initial_state = 0


class ActionTypes(object):
    SET_STATE = 'counter/SET_STATE'
    INCREMENT = 'counter/INCREMENT'
    DECREMENT = 'counter/DECREMENT'


class ActionCreators(object):
    @staticmethod
    def set_state(value):
        return dict(
            type=ActionTypes.SET_STATE,
            value=value
        )

    @staticmethod
    def increment():
        return dict(
            type=ActionTypes.INCREMENT
        )

    @staticmethod
    def decrement():
        return dict(
            type=ActionTypes.DECREMENT
        )


def reducer(state=None, action=None):
    if state is None:
        state = initial_state
    if not (isinstance(action, dict) and 'type' in action):
        return state
    if action['type'] == ActionTypes.SET_STATE:
        state = action['value']
    elif action['type'] == ActionTypes.INCREMENT:
        state += 1
    elif action['type'] == ActionTypes.DECREMENT:
        state -= 1
    return state


if __name__ == '__main__':
    import unittest


    class TestSuite(unittest.TestCase):
        def test_action_creators(self):
            self.assertEqual(ActionCreators.set_state(12), {'type': 'counter/SET_STATE', 'value': 12})
            self.assertEqual(ActionCreators.increment(), {'type': 'counter/INCREMENT'})
            self.assertEqual(ActionCreators.decrement(), {'type': 'counter/DECREMENT'})

        def test_reducer(self):
            self.assertEqual(reducer(67, None), 67)
            self.assertEqual(reducer(None, None), 0)
            self.assertEqual(reducer(None, ActionCreators.set_state(13)), 13)
            self.assertEqual(reducer(452, ActionCreators.set_state(13)), 13)
            self.assertEqual(reducer(None, ActionCreators.increment()), 1)
            self.assertEqual(reducer(341, ActionCreators.increment()), 342)
            self.assertEqual(reducer(None, ActionCreators.decrement()), -1)
            self.assertEqual(reducer(251, ActionCreators.decrement()), 250)


    unittest.main()