import java.io.*;
import java.net.*;
import java.util.*;

class general{
	public static byte[] rdtPacket= new byte[100];  // The structure of rdt packet is Ver-Type-Seq/Ack Number - data
							// for example for data =00101010 and type 0 and seqnumber 5
							// rdtPacket  = 0010010100101010 ---> 001(Ver) 00(type) 101 (seqNumber) 00101010 (data)

	// The rdt packet fields :
 	public static int type ;
	public static int seqNumber;
	public static byte[] data = new byte[99];

	// the following function creates rdtPacket. It computes the value of the header base on 
	// the value of type and seq Number and version. It attaches the data at the end of the packet.

	public static void makeRDTPacket ( ){
		
		byte header = (byte)0;
		// create Version
		header = 1 << 5;
		
		// shift left type such that it is moved to its correct position in the header and convert the result to byte, 
		type = (byte) type << 3;
		byte typeField = (byte)type;

		//convert seqNumber to byte
		byte seqField = (byte) seqNumber;

		// combine version, type and seqNumber and create the header 
		header = (byte)(header | typeField | seqField );
		rdtPacket[0] = header;
		// add data at the end of rdt packet.
		for (int i=0; i<data.length; i++)
			rdtPacket[i+1] = data[i];
		
	}
	

	//The following fuction extracts the data and infromation in the header from 
	// rdtPacket.

	
	public static void extractData ( ){
		
		Byte header = rdtPacket[0];
		
		Byte typeField = (byte)(header.byteValue() &((byte) 24));  // AND header with 00011000 to get the value of type in byte
		type = typeField.byteValue() >>3;    


		Byte seqNumberField = (byte) (header.byteValue() & (byte) 7);  //AND with 00000111
		seqNumber = seqNumberField.intValue(); //convert the result to int
		
		for (int i =1; i < rdtPacket.length ; i++)  //get data
			data[i-1] = rdtPacket[i];
		
	}


	
}