/*
 * Calculator.java
 *
 * Version:
 *    $Id$
 *
 * Revisions:
 *    $Log$
 */

/**
 * This class implements the model (logic) of a simple 4 function
 * calculator.  The calculator provides integer only arithmetic
 * and a clear key.
 *
 * @author     Paul Tymann
 */

public class Calculator {

    // Valid digits

    private static final String DIGITS = "0123456789" ;

    private boolean firstDigit = true;      // State for State machine
    private int lOperand = 0;               // "Left" operator
    private String operator = "=";          // Last operator

    private CalcGui gui;                    // The "view"

    /**
      * Constructor for a Calculator.
      *
      * @param String name to go into window frame.
      */

    public Calculator( String name ) {
        gui = new CalcGui( this, name );
    }

    /**
      * Routine to handle button presses.  Everytime the view detects
      * that a button has been pressed, this routine will be called.
      * The parameter will be the label that appears on the button
      * (i.e. "0", "1", "2", ... "C")
      *
      * @param String label of the button pressed.
      */

    public void handleButton( String keyPressed ) {
	// Figure out what type of button was pressed and
	// take care of it

	// The first digit pressed after an operand marks the
	// beginning of a new number.

	if ( DIGITS.indexOf( keyPressed ) != -1 ) { // It is a digit
	    if ( firstDigit ) {                     // first digit is just
		firstDigit = false;                 // stuffed into the
		gui.setDisplay( keyPressed );       // display
	    }
	    else
		gui.setDisplay( gui.getDisplay() + keyPressed ); // add to end
	}
	else if ( keyPressed.equals( "C" ) ) {      // Clear
	    firstDigit = true;
	    lOperand = 0;
	    operator = "=";
	    gui.setDisplay( "0" );
	}
	else {                                      // An operator
	    if ( !firstDigit ) {
		compute( Integer.parseInt( gui.getDisplay() ) );
		firstDigit = true;
	    }

	    operator = keyPressed;
	}
    }

    /**
     * Appply the last operator added to the numbers entered by
     * the user and display the result on the calculator.
     *
     * @param rOperand the last number entered by the user
     */
    
    private void compute( int rOperand ) {
	// The variable lOperand is used to store the number that was
	// entered by the user before the last operator.

        switch( operator.charAt( 0 ) ) {
	case '=':
	    lOperand = rOperand ;
	    break ;
	case '+':
	    lOperand = lOperand + rOperand ;
	    break ;
	case '-':
	    lOperand = lOperand - rOperand ;
	    break ;
	case 'X':
	    lOperand = lOperand * rOperand ;
	    break ;
	case '/':
	    lOperand = lOperand / rOperand ;
	    break ;
	}
	
	// Update the display

	gui.setDisplay( String.valueOf( lOperand ) );
    }

    /**
     * Create a calculator and let it do its thing.
     *
     * @param args[] command line arguments (ignored)
     */
    
    public static void main( String args[] ) {
	new Calculator( "JavaCalc" );
    }

} // Calculator