List Pages Shortcode Index - Create alphabetically indexes using the List Pages Shortcode plugin (http://wordpress.org/extend/plugins/list-pages-shortcode/)

list-pages-shortcode-index.php

<?php

/*
Plugin Name: List Pages Shortcode Index
Plugin URI: https://gist.github.com/benhuson/9c419282d8e05fff6eeb
Description: Add-on for the <a href="https://wordpress.org/plugins/list-pages-shortcode/">List Pages Shortcode</a> plugin.
Author: Ben Huson
Version: 0.1
Author URI: https://github.com/benhuson
*/

/**
 * Allows you to add an 'index' attribute to the List Pages Shortcode plugin.
 * https://wordpress.org/plugins/list-pages-shortcode/
 * Example usage:
 *
 * [list-pages sort_order="ASC" sort_column="post_title" index="0123456789ABCDEF" title_li="A-F" /]
 * [list-pages sort_order="ASC" sort_column="post_title" index="FGHIJKLM" title_li="F-M" /]
 * [list-pages sort_order="ASC" sort_column="post_title" index="NOPQRST" title_li="N-T" /]
 * [list-pages sort_order="ASC" sort_column="post_title" index="UVWXYZ" title_li="U-Z" /]
 */
class List_Pages_Shortcode_Index {

	protected $index = '';

	/**
	 * Setup Actions
	 */
	public function __construct() {
		add_action( 'shortcode_list_pages_before', array( $this, 'shortcode_list_pages_before' ) );
		add_action( 'shortcode_list_pages_after', array( $this, 'shortcode_list_pages_after' ) );
	}

	/**
	 * Filter the pages
	 *
	 * @param   array  $pages  Pages.
	 * @param   array  $r      List page args.
	 * @return  array          Filtered pages.
	 */
	public function shortcode_list_pages_get_pages( $pages, $r ) {
		$filtered_pages = array();

		// If no characters, return all pages
		if ( empty( $this->index ) || 0 == $r['depth'] ) {
			return $pages;
		}

		// Filter pages
		foreach ( $pages as $page ) {
			$character = strtolower( substr( $page->post_title, 0, 1 ) );
			if ( strpos( $this->index, $character ) !== false ) {
				$filtered_pages[] = $page;
			}
		}

		return $filtered_pages;
	}

	/**
	 * Filter page args
	 *
	 * @param   array  $args  List pages args.
	 * @return  array         Filtered args.
	 */
	public function shortcode_list_pages_attributes( $args ) {

		// If index is set we can currently only handle one depth, not nested lists
		if ( ! empty(  $this->index ) ) {
			$args['depth'] = 1;
		}

		return $args;
	}

	/**
	 * Store index characters and setup pages filter.
	 *
	 * @param   array  $atts  Shortcode attributes.
	 */
	public function shortcode_list_pages_before( $atts ) {

		// Store characters to index
		$this->index = '';
		if ( isset( $atts['index'] ) ) {
			$this->index = strtolower( $atts['index'] );
		}

		add_filter( 'shortcode_list_pages_attributes', array( $this, 'shortcode_list_pages_attributes' ), 10, 1 );
		add_filter( 'get_pages', array( $this, 'shortcode_list_pages_get_pages' ), 10, 2 );
	}

	/**
	 * Remove pages filter.
	 *
	 * @param   array  $atts  Shortcode attributes.
	 */
	public function shortcode_list_pages_after( $atts ) {
		remove_filter( 'shortcode_list_pages_attributes', array( $this, 'shortcode_list_pages_attributes' ), 10, 1 );
		remove_filter( 'get_pages', array( $this, 'shortcode_list_pages_get_pages' ), 10, 2 );
	}

}

global $list_pages_shortcode_index;
$list_pages_shortcode_index = new List_Pages_Shortcode_Index();