+  }
+
+  /**
+   * @return string
+   */
+  function getLevel() {
+    return $this->level;
+  }
+
+  /**
+   * @return null|string
+   */
+  function getMessage() {
+    return $this->message;
+  }
+
+  /**
+   * @return int|null
+   */
+  function getRetryInterval() {
+    return $this->retry_interval;
+  }
+}

lib/Mailer/Methods/AmazonSES.php

@@ -2,6 +2,7 @@
 namespace MailPoet\Mailer\Methods;
 
 use MailPoet\Mailer\Mailer;
+use MailPoet\Mailer\Methods\ErrorMappers\AmazonSESMapper;
 use MailPoet\WP\Functions as WPFunctions;
 
 if(!defined('ABSPATH')) exit;
@@ -28,7 +29,18 @@ class AmazonSES {
     'EU (Ireland)' => 'eu-west-1'
   );
 
-  function __construct($region, $access_key, $secret_key, $sender, $reply_to, $return_path) {
+  /** @var AmazonSESMapper */
+  private $error_mapper;
+
+  function __construct(
+    $region,
+    $access_key,
+    $secret_key,
+    $sender,
+    $reply_to,
+    $return_path,
+    AmazonSESMapper $error_mapper
+  ) {
     $this->aws_access_key = $access_key;
     $this->aws_secret_key = $secret_key;
     $this->aws_region = (in_array($region, $this->available_regions)) ? $region : false;
@@ -48,6 +60,7 @@ class AmazonSES {
       $this->sender['from_email'];
     $this->date = gmdate('Ymd\THis\Z');
     $this->date_without_time = gmdate('Ymd');
+    $this->error_mapper = $error_mapper;
   }
 
   function send($newsletter, $subscriber, $extra_params = array()) {
@@ -57,20 +70,17 @@ class AmazonSES {
         $this->request($newsletter, $subscriber, $extra_params)
       );
     } catch(\Exception $e) {
-      return Mailer::formatMailerSendErrorResult($e->getMessage());
+      $error = $this->error_mapper->getErrorFromException($e);
+      return Mailer::formatMailerErrorResult($error);
     }
     if(is_wp_error($result)) {
-      return Mailer::formatMailerConnectionErrorResult($result->get_error_message());
+      $error = $this->error_mapper->getConnectionError($result->get_error_message());
+      return Mailer::formatMailerErrorResult($error);
     }
     if(WPFunctions::wpRemoteRetrieveResponseCode($result) !== 200) {
       $response = simplexml_load_string(WPFunctions::wpRemoteRetrieveBody($result));
-      $response = ($response) ?
-        $response->Error->Message->__toString() :
-        sprintf(__('%s has returned an unknown error.', 'mailpoet'), Mailer::METHOD_AMAZONSES);
-      if(empty($extra_params['test_email'])) {
-        $response .= sprintf(' %s: %s', __('Unprocessed subscriber', 'mailpoet'), $subscriber);
-      }
-      return Mailer::formatMailerSendErrorResult($response);
+      $error = $this->error_mapper->getErrorFromResponse($response, $subscriber, $extra_params);
+      return Mailer::formatMailerErrorResult($error);
     }
     return Mailer::formatMailerSendSuccessResult();
   }

lib/Mailer/Methods/ErrorMappers/AmazonSESMapper.php

@@ -0,0 +1,23 @@
+<?php
+namespace MailPoet\Mailer\Methods\ErrorMappers;
+
+use MailPoet\Mailer\MailerError;
+use MailPoet\Mailer\Mailer;
+
+class AmazonSESMapper {
+  use ConnectionErrorMapperTrait;
+
+  function getErrorFromException(\Exception $e) {
+    return new MailerError(MailerError::OPERATION_SEND, MailerError::LEVEL_HARD, $e->getMessage());
+  }
+
+  function getErrorFromResponse($response, $subscriber, $extra_params) {
+    $response = ($response) ?
+      $response->Error->Message->__toString() :
+      sprintf(__('%s has returned an unknown error.', 'mailpoet'), Mailer::METHOD_AMAZONSES);
+    if(empty($extra_params['test_email'])) {
+      $response .= sprintf(' %s: %s', __('Unprocessed subscriber', 'mailpoet'), $subscriber);
+    }
+    return new MailerError(MailerError::OPERATION_SEND, MailerError::LEVEL_HARD, $response);
+  }
+}

lib/Mailer/Methods/ErrorMappers/ConnectionErrorMapperTrait.php

@@ -0,0 +1,14 @@
+<?php
+namespace MailPoet\Mailer\Methods\ErrorMappers;
+
+use MailPoet\Mailer\MailerError;
+
+trait ConnectionErrorMapperTrait {
+  function getConnectionError($message) {
+    return new MailerError(
+      MailerError::OPERATION_CONNECT,
+      MailerError::LEVEL_HARD,
+      $message
+    );
+  }
+}

lib/Mailer/Methods/ErrorMappers/MailPoetMapper.php

@@ -0,0 +1,80 @@
+<?php
+namespace MailPoet\Mailer\Methods\ErrorMappers;
+
+use MailPoet\Mailer\MailerError;
+use MailPoet\Services\Bridge\API;
+
+if(!defined('ABSPATH')) exit;
+
+class MailPoetMapper {
+  use ConnectionErrorMapperTrait;
+
+  const TEMPORARY_UNAVAILABLE_RETRY_INTERVAL = 300; // seconds
+
+  function getInvalidApiKeyError() {
+    return new MailerError(
+      MailerError::OPERATION_SEND,
+      MailerError::LEVEL_HARD,
+      __('MailPoet API key is invalid!', 'mailpoet')
+    );
+  }
+
+  function getErrorForResult(array $result, $subscribers) {
+    $message = $result['message'];
+    $level = MailerError::LEVEL_HARD;
+    $retry_interval = null;
+
+    if(!empty($result['code'])) {
+      switch($result['code']) {
+        case API::RESPONSE_CODE_NOT_ARRAY:
+          $message = __('JSON input is not an array', 'mailpoet');
+          break;
+        case API::RESPONSE_CODE_PAYLOAD_ERROR:
+          $message = $this->parseErrorResponse($result['message'], $subscribers);
+          break;
+        case API::RESPONSE_CODE_TEMPORARY_UNAVAILABLE:
+          $message = __('Email service is temporarily not available, please try again in a few minutes.', 'mailpoet');
+          $retry_interval = self::TEMPORARY_UNAVAILABLE_RETRY_INTERVAL;
+          break;
+        case API::RESPONSE_CODE_KEY_INVALID:
+        case API::RESPONSE_CODE_PAYLOAD_TOO_BIG:
+        default:
+          $message = $result['message'];
+      }
+    }
+    return new MailerError(MailerError::OPERATION_SEND, $level, $message, $retry_interval);
+  }
+
+  private function parseErrorResponse($result, $subscriber) {
+    $result_parsed = json_decode($result, true);
+    $errors = [];
+    if(is_array($result_parsed)) {
+      foreach($result_parsed as $result_error) {
+        $errors[] = $this->processSingleSubscriberError($result_error, $subscriber);
+      }
+    }
+    if(!empty($errors)) {
+      return __('Error while sending: ', 'mailpoet') . join(', ', $errors);
+    } else {
+      return __('Error while sending newsletters. ', 'mailpoet') . $result;
+    }
+  }
+
+  private function processSingleSubscriberError($result_error, $subscriber) {
+    $error = '';
+    if(is_array($result_error)) {
+      $subscriber_errors = [];
+      if(isset($result_error['errors']) && is_array($result_error['errors'])) {
+        array_walk_recursive($result_error['errors'], function($item) use (&$subscriber_errors) {
+          $subscriber_errors[] = $item;
+        });
+      }
+      $error .= join(', ', $subscriber_errors);
+
+      if(isset($result_error['index']) && isset($subscriber[$result_error['index']])) {
+        $error = '(' . $subscriber[$result_error['index']] . ': ' . $error . ')';
+      }
+    }
+    return $error;
+  }
+}

lib/Mailer/Methods/ErrorMappers/PHPMailMapper.php

@@ -0,0 +1,21 @@
+<?php
+namespace MailPoet\Mailer\Methods\ErrorMappers;
+
+use MailPoet\Mailer\MailerError;
+use MailPoet\Mailer\Mailer;
+
+class PHPMailMapper {
+  use ConnectionErrorMapperTrait;
+
+  function getErrorFromException(\Exception $e) {
+    return new MailerError(MailerError::OPERATION_SEND, MailerError::LEVEL_HARD, $e->getMessage());
+  }
+
+  function getErrorForSubscriber($subscriber, $extra_params) {
+    $message = sprintf(__('%s has returned an unknown error.', 'mailpoet'), Mailer::METHOD_PHPMAIL);
+    if(empty($extra_params['test_email'])) {
+      $message .= sprintf(' %s: %s', __('Unprocessed subscriber', 'mailpoet'), $subscriber);
+    }
+    return new MailerError(MailerError::OPERATION_SEND, MailerError::LEVEL_HARD, $message);
+  }
+}

lib/Mailer/Methods/ErrorMappers/SMTPMapper.php

@@ -0,0 +1,31 @@
+<?php
+namespace MailPoet\Mailer\Methods\ErrorMappers;
+
+use MailPoet\Mailer\MailerError;
+use MailPoet\Mailer\Mailer;
+
+class SMTPMapper {
+  use ConnectionErrorMapperTrait;
+
+  function getErrorFromException(\Exception $e) {
+    // remove redundant information appended by Swift logger to exception messages
+    $message = explode(PHP_EOL, $e->getMessage());
+    return new MailerError(MailerError::OPERATION_SEND, MailerError::LEVEL_HARD, $message[0]);
+  }
+
+  function getErrorFromLog($log, $subscriber, $extra_params = []) {
+    // extract error message from log
+    preg_match('/!! (.*?)>>/ism', $log, $message);
+    if(!empty($message[1])) {
+      $message = $message[1];
+      // remove line breaks from the message due to how logger's dump() method works
+      $message = preg_replace('/\r|\n/', '', $message);
+    } else {
+      $message = sprintf(__('%s has returned an unknown error.', 'mailpoet'), Mailer::METHOD_SMTP);
+    }
+    if(empty($extra_params['test_email'])) {
+      $message .= sprintf(' %s: %s', __('Unprocessed subscriber', 'mailpoet'), $subscriber);
+    }
+    return new MailerError(MailerError::OPERATION_SEND, MailerError::LEVEL_HARD, $message);
+  }
+}

lib/Mailer/Methods/ErrorMappers/SendGridMapper.php

@@ -0,0 +1,19 @@
+<?php
+namespace MailPoet\Mailer\Methods\ErrorMappers;
+
+use MailPoet\Mailer\MailerError;
+use MailPoet\Mailer\Mailer;
+
+class SendGridMapper {
+  use ConnectionErrorMapperTrait;
+
+  function getErrorFromResponse($response, $subscriber, $extra_params) {
+    $response = (!empty($response['errors'][0])) ?
+      $response['errors'][0] :
+      sprintf(__('%s has returned an unknown error.', 'mailpoet'), Mailer::METHOD_SENDGRID);
+    if(empty($extra_params['test_email'])) {
+      $response .= sprintf(' %s: %s', __('Unprocessed subscriber', 'mailpoet'), $subscriber);
+    }
+    return new MailerError(MailerError::OPERATION_SEND, MailerError::LEVEL_HARD, $response);
+  }
+}

lib/Mailer/Methods/MailPoet.php

@@ -3,31 +3,32 @@ namespace MailPoet\Mailer\Methods;
 
 use MailPoet\Mailer\Mailer;
 use MailPoet\Config\ServicesChecker;
+use MailPoet\Mailer\Methods\ErrorMappers\MailPoetMapper;
 use MailPoet\Services\Bridge;
 use MailPoet\Services\Bridge\API;
 
 if(!defined('ABSPATH')) exit;
 
 class MailPoet {
-
-  const TEMPORARY_UNAVAILABLE_RETRY_INTERVAL = 300; // seconds
-
   public $api;
   public $sender;
   public $reply_to;
   public $services_checker;
 
-  function __construct($api_key, $sender, $reply_to) {
+  /** @var MailPoetMapper */
+  private $error_mapper;
+
+  function __construct($api_key, $sender, $reply_to, MailPoetMapper $error_mapper) {
     $this->api = new API($api_key);
     $this->sender = $sender;
     $this->reply_to = $reply_to;
-    $this->services_checker = new ServicesChecker(false);
+    $this->services_checker = new ServicesChecker();
+    $this->error_mapper = $error_mapper;
   }
 
   function send($newsletter, $subscriber, $extra_params = array()) {
     if($this->services_checker->isMailPoetAPIKeyValid() === false) {
-      $response = __('MailPoet API key is invalid!', 'mailpoet');
-      return Mailer::formatMailerSendErrorResult($response);
+      return Mailer::formatMailerErrorResult($this->error_mapper->getInvalidApiKeyError());
     }
 
     $message_body = $this->getBody($newsletter, $subscriber, $extra_params);
@@ -35,9 +36,11 @@ class MailPoet {
 
     switch($result['status']) {
       case API::SENDING_STATUS_CONNECTION_ERROR:
-        return Mailer::formatMailerConnectionErrorResult($result['message']);
+        $error = $this->error_mapper->getConnectionError($result['message']);
+        return Mailer::formatMailerErrorResult($error);
       case API::SENDING_STATUS_SEND_ERROR:
-        return $this->processSendError($result, $subscriber);
+        $error = $this->processSendError($result, $subscriber);
+        return Mailer::formatMailerErrorResult($error);
       case API::SENDING_STATUS_OK:
       default:
         return Mailer::formatMailerSendSuccessResult();
@@ -45,27 +48,10 @@ class MailPoet {
   }
 
   function processSendError($result, $subscriber) {
-    if(!empty($result['code'])) {
-      switch($result['code']) {
-        case API::RESPONSE_CODE_NOT_ARRAY:
-          return Mailer::formatMailerSendErrorResult(__('JSON input is not an array', 'mailpoet'));
-        case API::RESPONSE_CODE_PAYLOAD_TOO_BIG:
-          return Mailer::formatMailerSendErrorResult($result['message']);
-        case API::RESPONSE_CODE_PAYLOAD_ERROR:
-          $error = $this->parseErrorResponse($result['message'], $subscriber);
-          return Mailer::formatMailerSendErrorResult($error);
-        case API::RESPONSE_CODE_TEMPORARY_UNAVAILABLE:
-          $error = Mailer::formatMailerSendErrorResult(__('Email service is temporarily not available, please try again in a few minutes.', 'mailpoet'));
-          $error['retry_interval'] = self::TEMPORARY_UNAVAILABLE_RETRY_INTERVAL;
-          return $error;
-        case API::RESPONSE_CODE_KEY_INVALID:
-          Bridge::invalidateKey();
-          break;
-        default:
-          return Mailer::formatMailerSendErrorResult($result['message']);
-      }
+    if(!empty($result['code']) && $result['code'] ===  API::RESPONSE_CODE_KEY_INVALID) {
+      Bridge::invalidateKey();
     }
-    return Mailer::formatMailerSendErrorResult($result['message']);
+    return $this->error_mapper->getErrorForResult($result, $subscriber);
   }
 
   function processSubscriber($subscriber) {
@@ -128,37 +114,4 @@ class MailPoet {
     }
     return $body;
   }
-
-  private function parseErrorResponse($result, $subscriber) {
-    $result_parsed = json_decode($result, true);
-    $errors = [];
-    if(is_array($result_parsed)) {
-      foreach($result_parsed as $result_error) {
-        $errors[] = $this->processSingleSubscriberError($result_error, $subscriber);
-      }
-    }
-    if(!empty($errors)) {
-      return __('Error while sending: ', 'mailpoet') . join(', ', $errors);
-    } else {
-      return __('Error while sending newsletters. ', 'mailpoet') . $result;
-    }
-  }
-
-  private function processSingleSubscriberError($result_error, $subscriber) {
-    $error = '';
-    if(is_array($result_error)) {
-      $subscriber_errors = [];
-      if(isset($result_error['errors']) && is_array($result_error['errors'])) {
-        array_walk_recursive($result_error['errors'], function($item) use (&$subscriber_errors) {
-          $subscriber_errors[] = $item;
-        });
-      }
-      $error .= join(', ', $subscriber_errors);
-      
-      if(isset($result_error['index']) && isset($subscriber[$result_error['index']])) {
-        $error = '(' . $subscriber[$result_error['index']] . ': ' . $error . ')';
-      }
-    }
-    return $error;
-  }
 }

lib/Mailer/Methods/PHPMail.php

@@ -3,6 +3,7 @@
 namespace MailPoet\Mailer\Methods;
 
 use MailPoet\Mailer\Mailer;
+use MailPoet\Mailer\Methods\ErrorMappers\PHPMailMapper;
 
 if(!defined('ABSPATH')) exit;
 
@@ -14,13 +15,17 @@ class PHPMail {
   public $return_path;
   public $mailer;
 
-  function __construct($sender, $reply_to, $return_path) {
+  /** @var PHPMailMapper  */
+  private $error_mapper;
+
+  function __construct($sender, $reply_to, $return_path, PHPMailMapper $error_mapper) {
     $this->sender = $sender;
     $this->reply_to = $reply_to;
     $this->return_path = ($return_path) ?
       $return_path :
       $this->sender['from_email'];
     $this->mailer = $this->buildMailer();
+    $this->error_mapper = $error_mapper;
   }
 
   function send($newsletter, $subscriber, $extra_params = array()) {
@@ -28,16 +33,13 @@ class PHPMail {
       $mailer = $this->configureMailerWithMessage($newsletter, $subscriber, $extra_params);
       $result = $mailer->send();
     } catch(\Exception $e) {
-      return Mailer::formatMailerSendErrorResult($e->getMessage());
+      return Mailer::formatMailerErrorResult($this->error_mapper->getErrorFromException($e));
     }
     if($result === true) {
       return Mailer::formatMailerSendSuccessResult();
     } else {
-      $result = sprintf(__('%s has returned an unknown error.', 'mailpoet'), Mailer::METHOD_PHPMAIL);
-      if(empty($extra_params['test_email'])) {
-        $result .= sprintf(' %s: %s', __('Unprocessed subscriber', 'mailpoet'), $subscriber);
-      }
-      return Mailer::formatMailerSendErrorResult($result);
+      $error = $this->error_mapper->getErrorForSubscriber($subscriber, $extra_params);
+      return Mailer::formatMailerErrorResult($error);
     }
   }
 

lib/Mailer/Methods/SMTP.php

@@ -2,6 +2,7 @@
 namespace MailPoet\Mailer\Methods;
 
 use MailPoet\Mailer\Mailer;
+use MailPoet\Mailer\Methods\ErrorMappers\SMTPMapper;
 use MailPoet\WP\Hooks;
 
 if(!defined('ABSPATH')) exit;
@@ -19,9 +20,12 @@ class SMTP {
   public $mailer;
   const SMTP_CONNECTION_TIMEOUT = 15; // seconds
 
+  /** @var SMTPMapper */
+  private $error_mapper;
+
   function __construct(
     $host, $port, $authentication, $login = null, $password = null, $encryption,
-    $sender, $reply_to, $return_path) {
+    $sender, $reply_to, $return_path, SMTPMapper $error_mapper) {
     $this->host = $host;
     $this->port = $port;
     $this->authentication = $authentication;
@@ -36,6 +40,7 @@ class SMTP {
     $this->mailer = $this->buildMailer();
     $this->mailer_logger = new \Swift_Plugins_Loggers_ArrayLogger();
     $this->mailer->registerPlugin(new \Swift_Plugins_LoggerPlugin($this->mailer_logger));
+    $this->error_mapper = $error_mapper;
   }
 
   function send($newsletter, $subscriber, $extra_params = array()) {
@@ -43,13 +48,16 @@ class SMTP {
       $message = $this->createMessage($newsletter, $subscriber, $extra_params);
       $result = $this->mailer->send($message);
     } catch(\Exception $e) {
-      return Mailer::formatMailerSendErrorResult(
-        $this->processExceptionMessage($e->getMessage())
+      return Mailer::formatMailerErrorResult(
+        $this->error_mapper->getErrorFromException($e)
       );
     }
-    return ($result === 1) ?
-      Mailer::formatMailerSendSuccessResult() :
-      Mailer::formatMailerSendErrorResult($this->processLogMessage($subscriber, $extra_params));
+    if($result === 1) {
+      return Mailer::formatMailerSendSuccessResult();
+    } else {
+      $error = $this->error_mapper->getErrorFromLog($this->mailer_logger->dump(), $subscriber, $extra_params);
+      return Mailer::formatMailerErrorResult($error);
+    }
   }
 
   function buildMailer() {
@@ -107,27 +115,4 @@ class SMTP {
         (isset($subscriber_data['name'])) ? $subscriber_data['name'] : ''
     );
   }
-
-  function processLogMessage($subscriber, $extra_params = array(), $log = false) {
-    $log = ($log) ? $log : $this->mailer_logger->dump();
-    // extract error message from log
-    preg_match('/!! (.*?)>>/ism', $log, $message);
-    if(!empty($message[1])) {
-      $message = $message[1];
-      // remove line breaks from the message due to how logger's dump() method works
-      $message = preg_replace('/\r|\n/', '', $message);
-    } else {
-      $message = sprintf(__('%s has returned an unknown error.', 'mailpoet'), Mailer::METHOD_SMTP);
-    }
-    if(empty($extra_params['test_email'])) {
-      $message .= sprintf(' %s: %s', __('Unprocessed subscriber', 'mailpoet'), $subscriber);
-    }
-    return $message;
-  }
-
-  function processExceptionMessage($message) {
-    // remove redundant information appended by Swift logger to exception messages
-    $message = explode(PHP_EOL, $message);
-    return $message[0];
-  }
 }

lib/Mailer/Methods/SendGrid.php

@@ -3,6 +3,7 @@
 namespace MailPoet\Mailer\Methods;
 
 use MailPoet\Mailer\Mailer;
+use MailPoet\Mailer\Methods\ErrorMappers\SendGridMapper;
 use MailPoet\WP\Functions as WPFunctions;
 
 if(!defined('ABSPATH')) exit;
@@ -13,10 +14,14 @@ class SendGrid {
   public $sender;
   public $reply_to;
 
-  function __construct($api_key, $sender, $reply_to) {
+  /** @var SendGridMapper */
+  private $error_mapper;
+
+  function __construct($api_key, $sender, $reply_to, SendGridMapper $error_mapper) {
     $this->api_key = $api_key;
     $this->sender = $sender;
     $this->reply_to = $reply_to;
+    $this->error_mapper = $error_mapper;
   }
 
   function send($newsletter, $subscriber, $extra_params = array()) {
@@ -25,17 +30,13 @@ class SendGrid {
       $this->request($newsletter, $subscriber, $extra_params)
     );
     if(is_wp_error($result)) {
-      return Mailer::formatMailerConnectionErrorResult($result->get_error_message());
+      $error = $this->error_mapper->getConnectionError($result->get_error_message());
+      return Mailer::formatMailerErrorResult($error);
     }
     if(WPFunctions::wpRemoteRetrieveResponseCode($result) !== 200) {
       $response = json_decode($result['body'], true);
-      $response = (!empty($response['errors'][0])) ?
-        $response['errors'][0] :
-        sprintf(__('%s has returned an unknown error.', 'mailpoet'), Mailer::METHOD_SENDGRID);
-      if(empty($extra_params['test_email'])) {
-        $response .= sprintf(' %s: %s', __('Unprocessed subscriber', 'mailpoet'), $subscriber);
-      }
-      return Mailer::formatMailerSendErrorResult($response);
+      $error = $this->error_mapper->getErrorFromResponse($response, $subscriber, $extra_params);
+      return Mailer::formatMailerErrorResult($error);
     }
     return Mailer::formatMailerSendSuccessResult();
   }

tests/unit/Mailer/Methods/AmazonSESTest.php

@@ -1,7 +1,9 @@
 <?php
 namespace MailPoet\Test\Mailer\Methods;
 
+use MailPoet\Mailer\MailerError;
 use MailPoet\Mailer\Methods\AmazonSES;
+use MailPoet\Mailer\Methods\ErrorMappers\AmazonSESMapper;
 
 class AmazonSESTest extends \MailPoetTest {
   function _before() {
@@ -34,7 +36,8 @@ class AmazonSESTest extends \MailPoetTest {
       $this->settings['secret_key'],
       $this->sender,
       $this->reply_to,
-      $this->return_path
+      $this->return_path,
+      new AmazonSESMapper()
     );
     $this->subscriber = 'Recipient <mailpoet-phoenix-test@mailinator.com>';
     $this->newsletter = array(
@@ -69,7 +72,8 @@ class AmazonSESTest extends \MailPoetTest {
       $this->settings['secret_key'],
       $this->sender,
       $this->reply_to,
-      $return_path = false
+      $return_path = false,
+      new AmazonSESMapper()
     );
     expect($mailer->return_path)->equals($this->sender['from_email']);
   }
@@ -82,7 +86,8 @@ class AmazonSESTest extends \MailPoetTest {
         $this->settings['secret_key'],
         $this->sender,
         $this->reply_to,
-        $this->return_path
+        $this->return_path,
+        new AmazonSESMapper()
       );
       $this->fail('Unsupported region exception was not thrown');
     } catch(\Exception $e) {
@@ -223,7 +228,8 @@ class AmazonSESTest extends \MailPoetTest {
       $invalid_subscriber
     );
     expect($result['response'])->false();
-    expect($result['error_message'])->contains('does not comply with RFC 2822');
+    expect($result['error'])->isInstanceOf(MailerError::class);
+    expect($result['error']->getMessage())->contains('does not comply with RFC 2822');
   }
 
   function testItCanSend() {

tests/unit/Mailer/Methods/ErrorMappers/MailPoetMapperTest.php

@@ -0,0 +1,80 @@
+<?php
+namespace MailPoet\Test\Mailer\Methods\ErrorMappers;
+
+use MailPoet\Mailer\MailerError;
+use MailPoet\Mailer\Methods\ErrorMappers\MailPoetMapper;
+use MailPoet\Services\Bridge\API;
+
+class MailPoetMapperTest extends \MailPoetTest {
+  /** @var MailPoetMapper */
+  private $mapper;
+
+  /** @var array */
+  private $subscribers;
+
+  function _before() {
+    $this->mapper = new MailPoetMapper();
+    $this->subscribers = ['a@example.com', 'c d <b@example.com>'];
+  }
+
+  function testCreateConnectionError() {
+    $error = $this->mapper->getConnectionError('connection error');
+    expect($error)->isInstanceOf(MailerError::class);
+    expect($error->getOperation())->equals(MailerError::OPERATION_CONNECT);
+    expect($error->getLevel())->equals(MailerError::LEVEL_HARD);
+    expect($error->getMessage())->equals('connection error');
+  }
+
+  function testGetErrorNotArray() {
+    $api_result = [
+      'code' => API::RESPONSE_CODE_NOT_ARRAY,
+      'status' => API::SENDING_STATUS_SEND_ERROR,
+      'message' => 'error not array',
+    ];
+    $error = $this->mapper->getErrorForResult($api_result, $this->subscribers);
+
+    expect($error)->isInstanceOf(MailerError::class);
+    expect($error->getOperation())->equals(MailerError::OPERATION_SEND);
+    expect($error->getLevel())->equals(MailerError::LEVEL_HARD);
+    expect($error->getMessage())->equals('JSON input is not an array');
+  }
+
+  function testGetErrorPayloadTooBig() {
+    $api_result = [
+      'code' => API::RESPONSE_CODE_PAYLOAD_TOO_BIG,
+      'status' => API::SENDING_STATUS_SEND_ERROR,
+      'message' => 'error too big',
+    ];
+    $error = $this->mapper->getErrorForResult($api_result, $this->subscribers);
+    expect($error)->isInstanceOf(MailerError::class);
+    expect($error->getOperation())->equals(MailerError::OPERATION_SEND);
+    expect($error->getLevel())->equals(MailerError::LEVEL_HARD);
+    expect($error->getMessage())->equals('error too big');
+  }
+
+  function testGetPayloadError() {
+    $api_result = [
+      'code' => API::RESPONSE_CODE_PAYLOAD_ERROR,
+      'status' => API::SENDING_STATUS_SEND_ERROR,
+      'message' => 'Api Error',
+    ];
+    $error = $this->mapper->getErrorForResult($api_result, $this->subscribers);
+    expect($error)->isInstanceOf(MailerError::class);
+    expect($error->getOperation())->equals(MailerError::OPERATION_SEND);
+    expect($error->getLevel())->equals(MailerError::LEVEL_HARD);
+    expect($error->getMessage())->equals('Error while sending newsletters. Api Error');
+  }
+
+  function testGetPayloadErrorWithErrorMessage() {
+    $api_result = [
+      'code' => API::RESPONSE_CODE_PAYLOAD_ERROR,
+      'status' => API::SENDING_STATUS_SEND_ERROR,
+      'message' => '[{"index":0,"errors":{"subject":"subject is missing"}},{"index":1,"errors":{"subject":"subject is missing"}}]'
+    ];
+    $error = $this->mapper->getErrorForResult($api_result, $this->subscribers);
+    expect($error)->isInstanceOf(MailerError::class);
+    expect($error->getOperation())->equals(MailerError::OPERATION_SEND);
+    expect($error->getLevel())->equals(MailerError::LEVEL_HARD);
+    expect($error->getMessage())->equals('Error while sending: (a@example.com: subject is missing), (c d <b@example.com>: subject is missing)');
+  }
+}

tests/unit/Mailer/Methods/ErrorMappers/SMTPMapperTest.php

@@ -0,0 +1,46 @@
+<?php
+namespace MailPoet\Test\Mailer\Methods\ErrorMappers;
+
+use MailPoet\Mailer\Mailer;
+use MailPoet\Mailer\Methods\ErrorMappers\SMTPMapper;
+
+class SMTPMapperTest extends \MailPoetTest {
+
+  /** @var SMTPMapper */
+  private $mapper;
+
+  function _before() {
+    $this->mapper = new SMTPMapper();
+  }
+
+  function testItCanProcessExceptionMessage() {
+    $message = 'Connection could not be established with host localhost [Connection refused #111]' . PHP_EOL
+      . 'Log data:' . PHP_EOL
+      . '++ Starting Swift_SmtpTransport' . PHP_EOL
+      . '!! Connection could not be established with host localhost [Connection refused #111] (code: 0)';
+    $error = $this->mapper->getErrorFromException(new \Exception($message));
+    expect($error->getMessage())
+      ->equals('Connection could not be established with host localhost [Connection refused #111]');
+  }
+
+  function testItCanProcessLogMessageWhenOneExists() {
+    $log = '++ Swift_SmtpTransport started' . PHP_EOL
+      . '>> MAIL FROM:<moi@mrcasual.com>' . PHP_EOL
+      . '<< 250 OK' . PHP_EOL
+      . '>> RCPT TO:<test2@ietsdoenofferte.nl>' . PHP_EOL
+      . '<< 550 No such recipient here' . PHP_EOL
+      . '!! Expected response code 250/251/252 but got code "550", with message "550 No such recipient here' . PHP_EOL
+      . '" (code: 550)' . PHP_EOL
+      . '>> RSET' . PHP_EOL
+      . '<< 250 Reset OK' . PHP_EOL;
+    $error = $this->mapper->getErrorFromLog($log, 'test@example.com', []);
+    expect($error->getMessage())
+      ->equals('Expected response code 250/251/252 but got code "550", with message "550 No such recipient here" (code: 550) Unprocessed subscriber: test@example.com');
+  }
+
+  function testItReturnsGenericMessageWhenLogMessageDoesNotExist() {
+    $error = $this->mapper->getErrorFromLog(null, 'test@example.com');
+    expect($error->getMessage())
+      ->equals(Mailer::METHOD_SMTP . ' has returned an unknown error. Unprocessed subscriber: test@example.com');
+  }
+}

tests/unit/Mailer/Methods/MailPoetAPITest.php

@@ -3,6 +3,8 @@ namespace MailPoet\Test\Mailer\Methods;
 
 use Codeception\Util\Stub;
 use MailPoet\Config\ServicesChecker;
+use MailPoet\Mailer\MailerError;
+use MailPoet\Mailer\Methods\ErrorMappers\MailPoetMapper;
 use MailPoet\Mailer\Methods\MailPoet;
 use MailPoet\Services\Bridge\API;
 
@@ -27,7 +29,8 @@ class MailPoetAPITest extends \MailPoetTest {
     $this->mailer = new MailPoet(
       $this->settings['api_key'],
       $this->sender,
-      $this->reply_to
+      $this->reply_to,
+      new MailPoetMapper()
     );
     $this->subscriber = 'Recipient <mailpoet-phoenix-test@mailinator.com>';
     $this->newsletter = array(
@@ -161,11 +164,9 @@ class MailPoetAPITest extends \MailPoetTest {
       $this
     );
     $result = $this->mailer->send($this->newsletter, $this->subscriber);
-    expect($result)->equals([
-      'response' => false,
-      'operation' => 'connect',
-      'error_message' => 'connection error',
-    ]);
+    expect($result['response'])->false();
+    expect($result['error'])->isInstanceOf(MailerError::class);
+    expect($result['error']->getOperation())->equals(MailerError::OPERATION_CONNECT);
   }
 
   function testFormatErrorNotArray() {
@@ -179,11 +180,9 @@ class MailPoetAPITest extends \MailPoetTest {
       $this
     );
     $result = $this->mailer->send($this->newsletter, $this->subscriber);
-    expect($result)->equals([
-      'response' => false,
-      'operation' => 'send',
-      'error_message' => 'JSON input is not an array',
-    ]);
+    expect($result['response'])->false();
+    expect($result['error'])->isInstanceOf(MailerError::class);
+    expect($result['error']->getOperation())->equals(MailerError::OPERATION_SEND);
   }
 
   function testFormatErrorTooBig() {
@@ -197,11 +196,8 @@ class MailPoetAPITest extends \MailPoetTest {
       $this
     );
     $result = $this->mailer->send($this->newsletter, $this->subscriber);
-    expect($result)->equals([
-      'response' => false,
-      'operation' => 'send',
-      'error_message' => 'error too big',
-    ]);
+    expect($result['response'])->false();
+    expect($result['error'])->isInstanceOf(MailerError::class);
   }
 
   function testFormatPayloadError() {
@@ -215,11 +211,9 @@ class MailPoetAPITest extends \MailPoetTest {
       $this
     );
     $result = $this->mailer->send([$this->newsletter, $this->newsletter], ['a@example.com', 'c d <b@example.com>']);
-    expect($result)->equals([
-      'response' => false,
-      'operation' => 'send',
-      'error_message' => 'Error while sending newsletters. Api Error',
-    ]);
+    expect($result['response'])->false();
+    expect($result['error'])->isInstanceOf(MailerError::class);
+    expect($result['error']->getOperation())->equals(MailerError::OPERATION_SEND);
   }
 
   function testFormatPayloadErrorWithErrorMessage() {
@@ -233,12 +227,8 @@ class MailPoetAPITest extends \MailPoetTest {
       $this
     );
     $result = $this->mailer->send([$this->newsletter, $this->newsletter], ['a@example.com', 'c d <b@example.com>']);
-    expect($result)->equals([
-      'response' => false,
-      'operation' => 'send',
-      'error_message' => 'Error while sending: (a@example.com: subject is missing), (c d <b@example.com>: subject is missing)',
-    ]);
+    expect($result['response'])->false();
+    expect($result['error'])->isInstanceOf(MailerError::class);
+    expect($result['error']->getOperation())->equals(MailerError::OPERATION_SEND);
   }
-
-
 }

tests/unit/Mailer/Methods/PHPMailTest.php

@@ -1,6 +1,7 @@
 <?php
 namespace MailPoet\Test\Mailer\Methods;
 
+use MailPoet\Mailer\Methods\ErrorMappers\PHPMailMapper;
 use MailPoet\Mailer\Methods\PHPMail;
 
 class PHPMailTest extends \MailPoetTest {
@@ -19,7 +20,8 @@ class PHPMailTest extends \MailPoetTest {
     $this->mailer = new PHPMail(
       $this->sender,
       $this->reply_to,
-      $this->return_path
+      $this->return_path,
+      new PHPMailMapper()
     );
     $this->subscriber = 'Recipient <mailpoet-phoenix-test@mailinator.com>';
     $this->newsletter = array(
@@ -44,7 +46,8 @@ class PHPMailTest extends \MailPoetTest {
     $mailer = new PHPMail(
       $this->sender,
       $this->reply_to,
-      $return_path = false
+      $return_path = false,
+      new PHPMailMapper()
     );
     expect($mailer->return_path)->equals($this->sender['from_email']);
   }

tests/unit/Mailer/Methods/SMTPTest.php

@@ -3,6 +3,7 @@ namespace MailPoet\Test\Mailer\Methods;
 
 use Helper\WordPressHooks as WPHooksHelper;
 use MailPoet\Mailer\Mailer;
+use MailPoet\Mailer\Methods\ErrorMappers\SMTPMapper;
 use MailPoet\Mailer\Methods\SMTP;
 use MailPoet\WP\Hooks;
 
@@ -43,7 +44,8 @@ class SMTPTest extends \MailPoetTest {
       $this->settings['encryption'],
       $this->sender,
       $this->reply_to,
-      $this->return_path
+      $this->return_path,
+      new SMTPMapper()
     );
     $this->subscriber = 'Recipient <mailpoet-phoenix-test@mailinator.com>';
     $this->newsletter = array(
@@ -82,7 +84,8 @@ class SMTPTest extends \MailPoetTest {
       $this->settings['encryption'],
       $this->sender,
       $this->reply_to,
-      $return_path = false
+      $return_path = false,
+      new SMTPMapper()
     );
     expect($mailer->return_path)->equals($this->sender['from_email']);
   }
@@ -128,36 +131,6 @@ class SMTPTest extends \MailPoetTest {
     expect($result['response'])->false();
   }
 
-  function testItCanProcessExceptionMessage() {
-    $message = 'Connection could not be established with host localhost [Connection refused #111]' . PHP_EOL
-      . 'Log data:' . PHP_EOL
-      . '++ Starting Swift_SmtpTransport' . PHP_EOL
-      . '!! Connection could not be established with host localhost [Connection refused #111] (code: 0)';
-    expect($this->mailer->processExceptionMessage($message))
-      ->equals('Connection could not be established with host localhost [Connection refused #111]');
-  }
-
-  function testItCanProcessLogMessageWhenOneExists() {
-    $message = '++ Swift_SmtpTransport started' . PHP_EOL
-      . '>> MAIL FROM:<moi@mrcasual.com>' . PHP_EOL
-      . '<< 250 OK' . PHP_EOL
-      . '>> RCPT TO:<test2@ietsdoenofferte.nl>' . PHP_EOL
-      . '<< 550 No such recipient here' . PHP_EOL
-      . '!! Expected response code 250/251/252 but got code "550", with message "550 No such recipient here' . PHP_EOL
-      . '" (code: 550)' . PHP_EOL
-      . '>> RSET' . PHP_EOL
-      . '<< 250 Reset OK' . PHP_EOL;
-    expect($this->mailer->processLogMessage('test@example.com', $extra_params = array(), $message))
-      ->equals('Expected response code 250/251/252 but got code "550", with message "550 No such recipient here" (code: 550) Unprocessed subscriber: test@example.com');
-    expect($this->mailer->processLogMessage('test@example.com', $extra_params = array(), $message))
-      ->equals('Expected response code 250/251/252 but got code "550", with message "550 No such recipient here" (code: 550) Unprocessed subscriber: test@example.com');
-  }
-
-  function testItReturnsGenericMessageWhenLogMessageDoesNotExist() {
-    expect($this->mailer->processLogMessage('test@example.com'))
-      ->equals(Mailer::METHOD_SMTP . ' has returned an unknown error. Unprocessed subscriber: test@example.com');
-  }
-
   function testItAppliesTransportFilter() {
     $mailer = $this->mailer->buildMailer();
     expect($mailer->getTransport()->getStreamOptions())->isEmpty();

tests/unit/Mailer/Methods/SendGridTest.php

@@ -1,6 +1,7 @@
 <?php
 namespace MailPoet\Test\Mailer\Methods;
 
+use MailPoet\Mailer\Methods\ErrorMappers\SendGridMapper;
 use MailPoet\Mailer\Methods\SendGrid;
 
 class SendGridTest extends \MailPoetTest {
@@ -24,7 +25,8 @@ class SendGridTest extends \MailPoetTest {
     $this->mailer = new SendGrid(
       $this->settings['api_key'],
       $this->sender,
-      $this->reply_to
+      $this->reply_to,
+      new SendGridMapper()
     );
     $this->subscriber = 'Recipient <mailpoet-phoenix-test@mailinator.com>';
     $this->newsletter = array(