# 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.
# ==============================================================================
"""Wrapper layer to apply every temporal slice of an input."""


import tensorflow.compat.v2 as tf

from keras import backend
from keras.engine.base_layer import Layer
from keras.engine.input_spec import InputSpec
from keras.layers.rnn.base_wrapper import Wrapper
from keras.utils import generic_utils
from keras.utils import layer_utils
from keras.utils import tf_utils

# isort: off
from tensorflow.python.util.tf_export import keras_export


@keras_export("keras.layers.TimeDistributed")
class TimeDistributed(Wrapper):
    """This wrapper allows to apply a layer to every temporal slice of an input.

    Every input should be at least 3D, and the dimension of index one of the
    first input will be considered to be the temporal dimension.

    Consider a batch of 32 video samples, where each sample is a 128x128 RGB
    image with `channels_last` data format, across 10 timesteps.
    The batch input shape is `(32, 10, 128, 128, 3)`.

    You can then use `TimeDistributed` to apply the same `Conv2D` layer to each
    of the 10 timesteps, independently:

    >>> inputs = tf.keras.Input(shape=(10, 128, 128, 3))
    >>> conv_2d_layer = tf.keras.layers.Conv2D(64, (3, 3))
    >>> outputs = tf.keras.layers.TimeDistributed(conv_2d_layer)(inputs)
    >>> outputs.shape
    TensorShape([None, 10, 126, 126, 64])

    Because `TimeDistributed` applies the same instance of `Conv2D` to each of
    the timestamps, the same set of weights are used at each timestamp.

    Args:
      layer: a `tf.keras.layers.Layer` instance.

    Call arguments:
      inputs: Input tensor of shape (batch, time, ...) or nested tensors,
        and each of which has shape (batch, time, ...).
      training: Python boolean indicating whether the layer should behave in
        training mode or in inference mode. This argument is passed to the
        wrapped layer (only if the layer supports this argument).
      mask: Binary tensor of shape `(samples, timesteps)` indicating whether
        a given timestep should be masked. This argument is passed to the
        wrapped layer (only if the layer supports this argument).

    Raises:
      ValueError: If not initialized with a `tf.keras.layers.Layer` instance.
    """

    def __init__(self, layer, **kwargs):
        if not isinstance(layer, Layer):
            raise ValueError(
                "Please initialize `TimeDistributed` layer with a "
                f"`tf.keras.layers.Layer` instance. Received: {layer}"
            )
        super().__init__(layer, **kwargs)
        self.supports_masking = True

        # It is safe to use the fast, reshape-based approach with all of our
        # built-in Layers.
        self._always_use_reshape = layer_utils.is_builtin_layer(
            layer
        ) and not getattr(layer, "stateful", False)

    def _get_shape_tuple(self, init_tuple, tensor, start_idx):
        """Finds non-specific dimensions in the static shapes.

        The static shapes are replaced with the corresponding dynamic shapes of
        the tensor.
        Args:
          init_tuple: a tuple, the first part of the output shape
          tensor: the tensor from which to get the (static and dynamic) shapes
            as the last part of the output shape
          start_idx: int, which indicate the first dimension to take from
            the static shape of the tensor
        Returns:
          The new shape with the first part from `init_tuple` and the last part
          from or `tensor.shape`, where every `None` is replaced by the
          corresponding dimension from `tf.shape(tensor)`.
        """
        # replace all None in int_shape by backend.shape
        int_shape = backend.int_shape(tensor)[start_idx:]
        if not any(s is None for s in int_shape):
            return init_tuple + int_shape
        shape = backend.shape(tensor)
        int_shape = list(int_shape)
        for i, s in enumerate(int_shape):
            if s is None:
                int_shape[i] = shape[start_idx + i]
        return init_tuple + tuple(int_shape)

    def _remove_timesteps(self, dims):
        dims = dims.as_list()
        return tf.TensorShape([dims[0]] + dims[2:])

    def build(self, input_shape):
        input_shape = tf_utils.convert_shapes(input_shape, to_tuples=False)
        input_dims = tf.nest.flatten(
            tf.nest.map_structure(lambda x: x.ndims, input_shape)
        )
        if any(dim < 3 for dim in input_dims):
            raise ValueError(
                "`TimeDistributed` Layer should be passed an `input_shape ` "
                f"with at least 3 dimensions, received: {input_shape}"
            )
        # Don't enforce the batch or time dimension.
        self.input_spec = tf.nest.map_structure(
            lambda x: InputSpec(shape=[None, None] + x.as_list()[2:]),
            input_shape,
        )
        child_input_shape = tf.nest.map_structure(
            self._remove_timesteps, input_shape
        )
        child_input_shape = tf_utils.convert_shapes(child_input_shape)
        super().build(tuple(child_input_shape))
        self.built = True

    def compute_output_shape(self, input_shape):
        input_shape = tf_utils.convert_shapes(input_shape, to_tuples=False)

        child_input_shape = tf.nest.map_structure(
            self._remove_timesteps, input_shape
        )
        child_output_shape = self.layer.compute_output_shape(child_input_shape)
        child_output_shape = tf_utils.convert_shapes(
            child_output_shape, to_tuples=False
        )
        timesteps = tf_utils.convert_shapes(input_shape)
        timesteps = tf.nest.flatten(timesteps)[1]

        def insert_timesteps(dims):
            dims = dims.as_list()
            return tf.TensorShape([dims[0], timesteps] + dims[1:])

        return tf.nest.map_structure(insert_timesteps, child_output_shape)

    def call(self, inputs, training=None, mask=None):
        kwargs = {}
        if generic_utils.has_arg(self.layer.call, "training"):
            kwargs["training"] = training

        input_shape = tf.nest.map_structure(
            lambda x: tf.TensorShape(backend.int_shape(x)), inputs
        )
        batch_size = tf_utils.convert_shapes(input_shape)
        batch_size = tf.nest.flatten(batch_size)[0]
        if batch_size and not self._always_use_reshape:
            inputs, row_lengths = backend.convert_inputs_if_ragged(inputs)
            is_ragged_input = row_lengths is not None
            input_length = tf_utils.convert_shapes(input_shape)
            input_length = tf.nest.flatten(input_length)[1]

            # batch size matters, use rnn-based implementation
            def step(x, _):
                output = self.layer(x, **kwargs)
                return output, []

            _, outputs, _ = backend.rnn(
                step,
                inputs,
                initial_states=[],
                input_length=row_lengths[0]
                if is_ragged_input
                else input_length,
                mask=mask,
                unroll=False,
            )

            y = tf.nest.map_structure(
                lambda output: backend.maybe_convert_to_ragged(
                    is_ragged_input, output, row_lengths
                ),
                outputs,
            )
        else:
            # No batch size specified, therefore the layer will be able
            # to process batches of any size.
            # We can go with reshape-based implementation for performance.
            is_ragged_input = tf.nest.map_structure(
                lambda x: isinstance(x, tf.RaggedTensor), inputs
            )
            is_ragged_input = tf.nest.flatten(is_ragged_input)
            if all(is_ragged_input):
                input_values = tf.nest.map_structure(lambda x: x.values, inputs)
                input_row_lenghts = tf.nest.map_structure(
                    lambda x: x.nested_row_lengths()[0], inputs
                )
                y = self.layer(input_values, **kwargs)
                y = tf.nest.map_structure(
                    tf.RaggedTensor.from_row_lengths, y, input_row_lenghts
                )
            elif any(is_ragged_input):
                raise ValueError(
                    "All inputs has to be either ragged or not, "
                    f"but not mixed. Received: {inputs}"
                )
            else:
                input_length = tf_utils.convert_shapes(input_shape)
                input_length = tf.nest.flatten(input_length)[1]
                if not input_length:
                    input_length = tf.nest.map_structure(
                        lambda x: tf.shape(x)[1], inputs
                    )
                    input_length = generic_utils.to_list(
                        tf.nest.flatten(input_length)
                    )[0]

                inner_input_shape = tf.nest.map_structure(
                    lambda x: self._get_shape_tuple((-1,), x, 2), inputs
                )
                # Shape: (num_samples * timesteps, ...). And track the
                # transformation in self._input_map.
                inputs = tf.__internal__.nest.map_structure_up_to(
                    inputs, tf.reshape, inputs, inner_input_shape
                )
                # (num_samples * timesteps, ...)
                if (
                    generic_utils.has_arg(self.layer.call, "mask")
                    and mask is not None
                ):
                    inner_mask_shape = self._get_shape_tuple((-1,), mask, 2)
                    kwargs["mask"] = backend.reshape(mask, inner_mask_shape)

                y = self.layer(inputs, **kwargs)

                # Reconstruct the output shape by re-splitting the 0th dimension
                # back into (num_samples, timesteps, ...)
                # We use batch_size when available so that the 0th dimension is
                # set in the static shape of the reshaped output
                reshape_batch_size = batch_size if batch_size else -1
                output_shape = tf.nest.map_structure(
                    lambda tensor: self._get_shape_tuple(
                        (reshape_batch_size, input_length), tensor, 1
                    ),
                    y,
                )
                y = tf.__internal__.nest.map_structure_up_to(
                    y, tf.reshape, y, output_shape
                )

        return y

    def compute_mask(self, inputs, mask=None):
        """Computes an output mask tensor for Embedding layer.

        This is based on the inputs, mask, and the inner layer.
        If batch size is specified:
        Simply return the input `mask`. (An rnn-based implementation with
        more than one rnn inputs is required but not supported in tf.keras yet.)
        Otherwise we call `compute_mask` of the inner layer at each time step.
        If the output mask at each time step is not `None`:
        (E.g., inner layer is Masking or RNN)
        Concatenate all of them and return the concatenation.
        If the output mask at each time step is `None` and the input mask is not
        `None`:(E.g., inner layer is Dense)
        Reduce the input_mask to 2 dimensions and return it.
        Otherwise (both the output mask and the input mask are `None`):
        (E.g., `mask` is not used at all)
        Return `None`.

        Args:
          inputs: Tensor with shape [batch size, timesteps, ...] indicating the
            input to TimeDistributed. If static shape information is available
            for "batch size", `mask` is returned unmodified.
          mask: Either None (indicating no masking) or a Tensor indicating the
            input mask for TimeDistributed. The shape can be static or dynamic.

        Returns:
          Either None (no masking), or a [batch size, timesteps, ...] Tensor
          with an output mask for the TimeDistributed layer with the shape
          beyond the second dimension being the value of the input mask shape(if
          the computed output mask is none), an output mask with the shape
          beyond the first dimension being the value of the mask shape(if mask
          is not None) or output mask with the shape beyond the first dimension
          being the value of the computed output shape.

        """
        # cases need to call the layer.compute_mask when input_mask is None:
        # Masking layer and Embedding layer with mask_zero
        input_shape = tf.nest.map_structure(
            lambda x: tf.TensorShape(backend.int_shape(x)), inputs
        )
        input_shape = tf_utils.convert_shapes(input_shape, to_tuples=False)
        batch_size = tf_utils.convert_shapes(input_shape)
        batch_size = tf.nest.flatten(batch_size)[0]
        is_ragged_input = tf.nest.map_structure(
            lambda x: isinstance(x, tf.RaggedTensor), inputs
        )
        is_ragged_input = generic_utils.to_list(
            tf.nest.flatten(is_ragged_input)
        )
        if batch_size and not self._always_use_reshape or any(is_ragged_input):
            # batch size matters, we currently do not handle mask explicitly, or
            # if the layer always uses reshape approach, or the input is a
            # ragged tensor.
            return mask
        inner_mask = mask
        if inner_mask is not None:
            inner_mask_shape = self._get_shape_tuple((-1,), mask, 2)
            inner_mask = backend.reshape(inner_mask, inner_mask_shape)
        inner_input_shape = tf.nest.map_structure(
            lambda tensor: self._get_shape_tuple((-1,), tensor, 2), inputs
        )
        inner_inputs = tf.__internal__.nest.map_structure_up_to(
            inputs, tf.reshape, inputs, inner_input_shape
        )
        output_mask = self.layer.compute_mask(inner_inputs, inner_mask)
        if output_mask is None:
            if mask is None:
                return None
            # input_mask is not None, and output_mask is None:
            # we should return a not-None mask
            output_mask = mask
            for _ in range(2, len(backend.int_shape(mask))):
                output_mask = backend.any(output_mask, axis=-1)
        else:
            # output_mask is not None. We need to reshape it
            input_length = tf_utils.convert_shapes(input_shape)
            input_length = tf.nest.flatten(input_length)[1]
            if not input_length:
                input_length = tf.nest.map_structure(
                    lambda x: backend.shape(x)[1], inputs
                )
                input_length = tf.nest.flatten(input_length)[0]
            reshape_batch_size = batch_size if batch_size else -1
            output_mask_shape = self._get_shape_tuple(
                (reshape_batch_size, input_length), output_mask, 1
            )
            output_mask = backend.reshape(output_mask, output_mask_shape)
        return output_mask