# Copyright 2017 The TensorFlow 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.
# ==============================================================================
"""Gast compatibility library. Supports 0.2.2 and 0.3.2."""
# TODO(mdan): Remove this file once it's safe to break compatibility.

import functools
import gast

from distutils.version import LooseVersion


def get_gast_version():
  """Gast exports `__version__` from 0.5.3 onwards, we need to look it up in a different way."""
  if hasattr(gast, '__version__'):
    return gast.__version__
  try:
    import pkg_resources
    return pkg_resources.get_distribution("gast").version
  except pkg_resources.DistributionNotFound:
    # Older gast had 'Str', check for the oldest supported version
    if hasattr(gast, 'Str'):
      return '0.2'
    else:
      try:
        # Try to call it with 3 arguments, to differentiate between 0.5+ and earlier.
        gast.Assign(None, None, None)
      except AssertionError as e:
        if "Bad argument number for Assign: 3, expecting 2" in str(e):
          return '0.4'
      return '0.5'


def is_constant(node):
  """Tests whether node represents a Python constant."""
  return isinstance(node, gast.Constant)


def is_literal(node):
  """Tests whether node represents a Python literal."""
  # Normal literals, True/False/None/Etc. in Python3
  if is_constant(node):
    return True

  # True/False/None/Etc. in Python2
  if isinstance(node, gast.Name) and node.id in ['True', 'False', 'None']:
    return True

  return False


def is_ellipsis(node):
  """Tests whether node represents a Python ellipsis."""
  return isinstance(node, gast.Constant) and node.value == Ellipsis


def _compat_assign_gast_4(targets, value, type_comment):
  """Wraps around gast.Assign to use same function signature across versions."""
  return gast.Assign(targets=targets, value=value)


def _compat_assign_gast_5(targets, value, type_comment):
  """Wraps around gast.Assign to use same function signature across versions."""
  return gast.Assign(targets=targets, value=value, type_comment=type_comment)


if get_gast_version() < LooseVersion("0.5"):
  compat_assign = _compat_assign_gast_4
else:
  compat_assign = _compat_assign_gast_5

Module = functools.partial(gast.Module, type_ignores=None)  # pylint:disable=invalid-name
Name = functools.partial(gast.Name, type_comment=None)  # pylint:disable=invalid-name
Str = functools.partial(gast.Constant, kind=None)  # pylint:disable=invalid-name
