Files for simple url shortener in PHP and MySQL

.htaccess

#just add comment
RewriteEngine On
RewriteBase /
RewriteRule ^shorten/(.*)$ shorten.php?url=$1 [L,QSA]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?code=$1 [L,QSA]

config.php

<?php
$config = array();

//MySQL config values
$config['mysql_host'] = 'localhost';
$config['mysql_user'] = 'shortener';
$config['mysql_password'] = 'shortener password';
$config['mysql_db'] = 'shortener';

//website to use app on
$config['domain'] = 'http://shorte.en/';
?>

database.sql

CREATE TABLE IF NOT EXISTS `shortener` (
  `shortcode` char(5) COLLATE utf8_unicode_ci NOT NULL,
  `real_url` text(255) COLLATE utf8_unicode_ci NOT NULL,
  `date_added` datetime NOT NULL,
  `visits` bigint(20) NOT NULL DEFAULT '0',
  PRIMARY KEY (`shortcode`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

functions.php

<?php

/**
 * create short url either by generating short code or splitting it up and using the last part as short url
 * 
 * @param string $url long url to be shortened
 * @param boolean $compact if we should compact last part to 5 characters
 * @return string
 */
function getShortURL($url, $compact = true) {

    //use urls last part as is for short code
    if(!$compact) {
        $url_parts = parse_url($url);
        $short_url = str_replace('www.', '', $url_parts['host']).'-';
        $parts = array_reverse(explode('/', $url_parts['path']));
        $short_url .= preg_replace('/[^a-z0-9_-\.]/i', '', str_replace('-', '_', $parts[0]));
    } else {
        $short_url = substr(hash('sha512', time()), 0, 5);
    }

    $i = 0;
    $original_short_url = $short_url;

    while(isOccupied($short_url)) {
        if($i > 0) {
            if($compact) {
                $short_url = substr(hash('sha512', time()), 0, 5);
            } else {
                $short_url = $original_short_url.'_'.$i;
            }
        }
        $i++;
    }

    return $short_url;
}

/**
 * returns true if selected short url is occupied
 * 
 * @param string $str
 * @return boolean
 */
function isOccupied($str) {
    global $db;
    $query = "SELECT COUNT(*) FROM shortener WHERE shortcode = '{$str}'";
    $result = $db->query($query);
    $rows = $result->fetch_array();
    return  $rows[0] === 1;
}

index.php

<?php 
require 'config.php';

if (isset($_GET['code'])) {

    $code = strip_tags(strtolower($_GET['code']));

    $db = new MySQLi($config['mysql_host'], $config['mysql_user'], $config['mysql_password'], $config['mysql_db']);
    $db->set_charset('utf8');

    $escapedCode = $db->real_escape_string($code);
    $redirectResult = $db->query('SELECT real_url FROM shortener WHERE shortcode = "' . $escapedCode . '"');

    if ($redirectResult && $redirectResult->num_rows > 0) {
        $db->query('UPDATE shortener SET visits = visits + 1 WHERE shortcode = "' . $escapedCode . '"');
        $url = $redirectResult->fetch_object()->real_url;
    } else {
        die('No such url found!');
    }

    $db->close();
    header('Location: ' . $url, null, 301);
    exit;
}
?>

shorten.php

<?php
require 'config.php';
require 'functions.php';

header('Content-Type: text/plain;charset=UTF-8');

$url = isset($_GET['url']) ? urldecode(trim($_GET['url'])) : '';

if (!filter_var($url, FILTER_VALIDATE_URL)) {
    die('Enter a URL.');  
} 

$db = new mysqli($config['mysql_host'], $config['mysql_user'], $config['mysql_password'], $config['mysql_db']); 
$db->set_charset('utf8');

$url = $db->real_escape_string($url);

$result = $db->query('SELECT shortcode FROM shortener WHERE real_url = "' . $url . '" LIMIT 1');
// If there’s already a short URL for this URL
if ($result && $result->num_rows > 0) { 
    die($config['website'] . $result->fetch_object()->shortcode);
} else {
        $shortcode = getShortURL($url);
        if ($db->query('INSERT INTO shortener (shortcode, real_url, date_added, visits) VALUES ("' . $shortcode . '", "' . $url . '", NOW(), 0)')) {
            header('HTTP/1.1 201 Created');
            echo $config['website'] . $shortcode;

        }
}
?>