ai_rulebased.py

'''
This module contains class implementating a rule-based algorithm 
for the snake. The policy is simple:

- Attempt to move towards the food in the y-direction if there is 
  no obstacle;
- Otherwise, attempt to move towards the food in the x-direction 
  if there is no obstacle;
- Otherwise, attempt to go around by moving away from the food direction
  if there is no obstacle;
- Otherwise, we can only let the snake to continue with its current 
  movement. When reaching this stage, the snake is already surrounded 
  by obstacles.
'''

from snake import GameOutcome
from ai_base import SystemState, AI_Base

class AI_RuleBased(AI_Base):
    '''
    This is the implementation of the rule-based algorithm.
    '''

    def __init__(self):
        super().__init__()
        self._name = "Rule-based algorithm"

    def callback_take_action(self, state:SystemState) -> (int,int):
        '''Here we implement the rule-based algorithm based on the 
        described policy.'''
        BLOCKED = -1 # define constants here for better code readability
        EAST = (+1,0); WEST = (-1,0)
        NORTH = (0,-1); SOUTH = (0,+1)
        movement = (state.dir_x,state.dir_y)

        if state.food_north and state.obj_north is not BLOCKED:   movement = NORTH 
        elif state.food_south and state.obj_south is not BLOCKED: movement = SOUTH 
        elif state.food_east and state.obj_east is not BLOCKED:   movement = EAST 
        elif state.food_west and state.obj_west is not BLOCKED:   movement = WEST
        else: # the following is where the snake can't move towards
              # the food & has to go around
            if state.dir_x!=0: # for east/west movement
                if state.obj_north is not BLOCKED:    movement = NORTH 
                elif state.obj_south is not BLOCKED:  movement = SOUTH 
            elif state.dir_y!=0: # for north/south movement
                if state.obj_east is not BLOCKED:     movement = EAST 
                elif state.obj_west is not BLOCKED:   movement = WEST 
            else: pass # by passing, the snake will continue its current movement
        return movement

    def callback_action_outcome(self, state:SystemState, outcome:GameOutcome):
        '''For this implementation, the rule-based algorithm is static. 
        It does not take feedback to refine its policy.'''
        pass