<?php

/**
 * @file
 * Contains metatag_page_manager.module.
 */

use Drupal\Core\Routing\RouteMatchInterface;
use Drupal\Core\Form\FormStateInterface;
use Drupal\page_manager\Entity\PageVariant;
use Drupal\metatag\Entity\MetatagDefaults;

/**
 * Implements hook_form_FORM_ID_alter().
 */
function metatag_page_manager_form_metatag_defaults_add_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  $variants_options['Page Variants'] = _metatag_page_manager_get_variants();
  $form['id']['#options'] = array_merge($form['id']['#options'], $variants_options);
}

/**
 * Implements hook_page_attachments().
 */
function metatag_page_manager_page_attachments(array &$attachments) {
  // Fetch entity from request.
  $entity = \Drupal::request()->attributes->get('_entity');
  if ($entity) {

    $key = $entity->getEntityType()->id() . '__' . $entity->id();
    // Get default metatags.
    $metatag_defaults = metatag_get_default_tags();
    // Load page variant metatags.
    $metatag_variant = MetatagDefaults::load($key);
    if ($metatag_variant) {
      // Overwrite the metatag defaults with the tags of the page variant.
      $metatag_defaults = array_merge($metatag_defaults, $metatag_variant->get('tags'));

      // Set the metatag in the static metatag attachments parameter so the
      // metatag module wouldn't overwrite them.
      $metatag_attachments = &drupal_static('metatag_attachments');

      $metatag_manager = \Drupal::service('metatag.manager');
      $metatag_attachments = $metatag_manager->generateElements($metatag_defaults, $entity);

      // If any Metatag items were found, append them.
      if (!empty($metatag_attachments['#attached']['html_head'])) {
        if (empty($attachments['#attached'])) {
          $attachments['#attached'] = [];
        }
        if (empty($attachments['#attached']['html_head'])) {
          $attachments['#attached']['html_head'] = [];
        }
        foreach ($metatag_attachments['#attached']['html_head'] as $item) {
          $attachments['#attached']['html_head'][] = $item;
        }
      }
    }
  }
}

/**
 * Returns all available page variants.
 *
 * @return string[]
 *   A list of page variants keyed by label.
 */
function _metatag_page_manager_get_variants() {
  /** @var \Drupal\page_manager\Entity\PageVariant[] $variants */
  $variants = PageVariant::loadMultiple();
  $variant_options = [];
  // Load all metatag defaults so we can filter the variants which already have
  // a metatag default configured.
  $metatag_defaults = MetatagDefaults::loadMultiple();
  foreach ($variants as $key => $variant) {
    $id = $variant->getEntityType()->id() . '__' . $key;
    if (!isset($metatag_defaults[$id])) {
      $label = $variant->getPage()->label() . ' : ' . $variant->label();
      $variant_options[$id] = $label;
    }
  }
  return $variant_options;
}

/**
 * Implements hook_metatag_alter().
 */
function metatag_page_manager_metatags_alter(array &$metatags, array &$context) {
  if (!$context['entity'] instanceof PageVariant) {
    return;
  }

  $key = $context['entity']->getEntityType()->id() . '__' . $context['entity']->id();
  $metatag_variant = MetatagDefaults::load($key);
  if ($metatag_variant) {
    $metatags = array_merge($metatags, $metatag_variant->get('tags'));
  }
}

/**
 * Implements hook_metatag_route_entity().
 */
function metatag_page_manager_metatag_route_entity(RouteMatchInterface $route_match) {
  if ($variant = $route_match->getParameter('page_manager_page_variant')) {
    return $variant;
  }
}