# 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.
# ==============================================================================
"""Embedding layer.
"""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

from tensorflow.python.distribute import sharded_variable
from tensorflow.python.eager import context
from tensorflow.python.framework import config as tf_config
from tensorflow.python.framework import ops
from tensorflow.python.keras import backend as K
from tensorflow.python.keras import constraints
from tensorflow.python.keras import initializers
from tensorflow.python.keras import regularizers
from tensorflow.python.keras.engine import base_layer_utils
from tensorflow.python.keras.engine.base_layer import Layer
from tensorflow.python.keras.utils import tf_utils
from tensorflow.python.ops import embedding_ops
from tensorflow.python.ops import math_ops
from tensorflow.python.util.tf_export import keras_export


@keras_export('keras.layers.Embedding')
class Embedding(Layer):
  """Turns positive integers (indexes) into dense vectors of fixed size.

  e.g. `[[4], [20]] -> [[0.25, 0.1], [0.6, -0.2]]`

  This layer can only be used as the first layer in a model.

  Example:

  >>> model = tf.keras.Sequential()
  >>> model.add(tf.keras.layers.Embedding(1000, 64, input_length=10))
  >>> # The model will take as input an integer matrix of size (batch,
  >>> # input_length), and the largest integer (i.e. word index) in the input
  >>> # should be no larger than 999 (vocabulary size).
  >>> # Now model.output_shape is (None, 10, 64), where `None` is the batch
  >>> # dimension.
  >>> input_array = np.random.randint(1000, size=(32, 10))
  >>> model.compile('rmsprop', 'mse')
  >>> output_array = model.predict(input_array)
  >>> print(output_array.shape)
  (32, 10, 64)

  Arguments:
    input_dim: Integer. Size of the vocabulary,
      i.e. maximum integer index + 1.
    output_dim: Integer. Dimension of the dense embedding.
    embeddings_initializer: Initializer for the `embeddings`
      matrix (see `keras.initializers`).
    embeddings_regularizer: Regularizer function applied to
      the `embeddings` matrix (see `keras.regularizers`).
    embeddings_constraint: Constraint function applied to
      the `embeddings` matrix (see `keras.constraints`).
    mask_zero: Boolean, whether or not the input value 0 is a special "padding"
      value that should be masked out.
      This is useful when using recurrent layers
      which may take variable length input.
      If this is `True`, then all subsequent layers
      in the model need to support masking or an exception will be raised.
      If mask_zero is set to True, as a consequence, index 0 cannot be
      used in the vocabulary (input_dim should equal size of
      vocabulary + 1).
    input_length: Length of input sequences, when it is constant.
      This argument is required if you are going to connect
      `Flatten` then `Dense` layers upstream
      (without it, the shape of the dense outputs cannot be computed).

  Input shape:
    2D tensor with shape: `(batch_size, input_length)`.

  Output shape:
    3D tensor with shape: `(batch_size, input_length, output_dim)`.
  """

  def __init__(self,
               input_dim,
               output_dim,
               embeddings_initializer='uniform',
               embeddings_regularizer=None,
               activity_regularizer=None,
               embeddings_constraint=None,
               mask_zero=False,
               input_length=None,
               **kwargs):
    if 'input_shape' not in kwargs:
      if input_length:
        kwargs['input_shape'] = (input_length,)
      else:
        kwargs['input_shape'] = (None,)
    if input_dim <= 0 or output_dim <= 0:
      raise ValueError('Both `input_dim` and `output_dim` should be positive, '
                       'found input_dim {} and output_dim {}'.format(
                           input_dim, output_dim))
    if (not base_layer_utils.v2_dtype_behavior_enabled() and
        'dtype' not in kwargs):
      # In TF1, the dtype defaults to the input dtype which is typically int32,
      # so explicitly set it to floatx
      kwargs['dtype'] = K.floatx()
    # We set autocast to False, as we do not want to cast floating- point inputs
    # to self.dtype. In call(), we cast to int32, and casting to self.dtype
    # before casting to int32 might cause the int32 values to be different due
    # to a loss of precision.
    kwargs['autocast'] = False
    super(Embedding, self).__init__(**kwargs)

    self.input_dim = input_dim
    self.output_dim = output_dim
    self.embeddings_initializer = initializers.get(embeddings_initializer)
    self.embeddings_regularizer = regularizers.get(embeddings_regularizer)
    self.activity_regularizer = regularizers.get(activity_regularizer)
    self.embeddings_constraint = constraints.get(embeddings_constraint)
    self.mask_zero = mask_zero
    self.supports_masking = mask_zero
    self.input_length = input_length

  @tf_utils.shape_type_conversion
  def build(self, input_shape):
    # Note: most sparse optimizers do not have GPU kernels defined. When
    # building graphs, the placement algorithm is able to place variables on CPU
    # since it knows all kernels using the variable only exist on CPU.
    # When eager execution is enabled, the placement decision has to be made
    # right now. Checking for the presence of GPUs to avoid complicating the
    # TPU codepaths which can handle sparse optimizers.
    if context.executing_eagerly() and tf_config.list_logical_devices('GPU'):
      with ops.device('cpu:0'):
        self.embeddings = self.add_weight(
            shape=(self.input_dim, self.output_dim),
            initializer=self.embeddings_initializer,
            name='embeddings',
            regularizer=self.embeddings_regularizer,
            constraint=self.embeddings_constraint,
            experimental_autocast=False)
    else:
      self.embeddings = self.add_weight(
          shape=(self.input_dim, self.output_dim),
          initializer=self.embeddings_initializer,
          name='embeddings',
          regularizer=self.embeddings_regularizer,
          constraint=self.embeddings_constraint,
          experimental_autocast=False)
    self.built = True

  def compute_mask(self, inputs, mask=None):
    if not self.mask_zero:
      return None

    return math_ops.not_equal(inputs, 0)

  @tf_utils.shape_type_conversion
  def compute_output_shape(self, input_shape):
    if self.input_length is None:
      return input_shape + (self.output_dim,)
    else:
      # input_length can be tuple if input is 3D or higher
      if isinstance(self.input_length, (list, tuple)):
        in_lens = list(self.input_length)
      else:
        in_lens = [self.input_length]
      if len(in_lens) != len(input_shape) - 1:
        raise ValueError('"input_length" is %s, '
                         'but received input has shape %s' % (str(
                             self.input_length), str(input_shape)))
      else:
        for i, (s1, s2) in enumerate(zip(in_lens, input_shape[1:])):
          if s1 is not None and s2 is not None and s1 != s2:
            raise ValueError('"input_length" is %s, '
                             'but received input has shape %s' % (str(
                                 self.input_length), str(input_shape)))
          elif s1 is None:
            in_lens[i] = s2
      return (input_shape[0],) + tuple(in_lens) + (self.output_dim,)

  def call(self, inputs):
    dtype = K.dtype(inputs)
    if dtype != 'int32' and dtype != 'int64':
      inputs = math_ops.cast(inputs, 'int32')
    if isinstance(self.embeddings, sharded_variable.ShardedVariable):
      out = embedding_ops.embedding_lookup_v2(self.embeddings.variables, inputs)
    else:
      out = embedding_ops.embedding_lookup_v2(self.embeddings, inputs)
    if self._dtype_policy.compute_dtype != self._dtype_policy.variable_dtype:
      # Instead of casting the variable as in most layers, cast the output, as
      # this is mathematically equivalent but is faster.
      out = math_ops.cast(out, self._dtype_policy.compute_dtype)
    return out

  def get_config(self):
    config = {
        'input_dim': self.input_dim,
        'output_dim': self.output_dim,
        'embeddings_initializer':
            initializers.serialize(self.embeddings_initializer),
        'embeddings_regularizer':
            regularizers.serialize(self.embeddings_regularizer),
        'activity_regularizer':
            regularizers.serialize(self.activity_regularizer),
        'embeddings_constraint':
            constraints.serialize(self.embeddings_constraint),
        'mask_zero': self.mask_zero,
        'input_length': self.input_length
    }
    base_config = super(Embedding, self).get_config()
    return dict(list(base_config.items()) + list(config.items()))