package com.vpnmore.shadowsocks.tcpip;

import java.net.Inet4Address;
import java.net.InetAddress;
import java.net.UnknownHostException;

public class CommonMethods {

	public static InetAddress ipIntToInet4Address(int ip){
		byte[] ipAddress=new byte[4];
		writeInt(ipAddress, 0, ip);
        try {
			return  Inet4Address.getByAddress(ipAddress);
		} catch (UnknownHostException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			return null;
		}
	}
	
	public static String ipIntToString(int ip) {
		return String.format("%s.%s.%s.%s", (ip >> 24) & 0x00FF,
				(ip >> 16) & 0x00FF, (ip >> 8) & 0x00FF, ip & 0x00FF);
	}
	
	public static String ipBytesToString(byte[] ip) {
		return String.format("%s.%s.%s.%s", ip[0] & 0x00FF,ip[1] & 0x00FF,ip[2] & 0x00FF,ip[3] & 0x00FF);
	}

	public static int ipStringToInt(String ip) {
		String[] arrStrings = ip.split("\\.");
		int r = (Integer.parseInt(arrStrings[0]) << 24)
				| (Integer.parseInt(arrStrings[1]) << 16)
				| (Integer.parseInt(arrStrings[2]) << 8)
				| Integer.parseInt(arrStrings[3]);
		return r;
	}

	public static int readInt(byte[] data, int offset) {
		int r = ((data[offset] & 0xFF) << 24)
				| ((data[offset + 1] & 0xFF) << 16)
				| ((data[offset + 2] & 0xFF) << 8) | (data[offset + 3] & 0xFF);
		return r;
	}

	public static short readShort(byte[] data, int offset) {
		int r = ((data[offset] & 0xFF) << 8) | (data[offset + 1] & 0xFF);
		return (short) r;
	}

	public static void writeInt(byte[] data, int offset, int value) {
		data[offset] = (byte) (value >> 24);
		data[offset + 1] = (byte) (value >> 16);
		data[offset + 2] = (byte) (value >> 8);
		data[offset + 3] = (byte) (value);
	}

	public static void writeShort(byte[] data, int offset, short value) {
		data[offset] = (byte) (value >> 8);
		data[offset + 1] = (byte) (value);
	}

	// 网络字节顺序与主机字节顺序的转换

	public static short htons(short u) {
		int r = ((u & 0xFFFF) << 8) | ((u & 0xFFFF) >> 8);
		return (short) r;
	}

	public static short ntohs(short u) {
		int r = ((u & 0xFFFF) << 8) | ((u & 0xFFFF) >> 8);
		return (short) r;
	}

	public static int hton(int u) {
		int r = (u >> 24) & 0x000000FF;
		r |= (u >> 8) & 0x0000FF00;
		r |= (u << 8) & 0x00FF0000;
		r |= (u << 24) & 0xFF000000;
		return r;
	}

	public static int ntoh(int u) {
		int r = (u >> 24) & 0x000000FF;
		r |= (u >> 8) & 0x0000FF00;
		r |= (u << 8) & 0x00FF0000;
		r |= (u << 24) & 0xFF000000;
		return r;
	}

	// 计算校验和
	public static short checksum(long sum, byte[] buf, int offset, int len) {
		sum += getsum(buf, offset, len);
		while ((sum >> 16) > 0)
			sum = (sum & 0xFFFF) + (sum >> 16);
		return (short) ~sum;
	}

	public static long getsum(byte[] buf, int offset, int len) {
		long sum = 0; /* assume 32 bit long, 16 bit short */
		while (len > 1) {
			sum += readShort(buf, offset) & 0xFFFF;
			offset += 2;
			len -= 2;
		}

		if (len > 0) /* take care of left over byte */
		{
			sum += (buf[offset] & 0xFF) << 8;
		}
		return sum;
	}

	// 计算IP包的校验和
	public static boolean ComputeIPChecksum(IPHeader ipHeader) {
		short oldCrc = ipHeader.getCrc();
		ipHeader.setCrc((short) 0);// 计算前置零
		short newCrc = CommonMethods.checksum(0, ipHeader.m_Data,
				ipHeader.m_Offset, ipHeader.getHeaderLength());
		ipHeader.setCrc(newCrc);
		return oldCrc == newCrc;
	}

	// 计算TCP或UDP的校验和
	public static boolean ComputeTCPChecksum(IPHeader ipHeader,TCPHeader tcpHeader) {
		ComputeIPChecksum(ipHeader);//计算IP校验和
		int ipData_len = ipHeader.getTotalLength() - ipHeader.getHeaderLength();// IP数据长度
		if (ipData_len < 0)
			return false;
		// 计算为伪首部和
		long sum = getsum(ipHeader.m_Data, ipHeader.m_Offset
				+ IPHeader.offset_src_ip, 8);
		sum += ipHeader.getProtocol()&0xFF;
		sum += ipData_len;

		short oldCrc = tcpHeader.getCrc();
		tcpHeader.setCrc((short) 0);// 计算前置0

		short newCrc = checksum(sum, tcpHeader.m_Data, tcpHeader.m_Offset, ipData_len);// 计算校验和

		tcpHeader.setCrc(newCrc);
		return oldCrc == newCrc;
	}

	// 计算TCP或UDP的校验和
	public static boolean ComputeUDPChecksum(IPHeader ipHeader,UDPHeader udpHeader) {
		ComputeIPChecksum(ipHeader);//计算IP校验和
		int ipData_len = ipHeader.getTotalLength() - ipHeader.getHeaderLength();// IP数据长度
		if (ipData_len < 0)
			return false;
		// 计算为伪首部和
		long sum = getsum(ipHeader.m_Data, ipHeader.m_Offset
				+ IPHeader.offset_src_ip, 8);
		sum += ipHeader.getProtocol()&0xFF;
		sum += ipData_len;

		short oldCrc = udpHeader.getCrc();
		udpHeader.setCrc((short) 0);// 计算前置0

		short newCrc = checksum(sum, udpHeader.m_Data, udpHeader.m_Offset, ipData_len);// 计算校验和

		udpHeader.setCrc(newCrc);
		return oldCrc == newCrc;
	}
}
