#!/usr/bin/env python
# encoding: utf-8

from .render import txt, tex


class Renderable(object):
    """
    A Renderable object is an object which can work with Render class. It means that it has to have attribute postfix_tokens.
    """
    STR_RENDER = tex
    DEFAULT_RENDER = tex

    @classmethod
    def set_render(cls, render):
        cls.STR_RENDER = render

    @classmethod
    def get_render(cls):
        return cls.STR_RENDER

    @classmethod
    def set_default_render(cls):
        cls.set_render(cls.DEFAULT_RENDER)

    @classmethod
    def tmp_render(cls, render=tex):
        """ Create a container in which Expression render is temporary modify

        The default temporary render is Expression in order to perform calculus inside numbers

        >>> from .expression import Expression
        >>> exp = Expression("2*3/5")
        >>> print(exp)
        2 \\times \\frac{ 3 }{ 5 }
        >>> for i in exp.simplify().explain():
        ...     print(i)
        2 \\times \\frac{ 3 }{ 5 }
        \\frac{ 3 }{ 5 } \\times 2
        \\frac{ 3 \\times 2 }{ 5 }
        \\frac{ 6 }{ 5 }
        >>> with Expression.tmp_render(txt):
        ...     for i in exp.simplify().explain():
        ...         print(i)
        2 * 3 / 5
        3 / 5 * 2
        ( 3 * 2 ) / 5
        6 / 5
        >>> for i in exp.simplify().explain():
        ...     print(i)
        2 \\times \\frac{ 3 }{ 5 }
        \\frac{ 3 }{ 5 } \\times 2
        \\frac{ 3 \\times 2 }{ 5 }
        \\frac{ 6 }{ 5 }

        # TODO: essayer de ne pas afficher ce changement de position. |lun. avril  6 17:29:56 CEST 2015

        """
        class TmpRenderEnv(object):

            def __enter__(self):
                self.old_render = Renderable.get_render()
                Renderable.set_render(render)

            def __exit__(self, type, value, traceback):
                Renderable.set_render(self.old_render)
        return TmpRenderEnv()

    def __eq__(self, other):
        """ Two Renderable objects are the same if they have same postfix_tokens """
        try:
            return self.postfix_tokens == other.postfix_tokens
        except AttributeError:
            return False


class Explicable(Renderable):

    """ An Explicable object is an object which can be explicable!

    It's a parent class of a more classical Expression, Fraction and Polynom (and later square root)
    Child class will have the following method
        * explain: Generator which return steps which leed to himself

    """

    def __init__(self, *args, **kwargs):
        self.steps = []

    def explain(self, noself=True):
        """ Generate and render steps  which leed to itself

        :param noself: does explain return self

        """
        old_s = ''
        # les étapes pour l'atteindre
        try:
            for s in self.steps:
                if hasattr(s, 'postfix_tokens'):
                    new_s = self.STR_RENDER(s.postfix_tokens)
                else:
                    new_s = self.STR_RENDER(s)
                if not self.is_same_step(new_s, old_s):
                    old_s = new_s
                    yield new_s
        except AttributeError:
            pass

        if noself:
            # Lui même
            new_s = self.STR_RENDER(self.postfix_tokens)
            if not self.is_same_step(new_s, old_s):
                yield new_s

    def is_same_step(self, new, old):
        """Return whether the new step is the same than old step
        """
        try:
            if new.replace(" ", "") == old.replace(" ", ""):
                return True
            else:
                return False
        except AttributeError:
            if new == old:
                return True
            else:
                return False


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