<?php
/**
 * Random_* Compatibility Library 
 * for using the new PHP 7 random_* API in PHP 5 projects
 * 
 * The MIT License (MIT)
 * 
 * Copyright (c) 2015 Paragon Initiative Enterprises
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

/**
 * Windows with PHP < 5.3.0 will not have the function
 * openssl_random_pseudo_bytes() available, so let's use
 * CAPICOM to work around this deficiency.
 * 
 * @param int $bytes
 * 
 * @throws Exception
 * 
 * @return string
 */
function random_bytes($bytes)
{
    try {
        $bytes = RandomCompat_intval($bytes);
    } catch (TypeError $ex) {
        throw new TypeError(
            'random_bytes(): $bytes must be an integer'
        );
    }

    if ($bytes < 1) {
        throw new Error(
            'Length must be greater than 0'
        );
    }

    $buf = '';
    $util = new COM('CAPICOM.Utilities.1');
    $execCount = 0;

    /**
     * Let's not let it loop forever. If we run N times and fail to
     * get N bytes of random data, then CAPICOM has failed us.
     */
    do {
        $buf .= base64_decode($util->GetRandom($bytes, 0));
        if (RandomCompat_strlen($buf) >= $bytes) {
            /**
             * Return our random entropy buffer here:
             */
            return RandomCompat_substr($buf, 0, $bytes);
        }
        ++$execCount; 
    } while ($execCount < $bytes);

    /**
     * If we reach here, PHP has failed us.
     */
    throw new Exception(
        'Could not gather sufficient random data'
    );
}