/*
		Name:		Chris Johnson
					johnson@dcs.gla.ac.uk
		
		Last modified:	26/10/98
		
		Description:	Part of a simple calculator applet based on a program in
					G.W. Rouse's An Introduction to Data Structures and
					Algorithms with Java, Prentice Hall, Hemel Hemstead, 1998.
					pp 65-78.

*/

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

public class Calculator extends Applet{
	
	private long operand1, operand2, answer;
	private String operation;
	private boolean newNumber;
	
	private Button	button1 = new Button("1");
	private Button	button2 = new Button("2");
	private Button	button3 = new Button("3");
	private Button	button4 = new Button("4");
	private Button	button5 = new Button("5");
	private Button	button6 = new Button("6");
	private Button	button7 = new Button("7");
	private Button	button8 = new Button("8");
	private Button	button9 = new Button("9");
	private Button	button0 = new Button("0");
		
		private TextField numberBox = new TextField("0", 12);
		
		private Button plusMinusButton = new Button("+/-");
		private Button CEButton = new Button("CE");
		private Button CButton = new Button("C");
		
		
		private Button plusButton = new Button("+");
		private Button minusButton = new Button("-");
		private Button timesButton = new Button("*");
		private Button divideButton = new Button("/");
		private Button equalsButton = new Button("=");

	public void init()
	{
		Panel numberPanel = new Panel();
		
		Panel signClearPanel = new Panel();
		
		Panel arithmeticPanel = new Panel();
		
		Panel masterPanel = new Panel();
		
		NewGridBagLayout numberLayout = new NewGridBagLayout();
		NewGridBagLayout masterLayout = new NewGridBagLayout();
		
		operand1 = operand2 = answer = 0;
		operation = "+";
		
		setFont(new Font("Helvetica", Font.BOLD, 14));
		
		
		signClearPanel.setLayout(new GridLayout(1,3,2,2));
		signClearPanel.add(plusMinusButton);
		signClearPanel.add(CEButton);
		signClearPanel.add(CButton);
		
		numberPanel.setLayout(numberLayout);
		numberLayout.setRareConstraints(
				GridBagConstraints.CENTER,
				GridBagConstraints.BOTH,
				new Insets(2,2,2,2), 0, 0, 1, 1);
				
		numberLayout.setPositionSizeAdd(button1, numberPanel, 0, 0, 1, 1);
		numberLayout.setPositionSizeAdd(button2, numberPanel, 1, 0, 1, 1);
		numberLayout.setPositionSizeAdd(button3, numberPanel, 2, 0, 1, 1);
		numberLayout.setPositionSizeAdd(button4, numberPanel, 0, 1, 1, 1);
		numberLayout.setPositionSizeAdd(button5, numberPanel, 1, 1, 1, 1);
		numberLayout.setPositionSizeAdd(button6, numberPanel, 2, 1, 1, 1);
		numberLayout.setPositionSizeAdd(button7, numberPanel, 0, 2, 1, 1);
		numberLayout.setPositionSizeAdd(button8, numberPanel, 1, 2, 1, 1);
		numberLayout.setPositionSizeAdd(button9, numberPanel, 2, 2, 1, 1);
		numberLayout.setPositionSizeAdd(button0, numberPanel, 1, 3, 1, 1);
		
		arithmeticPanel.setLayout(new GridLayout(5,1,2,2));
		arithmeticPanel.add(plusButton);
		arithmeticPanel.add(minusButton);
		arithmeticPanel.add(divideButton);
		arithmeticPanel.add(timesButton);
		arithmeticPanel.add(equalsButton);
		
		masterLayout.setRareConstraints(
			GridBagConstraints.NORTHEAST,
			GridBagConstraints.NONE,
			new Insets(2,2,2,2), 0, 0, 1, 1);
		
		masterPanel.setLayout(masterLayout);
		masterLayout.setPositionSizeAdd(numberBox, masterPanel, 0, 0, 2, 1);
		masterLayout.setPositionSizeAdd(signClearPanel, masterPanel, 0, 1, 2, 1);
		masterLayout.setPositionSizeAdd(numberPanel, masterPanel, 0, 2, 1, 1);
			masterLayout.setPositionSizeAdd(arithmeticPanel, masterPanel, 1, 2, 1, 1);
	
	
			add(masterPanel);
		
		}
		
		public boolean action(Event event, Object arg){
			
			if (event.target instanceof Button){
				String label = (String)arg;
				if(event.target== button1){
					addDigitToDisplay(1);
				}
				else if(event.target== button2){
					addDigitToDisplay(2);
				}
				else if(event.target== button3){
					addDigitToDisplay(3);
				}
				else if(event.target== button4){
					addDigitToDisplay(4);
				}
				else if(event.target== button5){
					addDigitToDisplay(5);
				}
				else if(event.target== button6){
					addDigitToDisplay(6);
				}
				else if(event.target== button7){
					addDigitToDisplay(7);
				}
				else if(event.target== button8){
					addDigitToDisplay(8);
				}
				else if(event.target== button9){
					addDigitToDisplay(9);
				}
				else if(event.target== button0){
					addDigitToDisplay(0);
				}
				else if(event.target== CEButton){
					clearDisplay();
				}
				else if(event.target== plusMinusButton){
					changeSign();
				}
				else if(event.target== CButton){
					clearAll();
				}
				else if(event.target== equalsButton){
					doEquals();
				}
				else if(event.target== plusButton){
					doOperation("+");
				}
				else if(event.target== minusButton){
					doOperation("-");
				}
				else if(event.target== timesButton){
					doOperation("*");
				}
				else if(event.target== divideButton){
					doOperation("/");
				}
				return true;
				
			}
			return super.action(event, arg);
		}
		
		private void addDigitToDisplay(int newDigit)
		{
			if(newNumber){
				numberBox.setText("0");
				newNumber = false;
			}
			
			long displayValue =
				Long.parseLong(numberBox.getText());
				
			if (displayValue >= 0 && displayValue <= 999999999)
				displayValue = displayValue*10 + newDigit;
			numberBox.setText(Long.toString(displayValue));
		}
		
		private void changeSign()
		{
			long display = Long.parseLong(numberBox.getText());
			display = -display;
			numberBox.setText(Long.toString(display));
		}
		
		private void clearDisplay()
		{
			numberBox.setText("0");
		}
		
		private void clearAll()
		{
			operand1 = operand2 = answer = 0;
			operation = "+";
			newNumber = true;
			numberBox.setText("0");
		}
		
		private void doEquals()
		{
			if(newNumber)
				return;
			operand2 = Long.parseLong(numberBox.getText());
			if (operation == "+")
				answer = operand1 + operand2;
			else if (operation == "-")
				answer = operand1 - operand2;
			else if (operation == "*")
				answer = operand1 * operand2;
			else if (operation == "/")
				answer = operand1 / operand2;
				
			numberBox.setText(Long.toString(answer));
			operand1 = operand2 = answer = 0;
			operation = "+";
		}
		
		private void doOperation(String newOperation)
		{
			
			if(newNumber)
				return;
			operand2 = Long.parseLong(numberBox.getText());
			if (operation=="+")
				answer = operand1 + operand2;
			else if (operation=="-")
				answer = operand1 - operand2;
			else if (operation=="*")
				answer = operand1 * operand2;
			else if (operation=="/")
				answer = operand1 / operand2;
				
			numberBox.setText(Long.toString(answer));
			operand1 = answer;
			operand2 = answer = 0;
			operation = newOperation;
			newNumber = true;
		}

}