# Copyright 2016 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.
# ==============================================================================
"""Weight broadcasting operations.

In `tf.losses` and `tf.metrics`, we support limited weight broadcasting. This
file includes operations for those broadcasting rules.
"""

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

from tensorflow.python.framework import ops
from tensorflow.python.framework import tensor_util
from tensorflow.python.ops import array_ops
from tensorflow.python.ops import control_flow_ops
from tensorflow.python.ops import math_ops
from tensorflow.python.ops import sets


def _has_valid_dims(weights_shape, values_shape):
  with ops.name_scope(
      None, "has_invalid_dims", (weights_shape, values_shape)) as scope:
    values_shape_2d = array_ops.expand_dims(values_shape, -1)
    valid_dims = array_ops.concat(
        (values_shape_2d, array_ops.ones_like(values_shape_2d)), axis=1)
    weights_shape_2d = array_ops.expand_dims(weights_shape, -1)
    invalid_dims = sets.set_difference(weights_shape_2d, valid_dims)
    num_invalid_dims = array_ops.size(
        invalid_dims.values, name="num_invalid_dims")
    return math_ops.equal(0, num_invalid_dims, name=scope)


def _has_valid_nonscalar_shape(
    weights_rank, weights_shape, values_rank, values_shape):
  with ops.name_scope(
      None, "has_valid_nonscalar_shape",
      (weights_rank, weights_shape, values_rank, values_shape)) as scope:
    is_same_rank = math_ops.equal(
        values_rank, weights_rank, name="is_same_rank")
    return control_flow_ops.cond(
        is_same_rank,
        lambda: _has_valid_dims(weights_shape, values_shape),
        lambda: is_same_rank,
        name=scope)


_ASSERT_BROADCASTABLE_ERROR_PREFIX = "weights can not be broadcast to values."


def assert_broadcastable(weights, values):
  """Asserts `weights` can be broadcast to `values`.

  In `tf.losses` and `tf.metrics`, we support limited weight broadcasting. We
  let weights be either scalar, or the same rank as the target values, with each
  dimension either 1, or the same as the corresponding values dimension.

  Args:
    weights: `Tensor` of weights.
    values: `Tensor` of values to which weights are applied.

  Returns:
    `Operation` raising `InvalidArgumentError` if `weights` has incorrect shape.
    `no_op` if static checks determine `weights` has correct shape.

  Raises:
    ValueError:  If static checks determine `weights` has incorrect shape.
  """
  with ops.name_scope(None, "assert_broadcastable", (weights, values)) as scope:
    with ops.name_scope(None, "weights", (weights,)) as weights_scope:
      weights = ops.convert_to_tensor(weights, name=weights_scope)
      weights_shape = array_ops.shape(weights, name="shape")
      weights_rank = array_ops.rank(weights, name="rank")
    weights_rank_static = tensor_util.constant_value(weights_rank)

    with ops.name_scope(None, "values", (values,)) as values_scope:
      values = ops.convert_to_tensor(values, name=values_scope)
      values_shape = array_ops.shape(values, name="shape")
      values_rank = array_ops.rank(values, name="rank")
    values_rank_static = tensor_util.constant_value(values_rank)

    # Try static checks.
    if weights_rank_static is not None and values_rank_static is not None:
      if weights_rank_static == 0:
        return control_flow_ops.no_op(name="static_scalar_check_success")
      if weights_rank_static != values_rank_static:
        raise ValueError(
            "%s values.rank=%s. weights.rank=%s."
            " values.shape=%s. weights.shape=%s." % (
                _ASSERT_BROADCASTABLE_ERROR_PREFIX, values_rank_static,
                weights_rank_static, values.shape, weights.shape))
      weights_shape_static = tensor_util.constant_value(weights_shape)
      values_shape_static = tensor_util.constant_value(values_shape)
      if weights_shape_static is not None and values_shape_static is not None:
        # Sanity check, this should always be true since we checked rank above.
        ndims = len(values_shape_static)
        assert ndims == len(weights_shape_static)

        for i in range(ndims):
          if weights_shape_static[i] not in (1, values_shape_static[i]):
            raise ValueError(
                "%s Mismatch at dim %s. values.shape=%s weights.shape=%s." % (
                    _ASSERT_BROADCASTABLE_ERROR_PREFIX, i, values_shape_static,
                    weights_shape_static))
        return control_flow_ops.no_op(name="static_dims_check_success")

    # Dynamic checks.
    is_scalar = math_ops.equal(0, weights_rank, name="is_scalar")
    data = (
        _ASSERT_BROADCASTABLE_ERROR_PREFIX,
        "weights.shape=", weights.name, weights_shape,
        "values.shape=", values.name, values_shape,
        "is_scalar=", is_scalar,
    )
    is_valid_shape = control_flow_ops.cond(
        is_scalar,
        lambda: is_scalar,
        lambda: _has_valid_nonscalar_shape(  # pylint: disable=g-long-lambda
            weights_rank, weights_shape, values_rank, values_shape),
        name="is_valid_shape")
    return control_flow_ops.Assert(is_valid_shape, data, name=scope)


def broadcast_weights(weights, values):
  """Broadcast `weights` to the same shape as `values`.

  This returns a version of `weights` following the same broadcast rules as
  `mul(weights, values)`, but limited to the weights shapes allowed by
  `assert_broadcastable`. When computing a weighted average, use this function
  to broadcast `weights` before summing them; e.g.,
  `reduce_sum(w * v) / reduce_sum(_broadcast_weights(w, v))`.

  Args:
    weights: `Tensor` whose shape is broadcastable to `values` according to the
      rules of `assert_broadcastable`.
    values: `Tensor` of any shape.

  Returns:
    `weights` broadcast to `values` shape according to the rules of
      `assert_broadcastable`.
  """
  with ops.name_scope(None, "broadcast_weights", (weights, values)) as scope:
    values = ops.convert_to_tensor(values, name="values")
    weights = ops.convert_to_tensor(
        weights, dtype=values.dtype.base_dtype, name="weights")

    # Try static check for exact match.
    weights_shape = weights.get_shape()
    values_shape = values.get_shape()
    if (weights_shape.is_fully_defined() and
        values_shape.is_fully_defined() and
        weights_shape.is_compatible_with(values_shape)):
      return weights

    with ops.control_dependencies((assert_broadcastable(weights, values),)):
      return math_ops.multiply(
          weights, array_ops.ones_like(values), name=scope)
