www.aleph1.co.uk Git - yaffs-website/blob - web/core/lib/Drupal/Core/Render/Placeholder/ChainedPlaceholderStrategy.php

   1 <?php
   2
   3 namespace Drupal\Core\Render\Placeholder;
   4
   5 /**
   6  * Renders placeholders using a chain of placeholder strategies.
   7  */
   8 class ChainedPlaceholderStrategy implements PlaceholderStrategyInterface {
   9
  10   /**
  11    * An ordered list of placeholder strategy services.
  12    *
  13    * Ordered according to service priority.
  14    *
  15    * @var \Drupal\Core\Render\Placeholder\PlaceholderStrategyInterface[]
  16    */
  17   protected $placeholderStrategies = [];
  18
  19   /**
  20    * Adds a placeholder strategy to use.
  21    *
  22    * @param \Drupal\Core\Render\Placeholder\PlaceholderStrategyInterface $strategy
  23    *   The strategy to add to the placeholder strategies.
  24    */
  25   public function addPlaceholderStrategy(PlaceholderStrategyInterface $strategy) {
  26     $this->placeholderStrategies[] = $strategy;
  27   }
  28
  29   /**
  30    * {@inheritdoc}
  31    */
  32   public function processPlaceholders(array $placeholders) {
  33     if (empty($placeholders)) {
  34       return [];
  35     }
  36
  37     // Assert that there is at least one strategy.
  38     assert('!empty($this->placeholderStrategies)', 'At least one placeholder strategy must be present; by default the fallback strategy \Drupal\Core\Render\Placeholder\SingleFlushStrategy is always present.');
  39
  40     $new_placeholders = [];
  41
  42     // Give each placeholder strategy a chance to replace all not-yet replaced
  43     // placeholders. The order of placeholder strategies is well defined
  44     // and this uses a variation of the "chain of responsibility" design pattern.
  45     foreach ($this->placeholderStrategies as $strategy) {
  46       $processed_placeholders = $strategy->processPlaceholders($placeholders);
  47       assert('array_intersect_key($processed_placeholders, $placeholders) === $processed_placeholders', 'Processed placeholders must be a subset of all placeholders.');
  48       $placeholders = array_diff_key($placeholders, $processed_placeholders);
  49       $new_placeholders += $processed_placeholders;
  50
  51       if (empty($placeholders)) {
  52         break;
  53       }
  54     }
  55
  56     return $new_placeholders;
  57   }
  58
  59 }