--Utility Functions for Tables

function create_list()
   t = {};
   t.elements = {};
   t.size = 0;

   return t;
end

function add_element_to(t, e)
   t.size = t.size + 1;
   t.elements[t.size] = e;

   return true;
end

function remove_element_from(t, index)
   for i = index,t.size-1,1 do
      t.elements[i] = t.elements[i+1];
   end
   t.size = t.size - 1;

   return true;
end

function get_element(t, index)
   return t.elements[index];
end

function find_in(t, e)
   not_found = true;
   i = 0;

   while (not_found and i < t.size) do
      i = i + 1;
	  if (match(t.elements[i], e)) then
	     not_found = false
		 return i;
	  end
   end

   return 0;
end

function get_neighbors(e, target, map)
   d = {};
   d[1] = {coords = {x = e.coords.x-1, y = e.coords.y}};
   d[2] = {coords = {x = e.coords.x, y = e.coords.y+1}};
   d[3] = {coords = {x = e.coords.x+1, y = e.coords.y}};
   d[4] = {coords = {x = e.coords.x, y = e.coords.y-1}};

   n = create_list();

   for i = 1,4,1 do
      if not wall_at(d[i].coords.y, d[i].coords.x) then
	     d[i].score = distance(d[i].coords, target.coords);
		 d[i].parent = e;
		 d[i].path_length = e.path_length + 1;
		 add_element_to(n, d[i]);
      end
   end

   return n;
end

function find_min(t)
   lowest = -1;
   lowest_index = -1;

   for i = 1,t.size,1 do
      if (lowest_index == -1 or t.elements[i].score < lowest) then
	     lowest = t.elements[i].score;
		 lowest_index = i;
	  end
   end

   return lowest_index;
end

function match(e1, e2)
   if (e1.coords.x == e2.coords.x and e1.coords.y == e2.coords.y) then
      return true;
   else
      return false;
   end
end

function get_parent(e)
   return e.parent;
end

function get_path_from(e, start)
  r = create_list();
  add_element_to(r, e);

  l = e;

  while not (l == nil) do
	 add_element_to(r, l);
	 l = get_parent(l);
  end

  return r;
end

function swap_elements(t, index1, index2)
   temp = t.elements[index1];
   t.elements[index1] = t.elements[index2]
   t.elements[index2] = temp;

   return true;
end

function sort_table(t)
   made_swaps = true;

   while(made_swaps) do
      made_swaps = false;
      for i = 1,t.size-1,1 do
	     if get_element(t, i).score > get_element(t, i+1).score then
		    swap_elements(t, i, i+1);
			made_swaps = true;
		 end
	  end
   end

   return true;
end