#   Copyright (c) 2018 PaddlePaddle Authors. 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.

from __future__ import print_function

import collections
from .wrapped_decorator import signature_safe_contextmanager
import six
import sys

__all__ = ['generate', 'switch', 'guard']


class UniqueNameGenerator(object):
    """
    Generate unique name with prefix.

    Args:
        prefix(str): The generated name prefix. All generated name will be
                     started with this prefix.
    """

    def __init__(self, prefix=None):
        self.ids = collections.defaultdict(int)
        if prefix is None:
            prefix = ""
        self.prefix = prefix

    def __call__(self, key):
        """
        Generate unique names with prefix

        Args:
            key(str): The key of return string.

        Returns(str): A unique string with the prefix
        """
        tmp = self.ids[key]
        self.ids[key] += 1
        return self.prefix + "_".join([key, str(tmp)])


generator = UniqueNameGenerator()


def generate(key):
    """
    Generate unique name with prefix key. Currently, Paddle distinguishes the
    names of the same key by numbering it from zero. For example, when key=fc,
    it continuously generates fc_0, fc_1, fc_2, etc.

    Args: 
        key(str): The prefix of generated name.

    Returns: 
        str: A unique string with the prefix key.

    Examples: 

        .. code-block:: python

            import paddle.fluid as fluid
            name1 = fluid.unique_name.generate('fc')
            name2 = fluid.unique_name.generate('fc')
            print(name1, name2) # fc_0, fc_1
    """
    return generator(key)


# FIXME(zjl): The previous naming rule in static graph would
# cause memory leak in dygraph mode. It is because the previous
# naming rule would use `conv_0.tmp` as the key, and in dygraph
# mode, `conv_i` increases as batch increases. Thus, keys would
# increase in a way like `conv_0.tmp`, `conv_1.tmp`, .... 
# Not find a better way to fix this bug in dygraph mode. In TF,
# variable name is meaningless in eager execution mode, and in
# PyTorch, there is no variable name at all. Maybe we should
# discard variable name in dygraph mode.
#
# Another concern is that save/load interfaces. Usually, user
# would save model in static graph mode, and load it in dygraph
# mode. Therefore, we keep the variable name of Parameter currently.
# 
# Please fix me if a better method is found.        
def generate_with_ignorable_key(key):
    from .framework import in_dygraph_mode
    if in_dygraph_mode():
        key = "tmp"

    return generator(key)


def switch(new_generator=None):
    """
    Switch the namespace of in current context to a new namespace. Though
    :code:`switch()` and :code:`guard()` can both change namespace, 
    :code:`guard()` is recommended since it can manage the context better 
    together with :code:`with` statement.

    Args: 
        new_generator(UniqueNameGenerator, optional): A new UniqueNameGenerator, not
            required normally. Default is None, which means switch to a new anonymous
            namespace.

    Returns: 
        UniqueNameGenerator: The previous UniqueNameGenerator.

    Examples: 

        .. code-block:: python

            import paddle.fluid as fluid
            name1 = fluid.unique_name.generate('fc')
            name2 = fluid.unique_name.generate('fc')
            print(name1, name2) # fc_0, fc_1

            pre_generator = fluid.unique_name.switch() # switch to a new anonymous namespace.
            name2 = fluid.unique_name.generate('fc')
            print(name2) # fc_0

            fluid.unique_name.switch(pre_generator) # switch back to pre_generator.
            name3 = fluid.unique_name.generate('fc')
            print(name3) # fc_2, since pre_generator has generated fc_0, fc_1.

    """
    global generator
    old = generator
    if new_generator is None:
        generator = UniqueNameGenerator()
    else:
        generator = new_generator
    return old


@signature_safe_contextmanager
def guard(new_generator=None):
    """
    Change the namespace of unique name with :code:`with` statement. After calling it,
    a new namespace in the context of :code:`with` will be created, and it will number
    names from zero again when calling :code:`generate()` with same key.

    Args: 
        new_generator(str|bytes, optional): New name of global namespace. Note that str
            in Python2 was spilted into str and bytes in Python3, so here are two 
            types. Default is None. If not None, new_generator will be added into 
            the prefix of unique name generated by :code:`generate()`.
    
    Returns:
        None.

    Examples: 

        .. code-block:: python

            import paddle.fluid as fluid
            with fluid.unique_name.guard():
              name_1 = fluid.unique_name.generate('fc')
            with fluid.unique_name.guard():
              name_2 = fluid.unique_name.generate('fc')
            print(name_1, name_2) # fc_0, fc_0

            with fluid.unique_name.guard('A'):
              name_1 = fluid.unique_name.generate('fc')
            with fluid.unique_name.guard('B'):
              name_2 = fluid.unique_name.generate('fc') 
            print(name_1, name_2) # Afc_0, Bfc_0
    """
    if isinstance(new_generator, six.string_types):
        new_generator = UniqueNameGenerator(new_generator)
    elif isinstance(new_generator, six.binary_type):
        new_generator = UniqueNameGenerator(new_generator.decode())
    old = switch(new_generator)
    yield
    switch(old)