# Copyright 2015 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.
# ==============================================================================
"""Contains the Lambda layer."""
# pylint: disable=g-classes-have-attributes,g-direct-tensorflow-import
import sys
import textwrap
import types as python_types
import warnings
from keras.engine.base_layer import Layer
from keras.utils import generic_utils
from keras.utils import tf_inspect
from keras.utils import tf_utils
import numpy as np
import tensorflow.compat.v2 as tf
from tensorflow.python.platform import tf_logging
from tensorflow.python.util.tf_export import keras_export


@keras_export('keras.layers.Lambda')
class Lambda(Layer):
  """Wraps arbitrary expressions as a `Layer` object.

  The `Lambda` layer exists so that arbitrary expressions can be used
  as a `Layer` when constructing `Sequential`
  and Functional API models. `Lambda` layers are best suited for simple
  operations or quick experimentation. For more advanced use cases, follow
  [this guide](https://www.tensorflow.org/guide/keras/custom_layers_and_models)
  for subclassing `tf.keras.layers.Layer`.

  WARNING: `tf.keras.layers.Lambda` layers have (de)serialization limitations!

  The main reason to subclass `tf.keras.layers.Layer` instead of using a
  `Lambda` layer is saving and inspecting a Model. `Lambda` layers
  are saved by serializing the Python bytecode, which is fundamentally
  non-portable. They should only be loaded in the same environment where
  they were saved. Subclassed layers can be saved in a more portable way
  by overriding their `get_config` method. Models that rely on
  subclassed Layers are also often easier to visualize and reason about.

  Examples:

  ```python
  # add a x -> x^2 layer
  model.add(Lambda(lambda x: x ** 2))
  ```
  ```python
  # add a layer that returns the concatenation
  # of the positive part of the input and
  # the opposite of the negative part

  def antirectifier(x):
      x -= K.mean(x, axis=1, keepdims=True)
      x = K.l2_normalize(x, axis=1)
      pos = K.relu(x)
      neg = K.relu(-x)
      return K.concatenate([pos, neg], axis=1)

  model.add(Lambda(antirectifier))
  ```

  Variables:
    While it is possible to use Variables with Lambda layers, this practice is
    discouraged as it can easily lead to bugs. For instance, consider the
    following layer:

    ```python
      scale = tf.Variable(1.)
      scale_layer = tf.keras.layers.Lambda(lambda x: x * scale)
    ```

    Because scale_layer does not directly track the `scale` variable, it will
    not appear in `scale_layer.trainable_weights` and will therefore not be
    trained if `scale_layer` is used in a Model.

    A better pattern is to write a subclassed Layer:

    ```python
      class ScaleLayer(tf.keras.layers.Layer):
        def __init__(self):
          super(ScaleLayer, self).__init__()
          self.scale = tf.Variable(1.)

        def call(self, inputs):
          return inputs * self.scale
    ```

    In general, Lambda layers can be convenient for simple stateless
    computation, but anything more complex should use a subclass Layer instead.

  Args:
    function: The function to be evaluated. Takes input tensor as first
      argument.
    output_shape: Expected output shape from function. This argument can be
      inferred if not explicitly provided. Can be a tuple or function. If a
      tuple, it only specifies the first dimension onward;
      sample dimension is assumed either the same as the input: `output_shape =
        (input_shape[0], ) + output_shape` or, the input is `None` and
      the sample dimension is also `None`: `output_shape = (None, ) +
        output_shape` If a function, it specifies the entire shape as a function
        of the
      input shape: `output_shape = f(input_shape)`
    mask: Either None (indicating no masking) or a callable with the same
      signature as the `compute_mask` layer method, or a tensor that will be
      returned as output mask regardless of what the input is.
    arguments: Optional dictionary of keyword arguments to be passed to the
      function.
  Input shape: Arbitrary. Use the keyword argument input_shape (tuple of
    integers, does not include the samples axis) when using this layer as the
    first layer in a model.
  Output shape: Specified by `output_shape` argument
  """

  @tf.__internal__.tracking.no_automatic_dependency_tracking
  def __init__(self,
               function,
               output_shape=None,
               mask=None,
               arguments=None,
               **kwargs):
    super(Lambda, self).__init__(**kwargs)

    self.arguments = arguments or {}
    self.function = function

    if mask is not None:
      self.supports_masking = True
    self.mask = mask
    self._output_shape = output_shape

    # Warning on every invocation will be quite irksome in Eager mode.
    self._already_warned = False

    function_args = tf_inspect.getfullargspec(function).args
    self._fn_expects_training_arg = 'training' in function_args
    self._fn_expects_mask_arg = 'mask' in function_args

  @tf_utils.shape_type_conversion
  def compute_output_shape(self, input_shape):
    if self._output_shape is None:
      # Make use of existing autocomputation but provide Lambda-specific
      # error message. This is always safe to run even when the outer context
      # is Graph mode because Lambda layers don't have side effects such as
      # `add_loss`.
      with tf.__internal__.eager_context.eager_mode():
        try:
          return super(Lambda, self).compute_output_shape(input_shape)
        except NotImplementedError:
          raise NotImplementedError(
              'We could not automatically infer the shape of the Lambda\'s '
              'output. Please specify `output_shape` for this Lambda.')

    if callable(self._output_shape):
      output_shapes = self._output_shape(input_shape)
      return tf_utils.convert_shapes(output_shapes, to_tuples=False)

    # Output shapes are passed directly and don't include batch dimension.
    input_tensor_shape = tf_utils.convert_shapes(input_shape, to_tuples=False)
    batch_size = tf.nest.flatten(
        input_tensor_shape)[0][0] if input_shape else None

    def _add_batch(shape):
      return tf.TensorShape([batch_size] + shape.as_list())

    output_shapes = tf_utils.convert_shapes(self._output_shape, to_tuples=False)
    return tf.nest.map_structure(_add_batch, output_shapes)

  def call(self, inputs, mask=None, training=None):
    # We must copy for thread safety, but it only needs to be a shallow copy.
    kwargs = {k: v for k, v in self.arguments.items()}
    if self._fn_expects_mask_arg:
      kwargs['mask'] = mask
    if self._fn_expects_training_arg:
      kwargs['training'] = training

    created_variables = []

    def _variable_creator(next_creator, **kwargs):
      var = next_creator(**kwargs)
      created_variables.append(var)
      return var

    with tf.GradientTape(watch_accessed_variables=True) as tape,\
        tf.variable_creator_scope(_variable_creator):
      result = self.function(inputs, **kwargs)
    self._check_variables(created_variables, tape.watched_variables())
    return result

  def _check_variables(self, created_variables, accessed_variables):
    if not created_variables and not accessed_variables:
      # In the common case that a Lambda layer does not touch a Variable, we
      # don't want to incur the runtime cost of assembling any state used for
      # checking only to immediately discard it.
      return

    tracked_weights = set(v.ref() for v in self.weights)
    untracked_new_vars = [
        v for v in created_variables if v.ref() not in tracked_weights
    ]
    if untracked_new_vars:
      variable_str = '\n'.join('  {}'.format(i) for i in untracked_new_vars)
      error_str = textwrap.dedent("""
          The following Variables were created within a Lambda layer ({name})
          but are not tracked by said layer:
          {variable_str}
          The layer cannot safely ensure proper Variable reuse across multiple
          calls, and consquently this behavior is disallowed for safety. Lambda
          layers are not well suited to stateful computation; instead, writing a
          subclassed Layer is the recommend way to define layers with
          Variables.""").format(
              name=self.name, variable_str=variable_str)
      raise ValueError(error_str)

    untracked_used_vars = [
        v for v in accessed_variables if v.ref() not in tracked_weights
    ]
    if untracked_used_vars and not self._already_warned:
      variable_str = '\n'.join('  {}'.format(i) for i in untracked_used_vars)
      self._warn(
          textwrap.dedent("""
          The following Variables were used a Lambda layer's call ({name}), but
          are not present in its tracked objects:
          {variable_str}
          It is possible that this is intended behavior, but it is more likely
          an omission. This is a strong indication that this layer should be
          formulated as a subclassed Layer rather than a Lambda layer.""")
          .format(name=self.name, variable_str=variable_str))
      self._already_warned = True

  def _warn(self, msg):
    # This method will be overridden in a unit test to raise an error, because
    # self.assertWarns is not universally implemented.
    return tf_logging.warning(msg)

  def compute_mask(self, inputs, mask=None):
    if callable(self.mask):
      return self.mask(inputs, mask)
    return self.mask

  def get_config(self):
    function_config = self._serialize_function_to_config(self.function)
    output_shape_config = self._serialize_function_to_config(
        self._output_shape, allow_raw=True)
    config = {
        'function': function_config[0],
        'function_type': function_config[1],
        'module': function_config[2],
        'output_shape': output_shape_config[0],
        'output_shape_type': output_shape_config[1],
        'output_shape_module': output_shape_config[2],
    }
    if self.mask is not None:
      mask_config = self._serialize_function_to_config(self.mask)
      config.update({
          'mask': mask_config[0],
          'mask_type': mask_config[1],
          'mask_module': mask_config[2]
      })
    config['arguments'] = self.arguments

    base_config = super(Lambda, self).get_config()
    return dict(list(base_config.items()) + list(config.items()))

  def _serialize_function_to_config(self, inputs, allow_raw=False):
    if isinstance(inputs, python_types.LambdaType):
      output = generic_utils.func_dump(inputs)
      output_type = 'lambda'
      module = inputs.__module__
    elif callable(inputs):
      output = inputs.__name__
      output_type = 'function'
      module = inputs.__module__
    elif allow_raw:
      output = inputs
      output_type = 'raw'
      module = None
    else:
      raise ValueError('Invalid input for serialization, type: %s ' %
                       type(inputs))

    return output, output_type, module

  @classmethod
  def from_config(cls, config, custom_objects=None):
    config = config.copy()
    function = cls._parse_function_from_config(config, custom_objects,
                                               'function', 'module',
                                               'function_type')

    output_shape = cls._parse_function_from_config(config, custom_objects,
                                                   'output_shape',
                                                   'output_shape_module',
                                                   'output_shape_type')
    if 'mask' in config:
      mask = cls._parse_function_from_config(config, custom_objects, 'mask',
                                             'mask_module', 'mask_type')
    else:
      mask = None

    config['function'] = function
    config['output_shape'] = output_shape
    config['mask'] = mask

    # If arguments were numpy array, they have been saved as
    # list. We need to recover the ndarray
    if 'arguments' in config:
      for key in config['arguments']:
        if isinstance(config['arguments'][key], dict):
          arg_dict = config['arguments'][key]
          if 'type' in arg_dict and arg_dict['type'] == 'ndarray':
            # Overwrite the argument with its numpy translation
            config['arguments'][key] = np.array(arg_dict['value'])

    return cls(**config)

  @classmethod
  def _parse_function_from_config(cls, config, custom_objects, func_attr_name,
                                  module_attr_name, func_type_attr_name):
    globs = globals().copy()
    module = config.pop(module_attr_name, None)
    if module in sys.modules:
      globs.update(sys.modules[module].__dict__)
    elif module is not None:
      # Note: we don't know the name of the function if it's a lambda.
      warnings.warn(
          '{} is not loaded, but a Lambda layer uses it. '
          'It may cause errors.'.format(module), UserWarning)
    if custom_objects:
      globs.update(custom_objects)
    function_type = config.pop(func_type_attr_name)
    if function_type == 'function':
      # Simple lookup in custom objects
      function = generic_utils.deserialize_keras_object(
          config[func_attr_name],
          custom_objects=custom_objects,
          printable_module_name='function in Lambda layer')
    elif function_type == 'lambda':
      # Unsafe deserialization from bytecode
      function = generic_utils.func_load(config[func_attr_name], globs=globs)
    elif function_type == 'raw':
      function = config[func_attr_name]
    else:
      raise TypeError('Unknown function type:', function_type)
    return function
