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) {
        $header_value = $this->drupalGetHeader($header_name);
        if (empty($header_value)) {
            return [];
        }
        else {
            return 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->drupalGetHeader('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->drupalGetHeader('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);
        $this->assertEqual($this->drupalGetHeader('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);
        $this->assertEqual($cache_entry->tags, $expected_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);
        $this->assertIdentical($actual_tags, $expected_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
     *   TRUE if the assertion succeeded, FALSE otherwise.
     */
    protected function assertCacheContexts(array $expected_contexts, $message = NULL, $include_default_contexts = TRUE) {
        if ($include_default_contexts) {
            $default_contexts = [
                'languages:language_interface',
                'theme',
            ];
            // Add the user.permission context to the list of default contexts except
            // when user is already there.
            if (!in_array('user', $expected_contexts)) {
                $default_contexts[] = 'user.permissions';
            }
            $expected_contexts = Cache::mergeContexts($expected_contexts, $default_contexts);
        }
        $actual_contexts = $this->getCacheHeaderValues('X-Drupal-Cache-Contexts');
        sort($expected_contexts);
        sort($actual_contexts);
        $this->assertIdentical($actual_contexts, $expected_contexts, $message);
        return $actual_contexts === $expected_contexts;
    }
    
    /**
     * Asserts the max age header.
     *
     * @param int $max_age
     */
    protected function assertCacheMaxAge($max_age) {
        $cache_control_header = $this->drupalGetHeader('Cache-Control');
        $this->assertStringContainsString('max-age:' . $max_age, $cache_control_header);
    }

}