# -*- coding: utf-8 -*-
#
# This file is part of the livelex Python package.
#
# Copyright © 2019 by Wilbert Berendsen <info@wilbertberendsen.nl>
#
# This module is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This module is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.


"""
Helper objects to construct regular expressions.

"""


class Pattern:
    """Base class for objects that build a regular expression."""
    def build(self):
        raise NotImplementedError


class Words(Pattern):
    """Creates a regular expression from a list of words."""
    def __init__(self, words, prefix="", suffix=""):
        self.words = words
        self.prefix = prefix
        self.suffix = suffix

    def build(self):
        from . import regex
        expr = regex.words2regexp(self.words)
        if self.prefix or self.suffix:
            return self.prefix + '(?:' + expr + ')' + self.suffix
        return expr


