// Photon.java Copyright (c) 2004 brising.com

import java.awt.Point;

/**
I travel across a field of GameButtons of various kinds.
*/
public
    class       Photon
    extends     Object
    implements  Runnable
    {
// INSTANCE VARIABLES /////////////////////////////////////////////////////////

        GamePanel   hoGamePanel;
        Point       hpDirection;
        Point       hpLocation;

// CONSTRUCTORS ///////////////////////////////////////////////////////////////

    public
        Photon
        (
        Point       apLocation,
        Point       apDirection,
        GamePanel   aoGamePanel
        )
        {
        hpDirection = new Point(apDirection);
        hpLocation  = new Point(apLocation);
        hoGamePanel = aoGamePanel;
        }

// PUBLIC INSTANCE METHODS ////////////////////////////////////////////////////

    /**
    Begin my travels.
    */
    public
        void        run
        (
        )
        {
        GameButton oGameButton = currentButton();
        oGameButton.initiate();
        while ((oGameButton = nextButton()).isPropagating())
            {/* do nothing, but propagate through space */}
        oGameButton.terminate();
        }

// PROTECTED INSTANCE METHODS /////////////////////////////////////////////////

    /**
    Which button am I currently in?
    */
    protected
        GameButton  currentButton
        (
        )
        {
        return getButton(hpLocation.x, hpLocation.y);
        }

    /**
    Get the button at the given coordinates.
    */
    protected
        GameButton  getButton
        (
        int         aiX,
        int         aiY
        )
        {
        return hoGamePanel.getButton(aiX, aiY);
        }

    /**
    Propagate to the next button.
    I do this by looking at the three buttons ahead of me:
    one directly in front,
    one diagonally to the left,
    one diagonally to the right.
    The combination of their occupiedness is combined into an integer,
    which is used to switch to the appropriate code.
    Return the next button in my travels.
    */
    protected
        GameButton  nextButton
        (
        )
        {
        int iXDirection = hpDirection.x;
        int iYDirection = hpDirection.y;
        int iXLocation  = hpLocation.x+iXDirection;
        int iYLocation  = hpLocation.y+iYDirection;
        int iState = 0x0
                | ((getButton(iXLocation-iYDirection,iYLocation-iXDirection)
                    .isOccupied()) ? 1 : 0) << 0
                | ((getButton(iXLocation,iYLocation)
                    .isOccupied()) ? 1 : 0) << 1
                | ((getButton(iXLocation+iYDirection,iYLocation+iXDirection)
                    .isOccupied()) ? 1 : 0) << 2;
        switch (iState)
            {
            default:
                throw new RuntimeException
                    ("Unknown case in nextButton(): "
                    +iState
                    );
            case 0: // go forward
            case 2: // go forward
            case 3: // go forward
            case 6: // go forward
            case 7: // go forward
                hpLocation.x +=  iXDirection;
                hpLocation.y +=  iYDirection;
                break;
            case 1: // turn one direction
                hpDirection.x =  iYDirection;
                hpDirection.y =  iXDirection;
                break;
            case 4: // turn the other direction
                hpDirection.x = -iYDirection;
                hpDirection.y = -iXDirection;
                break;
            case 5: // turn around and go back
                hpDirection.x = -iXDirection;
                hpDirection.y = -iYDirection;
                break;
            }
        return currentButton();
        }
    }