#!/usr/bin/env python
# -*- coding: utf-8 -*-

# Copyright (c) 2018, Facebook, Inc. All rights reserved.
#
# 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.


def _register_generic(module_dict, module_name, module):
    assert module_name not in module_dict
    module_dict[module_name] = module


class Registry(dict):
    '''
    A helper class for managing registering modules, it extends a dictionary
    and provides a register functions.

    Eg. creeting a registry:
        some_registry = Registry({"default": default_module})

    There're two ways of registering new modules:
    1): normal way is just calling register function:
        def foo():
            ...
        some_registry.register("foo_module", foo)
    2): used as decorator when declaring the module:
        @some_registry.register("foo_module")
        @some_registry.register("foo_modeul_nickname")
        def foo():
            ...

    Access of module is just like using a dictionary, eg:
        f = some_registry["foo_modeul"]
    '''
    def __init__(self, *args, **kwargs):
        super(Registry, self).__init__(*args, **kwargs)

    def register(self, module_name, module=None):
        # used as function call
        if module is not None:
            _register_generic(self, module_name, module)
            return

        # used as decorator
        def register_fn(fn):
            _register_generic(self, module_name, fn)
            return fn

        return register_fn