// AddBigNumbers
//
// This program adds two binary numbers together.
//
// The only part of this that is directly relevant to the class is
// the first function, AddBigNumbers. The rest, you can ignore if you'd
// like. (I'm not stopping you from looking over it, too, if you're
// interested, but it's not necessary.)
import java.awt.*;

public class AddBigNumbers extends Frame {
	protected Label header;
	protected TextField[] num = new TextField[2];
	protected Button dotest;
	protected Button doquit;
	protected int unfocused;
	
	// AddBigNumbers
	//
	// calculates the sum of two binary numbers <a> and <b>,
	// represented as arrays of ints whose entries are only 0's and
	// 1's, with the least significant bit (the right-hand side when
	// written) in the first slot.
	//
	// The sum is placed into <result>.
	//
	// The function returns 0 if successful and -1 if the sum doesn't
	// fit into <c>.
	public static int AddIntegers(int[] result, int[] a, int[] b) {
		return -1;
	}
	
	// AddBigNumbers
	//
	// creates the dialog box
	public AddBigNumbers() {
		super("Add numbers");

		Panel p;
		GridBagConstraints c;
		
		unfocused = 0;
		
		c = new GridBagConstraints();
		c.gridx = 0;
		c.gridwidth = 1;
		c.gridheight = 1;
		c.ipady = 5;
		c.anchor = GridBagConstraints.CENTER;
		c.weightx = 1.0;
		
		// create the label giving output to user
		this.setLayout(new GridBagLayout());
		header = new Label("Hello, world! Enter the numbers to add.");
		c.gridy = 0;
		c.weighty = 0.0;
		c.fill = GridBagConstraints.HORIZONTAL;
		((GridBagLayout) this.getLayout()).setConstraints(header, c);
		this.add(header);
		
		// create text field to get first bit string from user
		num[0] = new TextField("1010101");
		c.gridy = 1;
		c.weighty = 1.0;
		c.fill = GridBagConstraints.HORIZONTAL;
		((GridBagLayout) this.getLayout()).setConstraints(num[0], c);
		this.add(num[0]);

		// create text field to get second bit string from user
		num[1] = new TextField("0101010");
		c.gridy = 2;
		c.weighty = 1.0;
		c.fill = GridBagConstraints.HORIZONTAL;
		((GridBagLayout) this.getLayout()).setConstraints(num[1], c);
		this.add(num[1]);
		
		// create a Panel to hold the buttons.
		p = new Panel();
		p.setLayout(new FlowLayout(FlowLayout.CENTER, 15, 15));
		
		// add the ``Test'' button
		dotest = new Button("Test");
		p.add(dotest);
		
		// add the ``Quit'' button
		doquit = new Button("Quit");
		p.add(doquit);
		
		// put Panel in dialog
		c.gridy = 3;
		c.weighty = 0.0;
		c.fill = GridBagConstraints.NONE;
		((GridBagLayout) this.getLayout()).setConstraints(p, c);
		this.add(p);
		this.pack();
	}
	
	// action
	//
	// handle button clicks
	public boolean action(Event e, Object arg) {
		String input;
		String output;
		int[][] a = new int[2][];
		int[] result = new int[8];
		int err;
		int which;
		int i;
		
		if(e.target == num[0]) {
			num[1].requestFocus();
			return true;
		} else if(e.target == dotest || e.target == num[1]) {
			// find the sum

			// get the first number
			for(which = 0; which < 2; which++) {
				input = num[which].getText();
				a[which] = new int[input.length()];
				for(i = 0; i < a[which].length; i = i + 1) {
					if(input.charAt(i) == '0') {
						a[which][a[which].length - 1 - i] = 0;
					} else if(input.charAt(i) == '1') {
						a[which][a[which].length - 1 - i] = 1;
					} else {
						header.setText("The numbers contain a non-bit "
							+ "character ('" + input.charAt(i) + "').");
						return true;
					}
				}
			}

			// get result
			err = AddIntegers(result, a[0], a[1]);
			if(err != 0) {
				header.setText("The sum did not fit in "
					+ result.length + " bits.");
				return true;
			}

			// put output in the header label
			output = "The sum is ";
			for(i = result.length - 1; i >= 0; i = i - 1) {
				if(result[i] == 0) {
					output = output + "0";
				} else if(result[i] == 1) {
					output = output + "1";
				} else {
					header.setText("The output contains the invalid "
						+ "bit " + result[i] + ".");
					return true;
				}
			}
			header.setText(output + ".");
			return true;
		} else if(e.target == doquit) {
			this.dispose();
			return true;
		} else {
			return false;
		}
	}
	
	// gotFocus
	//
	// sets the default focus location
	public boolean gotFocus(Event e, Object arg) {
		if(e.target == num[1]) {
			num[1].requestFocus();
		} else if(e.target == num[0] || unfocused == 1) {
			unfocused = 0;
			num[0].requestFocus();
		}
		return true;
	}
	
	// main
	//
	// this is where the program begins
	public static void main(String[] args) {
		Frame f;
		AddBigNumbers dialog;
		
		// create the dialog box
		f = new AddBigNumbers();
		f.resize(300, 150);
		f.show();
	}
}