public class Puzzle
{
  public static void main(String[] args)
  {
    setup();
    play();
  }
  
  public static void setup()
  {
    Grid.window(8, 3);
    Draw.setTitle("Column Puzzle");
    Grid.setLineColor(0, 0, 0);
    drawArrows();
    drawAllTiles();
  }
  
  public static void drawArrows()
  {
    Grid.setImage(0, 0, "left.gif");
    Grid.setImage(0, 1, "left.gif");
    Grid.setImage(0, 2, "left.gif");
    Grid.setImage(7, 0, "right.gif");
    Grid.setImage(7, 1, "right.gif");
    Grid.setImage(7, 2, "right.gif");
  }
  
  public static boolean isEmpty(int x, int y)
  {
    return Grid.getRed(x, y) == 0 &&
      Grid.getGreen(x, y) == 0 &&
      Grid.getBlue(x, y) == 0;
  }
  
  public static void drawOneTile(int red, int green, int blue)
  {
    int x;
    int y;
    x = Util.random(1, 6);
    y = Util.random(0, 2);
    while (!isEmpty(x, y))
    {
      x = Util.random(1, 6);
      y = Util.random(0, 2);
    }
    Grid.setColor(x, y, red, green, blue);
  }
  
  public static void drawAllTiles()
  {
    //draw 3 tiles of each color but cyan
    int numTimes;
    numTimes = 0;
    while (numTimes < 3)
    {
      drawOneTile(0, 0, 255);  //blue
      drawOneTile(255, 0, 0);  //red
      drawOneTile(0, 255, 0);  //green
      drawOneTile(255, 255, 0);  //yellow
      drawOneTile(255, 0, 255);  //magenta
      numTimes = numTimes + 1;
    }
    
    //draw 2 cyan tiles
    drawOneTile(0, 255, 255);
    drawOneTile(0, 255, 255);
  }
  
  public static void swapTiles(int x1, int y1, int x2, int y2)
  {
    int red;
    int green;
    int blue;
    red = Grid.getRed(x1, y1);
    green = Grid.getGreen(x1, y1);
    blue = Grid.getBlue(x1, y1);
    Grid.setColor(x1, y1, Grid.getRed(x2, y2), Grid.getGreen(x2, y2), Grid.getBlue(x2, y2));
    Grid.setColor(x2, y2, red, green, blue);
  }
  
  public static void slideOneTile(int x, int y)
  {
    if (y > 0 && isEmpty(x, y - 1))  //can slide up?
    {
      swapTiles(x, y, x, y - 1);  //slide up
    }
    else
    {
      if (y < Grid.getHeight() - 1 && isEmpty(x, y + 1))  //can slide down?
      {
        swapTiles(x, y, x, y + 1);  //slide down
      }
    }
  }

  public static void slideLeft(int y)
  {
    int red;
    int green;
    int blue;
    
    //save leftmost color
    red = Grid.getRed(1, y);
    green = Grid.getGreen(1, y);
    blue = Grid.getBlue(1, y);
    
    //swap 1st with 2nd, then 2nd with 3rd, etc.
    int x;
    x = 0;
    while (x < Grid.getWidth() - 2)
    {
      swapTiles(x, y, x + 1, y);  //swap x with x + 1
      x = x + 1;
    }
    
    //set color of last tile
    Grid.setColor(Grid.getWidth() - 2, y, red, green, blue);
  }
  
  public static void slideRight(int y)
  {
    int red;
    int green;
    int blue;
    
    //save rightmost color
    red = Grid.getRed(Grid.getWidth() - 2, y);
    green = Grid.getGreen(Grid.getWidth() - 2, y);
    blue = Grid.getBlue(Grid.getWidth() - 2, y);
    
    //swap 2nd to last with last, then 3rd to 2nd to last, etc.
    int x;
    x = Grid.getWidth() - 3;
    while (x >= 1)
    {
      swapTiles(x, y, x + 1, y);  //swap x with x + 1
      x = x - 1;
    }
    
    //set color of first tile
    Grid.setColor(1, y, red, green, blue);
  }
  
  public static void play()
  {
    int x;
    int y;

    while (true)
    {
      Draw.pauseUntilMouse();
      x = Grid.getMouseX();
      y = Grid.getMouseY();
      
      if (x == 0)
      {
        //clicked on left arrow
        slideLeft(y);
      }
      else
      {
        if (x == 7)
        {
          //clicked right arrow
          slideRight(y);
        }
        else
        {
          //clicked on a tile
          slideOneTile(x, y);
        }
      }
    }
  }
}