package de.tudarmstadt.informatik.hostage.protocol;

import java.util.ArrayList;
import java.util.List;

import de.tudarmstadt.informatik.hostage.commons.HelperUtils;
import de.tudarmstadt.informatik.hostage.wrapper.Packet;

/**
 * TELNET protocol.
 * Implementation of RFC document 854.
 * @author Wulf Pfeiffer
 */
public class TELNET implements Protocol {
	/**
	 * Represents the states of the protocol
	 */
	private static enum STATE {
		NONE, OPEN, CLOSED, LOGIN, AUTHENTICATE, LOGGED_IN
	};
	
	/**
	 * Denotes in which state the protocol is right now
	 */
	private STATE state = STATE.NONE;
	
	@Override
	public int getDefaultPort() {
		return 23;
	}

	@Override
	public TALK_FIRST whoTalksFirst() {
		return TALK_FIRST.SERVER;
	}

	@Override
	public List<Packet> processMessage(Packet requestPacket) {
		byte[] request = null;
		if(requestPacket != null) {
			request = requestPacket.getMessage();
		}
		List<Packet> responsePackets = new ArrayList<Packet>();
		
		switch (state) {
		case NONE:
			responsePackets.add(new Packet(optionRequest));
			state = STATE.OPEN;
			break;
		case OPEN:
			if(request != null) {
				responsePackets.add(new Packet(getOptionResponse(request)));
				responsePackets.add(new Packet(serverName + " login: "));
				state = STATE.LOGIN;
			}
			break;
		case LOGIN:
			if(request == null) break;
			else if(checkForByte(request, (byte) 0x0d)) {
				if(request.length > 2) {
					byte[] buffer = new byte[request.length - 2]; 
					System.arraycopy(request, 0, buffer, 0, request.length - 2); 
					user = HelperUtils.concat(user, buffer);
					responsePackets.add(new Packet(buffer));
				}
				responsePackets.add(new Packet("\r\n"));
				responsePackets.add(new Packet("Password: "));
				state = STATE.AUTHENTICATE;
				sessionToken = HelperUtils.concat(sessionPrefix, user, "@".getBytes(), serverName.getBytes(), sessionMiddle, user, "@".getBytes(), serverName.getBytes(), sessionSuffix);
				break;
			} else if (checkForByte(request, (byte) 0x7f) && user != null && user.length != 0) {
				byte[] tmp = new byte[user.length - 1];
				System.arraycopy(user, 0, tmp, 0, user.length - 1);
				user = tmp;
				responsePackets.add(new Packet("\b \b"));
				break;
			} else if (!checkForByte(request, (byte) 0xff)){
				if(user == null)
					user = request;
				else
					user = HelperUtils.concat(user, request);
				responsePackets.add(requestPacket);
			}
			break;
		case AUTHENTICATE:
			if(request == null) break;
			else if(checkForByte(request, (byte) 0x0d)) {
				responsePackets.add(new Packet("\r\n"));
				responsePackets.add(new Packet(sessionToken));
				state = STATE.LOGGED_IN;
			} else if (checkForByte(request, (byte) 0x7f)) {
				responsePackets.add(new Packet("\b \b"));
			}			
			break;
		case LOGGED_IN:
			if(request == null) break;
			else if(checkForByte(request, (byte) 0x0d)) {
				if(request.length > 2) {
					byte[] buffer = new byte[request.length - 2]; 
					System.arraycopy(request, 0, buffer, 0, request.length - 2); 
					command = HelperUtils.concat(command, buffer);
					responsePackets.add(new Packet(buffer));
				}
				if(command == null) {
					responsePackets.add(new Packet("\r\n"));
					responsePackets.add(new Packet(sessionToken));
				} else if (new String(command).contains("exit")) {
					responsePackets.add(new Packet("\r\nlogout\r\n"));
					state = STATE.CLOSED;
				} else {
					String bash = "\r\n-bash: " + new String(command)+ ": command not found";
					responsePackets.add(new Packet(bash));
					responsePackets.add(new Packet("\r\n"));
					responsePackets.add(new Packet(sessionToken));
					command = null;
				}
			} else if (checkForByte(request, (byte) 0x7f) && command != null && command.length != 0) {
				byte[] tmp = new byte[command.length - 1];
				System.arraycopy(command, 0, tmp, 0, command.length - 1);
				command = tmp;
				responsePackets.add(new Packet("\b \b"));
				break;
			} else if (!checkForByte(request, (byte) 0xff)){
				if(command == null)
					command = request;
				else
					command = HelperUtils.concat(command, request);
				responsePackets.add(requestPacket);
			}
			break;
		default:
			responsePackets.add(new Packet("\r\nlogout\r\n"));
			state = STATE.CLOSED;
			break;
		}
		return responsePackets;
	}

	@Override
	public boolean isClosed() {
		return (state == STATE.CLOSED);
	}

	@Override
	public boolean isSecure() {
		return false;
	}
	
	@Override
	public String toString() {
		return "TELNET";
	}
	
	@Override
	public Class<byte[]> getType() {
		return byte[].class;
	}
	
	/**
	 * Checks a byte array for occurence of one byte.
	 * @param bytes byte array that is checked.
	 * @param b searched byte.
	 * @return true if the byte was found, else false.
	 */
	private boolean checkForByte(byte[] bytes, byte b) {
		for(byte oneByte : bytes) {
			if(oneByte == b) return true;
		}
		return false;
	}

	/**
	 * Determines which options that are requested by the client will be done and which not
	 * @param request requested options
	 * @return accepted and unaccepted options
	 */
	private byte[] getOptionResponse(byte[] request) {
		List<byte[]> responseList = new ArrayList<byte[]>();
		byte[] requestInverse;
		for(int i = 0; i < request.length - 2; i += 3) {
			if(request[i] == (byte) 0xff && request[i+2] != 0x03 && request[i+2] != 0x01) {
				requestInverse = new byte[3];
				requestInverse[0] = request[i];
				requestInverse[1] = request[i+1] == (byte) 0xfd ? (byte) 0xfc : (byte) 0xfe; 
				requestInverse[2] = request[i+2];
				responseList.add(requestInverse);
			}			
		}
		byte[] optionResponse = new byte[0];
		for(byte[] response : responseList) {
			optionResponse = HelperUtils.concat(optionResponse, response);
		}
		return optionResponse;
	}


	/** user entered by the client */
	private static byte[] user;
	/** last command sent by the client */
	private byte[] command;
	/** name of the server */
	private static String serverName = HelperUtils.getRandomString(16, false);
	/** command line prefix */
	private static byte[] sessionToken = null;
	
	/** options requested by the server */
	private static final byte[] optionRequest = {
			(byte) 0xff, (byte) 0xfb, 0x03,	//will suppress go ahead
			(byte) 0xff, (byte) 0xfb, 0x01 	//will echo
	};
	//session token prefix, mid and suffix
	private static final byte[] sessionPrefix = {0x1b, 0x5d, 0x30, 0x3b};
	private static final byte[] sessionMiddle = {0x3a, 0x20, 0x7e, 0x07, 0x1b, 0x5b, 0x30, 0x31, 
			0x3b, 0x33, 0x32, 0x6d};	
	private static final byte[] sessionSuffix = {0x1b, 0x5b, 0x30, 0x30, 0x6d, 0x20, 0x1b, 0x5b, 0x30, 0x31, 
			0x3b, 0x33, 0x34, 0x6d, 0x7e, 0x20, 0x24, 0x1b, 0x5b, 0x30, 0x30, 0x6d, 0x20};
}