<?php

namespace MailPoet\Tasks\Subscribers;

use MailPoet\Models\ScheduledTaskSubscriber;

/**
 * @implements \Iterator<null, array>
 */
class BatchIterator implements \Iterator, \Countable {
  private $taskId;
  private $batchSize;
  private $lastProcessedId = 0;
  private $batchLastId;

  public function __construct(
    $taskId,
    $batchSize
  ) {
    if ($taskId <= 0) {
      throw new \Exception('Task ID must be greater than zero');
    } elseif ($batchSize <= 0) {
      throw new \Exception('Batch size must be greater than zero');
    }
    $this->taskId = (int)$taskId;
    $this->batchSize = (int)$batchSize;
  }

  public function rewind(): void {
    $this->lastProcessedId = 0;
  }

  public function current() {
    $subscribers = $this->getSubscribers()
      ->orderByAsc('subscriber_id')
      ->limit($this->batchSize)
      ->findArray();
    $subscribers = array_column($subscribers, 'subscriber_id');
    $this->batchLastId = end($subscribers);
    return $subscribers;
  }

  public function key() {
    return null;
  }

  public function next(): void {
    $this->lastProcessedId = $this->batchLastId;
  }

  public function valid(): bool {
    return $this->count() > 0;
  }

  public function count(): int {
    return $this->getSubscribers()->count();
  }

  private function getSubscribers() {
    return ScheduledTaskSubscriber::select('subscriber_id')
      ->where('task_id', $this->taskId)
      ->whereGt('subscriber_id', $this->lastProcessedId)
      ->where('processed', ScheduledTaskSubscriber::STATUS_UNPROCESSED);
  }
}