return $this;
    }
    /**
     * Delete a batch of queued items.
     *
     * @param string $key Key.
     *
     * @return $this
     */
    public function delete($key)
    {
        delete_site_option($key);
        return $this;
    }
    /**
     * Delete entire job queue.
     */
    public function delete_all()
    {
        $batches = $this->get_batches();
        foreach ($batches as $batch) {
            $this->delete($batch->key);
        }
        delete_site_option($this->get_status_key());
        $this->cancelled();
    }
    /**
     * Cancel job on next batch.
     */
    public function cancel()
    {
        update_site_option($this->get_status_key(), self::STATUS_CANCELLED);
        // Just in case the job was paused at the time.
        $this->dispatch();
    }
    /**
     * Has the process been cancelled?
     *
     * @return bool
     */
    public function is_cancelled()
    {
        $status = get_site_option($this->get_status_key(), 0);
        return absint($status) === self::STATUS_CANCELLED;
    }
    /**
     * Called when background process has been cancelled.
     */
    protected function cancelled()
    {
        do_action($this->identifier . '_cancelled');
    }
    /**
     * Pause job on next batch.
     */
    public function pause()
    {
        update_site_option($this->get_status_key(), self::STATUS_PAUSED);
    }
    /**
     * Is the job paused?
     *
     * @return bool
     */
    public function is_paused()
    {
        $status = get_site_option($this->get_status_key(), 0);
        return absint($status) === self::STATUS_PAUSED;
    }
    /**
     * Called when background process has been paused.
     */
    protected function paused()
    {
        do_action($this->identifier . '_paused');
    }
    /**
     * Resume job.
     */
    public function resume()
    {
        delete_site_option($this->get_status_key());
        $this->schedule_event();
        $this->dispatch();
        $this->resumed();
    }
    /**
     * Called when background process has been resumed.
     */
    protected function resumed()
    {
        do_action($this->identifier . '_resumed');
    }
    /**
     * Is queued?
     *
     * @return bool
     */
    public function is_queued()
    {
        return !$this->is_queue_empty();
    }
    /**
     * Is the tool currently active, e.g. starting, working, paused or cleaning up?
     *
     * @return bool
     */
    public function is_active()
    {
        return $this->is_queued() || $this->is_processing() || $this->is_paused() || $this->is_cancelled();
    }
    /**
     * Generate key for a batch.
     *
     * Generates a unique key based on microtime. Queue items are
     * given a unique key so that they can be merged upon save.
     *
     * @param int    $length Optional max length to trim key to, defaults to 64 characters.
     * @param string $key    Optional string to append to identifier before hash, defaults to "batch".
     *
     * @return string
     */
    protected function generate_key($length = 64, $key = 'batch')
    {
        $unique = \md5(\microtime() . wp_rand());
        $prepend = $this->identifier . '_' . $key . '_';
        return \substr($prepend . $unique, 0, $length);
    }
    /**
     * Get the status key.
     *
     * @return string
     */
    protected function get_status_key()
    {
        return $this->identifier . '_status';
    }
    /**
     * Maybe process a batch of queued items.
     *
     * Checks whether data exists within the queue and that
     * the process is not already running.
     */
    public function maybe_handle()
    {
        // Don't lock up other requests while processing.
        \session_write_close();
        if ($this->is_processing()) {
            // Background process already running.
            return $this->maybe_wp_die();
        }
        if ($this->is_cancelled()) {
            $this->clear_scheduled_event();
            $this->delete_all();
            return $this->maybe_wp_die();
        }
        if ($this->is_paused()) {
            $this->clear_scheduled_event();
            $this->paused();
            return $this->maybe_wp_die();
        }
        if ($this->is_queue_empty()) {
            // No data to process.
            return $this->maybe_wp_die();
        }
        check_ajax_referer($this->identifier, 'nonce');
        $this->handle();
        return $this->maybe_wp_die();
    }
    /**
     * Is queue empty?
     *
     * @return bool
     */
    protected function is_queue_empty()
    {
        return empty($this->get_batch());
    }
    /**
     * Is process running?
     *
     * Check whether the current process is already running
     * in a background process.
     *
     * @return bool
     *
     * @deprecated 1.1.0 Superseded.
     * @see        is_processing()
     */
    protected function is_process_running()
    {
        return $this->is_processing();
    }
    /**
     * Is the background process currently running?
     *
     * @return bool
     */
    public function is_processing()
    {
        if (get_site_transient($this->identifier . '_process_lock')) {
            // Process already running.
            return \true;
        }
        return \false;
    }
    /**
     * Lock process.
     *
     * Lock the process so that multiple instances can't run simultaneously.
     * Override if applicable, but the duration should be greater than that
     * defined in the time_exceeded() method.
     */
    protected function lock_process()
    {
        $this->start_time = \time();
        // Set start time of current process.
        $lock_duration = \property_exists($this, 'queue_lock_time') ? $this->queue_lock_time : 60;
        // 1 minute
        $lock_duration = apply_filters($this->identifier . '_queue_lock_time', $lock_duration);
        set_site_transient($this->identifier . '_process_lock', \microtime(), $lock_duration);
    }
    /**
     * Unlock process.
     *
     * Unlock the process so that other instances can spawn.
     *
     * @return $this
     */
    protected function unlock_process()
    {
        delete_site_transient($this->identifier . '_process_lock');
        return $this;
    }
    /**
     * Get batch.
     *
     * @return stdClass Return the first batch of queued items.
     */
    protected function get_batch()
    {
        return \array_reduce($this->get_batches(1), static function ($carry, $batch) {
            return $batch;
        }, array());
    }
    /**
     * Get batches.
     *
     * @param int $limit Number of batches to return, defaults to all.
     *
     * @return array of stdClass
     */
    public function get_batches($limit = 0)
    {
        global $wpdb;
        if (empty($limit) || !\is_int($limit)) {
            $limit = 0;
        }
        $table = $wpdb->options;
        $column = 'option_name';
        $key_column = 'option_id';
        $value_column = 'option_value';
        if (is_multisite()) {
            $table = $wpdb->sitemeta;
            $column = 'meta_key';
            $key_column = 'meta_id';
            $value_column = 'meta_value';
        }
        $key = $wpdb->esc_like($this->identifier . '_batch_') . '%';
        $sql = '
			SELECT *
			FROM ' . $table . '
			WHERE ' . $column . ' LIKE %s
			ORDER BY ' . $key_column . ' ASC
			';
        $args = array($key);
        if (!empty($limit)) {
            $sql .= ' LIMIT %d';
            $args[] = $limit;
        }
        $items = $wpdb->get_results($wpdb->prepare($sql, $args));
        // phpcs:ignore WordPress.DB.PreparedSQL.NotPrepared
        $batches = array();
        if (!empty($items)) {
            $allowed_classes = $this->allowed_batch_data_classes;
            $batches = \array_map(static function ($item) use($column, $value_column, $allowed_classes) {
                $batch = new \stdClass();
                $batch->key = $item->{$column};
                $batch->data = static::maybe_unserialize($item->{$value_column}, $allowed_classes);
                return $batch;
            }, $items);
        }
        return $batches;
    }
    /**
     * Handle a dispatched request.
     *
     * Pass each queue item to the task handler, while remaining
     * within server memory and time limit constraints.
     */
    protected function handle()
    {
        $this->lock_process();
        /**
         * Number of seconds to sleep between batches. Defaults to 0 seconds, minimum 0.
         *
         * @param int $seconds
         */
        $throttle_seconds = \max(0, apply_filters($this->identifier . '_seconds_between_batches', apply_filters($this->prefix . '_seconds_between_batches', 0)));
        do {
            $batch = $this->get_batch();
            foreach ($batch->data as $key => $value) {
                $task = $this->task($value);
                if (\false !== $task) {
                    $batch->data[$key] = $task;
                } else {
                    unset($batch->data[$key]);
                }
                // Keep the batch up to date while processing it.
                if (!empty($batch->data)) {
                    $this->update($batch->key, $batch->data);
                }
                // Let the server breathe a little.
                \sleep($throttle_seconds);
                // Batch limits reached, or pause or cancel request.
                if ($this->time_exceeded() || $this->memory_exceeded() || $this->is_paused() || $this->is_cancelled()) {
                    break;
                }
            }
            // Delete current batch if fully processed.
            if (empty($batch->data)) {
                $this->delete($batch->key);
            }
        } while (!$this->time_exceeded() && !$this->memory_exceeded() && !$this->is_queue_empty() && !$this->is_paused() && !$this->is_cancelled());
        $this->unlock_process();
        // Start next batch or complete process.
        if (!$this->is_queue_empty()) {
            $this->dispatch();
        } else {
            $this->complete();
        }
        return $this->maybe_wp_die();
    }
    /**
     * Memory exceeded?
     *
     * Ensures the batch process never exceeds 90%
     * of the maximum WordPress memory.
     *
     * @return bool
     */
    protected function memory_exceeded()
    {
        $memory_limit = $this->get_memory_limit() * 0.9;
        // 90% of max memory
        $current_memory = \memory_get_usage(\true);
        $return = \false;
        if ($current_memory >= $memory_limit) {
            $return = \true;
        }
        return apply_filters($this->identifier . '_memory_exceeded', $return);
    }
    /**
     * Get memory limit in bytes.
     *
     * @return int
     */
    protected function get_memory_limit()
    {
        if (\function_exists('ini_get')) {
            $memory_limit = \ini_get('memory_limit');
        } else {
            // Sensible default.
            $memory_limit = '128M';
        }
        if (!$memory_limit || -1 === \intval($memory_limit)) {
            // Unlimited, set to 32GB.
            $memory_limit = '32000M';
        }
        return wp_convert_hr_to_bytes($memory_limit);
    }
    /**
     * Time limit exceeded?
     *
     * Ensures the batch never exceeds a sensible time limit.
     * A timeout limit of 30s is common on shared hosting.
     *
     * @return bool
     */
    protected function time_exceeded()
    {
        $finish = $this->start_time + apply_filters($this->identifier . '_default_time_limit', 20);
        // 20 seconds
        $return = \false;
        if (\time() >= $finish) {
            $return = \true;
        }
        return apply_filters($this->identifier . '_time_exceeded', $return);
    }
    /**
     * Complete processing.
     *
     * Override if applicable, but ensure that the below actions are
     * performed, or, call parent::complete().
     */
    protected function complete()
    {
        delete_site_option($this->get_status_key());
        // Remove the cron healthcheck job from the cron schedule.
        $this->clear_scheduled_event();
        $this->completed();
    }
    /**
     * Called when background process has completed.
     */
    protected function completed()
    {
        do_action($this->identifier . '_completed');
    }
    /**
     * Get the cron healthcheck interval in minutes.
     *
     * Default is 5 minutes, minimum is 1 minute.
     *
     * @return int
     */
    public function get_cron_interval()
    {
        $interval = 5;
        if (\property_exists($this, 'cron_interval')) {
            $interval = $this->cron_interval;
        }
        $interval = apply_filters($this->cron_interval_identifier, $interval);
        return \is_int($interval) && 0 < $interval ? $interval : 5;
    }
    /**
     * Schedule the cron healthcheck job.
     *
     * @access public
     *
     * @param mixed $schedules Schedules.
     *
     * @return mixed
     */
    public function schedule_cron_healthcheck($schedules)
    {
        $interval = $this->get_cron_interval();
        if (1 === $interval) {
            $display = __('Every Minute');
        } else {
            $display = \sprintf(__('Every %d Minutes'), $interval);
        }
        // Adds an "Every NNN Minute(s)" schedule to the existing cron schedules.
        $schedules[$this->cron_interval_identifier] = array('interval' => \MINUTE_IN_SECONDS * $interval, 'display' => $display);
        return $schedules;
    }
    /**
     * Handle cron healthcheck event.
     *
     * Restart the background process if not already running
     * and data exists in the queue.
     */
    public function handle_cron_healthcheck()
    {
        if ($this->is_processing()) {
            // Background process already running.
            exit;
        }
        if ($this->is_queue_empty()) {
            // No data to process.
            $this->clear_scheduled_event();
            exit;
        }
        $this->dispatch();
    }
    /**
     * Schedule the cron healthcheck event.
     */
    protected function schedule_event()
    {
        if (!wp_next_scheduled($this->cron_hook_identifier)) {
            wp_schedule_event(\time() + $this->get_cron_interval() * \MINUTE_IN_SECONDS, $this->cron_interval_identifier, $this->cron_hook_identifier);
        }
    }
    /**
     * Clear scheduled cron healthcheck event.
     */
    protected function clear_scheduled_event()
    {
        $timestamp = wp_next_scheduled($this->cron_hook_identifier);
        if ($timestamp) {
            wp_unschedule_event($timestamp, $this->cron_hook_identifier);
        }
    }
    /**
     * Cancel the background process.
     *
     * Stop processing queue items, clear cron job and delete batch.
     *
     * @deprecated 1.1.0 Superseded.
     * @see        cancel()
     */
    public function cancel_process()
    {
        $this->cancel();
    }
    /**
     * Perform task with queued item.
     *
     * Override this method to perform any actions required on each
     * queue item. Return the modified item for further processing
     * in the next pass through. Or, return false to remove the
     * item from the queue.
     *
     * @param mixed $item Queue item to iterate over.
     *
     * @return mixed
     */
    protected abstract function task($item);
    /**
     * Maybe unserialize data, but not if an object.
     *
     * @param mixed      $data            Data to be unserialized.
     * @param bool|array $allowed_classes Array of class names that can be unserialized.
     *
     * @return mixed
     */
    protected static function maybe_unserialize($data, $allowed_classes)
    {
        if (is_serialized($data)) {
            $options = array();
            if (\is_bool($allowed_classes) || \is_array($allowed_classes)) {
                $options['allowed_classes'] = $allowed_classes;
            }
            return @\unserialize($data, $options);
            // @phpcs:ignore
        }
        return $data;
    }
}