trait AssertPageCacheContextsAndTagsTrait

trait AssertPageCacheContextsAndTagsTrait {
  
  /**
   * Enables page caching.
   */
  protected function enablePageCaching() {
    $config = $this->config('system.performance');
    $config->set('cache.page.max_age', 300);
    $config->save();
  }
  
  /**
   * Gets a specific header value as array.
   *
   * @param string $header_name
   *   The header name.
   *
   * @return string[]
   *   The header value, potentially exploded by spaces.
   */
  protected function getCacheHeaderValues($header_name) : array {
    $header_value = $this->getSession()
      ->getResponseHeader($header_name);
    return empty($header_value) ? [] : explode(' ', $header_value);
  }
  
  /**
   * Asserts whether an expected cache context was present in the last response.
   *
   * @param string $expected_cache_context
   *   The expected cache context.
   */
  protected function assertCacheContext($expected_cache_context) {
    $cache_contexts = explode(' ', $this->getSession()
      ->getResponseHeader('X-Drupal-Cache-Contexts'));
    $this->assertContains($expected_cache_context, $cache_contexts, "'" . $expected_cache_context . "' is present in the X-Drupal-Cache-Contexts header.");
  }
  
  /**
   * Asserts that a cache context was not present in the last response.
   *
   * @param string $not_expected_cache_context
   *   The expected cache context.
   */
  protected function assertNoCacheContext($not_expected_cache_context) {
    $cache_contexts = explode(' ', $this->getSession()
      ->getResponseHeader('X-Drupal-Cache-Contexts'));
    $this->assertNotContains($not_expected_cache_context, $cache_contexts, "'" . $not_expected_cache_context . "' is not present in the X-Drupal-Cache-Contexts header.");
  }
  
  /**
   * Asserts page cache miss, then hit for the given URL; checks cache headers.
   *
   * @param \Drupal\Core\Url $url
   *   The URL to test.
   * @param string[] $expected_contexts
   *   The expected cache contexts for the given URL.
   * @param string[] $expected_tags
   *   The expected cache tags for the given URL.
   */
  protected function assertPageCacheContextsAndTags(Url $url, array $expected_contexts, array $expected_tags) {
    $absolute_url = $url->setAbsolute()
      ->toString();
    sort($expected_contexts);
    sort($expected_tags);
    // Assert cache miss + expected cache contexts + tags.
    $this->drupalGet($absolute_url);
    $this->assertSession()
      ->responseHeaderEquals('X-Drupal-Cache', 'MISS');
    $this->assertCacheTags($expected_tags);
    $this->assertCacheContexts($expected_contexts);
    // Assert cache hit + expected cache contexts + tags.
    $this->drupalGet($absolute_url);
    $this->assertCacheTags($expected_tags);
    $this->assertCacheContexts($expected_contexts);
    // Assert page cache item + expected cache tags.
    $cid_parts = [
      $url->setAbsolute()
        ->toString(),
      '',
    ];
    $cid = implode(':', $cid_parts);
    $cache_entry = \Drupal::cache('page')->get($cid);
    sort($cache_entry->tags);
    $this->assertEquals($expected_tags, $cache_entry->tags);
  }
  
  /**
   * Ensures that some cache tags are present in the current response.
   *
   * @param string[] $expected_tags
   *   The expected tags.
   * @param bool $include_default_tags
   *   (optional) Whether the default cache tags should be included.
   */
  protected function assertCacheTags(array $expected_tags, $include_default_tags = TRUE) {
    // The anonymous role cache tag is only added if the user is anonymous.
    if ($include_default_tags) {
      if (\Drupal::currentUser()->isAnonymous()) {
        $expected_tags = Cache::mergeTags($expected_tags, [
          'config:user.role.anonymous',
        ]);
      }
      $expected_tags[] = 'http_response';
    }
    $actual_tags = $this->getCacheHeaderValues('X-Drupal-Cache-Tags');
    $expected_tags = array_unique($expected_tags);
    sort($expected_tags);
    sort($actual_tags);
    $this->assertSame($expected_tags, $actual_tags);
  }
  
  /**
   * Ensures that some cache contexts are present in the current response.
   *
   * @param string[] $expected_contexts
   *   The expected cache contexts.
   * @param string $message
   *   (optional) A verbose message to output.
   * @param bool $include_default_contexts
   *   (optional) Whether the default contexts should automatically be included.
   *
   * @return bool
   *   Always returns TRUE.
   */
  protected function assertCacheContexts(array $expected_contexts, $message = NULL, $include_default_contexts = TRUE) : bool {
    if ($include_default_contexts) {
      $default_contexts = [
        'languages:language_interface',
        'theme',
      ];
      // Add the user based contexts to the list of default contexts except when
      // user is already there.
      if (!in_array('user', $expected_contexts)) {
        $default_contexts[] = 'user.permissions';
        if (!in_array('user.roles', $expected_contexts)) {
          // The system_page_attachments() hook is only called when dealing with
          // the HtmlRenderer, so check the Content-Type header.
          // @see \Drupal\Core\Render\MainContent\HtmlRenderer::invokePageAttachmentHooks()
          if ($this->getSession()
            ->getResponseHeader('Content-Type') === 'text/html; charset=UTF-8') {
            $default_contexts[] = 'user.roles:authenticated';
          }
        }
      }
      $expected_contexts = Cache::mergeContexts($expected_contexts, $default_contexts);
    }
    $actual_contexts = $this->getCacheHeaderValues('X-Drupal-Cache-Contexts');
    sort($expected_contexts);
    sort($actual_contexts);
    $this->assertSame($expected_contexts, $actual_contexts, $message ?? '');
    return TRUE;
  }
  
  /**
   * Asserts the max age header.
   *
   * @param int $max_age
   *   The maximum age of the cache.
   */
  protected function assertCacheMaxAge(int $max_age) {
    $this->assertSession()
      ->responseHeaderEquals('Cache-Control', "max-age={$max_age}, public");
  }

}