function move_to_empty_space(y, x)
  local path = unwind_path(find_path(level_state, player, {y=y, x=x}))
  if #path == 0 then return end
  local src = level_state[player.y][player.x]
  local dest = level_state[y][x]
  if dest == CELL_WALL or dest == CELL_CRATE or dest == CELL_CRATE_ON_TARGET then
    return
  end
  local u = {
    {x=player.x, y=player.y, cell=src},
    {x=x, y=y, cell=dest}}
  move_player_to(y, x)
  remove_player_from(player.y, player.x)
  player.x, player.y = x, y
  table.insert(undo_history, u)
end

  path = unwind_path(find_path(level_state, {x=15,y=12}, {x=12, y=9}))

  draw_path(path)

  if x > left and x < left+lw*side and y > top and y < top+lh*side then
    move_to_empty_space(1+floor((y-top)/side), 1+floor((x-left)/side))
  end