plugin.php

<?php
/*
Plugin Name: Fuzzy Keyword Suggestions
Plugin URI: https://github.com/philhagen/ltc-fuzzy-keyword-suggestions
Description: This plugin performs a levenshtein string lookup for any short url which does not appear in the database, then presents a list of possible matches
Version: 1.1
Author: Phil Hagen
Author URI: http://lewestech.com
*/

# no direct calls to this script allowed
if( !defined( 'YOURLS_ABSPATH' ) ) die();

yourls_add_action( 'redirect_keyword_not_found', 'ltc_fuzzy_suggest' );
yourls_add_action( 'loader_failed', 'ltc_fuzzy_suggest' );
function ltc_fuzzy_suggest($ltc_request) {
    if ($_SERVER['REQUEST_URI'] == '/') {
        # homepage redirect
        $keyword_supplied = FALSE;

    } else {
        $keyword_supplied = TRUE;
        header('X-PHP-Response-Code: 404', true, 404);

        global $ydb;
        $table_url = YOURLS_DB_TABLE_URL;

        $ltc_keyword = yourls_sanitize_keyword($ltc_request[0]);

        $sql = "SELECT keyword, url, title, LEVENSHTEIN(:keyword, keyword) AS `lev_dist` FROM `$table_url` HAVING `lev_dist` < 3 ORDER BY `lev_dist` DESC";
        $binds = array('keyword' => $ltc_keyword);
        $query = $ydb->fetchObjects($sql, $binds);

        if ($query) {
            $suggested_results = TRUE;

        } else {
            $suggested_results = FALSE;
        }
    }

    $default_template_file = dirname( __FILE__ ) . '/template-default.php';
    $custom_template_file = dirname( __FILE__ ) . '/template.php';

    if (file_exists($custom_template_file)) {
        require($custom_template_file);

    } else {
        require($default_template_file);
    }

    die();
}

# handle activation - determine if there is a LEVENSHTEIN() MySQL function available
yourls_add_action( 'activated_'.yourls_plugin_basename( __FILE__ ), 'ltc_fuzzy_keyword_suggestions_setup' );
function ltc_fuzzy_keyword_suggestions_setup() {
    global $ydb;
    $sql = "SELECT LEVENSHTEIN('teststring1', 'teststring2') AS lev_dist";
    $binds = array();
    $query = $ydb->fetchValue($sql, $binds);

    if (!$query) {
        $levenshtein_test_pass = FALSE;
    } else {
        $lev_test_dist = $query[0]->lev_dist;
        if ($lev_test_dist == 1) {
            $levenshtein_test_pass = TRUE;
        } else {
            $levenshtein_test_pass = FALSE;
        }
    }

    # if the test fails (due to lack of a levenshtein() function or incorrect results), display an error message.
    # then, deactivate the plugin.
    if (!$levenshtein_test_pass) {
        $msg = 'ERROR: MySQL "LEVENSHTEIN()" function not present or could not be verified.<br>
        See the following pages for potential solutions:
        <ul><li><a href="https://github.com/jmcejuela/Levenshtein-MySQL-UDF" target="_blank">GitHub user jmcejuela\'s User-Defined Function (UDF)</a></li>
        <li><a href="http://stackoverflow.com/questions/12617348/mysql-levenshtein" target="_blank">Create a function within MySQL</a><br>
        (Also see the <tt>mysql_levenshtein_function.sql</tt> file included with this plugin.)</li></ul>
        <strong>Note</strong>: UDF module has shown 500-1000x faster performance than the SQL function.
        Plugin failed to activate.<br>';

        yourls_deactivate_plugin( __FILE__ );

        $result = yourls_deactivate_plugin( __FILE__ );
        if( $result === true ) {
            yourls_redirect( yourls_admin_url( 'plugins.php?success=deactivated' ), 302 );
        }
    }
}

?>