First commit

fullcalendar_library.info.yml

+name: Fullcalendar library
+type: module
+description: Fullcalendar library
+core: 8.x
+package: Fullcalendar
\ No newline at end of file

fullcalendar_library.libraries.yml

+fullcalendar:
+  version: VERSION
+  js:
+    /libraries/fullcalendar/lib/moment.min.js: { minified: true }
+    /libraries/fullcalendar/fullcalendar.min.js: { minified: true }
+    /libraries/fullcalendar/locale-all.js: { minified: true }
+  dependencies:
+    - core/jquery
+  css:
+    theme:
+      /libraries/fullcalendar/fullcalendar.min.css: { minified: true }
+
+fullcalendar-scheduler:
+  version: VERSION
+  js:
+    /libraries/fullcalendar-scheduler/scheduler.min.js: { minified: true }
+  dependencies:
+    - fullcalendar_library/fullcalendar
+  css:
+    theme:
+      /libraries/fullcalendar-scheduler/scheduler.min.css: { minified: true }

fullcalendar_library.module

+<?php
+
+define('FULLCALENDAR_JS_CDN', 'https://cdn.jsdelivr.net/npm/fullcalendar@3.8.0/dist/fullcalendar.min.js');
+define('FULLCALENDAR_LOCALE_JS_CDN', 'https://cdn.jsdelivr.net/npm/fullcalendar@3.8.0/dist/locale-all.js');
+define('FULLCALENDAR_CSS_CDN', 'https://cdn.jsdelivr.net/npm/fullcalendar@3.8.0/dist/fullcalendar.min.css');
+define('FULLCALENDAR_SCHEDULER_JS_CDN', 'https://cdn.jsdelivr.net/npm/fullcalendar-scheduler@1.9.1/dist/scheduler.min.js');
+define('FULLCALENDAR_SCHEDULER_CSS_CDN', 'https://cdn.jsdelivr.net/npm/fullcalendar-scheduler@1.9.1/dist/scheduler.min.css');
+define('MOMENT_JS_CDN', 'https://cdn.jsdelivr.net/npm/moment@2.20.1/moment.min.js');
+
+/**
+ * Implements hook_library_info_alter().
+ */
+function fullcalendar_library_library_info_alter(&$libraries, $extension) {
+  if ($extension == 'fullcalendar_library') {
+    if (!file_exists(DRUPAL_ROOT . '/libraries/fullcalendar/lib/moment.min.js')) {
+      unset($libraries['fullcalendar']['js']['/libraries/fullcalendar/lib/moment.min.js']);
+      $libraries['fullcalendar']['js'][MOMENT_JS_CDN] = ['type' => 'external', 'minified' => TRUE];
+    }
+
+    if (!file_exists(DRUPAL_ROOT . '/libraries/fullcalendar/fullcalendar.min.js')) {
+      unset($libraries['fullcalendar']['js']['/libraries/fullcalendar/fullcalendar.min.js']);
+      $libraries['fullcalendar']['js'][FULLCALENDAR_JS_CDN] = ['type' => 'external', 'minified' => TRUE];
+    }
+
+    if (!file_exists(DRUPAL_ROOT . '/libraries/fullcalendar/locale-all.js')) {
+      unset($libraries['fullcalendar']['js']['/libraries/fullcalendar/locale-all.js']);
+      $libraries['fullcalendar']['js'][FULLCALENDAR_LOCALE_JS_CDN] = ['type' => 'external', 'minified' => TRUE];
+    }
+
+    if (!file_exists(DRUPAL_ROOT . '/libraries/fullcalendar/fullcalendar.min.css')) {
+      unset($libraries['fullcalendar']['css']['theme']['/libraries/fullcalendar/fullcalendar.min.css']);
+      $libraries['fullcalendar']['css']['theme'][FULLCALENDAR_CSS_CDN] = ['type' => 'external', 'minified' => TRUE];
+    }
+
+    if (!file_exists(DRUPAL_ROOT . '/libraries/fullcalendar-scheduler/scheduler.min.js')) {
+      unset($libraries['fullcalendar-scheduler']['js']['/libraries/fullcalendar-scheduler/scheduler.min.js']);
+      $libraries['fullcalendar-scheduler']['js'][FULLCALENDAR_SCHEDULER_JS_CDN] = ['type' => 'external', 'minified' => TRUE];
+    }
+
+    if (!file_exists(DRUPAL_ROOT . '/libraries/fullcalendar-scheduler/scheduler.min.css')) {
+      unset($libraries['fullcalendar-scheduler']['css']['theme']['/libraries/fullcalendar-scheduler/scheduler.min.css']);
+      $libraries['fullcalendar-scheduler']['css']['theme'][FULLCALENDAR_SCHEDULER_CSS_CDN] = ['type' => 'external', 'minified' => TRUE];
+    }
+  }
+}