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

class Advertiser extends Thread {
    DatagramSocket as;
    DatagramPacket ad;
    Advertiser(DatagramSocket a, String msg, InetAddress dsaddr) {
	as=a;
	ad= new DatagramPacket(msg.getBytes(),msg.length(),dsaddr,8888);
    }
    public void run() {
	try {
	    while (true) {
		as.send(ad);
		Thread.sleep(1000);
	    }
	} catch(Exception e) {
	    System.err.println("advertiser died: "+e);
	}
    }
}

class Worker extends Thread {
    Socket ts;
    String filename;
    Worker(Socket s,String n) {
	ts=s; filename=n;
    }

    public void run() {
	System.err.println("serving "+filename+" through "+ts);
	try {
	    OutputStream out=ts.getOutputStream();
	    InputStream in=new FileInputStream(filename);
	    int total=0;
	    while (in.available()>0) {
		byte b[]=new byte[1024];
		int len=in.read(b);
		out.write(b,0,len);
		out.flush();
		total+=len;
	    }
	    out.close();
	    in.close();
	    System.err.println("done: "+total+" bytes transferred");
	} catch (Exception any) {
	    System.err.println("worker died "+any);
	    System.exit(-1);
	}
    }
}


/** a thread that accepts new connections and fork off a worker for them */
class Welcomer extends Thread {
    ServerSocket ss;
    String fname;
    Welcomer(ServerSocket s,String fn) {
	ss=s;
	fname=fn;
    }
    public void run() {
	try {
	    while(true) {
		Socket ts=ss.accept();
		System.err.println("new client received on "+ss);
		Thread worker=new Worker(ts,fname);
		worker.start();
	    }
	} catch (Exception any) {
	    System.err.println("welcomer died "+any);
	    System.exit(-1);
	}

    }
}

class server {
    public static void main(String argv[]) throws Exception {
	if (argv.length<3) {
	    System.err.println("usage : java server <this-addr> <DS-ADDR> <filename> [morefiles]");
	    System.exit(-1);
	}
	int fileno=2;
	InetAddress dsaddr  = InetAddress.getByName(argv[1]);
	String thisaddr = argv[0];
	for (int port=8081;port<8100;port++) {
	    String fname=argv[fileno];
	    /** when trying to bind the socket to a given port, java.net
	     *  will throw a SocketException if the port is already bound.
	     */
	    try {
		ServerSocket listen=new ServerSocket(port);
		DatagramSocket advertise=new DatagramSocket(port);
		System.err.println("advertise to "+dsaddr+
				   ":8888, transfer over "
				   +thisaddr+":"+port);
		String msg=thisaddr+":"+port+":"+fname+"\n";
		
		/** nothing like a "check-if-accept-is-going-to-succeed" 
		 *  in java.net, so we have to fork a thread for advertisements
		 *  and another thread that waits for incoming transmissions.
		 */ 
		Thread adv=new Advertiser(advertise,msg,dsaddr);
		adv.start();
		Thread wlc=new Welcomer(listen,fname);
		wlc.start();
		fileno++;
		if (fileno>=argv.length) {
		    /** when all files have their advertiser/welcomer thread
		     * spawn, we simply halt the 'root' thread by making it
		     * join (i.e. wait for termination of) those threads.
		     * program is interrupted with CTRL-C or on transfer 
		     * errors.
		     */
		    adv.join();
		    wlc.join();
		    System.exit(0);
		}

	    } catch (SocketException se) {
		System.err.println("port "+port+" failed ("+se+")");
	    }
	}
    }
}