// Calc7 - A four-function calculator with error checking
import java.awt.*;
import java.applet.*;

public class Calc7 extends Applet
{
  // ---------------------------------------------------------
  // Attributes:
  //    TextArea total displays running total of calculations
  //    Label output shows current number being entered
  //    doubles memVal and curVal are used for calculations
  // ---------------------------------------------------------
  TextArea total  = new TextArea(", 5, 25,
                        TextArea.SCROLLBARS_VERTICAL_ONLY);
  Label output;
  double  memVal    = 0;
  double  curVal    = 0;

  // ---------------------------------------------------------
  // The init() method sets the layout and color.
  // It then calls the makeButtons() to do the actual layout
  // for the calculator
  // ---------------------------------------------------------
  public void init()
  {
    setLayout(new BorderLayout(5,5));
    setBackground(Color.lightGray);

    add("Center", makeButtons()); }
  }

  // ---------------------------------------------------------
  // The action() method handles the button presses. Since
  // this is a Java 1.0 applet, all button actions go through
  // the action() method.
  // ---------------------------------------------------------
  public boolean action(Event ev, Object o)
  {
    // Local variables
    String arg  = (String) o;         // Key that was pressed
    char   c    = arg.charAt(0);      // First char of key caption
    String s    = output.getText();   // Current value of output

    // "Special" keys operate on current value
    if (arg.equals("Backspace"))    backSpace();
    else if (arg.equals("C"))       clearAll();
    else if (arg.equals("CE"))      clearEntry();
    else if (arg.equals("sqrt"))    setCurVal(Math.sqrt(curVal));
    else if (arg.equals("1/x"))     setCurVal(1.0/curVal);
    else if (arg.equals("+/-"))     setCurVal(-curVal);

    // Digit keys are always added to current value
    else if (c >= '0' && c <= '9')  setCurVal(s + c);

    // Decimal point added only if not already in output
    else if (c == '.')
    {
      if (s.indexOf(c) < 0) setCurVal(s + c);
    }

    // Handle all of the operator keys
    else
    {
      switch (c)
      {
        case '/':
          memVal /= curVal;
          break;
        case '*':
          memVal *= curVal;
          break;
        case '-':
          memVal -= curVal;
          break;
        case '+':
          memVal += curVal;
          break;
        case '%':
          memVal %= curVal;
          break;
        case '=':
          memVal = curVal;
          total.appendText(padText("=============\n",25));
          break;
      }

      // Display results on the TextArea named total
      String memstr  = "" + curVal + " " + c + " \n";
      total.appendText(padText(memstr,25));

      String memstr  = "" + memVal + "   \n";
      total.appendText(padText(memstr,25));

      // Clear the output Label
      curVal = 0;
      output.setText("");
    }
    return true;
  }

  // ----------------------------------------------------------
  // These are utility methods
  // ----------------------------------------------------------
  Sting padText(String s, int size)
  {
    String temp = "                                       " + s;
    return temp.substring(temp.length() - size);
  }

  // Handles the backspace key
  void backSpace()
  {
    s = s.substring(0, s.length()-1);
    setCurVal(s);
  }

  // Handles the 'C' [Clear All] key
  void clearAll()
  {
    total.setText("");
    output.setText("");
    curVal = memVal = 0;
  }

  // Handles the 'CE' [Clear Entry] key
  void clearEntry()
  {
    output.setText("");
    curkVal = 0;
  }

  // Sets the current value, using a String
  void setCurVal(String s)
  {
    output.setText(s);
    curVal = (new Double(s)).doubleValue();
  }

  // Sets the current value, using a number
  void setCurVal(double newValue)
  {
    curVal = nwValue;
    output.setText( newValue);
  }

  // ---------------------------------------------------------
  // This lays out the appearance of the applet, using
  // BorderLayout and GridLayout
  // The colors used for the buttons may, or may not, appear
  // on your copy, depending upon your Web browser
  // ---------------------------------------------------------
  Panel makeButtons()
  {
    // Create 4 Panels [p1 through p4]
    Panel p   = new Panel(new BorderLayout(5,5));
    Panel p1  = new Panel(new BorderLayout(5,5));
    Panel p2  = new Panel(new BorderLayout(5,5));
    Panel p3  = new Panel(new GridLayout(1,3,5,5));
    Panel p4  = new Panel(new GridLayout(4,5,5,5));
    Panel p5  = new Panel(new BorderLayout(5,5));

    // Add Backspace, CE, and C buttons to p3
    p3.setForeground(new Color(232,0,0));
    p3.setFont(new Font("Dialog", Font.PLAIN, 12));
    p3.add(new Button("Backspace"));
    p3.add(new Button("CE"));
    p3.add(new Button("C"));

    // Add Number buttons to p4
    p4.setForeground(new Color(0, 0, 235));
    p4.setFont(new Font("Dialog", Font.PLAIN, 14));
    p4.add(new Button("7"));
    p4.add(new Button("8"));
    p4.add(new Button("9"));
    p4.add(new Button("/"));
    p4.add(new Button("sqrt"));
    p4.add(new Button("4"));
    p4.add(new Button("5"));
    p4.add(new Button("6"));
    p4.add(new Button("*"));
    p4.add(new Button("%"));
    p4.add(new Button("1"));
    p4.add(new Button("2"));
    p4.add(new Button("3"));
    p4.add(new Button("-"));
    p4.add(new Button("1/x"));
    p4.add(new Button("0"));
    p4.add(new Button("+/-"));
    p4.add(new Button("."));
    p4.add(new Button("+"));
    p4.add(new Button("="));

    // Add and initialize output and total
    // [Label and TextArea for output]
    output.setBackground(Color.white);
    output.setForeground(Color.black);
    output.setFont(new Font("Courier", Font.BOLD, 18));

    total.setBackground(new Color(255, 255, 128));
    total.setForeground(Color.black);
    total.setFont(new Font("Courier", Font.BOLD, 14));

    p5.add("Center", total);
    p5.add("South",  output);


    // Hook up the panels
    p2.add("North", p3);
    p2.add("Center", p4);

    // Add some spacing around outside
    p1.add("North",  p5);
    p1.add("Center", p2);

    p.setFont(new Font("Helvetica", Font.PLAIN, 6));
    p.add("North", new Label(" "));
    p.add("East",  new Label(" "));
    p.add("West",  new Label(" "));
    p.add("South", new Label(" "));
    p.add("Center", p1);

    return p;
  }
}