# -*- coding: utf-8 -*-



class Reduction(object):

    _MASK = '_'

    def __init__(self, source):
        self.source = source
        self.reduction = unicode()
        self.pointers = list()

    def __str__(self):
        return self.reduction

    def _append(self, char, source_index):
        assert len(char) == 1
        self.reduction += char
        self.pointers.append(source_index)

    def _expand(self, x, y):
        """ subclasses should override this method to recover elements
        of markup that lie on the border, but should be included in
        sentences """
        return x, y

    def _mask_char(self, offset):
        self._append(Reduction._MASK, offset)

    def get_source(self, x, y):
        """ return the substring that corresponds to the specified range """
        return self.source[x:y]

    def get_source_range(self, reduction_x, reduction_y):
        """ return the range in the source that corresponds to the
        specified range in the reduction """
        #x, y = self.pointers[reduction_x], self.pointers[reduction_y+1]
        x, y = self.pointers[reduction_x], self.pointers[reduction_y]
        x, y = self._expand(x, y)

        return x, y