#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# direction.py

"""
Causal directions.
"""

from enum import Enum


class Direction(Enum):
    """Constant that parametrizes cause and effect methods.

    Accessed using ``Direction.CAUSE`` and ``Direction.EFFECT``, etc.
    """
    CAUSE = 0
    EFFECT = 1
    BIDIRECTIONAL = 2

    def __str__(self):
        return self.name

    def to_json(self):
        return {'direction': self.name}

    @classmethod
    def from_json(cls, dct):
        return cls[dct['direction']]

    def order(self, mechanism, purview):
        """Order the mechanism and purview in time.

        If the direction is ``CAUSE``, then the purview is at |t-1| and the
        mechanism is at time |t|. If the direction is ``EFFECT``, then the
        mechanism is at time |t| and the purview is at |t+1|.
        """
        if self is Direction.CAUSE:
            return purview, mechanism
        elif self is Direction.EFFECT:
            return mechanism, purview

        from . import validate
        return validate.direction(self)