<?php
/*
Plugin Name: ETH Simple Shortlinks
Plugin URI: https://ethitter.com/plugins/
Description: Simple non-GET shortlinks using post IDs
Author: Erick Hitter
Version: 0.1
Author URI: https://ethitter.com/

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

class ETH_Simple_Shortlinks {
	/**
	 * PLUGIN SETUP
	 */

	/**
	 * Singleton
	 */
	private static $instance = null;

	/**
	 * Instantiate singleton
	 */
	public static function get_instance() {
		if ( ! is_a( self::$instance, __CLASS__ ) ) {
			self::$instance = new self;
		}

		return self::$instance;
	}

	/**
	 * Dummy magic methods
	 */
	public function __clone() {_doing_it_wrong( __FUNCTION__, 'Cheatin&#8217; huh?', '0.1' ); }
	public function __wakeup() { _doing_it_wrong( __FUNCTION__, 'Cheatin&#8217; huh?', '0.1' ); }
	public function __call( $name = '', $args = array() ) { unset( $name, $args ); return null; }

	/**
	 * Class properties
	 */
	private $qv = 'eth-shortlink';

	/**
	 *
	 */
	private function __construct() {
		add_action( 'init', array( $this, 'add_rewrite_rule' ) );
		add_filter( 'query_vars', array( $this, 'filter_query_vars' ) );
		add_action( 'parse_request', array( $this, 'action_parse_request' ) );
	}

	/**
	 * Register rewrite rule
	 */
	public function add_rewrite_rule() {
		add_rewrite_rule( '^p/([\d]+)/?$', 'index.php?p=$matches[1]&' . $this->qv . '=1', 'top' );
	}

	/**
	 * Add custom query var to those permitted, so it can be detected at `parse_request`
	 */
	public function filter_query_vars( $qv ) {
		$qv[] = $this->qv;

		return $qv;
	}

	/**
	 * Catch this plugin's requests and issue redirects, otherwise WP will serve content at duplicate URLs
	 */
	public function action_parse_request( $request ) {
		if ( isset( $request->query_vars[ $this->qv ] ) ) {
			$home_url = user_trailingslashit( home_url() );

			$dest = get_permalink( $request->query_vars['p'] );

			if ( $dest ) {
				$dest   = wp_validate_redirect( $dest, $home_url );
				$status = 301;
			} else {
				$dest   = $home_url;
				$status = 302;
			}

			wp_redirect( $dest, $status );
			exit;
		}
	}
}

ETH_Simple_Shortlinks::get_instance();