# 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.
# ==============================================================================
"""Operations for generating random numbers."""

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

import numpy as np
from tensorflow.python.framework import dtypes
from tensorflow.python.framework import ops
from tensorflow.python.framework import random_seed
from tensorflow.python.ops import array_ops
from tensorflow.python.ops import control_flow_ops
from tensorflow.python.ops import gen_random_ops
from tensorflow.python.ops import math_ops
# go/tf-wildcard-import
# pylint: disable=wildcard-import
from tensorflow.python.ops.gen_random_ops import *
from tensorflow.python.util.tf_export import tf_export

# pylint: enable=wildcard-import


def _ShapeTensor(shape):
  """Convert to an int32 or int64 tensor, defaulting to int32 if empty."""
  if isinstance(shape, (tuple, list)) and not shape:
    dtype = dtypes.int32
  else:
    dtype = None
  return ops.convert_to_tensor(shape, dtype=dtype, name="shape")


@tf_export("random_normal")
def random_normal(shape,
                  mean=0.0,
                  stddev=1.0,
                  dtype=dtypes.float32,
                  seed=None,
                  name=None):
  """Outputs random values from a normal distribution.

  Args:
    shape: A 1-D integer Tensor or Python array. The shape of the output tensor.
    mean: A 0-D Tensor or Python value of type `dtype`. The mean of the normal
      distribution.
    stddev: A 0-D Tensor or Python value of type `dtype`. The standard deviation
      of the normal distribution.
    dtype: The type of the output.
    seed: A Python integer. Used to create a random seed for the distribution.
      See
      @{tf.set_random_seed}
      for behavior.
    name: A name for the operation (optional).

  Returns:
    A tensor of the specified shape filled with random normal values.
  """
  with ops.name_scope(name, "random_normal", [shape, mean, stddev]) as name:
    shape_tensor = _ShapeTensor(shape)
    mean_tensor = ops.convert_to_tensor(mean, dtype=dtype, name="mean")
    stddev_tensor = ops.convert_to_tensor(stddev, dtype=dtype, name="stddev")
    seed1, seed2 = random_seed.get_seed(seed)
    rnd = gen_random_ops.random_standard_normal(
        shape_tensor, dtype, seed=seed1, seed2=seed2)
    mul = rnd * stddev_tensor
    value = math_ops.add(mul, mean_tensor, name=name)
    return value


ops.NotDifferentiable("RandomStandardNormal")


def parameterized_truncated_normal(shape,
                                   means=0.0,
                                   stddevs=1.0,
                                   minvals=-2.0,
                                   maxvals=2.0,
                                   dtype=dtypes.float32,
                                   seed=None,
                                   name=None):
  """Outputs random values from a truncated normal distribution.

  The generated values follow a normal distribution with specified mean and
  standard deviation, except that values whose magnitude is more than 2 standard
  deviations from the mean are dropped and re-picked.

  Args:
    shape: A 1-D integer Tensor or Python array. The shape of the output tensor.
    means: A 0-D Tensor or Python value of type `dtype`. The mean of the
      truncated normal distribution.
    stddevs: A 0-D Tensor or Python value of type `dtype`. The standard
      deviation of the truncated normal distribution.
    minvals: A 0-D Tensor or Python value of type `dtype`. The minimum value of
      the truncated normal distribution.
    maxvals: A 0-D Tensor or Python value of type `dtype`. The maximum value of
      the truncated normal distribution.
    dtype: The type of the output.
    seed: A Python integer. Used to create a random seed for the distribution.
      See
      @{tf.set_random_seed}
      for behavior.
    name: A name for the operation (optional).

  Returns:
    A tensor of the specified shape filled with random truncated normal values.
  """
  with ops.name_scope(name, "parameterized_truncated_normal",
                      [shape, means, stddevs, minvals, maxvals]) as name:
    shape_tensor = _ShapeTensor(shape)
    means_tensor = ops.convert_to_tensor(means, dtype=dtype, name="means")
    stddevs_tensor = ops.convert_to_tensor(stddevs, dtype=dtype, name="stddevs")
    minvals_tensor = ops.convert_to_tensor(minvals, dtype=dtype, name="minvals")
    maxvals_tensor = ops.convert_to_tensor(maxvals, dtype=dtype, name="maxvals")
    seed1, seed2 = random_seed.get_seed(seed)
    rnd = gen_random_ops.parameterized_truncated_normal(
        shape_tensor,
        means_tensor,
        stddevs_tensor,
        minvals_tensor,
        maxvals_tensor,
        seed=seed1,
        seed2=seed2)
    return rnd


@tf_export("truncated_normal")
def truncated_normal(shape,
                     mean=0.0,
                     stddev=1.0,
                     dtype=dtypes.float32,
                     seed=None,
                     name=None):
  """Outputs random values from a truncated normal distribution.

  The generated values follow a normal distribution with specified mean and
  standard deviation, except that values whose magnitude is more than 2 standard
  deviations from the mean are dropped and re-picked.

  Args:
    shape: A 1-D integer Tensor or Python array. The shape of the output tensor.
    mean: A 0-D Tensor or Python value of type `dtype`. The mean of the
      truncated normal distribution.
    stddev: A 0-D Tensor or Python value of type `dtype`. The standard deviation
      of the normal distribution, before truncation.
    dtype: The type of the output.
    seed: A Python integer. Used to create a random seed for the distribution.
      See
      @{tf.set_random_seed}
      for behavior.
    name: A name for the operation (optional).

  Returns:
    A tensor of the specified shape filled with random truncated normal values.
  """
  with ops.name_scope(name, "truncated_normal", [shape, mean, stddev]) as name:
    shape_tensor = _ShapeTensor(shape)
    mean_tensor = ops.convert_to_tensor(mean, dtype=dtype, name="mean")
    stddev_tensor = ops.convert_to_tensor(stddev, dtype=dtype, name="stddev")
    seed1, seed2 = random_seed.get_seed(seed)
    rnd = gen_random_ops.truncated_normal(
        shape_tensor, dtype, seed=seed1, seed2=seed2)
    mul = rnd * stddev_tensor
    value = math_ops.add(mul, mean_tensor, name=name)
    return value


ops.NotDifferentiable("ParameterizedTruncatedNormal")
ops.NotDifferentiable("TruncatedNormal")


@tf_export("random_uniform")
def random_uniform(shape,
                   minval=0,
                   maxval=None,
                   dtype=dtypes.float32,
                   seed=None,
                   name=None):
  """Outputs random values from a uniform distribution.

  The generated values follow a uniform distribution in the range
  `[minval, maxval)`. The lower bound `minval` is included in the range, while
  the upper bound `maxval` is excluded.

  For floats, the default range is `[0, 1)`.  For ints, at least `maxval` must
  be specified explicitly.

  In the integer case, the random integers are slightly biased unless
  `maxval - minval` is an exact power of two.  The bias is small for values of
  `maxval - minval` significantly smaller than the range of the output (either
  `2**32` or `2**64`).

  Args:
    shape: A 1-D integer Tensor or Python array. The shape of the output tensor.
    minval: A 0-D Tensor or Python value of type `dtype`. The lower bound on the
      range of random values to generate.  Defaults to 0.
    maxval: A 0-D Tensor or Python value of type `dtype`. The upper bound on
      the range of random values to generate.  Defaults to 1 if `dtype` is
      floating point.
    dtype: The type of the output: `float16`, `float32`, `float64`, `int32`,
      or `int64`.
    seed: A Python integer. Used to create a random seed for the distribution.
      See @{tf.set_random_seed}
      for behavior.
    name: A name for the operation (optional).

  Returns:
    A tensor of the specified shape filled with random uniform values.

  Raises:
    ValueError: If `dtype` is integral and `maxval` is not specified.
  """
  dtype = dtypes.as_dtype(dtype)
  if dtype not in (dtypes.float16, dtypes.bfloat16, dtypes.float32,
                   dtypes.float64, dtypes.int32, dtypes.int64):
    raise ValueError("Invalid dtype %r" % dtype)
  if maxval is None:
    if dtype.is_integer:
      raise ValueError("Must specify maxval for integer dtype %r" % dtype)
    maxval = 1
  with ops.name_scope(name, "random_uniform", [shape, minval, maxval]) as name:
    shape = _ShapeTensor(shape)
    minval = ops.convert_to_tensor(minval, dtype=dtype, name="min")
    maxval = ops.convert_to_tensor(maxval, dtype=dtype, name="max")
    seed1, seed2 = random_seed.get_seed(seed)
    if dtype.is_integer:
      return gen_random_ops.random_uniform_int(
          shape, minval, maxval, seed=seed1, seed2=seed2, name=name)
    else:
      rnd = gen_random_ops.random_uniform(shape, dtype, seed=seed1, seed2=seed2)
      return math_ops.add(rnd * (maxval - minval), minval, name=name)


ops.NotDifferentiable("RandomUniform")


@tf_export("random_shuffle")
def random_shuffle(value, seed=None, name=None):
  """Randomly shuffles a tensor along its first dimension.

  The tensor is shuffled along dimension 0, such that each `value[j]` is mapped
  to one and only one `output[i]`. For example, a mapping that might occur for a
  3x2 tensor is:

  ```python
  [[1, 2],       [[5, 6],
   [3, 4],  ==>   [1, 2],
   [5, 6]]        [3, 4]]
  ```

  Args:
    value: A Tensor to be shuffled.
    seed: A Python integer. Used to create a random seed for the distribution.
      See
      @{tf.set_random_seed}
      for behavior.
    name: A name for the operation (optional).

  Returns:
    A tensor of same shape and type as `value`, shuffled along its first
    dimension.
  """
  seed1, seed2 = random_seed.get_seed(seed)
  return gen_random_ops.random_shuffle(
      value, seed=seed1, seed2=seed2, name=name)


@tf_export("random_crop")
def random_crop(value, size, seed=None, name=None):
  """Randomly crops a tensor to a given size.

  Slices a shape `size` portion out of `value` at a uniformly chosen offset.
  Requires `value.shape >= size`.

  If a dimension should not be cropped, pass the full size of that dimension.
  For example, RGB images can be cropped with
  `size = [crop_height, crop_width, 3]`.

  Args:
    value: Input tensor to crop.
    size: 1-D tensor with size the rank of `value`.
    seed: Python integer. Used to create a random seed. See
      @{tf.set_random_seed}
      for behavior.
    name: A name for this operation (optional).

  Returns:
    A cropped tensor of the same rank as `value` and shape `size`.
  """
  # TODO(shlens): Implement edge case to guarantee output size dimensions.
  # If size > value.shape, zero pad the result so that it always has shape
  # exactly size.
  with ops.name_scope(name, "random_crop", [value, size]) as name:
    value = ops.convert_to_tensor(value, name="value")
    size = ops.convert_to_tensor(size, dtype=dtypes.int32, name="size")
    shape = array_ops.shape(value)
    check = control_flow_ops.Assert(
        math_ops.reduce_all(shape >= size),
        ["Need value.shape >= size, got ", shape, size],
        summarize=1000)
    shape = control_flow_ops.with_dependencies([check], shape)
    limit = shape - size + 1
    offset = random_uniform(
        array_ops.shape(shape),
        dtype=size.dtype,
        maxval=size.dtype.max,
        seed=seed) % limit
    return array_ops.slice(value, offset, size, name=name)


@tf_export("multinomial")
def multinomial(logits, num_samples, seed=None, name=None, output_dtype=None):
  """Draws samples from a multinomial distribution.

  Example:

  ```python
  # samples has shape [1, 5], where each value is either 0 or 1 with equal
  # probability.
  samples = tf.multinomial(tf.log([[10., 10.]]), 5)
  ```

  Args:
    logits: 2-D Tensor with shape `[batch_size, num_classes]`.  Each slice
      `[i, :]` represents the unnormalized log-probabilities for all classes.
    num_samples: 0-D.  Number of independent samples to draw for each row slice.
    seed: A Python integer. Used to create a random seed for the distribution.
      See
      @{tf.set_random_seed}
      for behavior.
    name: Optional name for the operation.
    output_dtype: integer type to use for the output. Defaults to int64.

  Returns:
    The drawn samples of shape `[batch_size, num_samples]`.
  """
  with ops.name_scope(name, "multinomial", [logits]):
    logits = ops.convert_to_tensor(logits, name="logits")
    seed1, seed2 = random_seed.get_seed(seed)
    return gen_random_ops.multinomial(
        logits, num_samples, seed=seed1, seed2=seed2, output_dtype=output_dtype)


ops.NotDifferentiable("Multinomial")


@tf_export("random_gamma")
def random_gamma(shape,
                 alpha,
                 beta=None,
                 dtype=dtypes.float32,
                 seed=None,
                 name=None):
  """Draws `shape` samples from each of the given Gamma distribution(s).

  `alpha` is the shape parameter describing the distribution(s), and `beta` is
  the inverse scale parameter(s).

  Note: Because internal calculations are done using `float64` and casting has
  `floor` semantics, we must manually map zero outcomes to the smallest
  possible positive floating-point value, i.e., `np.finfo(dtype).tiny`.  This
  means that `np.finfo(dtype).tiny` occurs more frequently than it otherwise
  should.  This bias can only happen for small values of `alpha`, i.e.,
  `alpha << 1` or large values of `beta`, i.e., `beta >> 1`.

  The samples are differentiable w.r.t. alpha and beta.
  The derivatives are computed using the approach described in the paper

  [Michael Figurnov, Shakir Mohamed, Andriy Mnih.
  Implicit Reparameterization Gradients, 2018](https://arxiv.org/abs/1805.08498)

  Example:

  ```python
  samples = tf.random_gamma([10], [0.5, 1.5])
  # samples has shape [10, 2], where each slice [:, 0] and [:, 1] represents
  # the samples drawn from each distribution

  samples = tf.random_gamma([7, 5], [0.5, 1.5])
  # samples has shape [7, 5, 2], where each slice [:, :, 0] and [:, :, 1]
  # represents the 7x5 samples drawn from each of the two distributions

  alpha = tf.constant([[1.],[3.],[5.]])
  beta = tf.constant([[3., 4.]])
  samples = tf.random_gamma([30], alpha=alpha, beta=beta)
  # samples has shape [30, 3, 2], with 30 samples each of 3x2 distributions.

  loss = tf.reduce_mean(tf.square(samples))
  dloss_dalpha, dloss_dbeta = tf.gradients(loss, [alpha, beta])
  # unbiased stochastic derivatives of the loss function
  alpha.shape == dloss_dalpha.shape  # True
  beta.shape == dloss_dbeta.shape  # True
  ```

  Args:
    shape: A 1-D integer Tensor or Python array. The shape of the output samples
      to be drawn per alpha/beta-parameterized distribution.
    alpha: A Tensor or Python value or N-D array of type `dtype`. `alpha`
      provides the shape parameter(s) describing the gamma distribution(s) to
      sample. Must be broadcastable with `beta`.
    beta: A Tensor or Python value or N-D array of type `dtype`. Defaults to 1.
      `beta` provides the inverse scale parameter(s) of the gamma
      distribution(s) to sample. Must be broadcastable with `alpha`.
    dtype: The type of alpha, beta, and the output: `float16`, `float32`, or
      `float64`.
    seed: A Python integer. Used to create a random seed for the distributions.
      See
      @{tf.set_random_seed}
      for behavior.
    name: Optional name for the operation.

  Returns:
    samples: a `Tensor` of shape
      `tf.concat([shape, tf.shape(alpha + beta)], axis=0)` with values of type
      `dtype`.
  """
  with ops.name_scope(name, "random_gamma", [shape, alpha, beta]):
    shape = ops.convert_to_tensor(shape, name="shape", dtype=dtypes.int32)
    alpha = ops.convert_to_tensor(alpha, name="alpha", dtype=dtype)
    beta = ops.convert_to_tensor(
        beta if beta is not None else 1, name="beta", dtype=dtype)
    alpha_broadcast = alpha + array_ops.zeros_like(beta)
    seed1, seed2 = random_seed.get_seed(seed)
    return math_ops.maximum(
        np.finfo(dtype.as_numpy_dtype).tiny,
        gen_random_ops.random_gamma(
            shape, alpha_broadcast, seed=seed1, seed2=seed2) / beta)


@tf_export("random_poisson")
def random_poisson(lam, shape, dtype=dtypes.float32, seed=None, name=None):
  """Draws `shape` samples from each of the given Poisson distribution(s).

  `lam` is the rate parameter describing the distribution(s).

  Example:

  ```python
  samples = tf.random_poisson([0.5, 1.5], [10])
  # samples has shape [10, 2], where each slice [:, 0] and [:, 1] represents
  # the samples drawn from each distribution

  samples = tf.random_poisson([12.2, 3.3], [7, 5])
  # samples has shape [7, 5, 2], where each slice [:, :, 0] and [:, :, 1]
  # represents the 7x5 samples drawn from each of the two distributions
  ```

  Args:
    lam: A Tensor or Python value or N-D array of type `dtype`.
      `lam` provides the rate parameter(s) describing the poisson
      distribution(s) to sample.
    shape: A 1-D integer Tensor or Python array. The shape of the output samples
      to be drawn per "rate"-parameterized distribution.
    dtype: The type of the output: `float16`, `float32`, `float64`, `int32` or
      `int64`.
    seed: A Python integer. Used to create a random seed for the distributions.
      See
      @{tf.set_random_seed}
      for behavior.
    name: Optional name for the operation.

  Returns:
    samples: a `Tensor` of shape `tf.concat([shape, tf.shape(lam)], axis=0)`
      with values of type `dtype`.
  """
  with ops.name_scope(name, "random_poisson", [lam, shape]):
    shape = ops.convert_to_tensor(shape, name="shape", dtype=dtypes.int32)
    seed1, seed2 = random_seed.get_seed(seed)
    return gen_random_ops.random_poisson_v2(
        shape, lam, dtype=dtype, seed=seed1, seed2=seed2)