text: """
  Copyright © 2021-2022 The Johns Hopkins University Applied Physics Laboratory LLC
  
  Permission is hereby granted, free of charge, to any person obtaining a copy 
  of this software and associated documentation files (the “Software”), to 
  deal in the Software without restriction, including without limitation the 
  rights to use, copy, modify, merge, publish, distribute, sublicense, and/or 
  sell copies of the Software, and to permit persons to whom the Software is 
  furnished to do so, subject to the following conditions:
  
  The above copyright notice and this permission notice shall be included in 
  all copies or substantial portions of the Software.
  
  THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, 
  WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR 
  IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  """
  
  from operator import add
  
  import gym
  from gym_minigrid.envs import DynamicObstaclesEnv, MiniGridEnv
  
  
  class CustomDynamicObstaclesEnv(DynamicObstaclesEnv):
      def __init__(
          self, size=8, agent_start_pos=(1, 1), agent_start_dir=0, n_obstacles=4
      ):
          super().__init__(size, agent_start_pos, agent_start_dir, n_obstacles)
  
          # DynamicObstaclesEnv limits actions, but we want that left for our wrapper
          self.action_space = gym.spaces.Discrete(7)
  
      # This method is a modified copy of the .step() method of the parent class,
      #   DynamicObstaclesEnv, obtained from https://github.com/maximecb/gym-minigrid
      #   under Apache License 2.0, Copyright 2019 Maxime Chevalier-Boisvert
      def step(self, action):
          # Check if there is an obstacle in front of the agent
          #   In the parent class, DynamicObstaclesEnv, touching a wall would end an episode.
          #   Now, only obstacles carry this penalty.
          front_cell = self.grid.get(*self.front_pos)
          not_clear = front_cell and front_cell.type == "ball"
  
          # Update obstacle positions
          for i_obst in range(len(self.obstacles)):
              old_pos = self.obstacles[i_obst].cur_pos
              top = tuple(map(add, old_pos, (-1, -1)))
  
              try:
                  self.place_obj(
                      self.obstacles[i_obst], top=top, size=(3, 3), max_tries=100
                  )
                  self.grid.set(*old_pos, None)
              except RecursionError:
                  pass
  
          # Update the agent's position/direction
          obs, reward, done, info = MiniGridEnv.step(self, action)
  
          # If the agent collided with an obstacle, end the episode
          if action == self.actions.forward and not_clear:
              reward = -1
              done = True
              return obs, reward, done, info
  
          return obs, reward, done, info
  
      def _gen_grid(self, width, height):
          super()._gen_grid(width, height)
  
          # DynamicObstaclesEnv uses the class Ball as obstacles, but those can be picked up.
          #   To prevent this, replace their .can_pickup() method with no_obstacle_pickup().
          def no_obstacle_pickup():
              return False
  
          for ball in self.obstacles:
              ball.can_pickup = no_obstacle_pickup
  
  
  class CustomDynamicObstaclesS6N1(CustomDynamicObstaclesEnv):
      def __init__(
          self,
          agent_start_pos=(1, 1),
          agent_start_dir=0,
      ):
          super().__init__(6, agent_start_pos, agent_start_dir, 1)
  
  
  class CustomDynamicObstaclesS8N2(CustomDynamicObstaclesEnv):
      def __init__(
          self,
          agent_start_pos=(1, 1),
          agent_start_dir=0,
      ):
          super().__init__(8, agent_start_pos, agent_start_dir, 2)
  
  
  class CustomDynamicObstaclesS10N3(CustomDynamicObstaclesEnv):
      def __init__(
          self,
          agent_start_pos=(1, 1),
          agent_start_dir=0,
      ):
          super().__init__(10, agent_start_pos, agent_start_dir, 3)
  