Artificial-Intelligence-Nanodegree/Term-I – AI Foundations/03 - Cargo Planning/lp_utils.py

from aimacode.logic import associate
from aimacode.utils import expr


class FluentState():
    """ state object for planning problems as positive and negative fluents

    """

    def __init__(self, pos_list, neg_list):
        self.pos = pos_list
        self.neg = neg_list

    def sentence(self):
        return expr(conjunctive_sentence(self.pos, self.neg))

    def pos_sentence(self):
        return expr(conjunctive_sentence(self.pos, []))


def conjunctive_sentence(pos_list, neg_list):
    """ returns expr conjuntive sentence given positive and negative fluent lists

    :param pos_list: list of fluents
    :param neg_list: list of fluents
    :return: expr sentence of fluent conjunction
        e.g. "At(C1, SFO) ∧ ~At(P1, SFO)"
    """
    clauses = []
    for f in pos_list:
        clauses.append(expr("{}".format(f)))
    for f in neg_list:
        clauses.append(expr("~{}".format(f)))
    return associate('&', clauses)


def encode_state(fs: FluentState, fluent_map: list) -> str:
    """ encode fluents to a string of T/F using mapping

    :param fs: FluentState object
    :param fluent_map: ordered list of possible fluents for the problem
    :return: str eg. "TFFTFT" string of mapped positive and negative fluents
    """
    state_tf = []
    for fluent in fluent_map:
        if fluent in fs.pos:
            state_tf.append('T')
        else:
            state_tf.append('F')
    return "".join(state_tf)


def decode_state(state: str, fluent_map: list) -> FluentState:
    """ decode string of T/F as fluent per mapping

    :param state: str eg. "TFFTFT" string of mapped positive and negative fluents
    :param fluent_map: ordered list of possible fluents for the problem
    :return: fs: FluentState object

    lengths of state string and fluent_map list must be the same
    """
    fs = FluentState([], [])
    for idx, char in enumerate(state):
        if char == 'T':
            fs.pos.append(fluent_map[idx])
        else:
            fs.neg.append(fluent_map[idx])
    return fs