<?php
/**
 * Zend Framework (http://framework.zend.com/)
 *
 * @link      http://github.com/zendframework/zf2 for the canonical source repository
 * @copyright Copyright (c) 2005-2013 Zend Technologies USA Inc. (http://www.zend.com)
 * @license   http://framework.zend.com/license/new-bsd New BSD License
 */

namespace Zend\Crypt;

/**
 * PHP implementation of the RFC 2104 Hash based Message Authentication Code
 */
class Hmac
{
    const OUTPUT_STRING = false;
    const OUTPUT_BINARY = true;

    /**
     * Last algorithm supported
     *
     * @var string|null
     */
    protected static $lastAlgorithmSupported;

    /**
     * Performs a HMAC computation given relevant details such as Key, Hashing
     * algorithm, the data to compute MAC of, and an output format of String,
     * or Binary.
     *
     * @param  string  $key
     * @param  string  $hash
     * @param  string  $data
     * @param  bool $output
     * @throws Exception\InvalidArgumentException
     * @return string
     */
    public static function compute($key, $hash, $data, $output = self::OUTPUT_STRING)
    {

        if (empty($key)) {
            throw new Exception\InvalidArgumentException('Provided key is null or empty');
        }

        if (!$hash || ($hash !== static::$lastAlgorithmSupported && !static::isSupported($hash))) {
            throw new Exception\InvalidArgumentException(
                "Hash algorithm is not supported on this PHP installation; provided '{$hash}'"
            );
        }

        return hash_hmac($hash, $data, $key, $output);
    }

    /**
     * Get the output size according to the hash algorithm and the output format
     *
     * @param  string  $hash
     * @param  bool $output
     * @return int
     */
    public static function getOutputSize($hash, $output = self::OUTPUT_STRING)
    {
        return strlen(static::compute('key', $hash, 'data', $output));
    }

    /**
     * Get the supported algorithm
     *
     * @return array
     */
    public static function getSupportedAlgorithms()
    {
        return hash_algos();
    }

    /**
     * Is the hash algorithm supported?
     *
     * @param  string $algorithm
     * @return bool
     */
    public static function isSupported($algorithm)
    {
        if ($algorithm === static::$lastAlgorithmSupported) {
            return true;
        }

        if (in_array(strtolower($algorithm), hash_algos(), true)) {
            static::$lastAlgorithmSupported = $algorithm;
            return true;
        }

        return false;
    }

    /**
     * Clear the cache of last algorithm supported
     */
    public static function clearLastAlgorithmCache()
    {
        static::$lastAlgorithmSupported = null;
    }
}
