<?php

/**
 * @file
 * Add a field to nodes containing the publication date.
 */

use Drupal\Core\Field\BaseFieldDefinition;
use Drupal\Core\Entity\EntityTypeInterface;
use Drupal\Core\Form\FormStateInterface;

/**
 * Define the value stored in the database when a node is unpublished and no
 * publication date has been set. We use the largest number that the database
 * field can hold so unpublished nodes will appear newer than published nodes
 * when sorted by publication date.
 *
 * @note: This is going to trigger the Year 2038 problem.
 */
define('PUBLICATION_DATE_DEFAULT', 2147483647);

/**
 * Implements hook_entity_base_field_info().
 *
 * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
 *
 * @return array
 */
function publication_date_entity_base_field_info(EntityTypeInterface $entity_type) {
  $fields = [];

  if ($entity_type->id() == 'node') {
    $fields['published_at'] = BaseFieldDefinition::create('published_at')
      ->setLabel(t('Published on'))
      ->setDescription(t('Keep the publication timestamp for each node.'))
      ->setRevisionable(TRUE)
      ->setTranslatable(TRUE)
      ->setDisplayOptions('view', array(
        'region' => 'hidden',
      ))
      ->setDisplayConfigurable('view', TRUE)
      ->setDisplayOptions('form', array(
        'type' => 'publication_date_timestamp',
        'weight' => 10,
      ))
      ->setDisplayConfigurable('form', TRUE);
  }

  return $fields;
}

/**
 * Implements hook_form_BASE_ID_alter().
 *
 * Display the publication date on the node edit form.
 * @note: This won't work where you have Display Suite/REL enabled.
 */
function publication_date_form_node_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  $account = \Drupal::currentUser();
  $node = $form_state->getFormObject()->getEntity();

  if (isset($form['published_at'])) {
    // Check if the user has permission to edit the publication date.
    $form['published_at']['#access'] = $account->hasPermission('set any published on date') || $account->hasPermission('set ' . $node->bundle() . ' published on date');
    $form['published_at']['#group'] = 'revision_information';
  }
}

/**
 * Implements hook_clone_node_alter().
 *
 * Reset the publication date when a node is cloned using the Node Clone module.
 *
 * @see clone.api.php
 */
function publication_date_clone_node_alter(&$node, $context) {
  $node->published_at->value = NULL;
}

/**
 * Implements hook_field_formatter_info_alter().
 */
function publication_date_field_formatter_info_alter(array &$info) {
  $info['timestamp']['field_types'][] = 'published_at';
  $info['timestamp_ago']['field_types'][] = 'published_at';
}