<?php
/*
Plugin Name: wp-shortslug
Plugin URI: https://github.com/petermolnar/wp-shortslug
Description: reversible automatic short slug based on post pubdate epoch
Version: 0.4.1
Author: Peter Molnar <hello@petermolnar.eu>
Author URI: http://petermolnar.eu/
License: GPLv3
Required minimum PHP version: 5.3
*/

/*  Copyright 2015 Peter Molnar ( hello@petermolnar.eu )

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License, version 3, as
    published by the Free Software Foundation.

    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
*/

namespace WP_SHORTSLUG;

define (
	'WP_SHORTSLUG\base',
	'0123456789abcdefghijklmnopqrstuvwxyz'
);
define (
	'WP_SHORTSLUG\base_camel',
	'0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
);


\register_activation_hook( __FILE__ , 'WP_SHORTSLUG\plugin_activate' );

// init all the things!
\add_action( 'init', 'WP_SHORTSLUG\init' );

// replace shortlink
\add_action( 'wp_head', 'WP_SHORTSLUG\shortlink');

// trigger fallback redirection by _wp_old_slug
\add_action( 'wp_head', 'WP_SHORTSLUG\try_redirect' );

// register new posts
\add_action(
	"transition_post_status",
	'WP_SHORTSLUG\maybe_generate_slug',
	1,
	3
);
\add_action(
	"transition_post_status",
	'WP_SHORTSLUG\check_shorturl',
	2,
	3
);

/**
 *
 */
function init() {
	// shortlink replacement
	\add_filter( 'get_shortlink', 'WP_SHORTSLUG\shorturl', 1, 1 );
}

/**
 * activate hook
 */
function plugin_activate() {
	if ( version_compare( phpversion(), 5.3, '<' ) ) {
		die( 'The minimum PHP version required for this plugin is 5.3' );
	}
}

/**
 * try to redirect by old slug in case the current result is 404
 *
 */
function try_redirect () {
	global $wp_query;
	if ($wp_query->is_404 == true) {
		\wp_old_slug_redirect();
	}
}

/**
 * absolute short url
 *
 */
function shorturl ( $shortlink = '' ) {
	global $post;
	$post = fix_post($post);

	if ($post === false )
		return $shortlink;

	$url = shortslug($post);

	if ( defined ('\SHORTSLUG_BASE') )
		$base = \SHORTSLUG_BASE . '/';
	else
		$base = rtrim( \get_bloginfo('url'), '/' ) . '/';

	return $base.$url;
}

/**
 * print meta shortlink
 *
 */
function shortlink () {
	if ( function_exists('\is_singular') && \is_singular() ) {
		$url = shorturl();
		if ( !empty($url) ) {
			printf ('<link rel="shortlink" href="%s" />%s', shorturl() , "\n");
		}
	}
}

/**
 *
 */
function shortslug ( &$post ) {
	$post = fix_post($post);

	if ($post === false)
		return false;

	$epoch = \get_the_time('U', $post->ID);
	$url36 = epoch2url($epoch);

	return $url36;
}

/**
 * since WordPress has it's built-in rewrite engine, it's eaiser to use
 * that for adding the short urls
 */
function check_shorturl( $new_status, $old_status, $post ) {
	$post = fix_post($post);

	if ($post === false)
		return false;

	$meta = \get_post_meta( $post->ID, '_wp_old_slug', false);
	$url36 = shortslug($post);
	$epoch = \get_the_time('U', $post->ID);
	$checked = array();

	foreach ($meta as $key => $slug ) {
		if ( empty ($slug) ) {
			debug( "there was an empty slug for '{$key}', deleting it early", 4 );
			\delete_post_meta($post->ID, '_wp_old_slug', $slug);
			continue;
		}

		if ( ! in_array( $slug, $checked ) ) {
			array_push ( $checked, $slug );
		}
		else {
			debug( "deleting slug '{$slug}' from #{$post->ID} - duplicate", 4 );
			\delete_post_meta($post->ID, '_wp_old_slug', $slug);
			unset($meta[$key]);
		}

		$decoded = url2epoch( $slug );
		if ( ! is_numeric( $decoded ) || empty( $decoded ) || $decoded > time() ) {
			continue;
		}

		// base36 matches which are older than the publish date should be deleted
		if ( preg_match('/^[0-9a-z]{5,6}$/', $slug) &&
				 $decoded < $epoch &&
				 $slug != $url36
			) {
			debug( "deleting slug '{$slug}' from #{$post->ID} "
				. "- it's older than publish date so it can't be in use", 4 );
			\delete_post_meta( $post->ID, '_wp_old_slug', $slug );
			unset($meta[$key]);
		}
	}

	// back away at this point if this post is not yet published
	if ( 'publish' != $new_status )
		return false;

	// if the generated url is the same as the current slug, walk away
	if ( $url36 == $post->post_name )
		return true;

	/*
	 * there should be only our shorturl living here, so in case
	 * WP did something nasty, clean up the too many shortslugs
	 *
	 * 3 is a by-the-guts number; posts with more then 3 _wp_old_slug,
	 * matching the criteria of lowecase-with-nums, 5 at max 6 char length
	 * shouldn't really exist
	 *
	 * also do this if this is a fresh post publish to clean up leftovers
	 *
	 *
	if ( count($meta) > 3 ) ) {
		foreach ($meta as $key => $slug ) {
			// base36 matches
			if (preg_match('/^[0-9a-z]{5,6}$/', $slug)) {
				debug('deleting slug ' . $slug . ' from ' . $post->ID );
				delete_post_meta($post->ID, '_wp_old_slug', $slug);
				unset($meta[$key]);
			}
		}
	}
	*/
	debug("generated slug for #{$post->ID}: '{$url36}'", 6 );
	// if we somehow deleted the actual slug, fix it
	if ( !in_array($url36,$meta)) {
		debug( "adding slug {$url36} to {$post->ID}", 6 );
		\add_post_meta($post->ID, '_wp_old_slug', $url36);
	}

	return true;
}

/**
 * since WordPress has it's built-in rewrite engine, it's eaiser to use
 * that for adding the short urls
 */
function maybe_generate_slug( $new_status, $old_status, $post ) {
	$post = fix_post($post);

	if ($post === false)
		return false;

	// auto-generated slug for empty title; this we should replace
	$pattern = '/^' . $post->ID . '-[0-9]$/';

	if ( ! preg_match( $pattern, $post->post_name ) && ! empty( $post->post_title ) ) {
		return false;
	}
	else {
		debug( "post {$post->ID} name is {$post->post_name} which matches"
			." pattern {$pattern} or the post_title is empty,"
			." so shortslug is required.", 6 );
	}

	// generate new
	$url36 = shortslug($post);
	debug( "replacing slug of {$post->ID} with shortslug: {$url36}", 5 );

	// save old, just in case
	\add_post_meta( $post->ID, '_wp_old_slug', $post->post_name );

	/*
	 * this is depricated, but I'll leave it in the code for the future me:
	 * in case you use wp_update_post, it will trigger a post transition, so
	 * that will trigger _everything_ that hooks to that, which is not what we
	 * want. In that case we'll end up with a duplicate event, for both the old
	 * and the new slug and, for example, in a webmention hook's case that is
	 * far from ideal.

	$_post = array(
		'ID' => $post->ID,
		'post_name' => $url36,
	);

	$wp_error = false;
	wp_update_post( $_post, $wp_error );

	if (is_wp_error($wp_error)) {
		$errors = json_encode($post_id->get_error_messages());
		debug( $errors );
	}
	*/

	global $wpdb;
	$dbname = "{$wpdb->prefix}posts";
	$req = false;

	debug( "Updating post slug for #{$post->ID}", 5);

	$q = $wpdb->prepare( "UPDATE `{$dbname}` SET `post_name`='%s' WHERE ".
		"`ID`='{$post->ID}' LIMIT 1", $url36 );

	try {
		$req = $wpdb->query( $q );
	}
	catch (Exception $e) {
		debug('Something went wrong: ' . $e->getMessage(), 4);
	}


	$meta = \get_post_meta( $post->ID, '_wp_old_slug', false);
	if ( in_array( $url36, $meta ) ) {
		debug( "removing slug {$url36} from {$post->ID}", 5 );
		\delete_post_meta($post->ID, '_wp_old_slug', $url36);
	}

	return true;
}


/**
 * decode short string and covert it back to UNIX EPOCH
 *
 */
function url2epoch( $str, $b = 36 ) {

	if ( empty ( $str ) ) {
		debug( 'url2epoch to empty string to match; trace: '
		 . json_encode( debug_backtrace() )
		);
		return false;
	}

	if ($b <= 36 )
		$base = base;
	else
		$base = base_camel;

	$limit = strlen($str);
	$res=strpos($base,$str[0]);
	for($i=1;$i<$limit;$i++) {
		$res = $b * $res + strpos($base,$str[$i]);
	}

	return $res;
}

/**
 * convert UNIX EPOCH to short string
 *
 * thanks to https://stackoverflow.com/questions/4964197/
 *
 */
function epoch2url($num, $b = 36 ) {

	if ($b <= 36 )
		$base = base;
	else
		$base = base_camel;

	$r = $num  % $b ;
	$res = $base[$r];
	$q = floor($num/$b);
	while ($q) {
		$r = $q % $b;
		$q =floor($q/$b);
		$res = $base[$r].$res;
	}

	return $res;
}

/**
 * do everything to get the Post object
 */
function fix_post ( &$post = null ) {
	if ($post === null || !is_post($post))
		global $post;

	if (is_post($post))
		return $post;

	return false;
}

/**
 * test if an object is actually a post
 */
function is_post ( &$post ) {
	if ( ! empty( $post ) &&
			 is_object( $post ) &&
			 isset( $post->ID ) &&
			 ! empty( $post->ID ) )
		return true;

	return false;
}

/**
 *
 * debug messages; will only work if WP_DEBUG is on
 * or if the level is LOG_ERR, but that will kill the process
 *
 * @param string $message
 * @param int $level
 *
 * @output log to syslog | wp_die on high level
 * @return false on not taking action, true on log sent
 */
function debug( $message, $level = LOG_NOTICE ) {
	if ( empty( $message ) )
		return false;

	if ( @is_array( $message ) || @is_object ( $message ) )
		$message = json_encode($message);

	$levels = array (
		LOG_EMERG => 0, // system is unusable
		LOG_ALERT => 1, // Alert 	action must be taken immediately
		LOG_CRIT => 2, // Critical 	critical conditions
		LOG_ERR => 3, // Error 	error conditions
		LOG_WARNING => 4, // Warning 	warning conditions
		LOG_NOTICE => 5, // Notice 	normal but significant condition
		LOG_INFO => 6, // Informational 	informational messages
		LOG_DEBUG => 7, // Debug 	debug-level messages
	);

	// number for number based comparison
	// should work with the defines only, this is just a make-it-sure step
	$level_ = $levels [ $level ];

	// in case WordPress debug log has a minimum level
	if ( defined ( '\WP_DEBUG_LEVEL' ) ) {
		$wp_level = $levels [ \WP_DEBUG_LEVEL ];
		if ( $level_ > $wp_level ) {
			return false;
		}
	}

	// ERR, CRIT, ALERT and EMERG
	if ( 3 >= $level_ ) {
		\wp_die( '<h1>Error:</h1>' . '<p>' . $message . '</p>' );
		exit;
	}

	$trace = debug_backtrace();
	$caller = $trace[1];
	$parent = $caller['function'];

	if (isset($caller['class']))
		$parent = $caller['class'] . '::' . $parent;

	return error_log( "{$parent}: {$message}" );
}