/*

The Rail class.  A Rail object is a piece of track.  It knows
whether there is a Train on it or not, and Trains can enter()
and leave().  Given an entrance, a Rail can report where the exit()
is.

*/

import java.awt.*;

abstract class Rail extends Canvas {
    
    // The amound of space in which Rails have to draw themselves.
    public static int size = 20;
    
    protected Color color;
    protected boolean haveATrain;
    protected Car currentCar;
    protected GridLoc location;

    // True if a car entered or left.  Used to speed up redrawing.
    public boolean stateChanged=true;
    
    public Rail(GridLoc loc) {
        location = loc;
        haveATrain = false;
    } 

    public Rail() {
        super();
        haveATrain = false;
        Rectangle b = bounds();
        resize(size, size);
    } 

    // Return true iff I have a Car.
    public boolean occupied () {
        return haveATrain;
    } 

    public void setLoc(GridLoc loc) {
        location = loc;
    } 

    public GridLoc getLoc () {
        return location;
    } 

    // Redraw myself.
    public void draw(Graphics g) {
    
        Rectangle b = bounds();
        g.setColor(Color.white);
        g.fillRect(0, 0, b.width-1, b.height-1);
        g.setColor(Color.lightGray);
        g.drawRect(0, 0, b.width-1, b.height-1);

        if (haveATrain) {
            currentCar.draw(g);
        }
    }
        
    // Register that a Train is on me.  Return true if succesful,
    // false otherwise.
    public boolean enter(Car newCar) {
        haveATrain = true;
        currentCar = newCar;
        return true;
    }

    // Register that a Train is no longer on me.
    public void leave() {
        haveATrain = false;
        repaint();
    }
        
    // Update my display.
    public void paint(Graphics g) {
        draw(g);
    }
        
    // Return true if d is a valid direction for me.
    abstract public boolean exitOK(Direction d);
        
    // Register that Rail r is in Direction d.
    abstract public void register(Rail r, Direction d);

    // Register that there is no Rail in Direction d.
    abstract public void unRegister(Direction d);

    // Given that d is the Direction from which a Car entered,
    // report where the Car will exit.
    abstract public Direction exit(Direction d);

    // Given that d is the Direction from which a Car entered,
    // report which Rail is next.
    abstract public Rail nextRail(Direction d);

    // Return myself as a string.
    public String toString() { return "Rail"; };

}