/**
 *  <PRE>
 *  EventHandler.java
 *
 *  Revisions: 1.1 Mar. 14, 2001
 *               Added minor modifications to event handling behavior.  Added
 *               some documentation.
 *             1.0 Jan. 13, 2001
 *               Created the EventHandler class
 *
 *  </PRE>
 *
 *  @author <A HREF="mailto:demox@cc.gatech.edu">Luke A. Olbrish</A>
 *  @version Version 1.0, Jan. 13, 2001
 */

import java.awt.event.*;

public class EventHandler implements ActionListener
{
  // Data Block

  /**
   *  The actual gui that will be the view for this program.
   */
  private CalculatorGUI gui = null;

  /**
   *  This is the model that will actually perform calculations.
   */
  private Calculator calc = null;

  /**
   *  This state variable will be used to keep track of whether the number
   *  on the display needs to be replaced by new digits.
   */
  private boolean isNumberStarted = false;

  // Constructors

  /**
   *  Creates a new event handler that is bound by the gui view thats passed
   *  as a parameter.
   *
   *  @param gui the view that this control connects to.
   */
  public EventHandler( CalculatorGUI gui )
  {
    // If the gui is null, then this class is being used improperly and should
    // exit.
    if( gui == null )
      System.exit( 0 );

    // Add the model and view to the control.
    this.gui = gui;
    this.calc = new Calculator();
  }// end of constructor( CalculatorGUI )

  // Action Listener

  /**
   *  This function recieves an action event and interprets the event to take
   *  the proper action.  It receives all the button actions from 
   *  CalculatorGUI.
   *
   *  @param ae the action event that needs to be processed.
   */
  public void actionPerformed( ActionEvent ae )
  {
    // No action to process.
    if(( ae == null ) ||
       ( ae.getActionCommand() == null ))
      return;

    // Clear the calculator screen and model.
    if( ae.getActionCommand().equals( "Clr" ) )
      doClearCalculator();

    // Find out if an operation was selected and handle it.
    switch( ae.getActionCommand().charAt(0) )
      {
      case '=':
	doCalculation();
	break;
      case '+':
	doSetOp( Calculator.ADD_OP );
	break;
      case '-':
	doSetOp( Calculator.SUB_OP );
	break;
      case '*':
	doSetOp( Calculator.MUL_OP );
	break;
      case '/':
	doSetOp( Calculator.DIV_OP );
	break;
      default:
	break;
      }// end of switch

    // Find out if a digit was pressed
    if( Character.isDigit( ae.getActionCommand().charAt(0) ) )
      doAddDigit( ae.getActionCommand() );
  }// end of actionPerformed( ActionEvent )

  // Operational Functions

  /**
   *  This function assists the EventHandler by doing the actions needed to
   *  add a digit to the display.
   *
   *  @see #actionPerformed
   *  @param digit a string that should have a single digit contents.
   */
  private void doAddDigit( String digit )
  {
    // If diplay needs to be cleared before the digit is added.
    if( !isNumberStarted )
      {
	gui.setDisplay( digit );
	isNumberStarted = true;
      }
    else
      gui.setDisplay( gui.getDisplay() + digit );
  }// end of doAddDigit( String )

  /**
   *  Clears the gui display and resets the calculator model.
   *
   *  @see #actionPerformed
   */
  private void doClearCalculator()
  {
    isNumberStarted = false;
    gui.setDisplay( " " );
    calc.clearCalulator();
    return;
  }// end of doClearCalculator()

  /**
   *  Attempts to do a calculation.  GUI is updated based on whether a
   *  calculation occurs and returns the calculation to the gui.
   *
   *  @see #actionPerformed
   */
  public void doCalculation()
  {
    // holds the parsed operator #2.
    int val = 0;

    try
      { 
	// Attempt to parse an int from the gui.
	val = Integer.parseInt( gui.getDisplay() );

	// If preconditions are met, then attempt a calculation.
	if(( calc.isOperator1Set() ) &&
	   ( calc.isOperationSet() ))
	  {
	    // Calculate and update gui.
	    calc.setOperator2( val );
	    gui.setDisplay( "" + calc.getCalculation() );
	    // Reset display to take in numbers.
	    isNumberStarted = false;
	  }// end of if
      }// end of try
    catch( NumberFormatException nfe )
      {  
	calc.clearCalulator();
	gui.setDisplay( "Error!" );
	return;
      }// end of catch( NumberFormatException )
    catch( ArithmeticException ae )
      {
	calc.clearCalulator();
	gui.setDisplay( "Calc. Error!" );
	return;
      }// end of catch( ArithmeticException )
  }// end of doCalculation()

  /**
   *  Set the operation for the calculation.  If the operation is already set,
   *  then do a calculation then set the operation.
   *
   *  @see #actionPerformed
   */
  public void doSetOp( int operation )
  {
    try
      {
	// Do calculation if operation is already set.
	if( calc.isOperationSet() )
	  doCalculation();

	// Set the first operator and set the operation.
	calc.setOperator1( Integer.parseInt( gui.getDisplay() ));
	calc.setOperation( operation );
	isNumberStarted = false;
      }// end of try.
    catch( NumberFormatException  nfe )
      {
	calc.clearCalulator();
	gui.setDisplay( "Error!" );
      }// catch( NumberFormatException )
  }// end of doSetOp( int )

}// end of class EventHandler