# Copyright 2018 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.
# ==============================================================================
"""TensorFlow-related utilities."""

import tensorflow.compat.v2 as tf

import collections
import copy
import numpy as np
from tensorflow.python.framework import ops
from keras import backend as K
from keras.engine import keras_tensor
from keras.utils import object_identity
from keras.utils import tf_contextlib
from tensorflow.python.util.tf_export import keras_export


def is_tensor_or_tensor_list(v):
  v = tf.nest.flatten(v)
  if v and isinstance(v[0], tf.Tensor):
    return True
  else:
    return False


def get_reachable_from_inputs(inputs, targets=None):
  """Returns the set of tensors/ops reachable from `inputs`.

  Stops if all targets have been found (target is optional).

  Only valid in Symbolic mode, not Eager mode.

  Args:
    inputs: List of tensors.
    targets: List of tensors.

  Returns:
    A set of tensors reachable from the inputs (includes the inputs themselves).
  """
  inputs = tf.nest.flatten(inputs, expand_composites=True)
  reachable = object_identity.ObjectIdentitySet(inputs)
  if targets:
    remaining_targets = object_identity.ObjectIdentitySet(tf.nest.flatten(targets))
  queue = collections.deque(inputs)

  while queue:
    x = queue.pop()
    if isinstance(x, tuple(_user_convertible_tensor_types)):
      # Can't find consumers of user-specific types.
      continue

    if isinstance(x, tf.Operation):
      outputs = x.outputs[:] or []
      outputs += x._control_outputs  # pylint: disable=protected-access
    elif isinstance(x, tf.Variable):
      try:
        outputs = [x.op]
      except AttributeError:
        # Variables can be created in an Eager context.
        outputs = []
    elif tf.is_tensor(x):
      outputs = x.consumers()
    else:
      raise TypeError(
          f'Expected tf.Operation, tf.Variable, or tf.Tensor. Received: {x}')

    for y in outputs:
      if y not in reachable:
        reachable.add(y)
        if targets:
          remaining_targets.discard(y)
        queue.appendleft(y)

    if targets and not remaining_targets:
      return reachable

  return reachable


# This function needs access to private functions of `nest`.
#  pylint: disable=protected-access
def map_structure_with_atomic(is_atomic_fn, map_fn, nested):
  """Maps the atomic elements of a nested structure.

  Args:
    is_atomic_fn: A function that determines if an element of `nested` is
      atomic.
    map_fn: The function to apply to atomic elements of `nested`.
    nested: A nested structure.

  Returns:
    The nested structure, with atomic elements mapped according to `map_fn`.

  Raises:
    ValueError: If an element that is neither atomic nor a sequence is
      encountered.
  """
  if is_atomic_fn(nested):
    return map_fn(nested)

  # Recursively convert.
  if not tf.nest.is_nested(nested):
    raise ValueError(
        f'Received non-atomic and non-sequence element: {nested}')
  if tf.__internal__.nest.is_mapping(nested):
    values = [nested[k] for k in sorted(nested.keys())]
  elif tf.__internal__.nest.is_attrs(nested):
    values = _astuple(nested)
  else:
    values = nested
  mapped_values = [
      map_structure_with_atomic(is_atomic_fn, map_fn, ele) for ele in values
  ]
  return tf.__internal__.nest.sequence_like(nested, mapped_values)


def get_shapes(tensors):
  """Gets shapes from tensors."""
  return tf.nest.map_structure(lambda x: x.shape, tensors)


#  pylint: enable=protected-access


def convert_shapes(input_shape, to_tuples=True):
  """Converts nested shape representations to desired format.

  Performs:

  TensorShapes -> tuples if `to_tuples=True`.
  tuples of int or None -> TensorShapes if `to_tuples=False`.

  Valid objects to be converted are:
  - TensorShapes
  - tuples with elements of type int or None.
  - ints
  - None

  Args:
    input_shape: A nested structure of objects to be converted to TensorShapes.
    to_tuples: If `True`, converts all TensorShape to tuples. Otherwise converts
      all tuples representing shapes to TensorShapes.

  Returns:
    Nested structure of shapes in desired format.

  Raises:
    ValueError: when the input tensor shape can't be converted to tuples, eg
      unknown tensor shape.
  """

  def _is_shape_component(value):
    return value is None or isinstance(value, (int, tf.compat.v1.Dimension))

  def _is_atomic_shape(input_shape):
    # Ex: TensorShape or (None, 10, 32) or 5 or `None`
    if _is_shape_component(input_shape):
      return True
    if isinstance(input_shape, tf.TensorShape):
      return True
    if (isinstance(input_shape, (tuple, list)) and
        all(_is_shape_component(ele) for ele in input_shape)):
      return True
    return False

  def _convert_shape(input_shape):
    input_shape = tf.TensorShape(input_shape)
    if to_tuples:
      input_shape = tuple(input_shape.as_list())
    return input_shape

  return map_structure_with_atomic(_is_atomic_shape, _convert_shape,
                                   input_shape)


class ListWrapper:
  """A wrapper for lists to be treated as elements for `nest`."""

  def __init__(self, list_to_wrap):
    self._list = list_to_wrap

  def as_list(self):
    return self._list


def convert_inner_node_data(nested, wrap=False):
  """Either wraps or unwraps innermost node data lists in `ListWrapper` objects.

  Args:
    nested: A nested data structure.
    wrap: If `True`, wrap innermost lists in `ListWrapper` objects. If `False`,
      unwraps `ListWrapper` objects into lists.

  Returns:
    Structure of same type as nested, with lists wrapped/unwrapped.
  """

  def _is_serialized_node_data(nested):
    # Node data can be of form `[layer_name, node_id, tensor_id]` or
    # `[layer_name, node_id, tensor_id, kwargs]`.
    if (isinstance(nested, list) and (len(nested) in [3, 4]) and
        isinstance(nested[0], str)):
      return True
    return False

  def _is_atomic_nested(nested):
    """Returns `True` if `nested` is a list representing node data."""
    if isinstance(nested, ListWrapper):
      return True
    if _is_serialized_node_data(nested):
      return True
    return not tf.nest.is_nested(nested)

  def _convert_object_or_list(nested):
    """Convert b/t `ListWrapper` object and list representations."""
    if wrap:
      if isinstance(nested, ListWrapper):
        return nested
      if _is_serialized_node_data(nested):
        return ListWrapper(nested)
      return nested
    else:
      if isinstance(nested, ListWrapper):
        return nested.as_list()
      return nested

  return map_structure_with_atomic(_is_atomic_nested, _convert_object_or_list,
                                   nested)


def shape_type_conversion(fn):
  """Decorator that handles tuple/TensorShape conversion.

  Used in `compute_output_shape` and `build`.

  Args:
    fn: function to wrap.

  Returns:
    Wrapped function.
  """

  def wrapper(instance, input_shape):
    # Pass shapes as tuples to `fn`
    # This preserves compatibility with external Keras.
    if input_shape is not None:
      input_shape = convert_shapes(input_shape, to_tuples=True)
    output_shape = fn(instance, input_shape)
    # Return shapes from `fn` as TensorShapes.
    if output_shape is not None:
      output_shape = convert_shapes(output_shape, to_tuples=False)
    return output_shape

  return wrapper


def are_all_symbolic_tensors(tensors):
  return all(map(is_symbolic_tensor, tensors))


_user_convertible_tensor_types = set()


def is_extension_type(tensor):
  """Returns whether a tensor is of an ExtensionType.

  github.com/tensorflow/community/pull/269
  Currently it works by checking if `tensor` is a `CompositeTensor` instance,
  but this will be changed to use an appropriate extensiontype protocol
  check once ExtensionType is made public.

  Args:
    tensor: An object to test

  Returns:
    True if the tensor is an extension type object, false if not.
  """
  return isinstance(tensor, tf.__internal__.CompositeTensor)


def is_symbolic_tensor(tensor):
  """Returns whether a tensor is symbolic (from a TF graph) or an eager tensor.

  A Variable can be seen as either: it is considered symbolic
  when we are in a graph scope, and eager when we are in an eager scope.

  Args:
    tensor: A tensor instance to test.

  Returns:
    True for symbolic tensors, False for eager tensors.
  """
  if isinstance(tensor, tf.Tensor):
    return hasattr(tensor, 'graph')
  elif is_extension_type(tensor):
    component_tensors = tf.nest.flatten(tensor, expand_composites=True)
    return any(hasattr(t, 'graph') for t in component_tensors)
  elif isinstance(tensor, tf.Variable):
    # Variables that are output of a Keras Layer in Functional API mode
    # should be considered symbolic.
    # TODO(omalleyt): We need a better way to check this in order to
    # enable `run_eagerly=True` for Models containing Layers that
    # return Variables as outputs.
    return (getattr(tensor, '_keras_history', False) or
            not tf.executing_eagerly())
  elif isinstance(tensor, tuple(_user_convertible_tensor_types)):
    tensor = ops.convert_to_tensor_or_composite(tensor)
    return is_symbolic_tensor(tensor)
  else:
    return False


@keras_export('keras.__internal__.utils.register_symbolic_tensor_type', v1=[])
def register_symbolic_tensor_type(cls):
  """Allows users to specify types regarded as symbolic `Tensor`s.

  Used in conjunction with `tf.register_tensor_conversion_function`, calling
  `tf.keras.__internal__.utils.register_symbolic_tensor_type(cls)`
  allows non-`Tensor` objects to be plumbed through Keras layers.

  Example:

  ```python
  # One-time setup.
  class Foo:
    def __init__(self, input_):
      self._input = input_
    def value(self):
      return tf.constant(42.)

  tf.register_tensor_conversion_function(
      Foo, lambda x, *args, **kwargs: x.value())

  tf.keras.__internal__.utils.register_symbolic_tensor_type(Foo)

  # User-land.
  layer = tf.keras.layers.Lambda(lambda input_: Foo(input_))
  ```

  Args:
    cls: A `class` type which shall be regarded as a symbolic `Tensor`.
  """
  global _user_convertible_tensor_types
  if cls not in _user_convertible_tensor_types:
    keras_tensor.register_keras_tensor_specialization(
        cls, keras_tensor.UserRegisteredTypeKerasTensor)
  _user_convertible_tensor_types.add(cls)


def type_spec_from_value(value):
  """Grab type_spec without converting array-likes to tensors."""
  if is_extension_type(value):
    return value._type_spec  # pylint: disable=protected-access
  # Get a TensorSpec for array-like data without
  # converting the data to a Tensor
  if hasattr(value, 'shape') and hasattr(value, 'dtype'):
    return tf.TensorSpec(value.shape, value.dtype)
  else:
    return tf.type_spec_from_value(value)


def is_ragged(tensor):
  """Returns true if `tensor` is a ragged tensor or ragged tensor value."""
  return isinstance(
      tensor,
      (tf.RaggedTensor, tf.compat.v1.ragged.RaggedTensorValue))


def is_sparse(tensor):
  """Returns true if `tensor` is a sparse tensor or sparse tensor value."""
  return isinstance(
      tensor,
      (tf.SparseTensor, tf.compat.v1.SparseTensorValue))


def is_tensor_or_variable(x):
  return tf.is_tensor(x) or isinstance(x, tf.Variable)


def assert_no_legacy_layers(layers):
  """Prevent tf.layers.Layers from being used with Keras.

  Certain legacy layers inherit from their keras analogs; however they are
  not supported with keras and can lead to subtle and hard to diagnose bugs.

  Args:
    layers: A list of layers to check

  Raises:
    TypeError: If any elements of layers are tf.layers.Layers
  """

  # isinstance check for tf.layers.Layer introduces a circular dependency.
  legacy_layers = [l for l in layers if getattr(l, '_is_legacy_layer', None)]
  if legacy_layers:
    layer_str = '\n'.join('  ' + str(l) for l in legacy_layers)
    raise TypeError(
        f'The following are legacy tf.layers.Layers:\n{layer_str}\n'
        'To use keras as a '
        'framework (for instance using the Network, Model, or Sequential '
        'classes), please use the tf.keras.layers implementation instead. '
        '(Or, if writing custom layers, subclass from tf.keras.layers rather '
        'than tf.layers)')


@tf_contextlib.contextmanager
def maybe_init_scope(layer):
  """Open an `init_scope` if in V2 mode and using the keras graph.

  Args:
    layer: The Layer/Model that is currently active.

  Yields:
    None
  """
  # Don't open an init_scope in V1 mode or when using legacy tf.layers.
  if (tf.compat.v1.executing_eagerly_outside_functions() and
      getattr(layer, '_keras_style', True)):
    with tf.init_scope():
      yield
  else:
    yield


@tf_contextlib.contextmanager
def graph_context_for_symbolic_tensors(*args, **kwargs):
  """Returns graph context manager if any of the inputs is a symbolic tensor."""
  if any(is_symbolic_tensor(v) for v in list(args) + list(kwargs.values())):
    with K.get_graph().as_default():
      yield
  else:
    yield


def dataset_is_infinite(dataset):
  """True if the passed dataset is infinite."""
  if tf.compat.v1.executing_eagerly_outside_functions():
    return tf.equal(
        tf.data.experimental.cardinality(dataset), tf.data.experimental.INFINITE_CARDINALITY)
  else:
    dataset_size = K.get_session().run(tf.data.experimental.cardinality(dataset))
    return dataset_size == tf.data.experimental.INFINITE_CARDINALITY


def get_tensor_spec(t, dynamic_batch=False, name=None):
  """Returns a `TensorSpec` given a single `Tensor` or `TensorSpec`."""
  # pylint: disable=protected-access
  if isinstance(t, tf.TypeSpec):
    spec = t
  elif is_extension_type(t):
    # TODO(b/148821952): Should these specs have a name attr?
    spec = t._type_spec
  elif (hasattr(t, '_keras_history') and
        hasattr(t._keras_history[0], '_type_spec')):
    return t._keras_history[0]._type_spec
  elif hasattr(t, 'shape') and hasattr(t, 'dtype'):
    spec = tf.TensorSpec(shape=t.shape, dtype=t.dtype, name=name)
  else:
    return None  # Allow non-Tensors to pass through.

  if not dynamic_batch:
    return spec

  dynamic_batch_spec = copy.deepcopy(spec)
  # RaggedTensorSpec only has a private _shape.
  shape = dynamic_batch_spec._shape
  if shape.rank is not None and shape.rank > 0:
    shape_list = shape.as_list()
    shape_list[0] = None
    dynamic_batch_spec._shape = tf.TensorShape(shape_list)
  return dynamic_batch_spec
  # pylint: enable=protected-access


def sync_to_numpy_or_python_type(tensors):
  """Syncs and converts a structure of `Tensor`s to `NumPy` arrays or Python scalar types.

  For each tensor, it calls `tensor.numpy()`. If the result is a scalar value,
  it converts it to a Python type, such as a float or int, by calling
  `result.item()`.

  Numpy scalars are converted, as Python types are often more convenient to deal
  with. This is especially useful for bfloat16 Numpy scalars, which don't
  support as many operations as other Numpy values.

  Async strategies (such as `TPUStrategy` and `ParameterServerStrategy`) are
  forced to
  sync during this process.

  Args:
    tensors: A structure of tensors.

  Returns:
    `tensors`, but scalar tensors are converted to Python types and non-scalar
    tensors are converted to Numpy arrays.
  """
  if isinstance(tensors, tf.distribute.experimental.coordinator.RemoteValue):
    return tensors.fetch()

  def _to_single_numpy_or_python_type(t):
    if isinstance(t, tf.Tensor):
      x = t.numpy()
      return x.item() if np.ndim(x) == 0 else x
    return t  # Don't turn ragged or sparse tensors to NumPy.

  return tf.nest.map_structure(_to_single_numpy_or_python_type, tensors)


def _astuple(attrs):
  """Converts the given attrs to tuple non-recursively."""
  cls = type(attrs)
  fields = getattr(cls, '__attrs_attrs__', None)
  if fields is None:
    raise ValueError(f'{cls} is not an attrs-decorated class.')
  values = []
  for field in fields:
    values.append(getattr(attrs, field.name))
  return tuple(values)
