class QueueExampleForm

class QueueExampleForm extends FormBase {
    
    /**
     * The queue object.
     *
     * @var \Drupal\Core\Queue\QueueFactory
     */
    protected $queueFactory;
    
    /**
     * The database object.
     *
     * @var \Drupal\Core\Database\Connection
     */
    protected $database;
    
    /**
     * The CronInterface object.
     *
     * @var \Drupal\Core\CronInterface
     */
    protected $cron;
    
    /**
     * What kind of queue backend are we using?
     *
     * @var string
     */
    protected $queueType;
    
    /**
     * Constructor.
     *
     * @param \Drupal\Core\Queue\QueueFactory $queue_factory
     *   Queue factory service to get new/existing queues for use.
     * @param \Drupal\Core\Database\Connection $database
     *   The database connection to be used.
     * @param Drupal\Core\CronInterface $cron
     *   The cron service.
     * @param Drupal\Core\Site\Settings $settings
     *   The site settings.
     */
    public function __construct(QueueFactory $queue_factory, Connection $database, CronInterface $cron, Settings $settings) {
        $this->queueFactory = $queue_factory;
        $this->queueType = $settings->get('queue_default', 'queue.database');
        $this->database = $database;
        $this->cron = $cron;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        $form = new static($container->get('queue'), $container->get('database'), $container->get('cron'), $container->get('settings'));
        $form->setMessenger($container->get('messenger'));
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        // Return a string that is the unique ID of our form. Best practice here is
        // to namespace the form based on your module's name.
        return 'queue_example';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        // Simple counter that makes it possible to put auto-incrementing default
        // string into the string to insert.
        if (empty($form_state->get('insert_counter'))) {
            $form_state->set('insert_counter', 1);
        }
        $queue_name = $form_state->getValue('queue_name') ?: 'queue_example_first_queue';
        $items = $this->retrieveQueue($queue_name);
        $form['help'] = [
            '#type' => 'markup',
            '#markup' => '<div>' . $this->t('This page is an interface on the Drupal queue API. You can add new items to the queue, "claim" one (retrieve the next item and keep a lock on it), and delete one (remove it from the queue). Note that claims are not expired until cron runs, so there is a special button to run cron to perform any necessary expirations.') . '</div>',
        ];
        $form['wrong_queue_warning'] = [
            '#type' => 'markup',
            '#markup' => '<div>' . $this->t('Note: the example works only with the default queue implementation, which is not currently configured!!') . '</div>',
            '#access' => !$this->doesQueueUseDB(),
        ];
        $queue_names = [
            'queue_example_first_queue',
            'queue_example_second_queue',
        ];
        $form['queue_name'] = [
            '#type' => 'select',
            '#title' => $this->t('Choose queue to examine'),
            '#options' => array_combine($queue_names, $queue_names),
            '#default_value' => $queue_name,
        ];
        $form['queue_show'] = [
            '#type' => 'submit',
            '#value' => $this->t('Show queue'),
            '#submit' => [
                '::submitShowQueue',
            ],
        ];
        $form['status_fieldset'] = [
            '#type' => 'fieldset',
            '#title' => $this->t('Queue status for @name', [
                '@name' => $queue_name,
            ]),
            '#collapsible' => TRUE,
        ];
        if (count($items) > 0) {
            $form['status_fieldset']['status'] = [
                '#theme' => 'table',
                '#header' => [
                    $this->t('Item ID'),
                    $this->t('Claimed/Expiration'),
                    $this->t('Created'),
                    $this->t('Content/Data'),
                ],
                '#rows' => array_map([
                    $this,
                    'processQueueItemForTable',
                ], $items),
            ];
        }
        else {
            $form['status_fieldset']['status'] = [
                '#type' => 'markup',
                '#markup' => $this->t('There are no items in the queue.'),
            ];
        }
        $form['insert_fieldset'] = [
            '#type' => 'fieldset',
            '#title' => $this->t('Insert into @name', [
                '@name' => $queue_name,
            ]),
        ];
        $form['insert_fieldset']['string_to_add'] = [
            '#type' => 'textfield',
            '#size' => 10,
            '#default_value' => $this->t('item @counter', [
                '@counter' => $form_state->get('insert_counter'),
            ]),
        ];
        $form['insert_fieldset']['add_item'] = [
            '#type' => 'submit',
            '#value' => $this->t('Insert into queue'),
            '#submit' => [
                '::submitAddQueueItem',
            ],
        ];
        $form['claim_fieldset'] = [
            '#type' => 'fieldset',
            '#title' => $this->t('Claim from queue'),
            '#collapsible' => TRUE,
        ];
        $form['claim_fieldset']['claim_time'] = [
            '#type' => 'radios',
            '#title' => $this->t('Claim time, in seconds'),
            '#options' => [
                0 => $this->t('none'),
                5 => $this->t('5 seconds'),
                60 => $this->t('60 seconds'),
            ],
            '#description' => $this->t('This time is only valid if cron runs during this time period. You can run cron manually below.'),
            '#default_value' => $form_state->getValue('claim_time') ?: 5,
        ];
        $form['claim_fieldset']['claim_item'] = [
            '#type' => 'submit',
            '#value' => $this->t('Claim the next item from the queue'),
            '#submit' => [
                '::submitClaimItem',
            ],
        ];
        $form['claim_fieldset']['claim_and_delete_item'] = [
            '#type' => 'submit',
            '#value' => $this->t('Claim the next item and delete it'),
            '#submit' => [
                '::submitClaimDeleteItem',
            ],
        ];
        $form['claim_fieldset']['run_cron'] = [
            '#type' => 'submit',
            '#value' => $this->t('Run cron manually to expire claims'),
            '#submit' => [
                '::submitRunCron',
            ],
        ];
        $form['delete_queue'] = [
            '#type' => 'submit',
            '#value' => $this->t('Delete the queue and items in it'),
            '#submit' => [
                '::submitDeleteQueue',
            ],
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
    }
    
    /**
     * Retrieves the queue from the database for display purposes only.
     *
     * It is not recommended to access the database directly, and this is only
     * here so that the user interface can give a good idea of what's going on
     * in the queue.
     *
     * @param string $queue_name
     *   The name of the queue from which to fetch items.
     *
     * @return array
     *   An array of item arrays.
     */
    public function retrieveQueue($queue_name) {
        $items = [];
        // This example requires the default queue implementation to work,
        // so we bail if some other queue implementation has been installed.
        if (!$this->doesQueueUseDb()) {
            return $items;
        }
        // Make sure there are queue items available. The queue will not create our
        // database table if there are no items.
        if ($this->queueFactory
            ->get($queue_name)
            ->numberOfItems() >= 1) {
            $result = $this->database
                ->query('SELECT item_id, data, expire, created FROM {' . DatabaseQueue::TABLE_NAME . '} WHERE name = :name ORDER BY item_id', [
                ':name' => $queue_name,
            ], [
                'fetch' => \PDO::FETCH_ASSOC,
            ]);
            foreach ($result as $item) {
                $items[] = $item;
            }
        }
        return $items;
    }
    
    /**
     * Check if we are using the default database queue.
     *
     * @return bool
     *   TRUE if we are using the default database queue implementation.
     */
    protected function doesQueueUseDb() {
        return $this->queueType == 'queue.database';
    }
    
    /**
     * Submit function for the show-queue button.
     *
     * @param array $form
     *   Form definition array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   Form state object.
     */
    public function submitShowQueue(array &$form, FormStateInterface $form_state) {
        $queue = $this->queueFactory
            ->get($form_state->getValue('queue_name'));
        // There is no harm in trying to recreate existing.
        $queue->createQueue();
        // Get the number of items.
        $count = $queue->numberOfItems();
        // Update the form item counter.
        $form_state->set('insert_counter', $count + 1);
        // Unset the string_to_add textbox.
        $form_state->unsetValue('string_to_add');
        $form_state->setRebuild();
    }
    
    /**
     * Submit function for the insert-into-queue button.
     *
     * @param array $form
     *   Form definition array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   Form state object.
     */
    public function submitAddQueueItem(array &$form, FormStateInterface $form_state) {
        // Get a queue (of the default type) called 'queue_example_queue'.
        // If the default queue class is SystemQueue this creates a queue that
        // stores its items in the database.
        $queue = $this->queueFactory
            ->get($form_state->getValue('queue_name'));
        // There is no harm in trying to recreate existing.
        $queue->createQueue();
        // Queue the string.
        $queue->createItem($form_state->getValue('string_to_add'));
        $count = $queue->numberOfItems();
        $this->messenger()
            ->addMessage($this->t('Queued your string (@string_to_add). There are now @count items in the queue.', [
            '@count' => $count,
            '@string_to_add' => $form_state->getValue('string_to_add'),
        ]));
        // Allows us to keep information in $form_state.
        $form_state->setRebuild();
        // Unsetting the string_to_add allows us to set the incremented default
        // value for the user so they don't have to type anything.
        $form_state->unsetValue('string_to_add');
        $form_state->set('insert_counter', $count + 1);
    }
    
    /**
     * Submit function for the "claim" button.
     *
     * Claims (retrieves) an item from the queue and reports the results.
     *
     * @param array $form
     *   Form definition array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   Form state object.
     */
    public function submitClaimItem(array &$form, FormStateInterface $form_state) {
        $queue = $this->queueFactory
            ->get($form_state->getValue('queue_name'));
        // There is no harm in trying to recreate existing.
        $queue->createQueue();
        $item = $queue->claimItem($form_state->getValue('claim_time'));
        $count = $queue->numberOfItems();
        if (!empty($item)) {
            $this->messenger()
                ->addMessage($this->t('Claimed item id=@item_id string=@string for @seconds seconds. There are @count items in the queue.', [
                '@count' => $count,
                '@item_id' => $item->item_id,
                '@string' => $item->data,
                '@seconds' => $form_state->getValue('claim_time'),
            ]));
        }
        else {
            $this->messenger()
                ->addMessage($this->t('There were no items in the queue available to claim. There are @count items in the queue.', [
                '@count' => $count,
            ]));
        }
        $form_state->setRebuild();
    }
    
    /**
     * Submit function for "Claim and delete" button.
     *
     * @param array $form
     *   Form definition array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   Form state object.
     */
    public function submitClaimDeleteItem(array &$form, FormStateInterface $form_state) {
        $queue = $this->queueFactory
            ->get($form_state->getValue('queue_name'));
        // There is no harm in trying to recreate existing.
        $queue->createQueue();
        $count = $queue->numberOfItems();
        $item = $queue->claimItem(60);
        if (!empty($item)) {
            $this->messenger()
                ->addMessage($this->t('Claimed and deleted item id=@item_id string=@string for @seconds seconds. There are @count items in the queue.', [
                '@count' => $count,
                '@item_id' => $item->item_id,
                '@string' => $item->data,
                '@seconds' => $form_state->getValue('claim_time'),
            ]));
            $queue->deleteItem($item);
            $count = $queue->numberOfItems();
            $this->messenger()
                ->addMessage($this->t('There are now @count items in the queue.', [
                '@count' => $count,
            ]));
        }
        else {
            $count = $queue->numberOfItems();
            $this->messenger()
                ->addMessage($this->t('There were no items in the queue available to claim/delete. There are currently @count items in the queue.', [
                '@count' => $count,
            ]));
        }
        $form_state->setRebuild();
    }
    
    /**
     * Submit function for "run cron" button.
     *
     * Runs cron (to release expired claims) and reports the results.
     *
     * @param array $form
     *   Form definition array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   Form state object.
     */
    public function submitRunCron(array &$form, FormStateInterface $form_state) {
        $this->cron
            ->run();
        $queue = $this->queueFactory
            ->get($form_state->getValue('queue_name'));
        // @see https://www.drupal.org/node/2705809
        if ($queue instanceof QueueGarbageCollectionInterface) {
            $queue->garbageCollection();
        }
        // There is no harm in trying to recreate existing.
        $queue->createQueue();
        $count = $queue->numberOfItems();
        $this->messenger()
            ->addMessage($this->t('Ran cron. If claimed items expired, they should be expired now. There are now @count items in the queue', [
            '@count' => $count,
        ]));
        $form_state->setRebuild();
    }
    
    /**
     * Submit handler for clearing/deleting the queue.
     *
     * @param array $form
     *   Form definition array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   Form state object.
     */
    public function submitDeleteQueue(array &$form, FormStateInterface $form_state) {
        $queue = $this->queueFactory
            ->get($form_state->getValue('queue_name'));
        $queue->deleteQueue();
        $this->messenger()
            ->addMessage($this->t('Deleted the @queue_name queue and all items in it', [
            '@queue_name' => $form_state->getValue('queue_name'),
        ]));
    }
    
    /**
     * Helper method to format a queue item for display in a summary table.
     *
     * @param array $item
     *   Queue item array with keys for item_id, expire, created, and data.
     *
     * @return array
     *   An array with the queue properties in the right order for display in a
     *   summary table.
     */
    private function processQueueItemForTable(array $item) {
        if ($item['expire'] > 0) {
            $item['expire'] = $this->t('Claimed: expires %expire', [
                '%expire' => date('r', $item['expire']),
            ]);
        }
        else {
            $item['expire'] = $this->t('Unclaimed');
        }
        $item['created'] = date('r', $item['created']);
        $item['content'] = Html::escape(unserialize($item['data']));
        unset($item['data']);
        return $item;
    }

}