import java.applet.Applet;
import java.awt.*;

public class calclet extends Applet {
  // Setup our operators
  // OP_BASE provided to separate operators from digits.  Operator value
  // should be OP_BASE + index of operator key in myLabels[]
  private static final int OP_BASE = 90;
  private static final int ADD = OP_BASE + 10;
  private static final int EQU = OP_BASE + 11;
  private static final int SUB = OP_BASE + 12;
  private static final int MUL = OP_BASE + 13;
  private static final int DIV = OP_BASE + 14;
  // setup possible calculator states...
  private static final int V = 0;
  private static final int VO = 1;
  private static final int VOV = 2;
  private static final int VOVE = 3;

  private static String myLabels[] = {
    "7", "8", "9", "4", "5", "6", "1", "2", "3", "0", "+", "=", "-", "*", "/"
  };

  // Setup initial calculator values and states
  private int value1 = 0;
  private int state = V;
  private int Op = EQU;
  private int displayValue = 0;

  TextField display;

/**
 * calclet()
 * Our Constructor--just builds the interface...
 */
  public void init() {
	setLayout(new BorderLayout());
        Button[] calcButtons = new Button[15];

	Panel displayPanel = new Panel();
	Panel keyPanel = new Panel();
	keyPanel.setLayout(new GridLayout(5,3));

	// Add buttons to their own panel
	for (int i=0; i < myLabels.length; i++) {
	  calcButtons[i] = new Button(myLabels[i]);
	  keyPanel.add(calcButtons[i]);
	}

	// Add text fields
	display = new TextField(Integer.toString(displayValue),10);
	display.setEditable(false);
	displayPanel.add(display);

	// Add the panels
	add("North",displayPanel);
	add("Center",keyPanel);
  }
  
/**
 * start
 * Show our frame
 */
  public void start() {
	resize(100,200);
	show();
  }

  // show the current display value
  public void updateDisplay() {
	display.setText(Integer.toString(displayValue));
  }

  // add the next digit to the display value
  public void addDisplay(int i) {
    displayValue = (displayValue * 10) + i;
    updateDisplay();
  }

  // set the display value and update the display
  public void setDisplay(int i) {
    displayValue = i;
    updateDisplay();
  }

  // perform the operation requested on the saved value (value1) and
  // the current value (displayValue)
  // Then, update the display
  public void doOp() {
    switch (Op) {
      case EQU:
	break;
      case ADD:
	displayValue += value1;
	updateDisplay();
	break;
      case SUB:
	displayValue = value1 - displayValue;
	updateDisplay();
	break;
      case MUL:
	displayValue *= value1;
	updateDisplay();
	break;
      case DIV:
	if (displayValue == 0) {
	  display.setText("DIV ZER ERR");
	} else {
	  displayValue = value1 / displayValue;
	  updateDisplay();
	}
	break;
    }
  }

  /**
   *  Find the key in the Labels list and return an int for it
   */
  private int key(String k) {
    int i;
    for (i=0; i<15; i++) {
      if (myLabels[i].equals(k))
        break;
    }
    return (i<10 ? Integer.parseInt(k) : i+OP_BASE);
  }

  public boolean handleEvent(Event evt) {
	if (evt.target instanceof Button) {
	  int which = key(((Button)evt.target).getLabel());
	  switch (which) {
	    // Check the digit keys...
	    case 0:
	    case 1:
	    case 2:
	    case 3:
	    case 4:
	    case 5:
	    case 6:
	    case 7:
	    case 8:
 	    case 9:  
		// If we're typing in a number, keep going
		if ((state == V) || (state == VOV)) {
		  addDisplay(which);
		}
		// We're typing in the second number, so save the current
		// value and reset the display
		else if (state == VO) {
		  value1 = displayValue;
		  setDisplay(which);
		  state = VOV;
                }
		// We're starting over from scratch, so reset the display
		else {
		  setDisplay(which);
		  state = V;
		}
		break;
	   // Now check for an operator
	   case ADD:
	   case SUB: 
	   case MUL:  
	   case DIV:  
		// We have two values, already, so perform the stored operation
		// and the set the operator to the newly pressed operator
		if (state == VOV) {
		  doOp();
		}
		Op = which;
		state = VO;
		break;
	   // Now check for the "=" key
	   case EQU:  
		// Do we have two values? if so, perform the operation
		// Otherwise, leave the display alone
		if (state == VOV) {
		  doOp();
		}
		// Set the state of the calculator to its final state (The
		// "=" key has been pressed, so the next operation will be
		// starting fresh
		Op = EQU;
		state = VOVE;
		break;
	  }
	  return true;
	}
	return false;
  }
}