Wordpress - force to refresh the cached TinyMCE editor style css file

force-to-refresh-tinymce-css.php

<?php
add_filter( 'mce_css', 'fresh_editor_style' );
function fresh_editor_style( $css ) {
  global $editor_styles;
  if ( empty ( $css ) or empty ( $editor_styles ) ) {
    return $css;
  }
  $mce_css   = array();
  $style_uri = get_stylesheet_directory_uri();
  $style_dir = get_stylesheet_directory();
  if ( is_child_theme() ) {
    $template_uri = get_template_directory_uri();
    $template_dir = get_template_directory();
    foreach ( $editor_styles as $key => $file ) {
      if ( $file && file_exists( "$template_dir/$file" ) ) {
        $mce_css[] = add_query_arg(
          'version',
          filemtime( "$template_dir/$file" ),
          "$template_uri/$file"
        );
      }
    }
  }
  foreach ( $editor_styles as $file ) {
    if ( $file && file_exists( "$style_dir/$file" ) ) {
      $mce_css[] = add_query_arg(
        'version',
        filemtime( "$style_dir/$file" ),
        "$style_uri/$file"
      );
    }
  }
  return implode( ',', $mce_css );
}
?>