#    This file is part of MDANSE.
#
#    MDANSE 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 program 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/>.
#


class Singleton(type):
    """
    Metaclass that implements the singleton pattern.
    """

    __instances = {}

    def __call__(self, *args, **kwargs):
        """
        Creates (or returns if it has already been instanciated) an instance of the class.
        """

        if self.__name__ not in self.__instances:
            self.__instances[self.__name__] = super(Singleton, self).__call__(
                *args, **kwargs
            )

        return self.__instances[self.__name__]
