# Copyright 2016 Splunk, Inc.
#
# Licensed under the Apache License, Version 2.0 (the 'License'): you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an 'AS IS' BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.

'''
This module provides some common used patterns.
'''

__all__ = ['Singleton']


class Singleton(type):
    '''
    Singleton meta class

    Usage:

       >>> class Test(object):
       >>>     __metaclass__ = Singleton
       >>>
       >>>     def __init__(self):
       >>>         pass
    '''

    def __init__(cls, name, bases, attrs):
        super(Singleton, cls).__init__(name, bases, attrs)
        cls._instance = None

    def __call__(cls, *args, **kwargs):
        if cls._instance is None:
            cls._instance = super(Singleton, cls).__call__(*args, **kwargs)
        return cls._instance
