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

public class iCheck
{
	
	public static final String PASSWORD="geslo";
	public static final String LOGFILE="/var/log/iCheck.log";
	public static final int DELAY=30;
	public static final int PORT=4444;
	public static final int TIMEOUT=10;
	public static String[] HOSTS={"server1.firma.si","server2.firma.si"};

	public static void main(String[] args)
	{
		System.out.println(HOSTS.length);
		Check[] checks=new Check[HOSTS.length];
		for (int i=0;i<HOSTS.length;i++)
		{			
			checks[i]=new Check(HOSTS[i]);
			checks[i].start();
		}
	}	
	 
	public static void err(String msg) 
	{
		try
		{
			File outFile=new File(LOGFILE);
			FileWriter out=new FileWriter(outFile,outFile.exists());
			Date datum=new Date();
			out.write(datum.toString()+": "+msg+"\n");
			out.close();
		}
		catch (IOException e)
		{
			System.out.println("Cannot open log file for writing!");
		}
	}
}

class Check extends Thread
{
	InetAddress target;
		
	public Check(String ip)
	{
		try
		{
			target = InetAddress.getByName(ip);
		}
		catch (UnknownHostException e)
		{
			iCheck.err("Cannot resolve server's IP address!");
		}
	}

	public void run()
	{
		while (true)
		{
			try
			{
				UDPClient klient=new UDPClient(target,iCheck.PORT);
				klient.send(iCheck.PASSWORD);
			}
			catch (SocketException e)
			{
				iCheck.err("Error sending packet!");
			}
			catch (IOException e)
			{
				iCheck.err("UDP packet too big!");
			}
			
			byte[] buffer=new byte[11];
			DatagramPacket paket=new DatagramPacket(buffer,buffer.length);
			DatagramSocket vticnica;

			try
			{
				vticnica=new DatagramSocket(iCheck.PORT);
				vticnica.setSoTimeout(iCheck.TIMEOUT*1000);
				vticnica.receive(paket);
			}
			catch (SocketTimeoutException e)
			{
				iCheck.err("Streznik "+target.getHostName()+" trenutno ni dosegljiv! Ponovni poskus bo cez "+iCheck.DELAY+" sekund.");
			}					
			catch (SocketException e)
			{
				iCheck.err("Error creating socket for sending!");
			}
			catch (IOException e)
			{
				iCheck.err("I/O error!");
			}
			
			if (!(String.valueOf(paket.getData()).equals(iCheck.PASSWORD)))
			{
				iCheck.err("Streznik "+target.getHostName()+" se ni pravilno predstavil (napacno geslo)!");
			}
			
			try
			{
				Thread.sleep(iCheck.DELAY*1000);
			}
			catch (InterruptedException e) {}
		}
	}
}