# 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.
# ==============================================================================
"""Base TFDecorator class and utility functions for working with decorators.

There are two ways to create decorators that TensorFlow can introspect into.
This is important for documentation generation purposes, so that function
signatures aren't obscured by the (*args, **kwds) signature that decorators
often provide.

1. Call `tf_decorator.make_decorator` on your wrapper function. If your
decorator is stateless, or can capture all of the variables it needs to work
with through lexical closure, this is the simplest option. Create your wrapper
function as usual, but instead of returning it, return
`tf_decorator.make_decorator(target, your_wrapper)`. This will attach some
decorator introspection metadata onto your wrapper and return it.

Example:

  def print_hello_before_calling(target):
    def wrapper(*args, **kwargs):
      print('hello')
      return target(*args, **kwargs)
    return tf_decorator.make_decorator(target, wrapper)

2. Derive from TFDecorator. If your decorator needs to be stateful, you can
implement it in terms of a TFDecorator. Store whatever state you need in your
derived class, and implement the `__call__` method to do your work before
calling into your target. You can retrieve the target via
`super(MyDecoratorClass, self).decorated_target`, and call it with whatever
parameters it needs.

Example:

  class CallCounter(tf_decorator.TFDecorator):
    def __init__(self, target):
      super(CallCounter, self).__init__('count_calls', target)
      self.call_count = 0

    def __call__(self, *args, **kwargs):
      self.call_count += 1
      return super(CallCounter, self).decorated_target(*args, **kwargs)

  def count_calls(target):
    return CallCounter(target)
"""
import inspect


def make_decorator(target,
                   decorator_func,
                   decorator_name=None,
                   decorator_doc='',
                   decorator_argspec=None):
  """Make a decorator from a wrapper and a target.

  Args:
    target: The final callable to be wrapped.
    decorator_func: The wrapper function.
    decorator_name: The name of the decorator. If `None`, the name of the
      function calling make_decorator.
    decorator_doc: Documentation specific to this application of
      `decorator_func` to `target`.
    decorator_argspec: The new callable signature of this decorator.

  Returns:
    The `decorator_func` argument with new metadata attached.
  """
  if decorator_name is None:
    decorator_name = inspect.currentframe().f_back.f_code.co_name
  decorator = TFDecorator(decorator_name, target, decorator_doc,
                          decorator_argspec)
  setattr(decorator_func, '_tf_decorator', decorator)
  # Objects that are callables (e.g., a functools.partial object) may not have
  # the following attributes.
  if hasattr(target, '__name__'):
    decorator_func.__name__ = target.__name__
  if hasattr(target, '__qualname__'):
    decorator_func.__qualname__ = target.__qualname__
  if hasattr(target, '__module__'):
    decorator_func.__module__ = target.__module__
  if hasattr(target, '__dict__'):
    # Copy dict entries from target which are not overridden by decorator_func.
    for name in target.__dict__:
      if name not in decorator_func.__dict__:
        decorator_func.__dict__[name] = target.__dict__[name]
  if hasattr(target, '__doc__'):
    decorator_func.__doc__ = decorator.__doc__
  decorator_func.__wrapped__ = target
  # Keeping a second handle to `target` allows callers to detect whether the
  # decorator was modified using `rewrap`.
  decorator_func.__original_wrapped__ = target
  return decorator_func


def _has_tf_decorator_attr(obj):
  """Checks if object has _tf_decorator attribute.

  This check would work for mocked object as well since it would
  check if returned attribute has the right type.

  Args:
    obj: Python object.
  """
  return (
      hasattr(obj, '_tf_decorator') and
      isinstance(getattr(obj, '_tf_decorator'), TFDecorator))


def rewrap(decorator_func, previous_target, new_target):
  """Injects a new target into a function built by make_decorator.

  This function allows replacing a function wrapped by `decorator_func`,
  assuming the decorator that wraps the function is written as described below.

  The decorator function must use `<decorator name>.__wrapped__` instead of the
  wrapped function that is normally used:

  Example:

      # Instead of this:
      def simple_parametrized_wrapper(*args, **kwds):
        return wrapped_fn(*args, **kwds)

      tf_decorator.make_decorator(simple_parametrized_wrapper, wrapped_fn)

      # Write this:
      def simple_parametrized_wrapper(*args, **kwds):
        return simple_parametrized_wrapper.__wrapped__(*args, **kwds)

      tf_decorator.make_decorator(simple_parametrized_wrapper, wrapped_fn)

  Note that this process modifies decorator_func.

  Args:
    decorator_func: Callable returned by `wrap`.
    previous_target: Callable that needs to be replaced.
    new_target: Callable to replace previous_target with.

  Returns:
    The updated decorator. If decorator_func is not a tf_decorator, new_target
    is returned.
  """
  # Because the process mutates the decorator, we only need to alter the
  # innermost function that wraps previous_target.
  cur = decorator_func
  innermost_decorator = None
  target = None
  while _has_tf_decorator_attr(cur):
    innermost_decorator = cur
    target = getattr(cur, '_tf_decorator')
    if target.decorated_target is previous_target:
      break
    cur = target.decorated_target
    assert cur is not None

  # If decorator_func is not a decorator, new_target replaces it directly.
  if innermost_decorator is None:
    # Consistency check. The caller should always pass the result of
    # tf_decorator.unwrap as previous_target. If decorator_func is not a
    # decorator, that will have returned decorator_func itself.
    assert decorator_func is previous_target
    return new_target

  target.decorated_target = new_target

  if inspect.ismethod(innermost_decorator):
    # Bound methods can't be assigned attributes. Thankfully, they seem to
    # be just proxies for their unbound counterpart, and we can modify that.
    if hasattr(innermost_decorator, '__func__'):
      innermost_decorator.__func__.__wrapped__ = new_target
    elif hasattr(innermost_decorator, 'im_func'):
      innermost_decorator.im_func.__wrapped__ = new_target
    else:
      innermost_decorator.__wrapped__ = new_target
  else:
    innermost_decorator.__wrapped__ = new_target

  return decorator_func


def unwrap(maybe_tf_decorator):
  """Unwraps an object into a list of TFDecorators and a final target.

  Args:
    maybe_tf_decorator: Any callable object.

  Returns:
    A tuple whose first element is an list of TFDecorator-derived objects that
    were applied to the final callable target, and whose second element is the
    final undecorated callable target. If the `maybe_tf_decorator` parameter is
    not decorated by any TFDecorators, the first tuple element will be an empty
    list. The `TFDecorator` list is ordered from outermost to innermost
    decorators.
  """
  decorators = []
  cur = maybe_tf_decorator
  while True:
    if isinstance(cur, TFDecorator):
      decorators.append(cur)
    elif _has_tf_decorator_attr(cur):
      decorators.append(getattr(cur, '_tf_decorator'))
    else:
      break
    if not hasattr(decorators[-1], 'decorated_target'):
      break
    cur = decorators[-1].decorated_target
  return decorators, cur


class TFDecorator(object):
  """Base class for all TensorFlow decorators.

  TFDecorator captures and exposes the wrapped target, and provides details
  about the current decorator.
  """

  def __init__(self,
               decorator_name,
               target,
               decorator_doc='',
               decorator_argspec=None):
    self._decorated_target = target
    self._decorator_name = decorator_name
    self._decorator_doc = decorator_doc
    self._decorator_argspec = decorator_argspec
    if hasattr(target, '__name__'):
      self.__name__ = target.__name__
    if hasattr(target, '__qualname__'):
      self.__qualname__ = target.__qualname__
    if self._decorator_doc:
      self.__doc__ = self._decorator_doc
    elif hasattr(target, '__doc__') and target.__doc__:
      self.__doc__ = target.__doc__
    else:
      self.__doc__ = ''

  def __get__(self, instance, owner):
    return self._decorated_target.__get__(instance, owner)

  def __call__(self, *args, **kwargs):
    return self._decorated_target(*args, **kwargs)

  @property
  def decorated_target(self):
    return self._decorated_target

  @decorated_target.setter
  def decorated_target(self, decorated_target):
    self._decorated_target = decorated_target

  @property
  def decorator_name(self):
    return self._decorator_name

  @property
  def decorator_doc(self):
    return self._decorator_doc

  @property
  def decorator_argspec(self):
    return self._decorator_argspec