/* peterm@langmuir.eecs.berkeley.edu:  this function generates a random
blocked maze with the property that there is only one path from one spot
to any other, and there is always a path from one spot to any other.

input:  xsize, ysize;
output:  a char** array with # and . for closed and open respectively.

a char value of 0 represents a blank space:  a '#' is
a wall.

*/

/* we need to maintain a list of wall points to generate
   reasonable mazes:  a straightforward recursive random walk maze
   generator would generate a map with a trivial circle-the-outer-wall solution */

#include <global.h>

#include "random_map.h"
#include "rproto.h"

/* global variables that everyone needs:  don't want to pass them in
   as parameters every time. */
static int *wall_x_list = 0;
static int *wall_y_list = 0;
static int wall_free_size = 0;

/*  the free wall points are those outer points which aren't corners or
    near corners, and don't have a maze wall growing out of them already. */
static void
make_wall_free_list (int xsize, int ysize)
{
  int i, j, count;

  count = 0;                    /* entries already placed in the free list */
  /*allocate it */
  if (wall_free_size < 0)
    return;

  wall_x_list = (int *)calloc (sizeof (int), wall_free_size);
  wall_y_list = (int *)calloc (sizeof (int), wall_free_size);

  /* top and bottom wall */
  for (i = 2; i < xsize - 2; i++)
    {
      wall_x_list[count] = i;
      wall_y_list[count] = 0;
      count++;
      wall_x_list[count] = i;
      wall_y_list[count] = ysize - 1;
      count++;
    }

  /* left and right wall */
  for (j = 2; j < ysize - 2; j++)
    {
      wall_x_list[count] = 0;
      wall_y_list[count] = j;
      count++;
      wall_x_list[count] = xsize - 1;
      wall_y_list[count] = j;
      count++;
    }
}

/* randomly returns one of the elements from the wall point list */
static void
pop_wall_point (int *x, int *y)
{
  int index = rmg_rndm (wall_free_size);

  *x = wall_x_list[index];
  *y = wall_y_list[index];
  /* write the last array point here */
  wall_x_list[index] = wall_x_list[wall_free_size - 1];
  wall_y_list[index] = wall_y_list[wall_free_size - 1];
  wall_free_size--;
}

/* find free point:  randomly look for a square adjacent to this one where
we can place a new block without closing a path.  We may only look
up, down, right, or left. */
static int
find_free_point (char **maze, int *x, int *y, int xc, int yc, int xsize, int ysize)
{
  /* we will randomly pick from this list, 1=up,2=down,3=right,4=left */
  int dirlist[4];
  int count = 0;                /* # elements in dirlist */

  /* look up */
  if (yc < ysize - 2 && xc > 2 && xc < xsize - 2)       /* it is valid to look up */
    {
      int cleartest = (int) maze[xc][yc + 1] + (int) maze[xc - 1][yc + 1] + (int) maze[xc + 1][yc + 1];

      cleartest += (int) maze[xc][yc + 2] + (int) maze[xc - 1][yc + 2] + (int) maze[xc + 1][yc + 2];

      if (cleartest == 0)
        dirlist[count++] = 1;
    }

  /* look down */
  if (yc > 2 && xc > 2 && xc < xsize - 2)       /* it is valid to look down */
    {
      int cleartest = (int) maze[xc][yc - 1] + (int) maze[xc - 1][yc - 1] + (int) maze[xc + 1][yc - 1];

      cleartest += (int) maze[xc][yc - 2] + (int) maze[xc - 1][yc - 2] + (int) maze[xc + 1][yc - 2];

      if (cleartest == 0)
        dirlist[count++] = 2;
    }

  /* look right */
  if (xc < xsize - 2 && yc > 2 && yc < ysize - 2)       /* it is valid to look left */
    {
      int cleartest = (int) maze[xc + 1][yc] + (int) maze[xc + 1][yc - 1] + (int) maze[xc + 1][yc + 1];

      cleartest += (int) maze[xc + 2][yc] + (int) maze[xc + 2][yc - 1] + (int) maze[xc + 2][yc + 1];

      if (cleartest == 0)
        dirlist[count++] = 3;
    }

  /* look left */
  if (xc > 2 && yc > 2 && yc < ysize - 2)       /* it is valid to look down */
    {
      int cleartest = (int) maze[xc - 1][yc] + (int) maze[xc - 1][yc - 1] + (int) maze[xc - 1][yc + 1];

      cleartest += (int) maze[xc - 2][yc] + (int) maze[xc - 2][yc - 1] + (int) maze[xc - 2][yc + 1];

      if (cleartest == 0)
        dirlist[count++] = 4;
    }

  if (count == 0)
    return -1;                  /* failed to find any clear points */

  /* choose a random direction */
  switch (dirlist [rmg_rndm (count)])
    {
      case 1:                  /* up */
        *y = yc + 1;
        *x = xc;
        break;

      case 2:                  /* down */
        *y = yc - 1;
        *x = xc;
        break;

      case 3:                  /* right */
        *y = yc;
        *x = xc + 1;
        break;
        
      case 4:                  /* left */
        *x = xc - 1;
        *y = yc;
        break;

      default:                 /* ??? */
        return -1;

    }

  return 1;
}

/* recursive routine which will fill every available space in the maze
        with walls*/
static void
fill_maze_full (char **maze, int x, int y, int xsize, int ysize)
{
  int xc, yc;

  /* write a wall here */
  maze[x][y] = '#';

  /* decide if we're going to pick from the wall_free_list */
  if (rmg_rndm (4) && wall_free_size > 0)
    {
      pop_wall_point (&xc, &yc);
      fill_maze_full (maze, xc, yc, xsize, ysize);
    }

  /* change the if to a while for a complete maze.  */
  while (find_free_point (maze, &xc, &yc, x, y, xsize, ysize) != -1)
    fill_maze_full (maze, xc, yc, xsize, ysize);
}

/* recursive routine which will fill much of the maze, but will leave
        some free spots (possibly large) toward the center.*/
static void
fill_maze_sparse (char **maze, int x, int y, int xsize, int ysize)
{
  int xc, yc;

  /* write a wall here */
  maze[x][y] = '#';

  /* decide if we're going to pick from the wall_free_list */
  if (rmg_rndm (4) && wall_free_size > 0)
    {
      pop_wall_point (&xc, &yc);
      fill_maze_sparse (maze, xc, yc, xsize, ysize);
    }

  /* change the if to a while for a complete maze.  */
  if (find_free_point (maze, &xc, &yc, x, y, xsize, ysize) != -1)
    fill_maze_sparse (maze, xc, yc, xsize, ysize);
}

/* the outsize interface routine:  accepts sizes, returns a char
** maze.  option is a flag for either a sparse or a full maze. Sparse
mazes have sizable rooms. option = 1, full, 0, sparse.*/
void
maze_gen (Layout maze, int option)
{
  maze->clear ();
  maze->border ();

  /* find how many free wall spots there are */
  wall_free_size = 2 * (maze->w - 4) + 2 * (maze->h - 4);

  make_wall_free_list (maze->w, maze->h);

  /* return the empty maze */
  if (wall_free_size <= 0)
    return;

  /* recursively generate the walls of the maze */
  /* first pop a random starting point */
  while (wall_free_size > 0)
    {
      int i, j;

      pop_wall_point (&i, &j);

      if (option)
        fill_maze_full (maze, i, j, maze->w, maze->h);
      else
        fill_maze_sparse (maze, i, j, maze->w, maze->h);
    }

  /* clean up our intermediate data structures. */

  free (wall_x_list);
  free (wall_y_list);
}