class RpgGrid
  @mc = nil
  @gridSize = nil

  # need the @mc to query occupied locations.
  def initialize(mc, grid_size=25)
    @mc = mc
    @gridSize = grid_size
  end

  # Finds a place to put either a player or a monster that isn't currently occupied
  # Players need to spawn in a non-player cell, monsters can replace an existing monster
  def find_location()
    loop do
      x = rand(@gridSize)
      y = rand(@gridSize)

      loc = [x, y]

      n = @mc.collection().find({'location' => [x, y]})
      if n.count == 0 then
        return loc
      elsif n.first["type"] == :monster then
        @mc.collection().delete_one({"_id" => n.first["_id"]})
        return loc
      end
    end
  end

  # Move the +/- 1 on the x/y with them "bumping" off the walls to find a new position.
  # Gotta keep em in the grid.
  def get_move_location(cur_loc=nil)
    if cur_loc == nil then
      cur_loc = [0, 0]
    end

    # get the x/y differences
    dx = get_move_diff(cur_loc[0])
    dy = get_move_diff(cur_loc[1])

    # Build a new [x,y] to save to location
    new_loc = [cur_loc[0] + dx, cur_loc[1] + dy]

    return new_loc
  end

  # Should keep all chars inside the @gridSize playfield though without getting locked on an edge
  def get_move_diff(cur_loc)
    # i should be a num between 0 and 2.  If 0 == 0, 1 == 1, 2 == -1.  Intuitive right?
    i = rand(3)
    d = 0

    if i == 2 then
      d = -1
    else
      d = i
    end

    if cur_loc == 0 and d == -1 then
      d = rand(2)
    elsif cur_loc == @gridSize - 1 and d == 1 then
      d = rand(2) - 1
    end

    return d
  end
end