uninstall.php

<?php

if (defined('WP_UNINSTALL_PLUGIN')) {
  // multisite uninstall
  if (function_exists('is_multisite') && is_multisite()) {
    global $wpdb;
    $old_blog =  $wpdb->blogid;

    // get all blog ids
    $blogids =  $wpdb->get_col('SELECT blog_id FROM ' .  $wpdb->blogs);

    foreach ($blogids as $blog_id) {
      switch_to_blog($blog_id);
      removeDatabaseTables();
    }

    switch_to_blog($old_blog);
  }

  // uninstall from regular site
  removeDatabaseTables();

  // remove file directories
  removeFiles((wp_upload_dir())['basedir'] . '/utubevideo-cache');
}

function removeDatabaseTables()
{
  global $wpdb;

  $wpdb->query('DROP TABLE ' . $wpdb->prefix . 'utubevideo_playlist');
  $wpdb->query('DROP TABLE ' . $wpdb->prefix . 'utubevideo_video');
  $wpdb->query('DROP TABLE ' . $wpdb->prefix . 'utubevideo_album');
  $wpdb->query('DROP TABLE ' . $wpdb->prefix . 'utubevideo_dataset');

  delete_option('utubevideo_main_opts');
}

function removeFiles($dir)
{
  foreach (glob($dir . '/*') as $file) {
    if (is_dir($file))
      rrmdir($file);
    else
      unlink($file);
  }

  rmdir($dir);
}