var crypto = require('crypto');
var bigInt = require('big-integer');

function addPadding(encText, modulus) {
    var ml = modulus.length;
    for (i = 0; ml > 0 && modulus[i] == '0'; i++) ml--;
    var num = ml - encText.length,
        prefix = '';
    for (var i = 0; i < num; i++) {
        prefix += '0';
    }
    return prefix + encText;
}


function aesEncrypt(text, secKey) {
    var cipher = crypto.createCipheriv('AES-128-CBC', secKey, '0102030405060708');
    return cipher.update(text, 'utf-8', 'base64') + cipher.final('base64');
}

/**
 * RSA Encryption algorithm.
 * @param text {string} - raw data to encrypt
 * @param exponent {string} - public exponent
 * @param modulus {string} - modulus
 * @returns {string} - encrypted data: reverseText^pubKey%modulus
 */
function rsaEncrypt(text, exponent, modulus) {
    var rText = '',
        radix = 16;
    for (var i = text.length - 1; i >= 0; i--) rText += text[i]; //reverse text
    var biText = bigInt(new Buffer(rText).toString('hex'), radix),
        biEx = bigInt(exponent, radix),
        biMod = bigInt(modulus, radix),
        biRet = biText.modPow(biEx, biMod);
    return addPadding(biRet.toString(radix), modulus);
}

function createSecretKey(size) {
    var keys = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
    var key = "";
    for (var i = 0; i < size; i++) {
        var pos = Math.random() * keys.length;
        pos = Math.floor(pos);
        key = key + keys.charAt(pos)
    }
    return key;
}
var modulus = '00e0b509f6259df8642dbc35662901477df22677ec152b5ff68ace615bb7b725152b3ab17a876aea8a5aa76d2e417629ec4ee341f56135fccf695280104e0312ecbda92557c93870114af6c9d05c4f7f0c3685b7a46bee255932575cce10b424d813cfe4875d3e82047b97ddef52741d546b8e289dc6935b3ece0462db0a22b8e7';
var nonce = '0CoJUm6Qyw8W8jud';
var pubKey = '010001';
var Crypto = {
    MD5: function(text) {
        return crypto.createHash('md5').update(text).digest('hex');
    },
    aesRsaEncrypt: function(text) {
        var secKey = createSecretKey(16);
        return {
            params: aesEncrypt(aesEncrypt(text, nonce), secKey),
            encSecKey: rsaEncrypt(secKey, pubKey, modulus)
        }
    },
    encrypted_id: function(id) {
        var magic = Buffer.from('3go8&$8*3*3h0k(2)2', 'ascii');
        var len = magic.length;
        var sid = Buffer.from(id, 'ascii');
        for (var i in sid) {
            sid[i] = sid[i] ^ magic[i % len];
        }
        sid = crypto.createHash('md5').update(sid).digest();
        return sid.toString('base64').replace(/\//g, '_').replace(/\+/g, '-');
    }

};
module.exports = Crypto;