<?php

namespace Leenooks\OpenPGP;

use Leenooks\OpenPGP;

class S2K
{
	public $type, $hash_algorithm, $salt, $count;

	function __construct($salt='BADSALT',$hash_algorithm=10,$count=65536,$type=3)
	{
		$this->type = $type;
		$this->hash_algorithm = $hash_algorithm;
		$this->salt = $salt;
		$this->count = $count;
	}

	static function parse(&$input)
	{
		$s2k = new self;

		switch($s2k->type = ord($input[0])) {
			case 0:
				$s2k->hash_algorithm = ord($input[1]);
				$input = substr($input,2);
				break;

			case 1:
				$s2k->hash_algorithm = ord($input[1]);
				$s2k->salt = substr($input,2,8);
				$input = substr($input,10);
				break;

			case 3:
				$s2k->hash_algorithm = ord($input[1]);
				$s2k->salt = substr($input,2,8);
				$s2k->count = OpenPGP::decode_s2k_count(ord($input[10]));
				$input = substr($input,11);
				break;
		}

		return $s2k;
	}

	function to_bytes()
	{
		$bytes = chr($this->type);

		switch($this->type) {
			case 0:
				$bytes .= chr($this->hash_algorithm);
				break;

			case 1:
				if (strlen($this->salt) != 8)
					throw new Exception('Invalid salt length');

				$bytes .= chr($this->hash_algorithm);
				$bytes .= $this->salt;
				break;

			case 3:
				if (strlen($this->salt) != 8)
					throw new Exception('Invalid salt length');

				$bytes .= chr($this->hash_algorithm);
				$bytes .= $this->salt;
				$bytes .= chr(OpenPGP::encode_s2k_count($this->count));
				break;
		}

		return $bytes;
	}

	function raw_hash($s)
	{
		return hash(strtolower(SignaturePacket::$hash_algorithms[$this->hash_algorithm]),$s,true);
	}

	function sized_hash($s,$size)
	{
		$hash = $this->raw_hash($s);

		while(strlen($hash) < $size) {
			$s = "\0".$s;
			$hash .= $this->raw_hash($s);
		}

		return substr($hash,0,$size);
	}

	function iterate($s)
	{
		if (strlen($s) >= $this->count)
			return $s;

		$s = str_repeat($s,ceil($this->count/strlen($s)));

		return substr($s,0,$this->count);
	}

	function make_key($pass,$size)
	{
		switch($this->type) {
			case 0:
				return $this->sized_hash($pass, $size);

			case 1:
				return $this->sized_hash($this->salt . $pass, $size);

			case 3:
				return $this->sized_hash($this->iterate($this->salt . $pass), $size);
		}
	}
}