<?php namespace System;

class Crypt {

	/**
	 * The encryption cipher.
	 *
	 * @var string
	 */
	public static $cipher = 'rijndael-256';

	/**
	 * The encryption mode.
	 *
	 * @var string
	 */
	public static $mode = 'cbc';

	/**
	 * Encrypt a value using the MCrypt library.
	 *
	 * @param  string  $value
	 * @return string
	 */
	public static function encrypt($value)
	{
		$iv = mcrypt_create_iv(static::iv_size(), static::randomizer());

		return base64_encode($iv.mcrypt_encrypt(static::$cipher, static::key(), $value, static::$mode, $iv));
	}

	/**
	 * Get the random number source available to the OS.
	 *
	 * @return int
	 */
	protected static function randomizer()
	{
		if (defined('MCRYPT_DEV_URANDOM'))
		{
			return MCRYPT_DEV_URANDOM;
		}
		elseif (defined('MCRYPT_DEV_RANDOM'))
		{
			return MCRYPT_DEV_RANDOM;
		}

		return MCRYPT_RAND;
	}

	/**
	 * Decrypt a value using the MCrypt library.
	 *
	 * @param  string  $value
	 * @return string
	 */
	public static function decrypt($value)
	{
		if ( ! is_string($value = base64_decode($value, true)))
		{
			throw new \Exception('Decryption error. Input value is not valid base64 data.');
		}

		list($iv, $value) = array(substr($value, 0, static::iv_size()), substr($value, static::iv_size()));

		return rtrim(mcrypt_decrypt(static::$cipher, static::key(), $value, static::$mode, $iv), "\0");
	}

	/**
	 * Get the application key from the application configuration file.
	 *
	 * @return string
	 */
	private static function key()
	{
		if ( ! is_null($key = Config::get('application.key')) and $key !== '') return $key;

		throw new \Exception("The encryption class can not be used without an encryption key.");
	}

	/**
	 * Get the input vector size for the cipher and mode.
	 *
	 * Different ciphers and modes use varying lengths of input vectors.
	 *
	 * @return int
	 */
	private static function iv_size()
	{
		return mcrypt_get_iv_size(static::$cipher, static::$mode);
	}

}