<?php

namespace App\Helper;

class XXTEA
{
    const DELTA = 0x9E3779B9;
    private static function long2str($v, $w)
    {
        $len = count($v);
        $n = $len << 2;
        if ($w) {
            $m = $v[$len - 1];
            $n -= 4;
            if (($m < $n - 3) || ($m > $n)) {
                return false;
            }
            $n = $m;
        }
        $s = array();
        for ($i = 0; $i < $len; $i++) {
            $s[$i] = pack("V", $v[$i]);
        }
        if ($w) {
            return substr(join('', $s), 0, $n);
        } else {
            return join('', $s);
        }
    }

    private static function str2long($s, $w)
    {
        $v = unpack("V*", $s. str_repeat("\0", (4 - strlen($s) % 4) & 3));
        $v = array_values($v);
        if ($w) {
            $v[count($v)] = strlen($s);
        }
        return $v;
    }

    private static function int32($n)
    {
        return ($n & 0xffffffff);
    }

    private static function mx($sum, $y, $z, $p, $e, $k)
    {
        return ((($z >> 5 & 0x07ffffff) ^ $y << 2) + (($y >> 3 & 0x1fffffff) ^ $z << 4)) ^ (($sum ^ $y) + ($k[$p & 3 ^ $e] ^ $z));
    }

    private static function fixk($k)
    {
        if (count($k) < 4) {
            for ($i = count($k); $i < 4; $i++) {
                $k[$i] = 0;
            }
        }
        return $k;
    }
    // $str is the string to be encrypted.
    // $key is the encrypt key. It is the same as the decrypt key.
    public static function encrypt($str, $key)
    {
        if ($str == "") {
            return "";
        }

        if (is_array($str)) {
            $str = json_encode($str);
        }

        $v = self::str2long($str, true);
        $k = self::fixk(self::str2long($key, false));
        $n = count($v) - 1;
        $z = $v[$n];
        $q = floor(6 + 52 / ($n + 1));
        $sum = 0;
        while (0 < $q--) {
            $sum = self::int32($sum + self::DELTA);
            $e = $sum >> 2 & 3;
            for ($p = 0; $p < $n; $p++) {
                $y = $v[$p + 1];
                $z = $v[$p] = self::int32($v[$p] + self::mx($sum, $y, $z, $p, $e, $k));
            }
            $y = $v[0];
            $z = $v[$n] = self::int32($v[$n] + self::mx($sum, $y, $z, $p, $e, $k));
        }
        return self::long2str($v, false);
    }

    // $str is the string to be decrypted.
    // $key is the decrypt key. It is the same as the encrypt key.
    public static function decrypt($str, $key = false)
    {
        if (!$key) {
            $key = config('security.xxtea_key');
        }

        if ($str == "") {
            return "";
        }
        $v = self::str2long($str, false);
        $k = self::fixk(self::str2long($key, false));
        $n = count($v) - 1;

        $y = $v[0];
        $q = floor(6 + 52 / ($n + 1));
        $sum = self::int32($q * self::DELTA);
        while ($sum != 0) {
            $e = $sum >> 2 & 3;
            for ($p = $n; $p > 0; $p--) {
                $z = $v[$p - 1];
                $y = $v[$p] = self::int32($v[$p] - self::mx($sum, $y, $z, $p, $e, $k));
            }
            $z = $v[$n];
            $y = $v[0] = self::int32($v[0] - self::mx($sum, $y, $z, $p, $e, $k));
            $sum = self::int32($sum - self::DELTA);
        }
        return self::long2str($v, true);
    }
}
