- Adds new task scheduler configuration class

- Introduces method to start cron on demand when there are
  scheduled newsletters or queues in progress

lib/Config/Initializer.php

@@ -107,7 +107,7 @@ class Initializer {
       $this->setupShortcodes();
       $this->setupHooks();
       $this->setupImages();
-      $this->runQueueSupervisor();
+      $this->setupTaskScheduler();
 
       $this->plugin_initialized = true;
     } catch(\Exception $e) {
@@ -192,14 +192,9 @@ class Initializer {
     $router->init();
   }
 
-  function runQueueSupervisor() {
-    if(php_sapi_name() === 'cli') return;
-    try {
-      $supervisor = new Supervisor();
-      $supervisor->checkDaemon();
-    } catch(\Exception $e) {
-      // Prevent Daemon exceptions from breaking out and breaking UI
-    }
+  function setupTaskScheduler() {
+    $task_scheduler = new TaskScheduler();
+    $task_scheduler->init();
   }
 
   function setupImages() {

lib/Config/TaskScheduler.php

@@ -0,0 +1,65 @@
+<?php
+namespace MailPoet\Config;
+
+use MailPoet\Cron\Supervisor;
+use MailPoet\Cron\Workers\Scheduler as SchedulerWorker;
+use MailPoet\Cron\Workers\SendingQueue\SendingQueue as SendingQueueWorker;
+use MailPoet\Models\Setting;
+
+if(!defined('ABSPATH')) exit;
+
+class TaskScheduler {
+  const METHOD_WORDPRESS = 'WordPress';
+  const METHOD_MAILPOET = 'MailPoet';
+
+  function __construct() {
+    $this->method = self::getCurrentMethod();
+  }
+
+  function init() {
+    // configure task scheduler only outside of cli environment
+    if(php_sapi_name() === 'cli') return;
+    switch($this->method) {
+      case self::METHOD_MAILPOET:
+        return $this->configureMailpoetScheduler();
+      break;
+      case self::METHOD_WORDPRESS:
+        return $this->configureWordpressScheduler();
+      break;
+      default:
+        throw new \Exception(__("Task scheduler is not configured"));
+      break;
+    };
+  }
+
+  function configureMailpoetScheduler() {
+    try {
+      $supervisor = new Supervisor();
+      $supervisor->checkDaemon();
+    } catch(\Exception $e) {
+      // exceptions should not prevent the rest of the site loading
+    }
+  }
+
+  function configureWordpressScheduler() {
+    $scheduled_queues = SchedulerWorker::getScheduledQueues();
+    $running_queues = SendingQueueWorker::getRunningQueues();
+    // run cron only when there are scheduled queues ready to be processed
+    // or are already being processed
+    if($scheduled_queues || $running_queues) {
+      return $this->configureMailpoetScheduler();
+    }
+    return;
+  }
+
+  static function getAvailableMethods() {
+    return array(
+      'mailpoet' => self::METHOD_MAILPOET,
+      'wordpress' => self::METHOD_WORDPRESS
+    );
+  }
+
+  static function getCurrentMethod() {
+    return Setting::getValue('task_scheduler.method');
+  }
+}

lib/Cron/Workers/Scheduler.php

@@ -24,9 +24,7 @@ class Scheduler {
   }
 
   function process() {
-    $scheduled_queues = SendingQueue::where('status', 'scheduled')
-      ->whereLte('scheduled_at', Carbon::createFromTimestamp(current_time('timestamp')))
-      ->findMany();
+    $scheduled_queues = self::getScheduledQueues();
     if(!count($scheduled_queues)) return;
     foreach($scheduled_queues as $i => $queue) {
       $newsletter = Newsletter::filter('filterWithOptions')
@@ -185,4 +183,10 @@ class Scheduler {
       $notification_history :
       false;
   }
+  
+  static function getScheduledQueues() {
+    return SendingQueue::where('status', 'scheduled')
+      ->whereLte('scheduled_at', Carbon::createFromTimestamp(current_time('timestamp')))
+      ->findMany();
+  }
 }

lib/Cron/Workers/SendingQueue/SendingQueue.php

@@ -27,7 +27,7 @@ class SendingQueue {
 
   function process() {
     $this->mailer_task->checkSendingLimit();
-    foreach($this->getQueues() as $queue) {
+    foreach(self::getRunningQueues() as $queue) {
       // get and pre-process newsletter (render, replace shortcodes/links, etc.)
       $newsletter = $this->newsletter_task->getAndPreProcess($queue->asArray());
       if(!$newsletter) {
@@ -168,6 +168,13 @@ class SendingQueue {
       ->findMany();
   }
 
+  static function getRunningQueues() {
+    return SendingQueueModel::orderByDesc('priority')
+      ->whereNull('deleted_at')
+      ->whereNull('status')
+      ->findMany();
+  }
+
   function updateQueue($queue) {
     $queue->count_processed =
       count($queue->subscribers['processed']) + count($queue->subscribers['failed']);