import util.comm.*;

/**
 * Our computation class.
 */
public class Computer implements Runnable {

    public final static int ADD = 1;
    public final static int SUB = 2;
    public final static int MUL = 3;
    public final static int DIV = 4;

    private int	op;
    private Thread tid;

    DataChannel aChannel;
    DataChannel bChannel;
    DataChannel outChannel;

    public static Computer create(String inA, String inB, String out, int doOp) {

	if ((doOp < 1) || (doOp > 4))
	    return null;

	Computer result   = new Computer();
	result.tid        = new Thread(result);
	result.tid.setName("Computer ("+out+")");
	result.outChannel = DataChannel.getChannel(out);
	result.aChannel   = DataChannel.getChannel(inA, result.tid, 4);
	result.bChannel   = DataChannel.getChannel(inB, result.tid, 4);
	result.op         = doOp;
        return result;
   }

    public void start() {
	tid.start();
    }

    public void stop() {
	op = 0;
	Integer i = new Integer(0);
	/** make sure our thread wakes up. */
	aChannel.releaseChannel(tid);
	bChannel.releaseChannel(tid);
   }

    public void run() {
	int	a, b;
	
	while (true) {
	    try {
	        a = ((Integer) aChannel.getValue()).intValue();
	        b = ((Integer) bChannel.getValue()).intValue();
	    } catch (DataChannelOverrun e) { 
		System.out.println("OVERRUN on "+tid);
		break;
	    } catch (DataChannelShutdown x) {
		System.out.println("Shutting down "+tid.getName());
		return;
	    } catch (DataChannelTimeout y) {
		System.out.println("Timed out "+tid.getName());
		return;
	    } catch (Throwable tt) {
		return;
	    }
	    System.out.print(tid.getName()+" : ");
	    switch (op) {
		case 0:
		    System.out.println(" exiting.");
		    return; 
		case ADD:
		    System.out.println("ADD "+a+" + "+b+" -> "+(a+b));
		    outChannel.putValue(new Integer(a+b));
		    break;
		case SUB:
		    System.out.println("SUB "+a+" - "+b+" -> "+(a-b));
		    outChannel.putValue(new Integer(a-b));
		    break;
		case MUL:
		    System.out.println("MUL "+a+" * "+b+" -> "+(a*b));
		    outChannel.putValue(new Integer(a * b));
		    break;
		case DIV:
		    System.out.println("DIV "+a+" / "+b+" -> "+(a/b));
		    if (b == 0) {
			outChannel.putValue(new Integer(Integer.MAX_VALUE));
		    } else {
			outChannel.putValue(new Integer(a / b));
		    }
		    break;
	    }
	}
    }
}