<?php

/**
 * @file
 * Test module.
 */

/**
 * Implements hook_page_top().
 */
function session_exists_cache_context_test_page_top(array &$page_top) {
  // Ensure this hook is invoked on every page load.
  $page_top['#cache']['max-age'] = 0;

  $request = \Drupal::request();
  $session_exists = \Drupal::service('session_configuration')->hasSession($request);
  $page_top['session_exists_cache_context_test'] = [
    'label' => [
      '#markup' => '<p>' . ($session_exists ? 'Session exists!' : 'Session does not exist!') . '</p>',
    ],
    'cache_context_value' => [
      '#markup' => '<code>[session.exists]=' . \Drupal::service('cache_context.session.exists')->getContext() . '</code>',
    ],
  ];

  if (\Drupal::request()->query->get('trigger_session')) {
    $_SESSION['session_exists_cache_context_test'] = TRUE;
  }
}
