WordPress Theme Switch Prevention

functions.php

/**
* Add this code to functions.php
* Modify as needed to prevent a WordPress theme from becoming active if one or more plugin dependencies are not found.
* If you know of a better way to detect if a plugin is installed and active, please share! ^_^
*/

// Intercept theme switch
add_action( 'after_switch_theme', 'check_theme_dependencies', 10, 2 );

/**
* Returns missing plugin names
* @return array
*/
function get_missing_plugins(){

  /**
  * Folder names of plugins, in this format:
  * 'Plugin Name for Error Message' => 'plugin-folder-name-lowercase'
  */
  $neededplugins = array(
    'Plugin Name' => 'plugin-name'
  );

  // Directories of each plugin's main file
  $siteplugins = array_map( 'strtolower', get_option('active_plugins') );
  $networkplugins = array_map( 'strtolower',
    str_replace( WP_PLUGIN_DIR . '/', '', wp_get_active_network_plugins())
  );
  $activeplugins = array_merge( $siteplugins, $networkplugins );

  // Missing plugins
  $missing = array();

  foreach($neededplugins as $key => $value){

    // Test each needed plugin against all active plugins
    $found = false;

    foreach($activeplugins as $plugin){

      // Compare needed plugin name to each active plugin name
      $match = preg_match('/^' . $value . '/', $plugin);

      if($match){

        // Needed plugin is active
        $found = true;

      }

    }

    // If needed plugin is not active, return its name
    if(!$found){

      $missing[$key] = $value;

    }

  }

  // Return array of missing plugin names
  return $missing;

}

/**
 * Revert theme and display error message if dependencies not met
 * @return void
 */
function check_theme_dependencies( $oldtheme_name, $oldtheme ) {

  // Get array of missing plugins
  $missing_plugins = $this->get_missing_plugins();

  if ( count( $missing_plugins ) > 0 ){

    // Update default admin notice: Theme not activated.
    add_filter( 'gettext', 'update_activation_admin_notice', 10, 3 );

    // Custom styling for default admin notice.
    add_action( 'admin_head', 'error_activation_admin_notice' );

    // Switch back to previous theme.
    switch_theme( $oldtheme->stylesheet );
      return false;

  }

}

/**
 * Replace success message with error
 * @return void
 */
function update_activation_admin_notice( $translated, $original, $domain ) {

  $message = 'Theme Switch Error. The following plugin(s) are not installed and active: %s. Restoring previous theme.';

  // Specify error
  $error = array();

  // Get array of missing plugins
  $missing_plugins = $this->get_missing_plugins();
  foreach($missing_plugins as $key => $value){
    $error[] = $key;
  }

  $message = sprintf($message, implode($error, ', '));
   
  $strings = array(
    'New theme activated.' => $message
  );

  if ( isset( $strings[$original] ) ) {

    // Translate but without running all the filters again.
    $translations = get_translations_for_domain( $domain );
    $translated = $translations->translate( $strings[$original] );

  }

  return $translated;
}

/**
 * Style success message as error
 * @since 1.1.6
 * @return void
 */
function error_activation_admin_notice() {

  echo '<style>#message2{border-left-color:#dc3232;}</style>';

}