package com.jaalee.sdk.utils;

import com.jaalee.sdk.internal.UnsignedInteger;
import com.jaalee.sdk.internal.UnsignedLong;
import com.jaalee.sdk.internal.UnsignedLongs;

import java.math.BigInteger;
import java.security.SecureRandom;
import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;
/**
 * @author JAALEE, Inc
 * 
 * @Support dev@jaalee.com
 * @Sales: sales@jaalee.com
 * 
 * @see http://www.jaalee.com/
 */

public class AuthMath
{
	private static final SecureRandom RANDOM = new SecureRandom();
	private static final long G_BASE = 5L;
	private static final long P_MODULO = 4294967291L;
	static final byte[] FIXED_KEY = { -1, -118, -14, 7, 1, 54, 37, -62, -40, 16, 9, 127, 32, -45, 5, 15 };

	public static long randomUnsignedInt()
	{
		return UnsignedInteger.fromIntBits(RANDOM.nextInt(2147483646)).longValue() + 1L;
	}

	public static int firstStepSecret(long aAuth)
	{
		return modExpWithBase(5L, aAuth, 4294967291L);
	}

	public static byte[] secondStepSecret(long aAuth, long bAuth, String macAddress)
	{
		byte[] sessionKey = sessionKey(aAuth, bAuth);
		byte[] macSecret = macAddressToMacSecret(macAddress);
		try
		{
			return aesDecrypt(sessionKey, aesEncrypt(FIXED_KEY, macSecret)); 
		}
		catch (Exception e) {
		}
		return null;
	}

	static int modExpWithBase(long base, long exp, long mod)
	{
		long result = 1L;

		for (; exp > 0L; exp /= 2L) {
			if ((exp & 1L) != 0L) {
				result = UnsignedLongs.remainder(result * base, mod);
			}
			base = UnsignedLongs.remainder(base * base, mod);
		}
		return (int)result;
	}

	static long modExpWithBaseAsLong(long base, long exp, long mod) {
		return UnsignedInteger.fromIntBits(modExpWithBase(base, exp, mod)).longValue();
	}

	static long hexStringToUnsignedLong(String hex) {
		return UnsignedLong.valueOf(new BigInteger(hex, 16)).longValue();
	}

	private static byte[] sessionKey(long aAuth, long bAuth) {
		int sessionInt = modExpWithBase(bAuth, aAuth, 4294967291L);

		byte s0 = (byte)sessionInt;
		byte s1 = (byte)(sessionInt >> 8);
		byte s2 = (byte)(sessionInt >> 16);
		byte s3 = (byte)(sessionInt >> 24);

		return new byte[] { s0, s1, s2, s3, s3, s2, s1, s0, s0, s3, s1, s2, s3, s0, s2, s1 };
	}

	static byte[] macAddressToMacSecret(String macAddress) {
		long macAddressValue = hexStringToUnsignedLong(macAddress);

		byte b0 = (byte)(int)macAddressValue;
		byte b1 = (byte)(int)(macAddressValue >> 8);
		byte b2 = (byte)(int)(macAddressValue >> 16);
		byte b3 = (byte)(int)(macAddressValue >> 24);
		byte b4 = (byte)(int)(macAddressValue >> 32);
		byte b5 = (byte)(int)(macAddressValue >> 40);

		return new byte[] { b0, b1, b2, b3, b4, b5, b2, b1, b0, b5, b4, b3, b4, b2, b3, b1 };
	}

	static byte[] aesEncrypt(byte[] key, byte[] text) throws Exception {
		SecretKeySpec secretKeySpec = new SecretKeySpec(key, "AES");
		Cipher cipher = Cipher.getInstance("AES/ECB/NoPadding");
		cipher.init(1, secretKeySpec);
		return cipher.doFinal(text);
	}

	static byte[] aesDecrypt(byte[] key, byte[] text) throws Exception {
		SecretKeySpec secretKeySpec = new SecretKeySpec(key, "AES");
		Cipher cipher = Cipher.getInstance("AES/ECB/NoPadding");
		cipher.init(2, secretKeySpec);
		return cipher.doFinal(text);
	}
}