<?php
/**
 * Random_* Compatibility Library
 * for using the new PHP 7 random_* API in PHP 5 projects
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2015 - 2017 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.
 */
defined('BASEPATH') OR exit('No direct script access allowed');

if (!is_callable('random_int'))
{
	/**
	 * Fetch a random integer between $min and $max inclusive
	 *
	 * @param int $min
	 * @param int $max
	 *
	 * @throws Exception
	 *
	 * @return int
	 */
	function random_int($min, $max)
	{
		/**
		 * Type and input logic checks
		 *
		 * If you pass it a float in the range (~PHP_INT_MAX, PHP_INT_MAX)
		 * (non-inclusive), it will sanely cast it to an int. If you it's equal to
		 * ~PHP_INT_MAX or PHP_INT_MAX, we let it fail as not an integer. Floats
		 * lose precision, so the <= and => operators might accidentally let a float
		 * through.
		 */
		
		try
		{
			$min = RandomCompat_intval($min);
		}
		catch (TypeError $ex)
		{
			throw new TypeError('random_int(): $min must be an integer');
		}
		
		try
		{
			$max = RandomCompat_intval($max);
		}
		catch (TypeError $ex)
		{
			throw new TypeError('random_int(): $max must be an integer');
		}
		
		/**
		 * Now that we've verified our weak typing system has given us an integer,
		 * let's validate the logic then we can move forward with generating random
		 * integers along a given range.
		 */
		if ($min > $max)
		{
			throw new Error('Minimum value must be less than or equal to the maximum value');
		}
		
		if ($max === $min)
		{
			return (int) $min;
		}
		
		/**
		 * Initialize variables to 0
		 *
		 * We want to store:
		 * $bytes => the number of random bytes we need
		 * $mask => an integer bitmask (for use with the &) operator
		 *          so we can minimize the number of discards
		 */
		$attempts = $bits = $bytes = $mask = $valueShift = 0;
		
		/**
		 * At this point, $range is a positive number greater than 0. It might
		 * overflow, however, if $max - $min > PHP_INT_MAX. PHP will cast it to
		 * a float and we will lose some precision.
		 */
		$range = $max - $min;
		
		/**
		 * Test for integer overflow:
		 */
		if (!is_int($range))
		{
			
			/**
			 * Still safely calculate wider ranges.
			 * Provided by @CodesInChaos, @oittaa
			 *
			 * @ref https://gist.github.com/CodesInChaos/03f9ea0b58e8b2b8d435
			 *
			 * We use ~0 as a mask in this case because it generates all 1s
			 *
			 * @ref https://eval.in/400356 (32-bit)
			 * @ref http://3v4l.org/XX9r5  (64-bit)
			 */
			$bytes = PHP_INT_SIZE;
			$mask  = ~0;
			
		}
		else
		{
			
			/**
			 * $bits is effectively ceil(log($range, 2)) without dealing with
			 * type juggling
			 */
			while ($range > 0)
			{
				if ($bits % 8 === 0)
				{
					++$bytes;
				}
				++$bits;
				$range >>= 1;
				$mask = $mask << 1 | 1;
			}
			$valueShift = $min;
		}
		
		$val = 0;
		/**
		 * Now that we have our parameters set up, let's begin generating
		 * random integers until one falls between $min and $max
		 */
		do
		{
			/**
			 * The rejection probability is at most 0.5, so this corresponds
			 * to a failure probability of 2^-128 for a working RNG
			 */
			if ($attempts > 128)
			{
				throw new Exception('random_int: RNG is broken - too many rejections');
			}
			
			/**
			 * Let's grab the necessary number of random bytes
			 */
			$randomByteString = random_bytes($bytes);
			
			/**
			 * Let's turn $randomByteString into an integer
			 *
			 * This uses bitwise operators (<< and |) to build an integer
			 * out of the values extracted from ord()
			 *
			 * Example: [9F] | [6D] | [32] | [0C] =>
			 *   159 + 27904 + 3276800 + 201326592 =>
			 *   204631455
			 */
			$val &= 0;
			for ($i = 0; $i < $bytes; ++$i)
			{
				$val |= ord($randomByteString[$i]) << ($i * 8);
			}
			
			/**
			 * Apply mask
			 */
			$val &= $mask;
			$val += $valueShift;
			
			++$attempts;
			/**
			 * If $val overflows to a floating point number,
			 * ... or is larger than $max,
			 * ... or smaller than $min,
			 * then try again.
			 */
		} while (!is_int($val) || $val > $max || $val < $min);
		
		return (int) $val;
	}
}
