tinymce-custom-link-class.php

 <?php
/**
 * Plugin Name: TinyMCE Custom Link Class
 * Plugin URI: http://wpbeginner.com
 * Version: 1.0
 * Author: Tim Carr
 * Author URI: http://www.n7studios.co.uk
 * Description: A simple TinyMCE Plugin to add a custom link class in the Visual Editor
 * License: GPL2
 */

class TinyMCE_Custom_Link_Class {
	
	/**
	 * Constructor. Called when the plugin is initialised.
	 */
	function __construct() {
	
		if ( is_admin() ) {
			add_action( 'init', array( &$this, 'setup_tinymce_plugin' ) );
		}

	}

	/**
	 * Check if the current user can edit Posts or Pages, and is using the Visual Editor
	 * If so, add some filters so we can register our plugin
	 */
	function setup_tinymce_plugin() {

		// Check if the logged in WordPress User can edit Posts or Pages
		// If not, don't register our TinyMCE plugin
		if ( ! current_user_can( 'edit_posts' ) && ! current_user_can( 'edit_pages' ) ) {
	        return;
	    }

	    // Check if the logged in WordPress User has the Visual Editor enabled
		// If not, don't register our TinyMCE plugin
		if ( get_user_option( 'rich_editing' ) !== 'true' ) {
			return;
		}

		// Setup some filters
		add_filter( 'mce_external_plugins', array( &$this, 'add_tinymce_plugin' ) );
    	add_filter( 'mce_buttons', array( &$this, 'add_tinymce_toolbar_button' ) );
		
	}

	/**
     * Adds a TinyMCE plugin compatible JS file to the TinyMCE / Visual Editor instance
	 *
	 * @param array $plugin_array Array of registered TinyMCE Plugins
	 * @return array Modified array of registered TinyMCE Plugins
     */
	function add_tinymce_plugin( $plugin_array ) {

	    $plugin_array['custom_link_class'] = plugin_dir_url( __FILE__ ) . 'tinymce-custom-link-class.js';
	    return $plugin_array;

	}
    
    /**
     * Adds a button to the TinyMCE / Visual Editor which the user can click
     * to insert a link with a custom CSS class.
     *
     * @param array $buttons Array of registered TinyMCE Buttons
     * @return array Modified array of registered TinyMCE Buttons
     */
	function add_tinymce_toolbar_button( $buttons ) {

	    array_push( $buttons, '|', 'custom_link_class' );
	    return $buttons;

	}

}

$tinymce_custom_link_class = new TinyMCE_Custom_Link_Class;