/*************************************************************************
 *
 *  A cell in a 2d grid. A helper class for Maze.java.
 *
 *************************************************************************/

public class Cell {
   private Cell north, east, south, west;  // neighboring cells
   private boolean northWall, eastWall;    // does the wall to the north exist
   private boolean southWall, westWall;
   private boolean visited;
   private double x, y;                           // Euclidean coordinates of cell center

   public Cell(double x, double y) { 
      this.x = x;
      this.y = y;
      northWall = eastWall = southWall = westWall = true;
   }

   void setVisited(boolean b) { visited = b; }

   boolean isVisited() { return visited; }

   void setNeighbors(Cell north, Cell east, Cell south, Cell west) {
      this.north = north;
      this.east  = east;
      this.south = south;
      this.west  = west;
   }

   Cell getNorth() { if (!northWall) return north; else return null; }
   Cell getEast()  { if (!eastWall)  return east;  else return null; }
   Cell getSouth() { if (!southWall) return south; else return null; }
   Cell getWest()  { if (!westWall)  return west;  else return null; }

  /********************************************************************
   * Find a random neighbor that leads to a previously unvisited
   * neighbor. If you find one, delete the wall and return the
   * neighbor; otherwise return null.
   ********************************************************************/
   Cell deleteRandomWall() {
      if (north.visited && east.visited && south.visited && west.visited)
         return null;

      // pick random neighbor (could use Knuth's trick instead)
      while (true) {
         double r = Math.random();
         if (r < 0.25 && !north.visited) {
            northWall = north.southWall = false;
            return north;
         }
         else if (r >= 0.25 && r < 0.50 && !east.visited) {
            eastWall = east.westWall = false;
            return east;
         }
         else if (r >= 0.5 && r < 0.75 && !south.visited) {
            southWall = south.northWall = false;
            return south;
         }
         else if (r >= 0.75 && r < 1.00 && !west.visited) {
            westWall = west.eastWall = false;
            return west;
         }
      }
   }


  /********************************************************************
   * Draw cell cornered at (x, y) of given size.
   ********************************************************************/
   public void spot(Draw d, double size) {
      d.moveTo(x + size / 2, y + size / 2);
      d.spot(size / 2);
   }

  /********************************************************************
   * Draw cell cornered at (x, y) of given size.
   ********************************************************************/
   public void draw(Draw d, double size) {
       d.moveTo(x, y);

       // south wall
       if (southWall) d.moveTo(x + size, y);
       else           d.lineTo(x + size, y);

       // east wall
       if (eastWall)  d.moveTo(x + size, y + size);
       else           d.lineTo(x + size, y + size);

       // north wall
       if (northWall) d.moveTo(x, y + size);
       else           d.lineTo(x, y + size);

       // west wall
       if (westWall)  d.moveTo(x, y);
       else           d.lineTo(x, y);
    }
}