Blocks as plugins

ActiveTopicsBlock.php

<?php

/**
 * @file
 * Contains \Drupal\forum\Plugin\Block\ActiveTopicsBlock.
 */

namespace Drupal\forum\Plugin\Block;

/**
 * Provides an 'Active forum topics' block.
 *
 * @Block(
 *   id = "forum_active_block",
 *   admin_label = @Translation("Active forum topics"),
 *   category = @Translation("Lists (Views)")
 * )
 */
class ActiveTopicsBlock extends ForumBlockBase {

  /**
   * {@inheritdoc}
   */
  public function build() {
    $query = db_select('forum_index', 'f')
      ->fields('f')
      ->addTag('node_access')
      ->addMetaData('base_table', 'forum_index')
      ->orderBy('f.last_comment_timestamp', 'DESC')
      ->range(0, $this->configuration['block_count']);

    return array(
      drupal_render_cache_by_query($query, 'forum_block_view'),
    );
  }

}

ForumBlockBase.php

<?php

/**
 * @file
 * Contains \Drupal\forum\Plugin\Block\ForumBlockBase.
 */

namespace Drupal\forum\Plugin\Block;

use Drupal\block\BlockBase;
use Drupal\Core\Session\AccountInterface;

/**
 * Provides a base class for Forum blocks.
 */
abstract class ForumBlockBase extends BlockBase {

  /**
   * {@inheritdoc}
   */
  public function defaultConfiguration() {
    return array(
      'cache' => DRUPAL_CACHE_CUSTOM,
      'properties' => array(
        'administrative' => TRUE,
      ),
      'block_count' => 5,
    );
  }

  /**
   * {@inheritdoc}
   */
  public function access(AccountInterface $account) {
    return $account->hasPermission('access content');
  }

  /**
   * Overrides \Drupal\block\BlockBase::blockForm().
   */
  public function blockForm($form, &$form_state) {
    $form['block_count'] = array(
      '#type' => 'select',
      '#title' => t('Number of topics'),
      '#default_value' => $this->configuration['block_count'],
      '#options' => drupal_map_assoc(range(2, 20)),
    );
    return $form;
  }

  /**
   * Overrides \Drupal\block\BlockBase::blockSubmit().
   */
  public function blockSubmit($form, &$form_state) {
    $this->configuration['block_count'] = $form_state['values']['block_count'];
  }

}

NewTopicsBlock.php

<?php

/**
 * @file
 * Contains \Drupal\forum\Plugin\Block\NewTopicsBlock.
 */

namespace Drupal\forum\Plugin\Block;

/**
 * Provides a 'New forum topics' block.
 *
 * @Block(
 *   id = "forum_new_block",
 *   admin_label = @Translation("New forum topics"),
 *   category = @Translation("Lists (Views)")
 * )
 */
class NewTopicsBlock extends ForumBlockBase {

  /**
   * {@inheritdoc}
   */
  public function build() {
    $query = db_select('forum_index', 'f')
      ->fields('f')
      ->addTag('node_access')
      ->addMetaData('base_table', 'forum_index')
      ->orderBy('f.created', 'DESC')
      ->range(0, $this->configuration['block_count']);

    return array(
      drupal_render_cache_by_query($query, 'forum_block_view'),
    );
  }

}