# Copyright 2017 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.
# ==============================================================================
"""TensorFlow Debugger: Tools for debugging gradients."""

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

import re
import uuid

import six

from tensorflow.python.debug.lib import debug_data
from tensorflow.python.framework import ops
from tensorflow.python.ops import gen_array_ops
from tensorflow.python.ops import variables

_GRADIENT_DEBUG_TAG = "gradient_debug_"

_gradient_debuggers = {}


def _tensor_to_grad_debug_op_name(tensor, grad_debugger_uuid):
  op_name, slot = debug_data.parse_node_or_tensor_name(tensor.name)
  return "%s_%d/%s%s" % (op_name, slot, _GRADIENT_DEBUG_TAG, grad_debugger_uuid)


def _parse_grad_debug_op_name(op_name):
  """Parse the name of a debug gradient op.

  Args:
    op_name: the name of the debug gradient op.

  Returns:
    1) The UUID of the GradientsDebugger that created the debug gradient op.
    2) Name of the original tensor whose gradient is debugged by the debug
       gradient op.
  """
  name_items = op_name.split("/")
  assert len(name_items) > 1
  assert name_items[-1].startswith(_GRADIENT_DEBUG_TAG)

  grad_debugger_uuid = name_items[-1][len(_GRADIENT_DEBUG_TAG):]
  if "_" in grad_debugger_uuid:
    grad_debugger_uuid = grad_debugger_uuid[:grad_debugger_uuid.index("_")]
  orig_tensor_slot = int(name_items[-2][name_items[-2].rfind("_") + 1:])
  orig_base_op_name = name_items[-2][:name_items[-2].rfind("_")]
  orig_tensor_name = ("/".join(name_items[:-2] + [orig_base_op_name]) +
                      ":%d" % orig_tensor_slot)

  return grad_debugger_uuid, orig_tensor_name


class GradientsDebugger(object):
  """Gradients Debugger.

  Allows retrieval of gradient tensors created by TensorFlow's automatic
  differentiation algorithm, i.e., @{tf.gradients} and optimizer classes that
  use it.
  """
  # TODO(cais): Add examples code in the doc string?

  def __init__(self, y_tensor=None):
    """Constructor of GradientsDebugger.

    Args:
      y_tensor: optional: the `tf.Tensor` to be differentiated, i.e., the tensor
        on the numerator of the differentiation.
    """

    self._uuid = uuid.uuid4().hex
    _gradient_debuggers[self._uuid] = self

    # A dict mapping x-tensor names to gradient tensor. x-tensor refers to the
    # independent tf.Tensor, i.e., the tensor on the denominator of the
    # differentiation.
    self._gradient_tensors = {}
    self._y_tensor = y_tensor

    self._graph = None
    if y_tensor:
      self._graph = y_tensor.graph

    self._is_active_context = False

  @property
  def y_tensor(self):
    return self._y_tensor

  @property
  def graph(self):
    return self._graph

  def __enter__(self):
    self._is_active_context = True

  def __exit__(self, unused_type, unused_value, unused_traceback):
    self._is_active_context = False

  def identify_gradient(self, input_tensor):
    """Create a debug identity tensor that registers and forwards gradients.

    The side effect of this method is that when gradient tensor(s) are created
    with respect to the any paths that include the `input_tensor`, the gradient
    tensor(s) with repsect to `input_tensor` will be registered with this
    this `GradientsDebugger` instance and can later be retrieved, with the
    methods `gradient_tensor` and `gradient_tensors`.

    Example:

    ```python
    x = tf.Variable(1.0)
    y = tf.add(x, x)

    grad_debugger = tf_debug.GradientsDebugger()
    debug_y = grad_debugger.identify_gradient(y)
    z = tf.square(debug_y)

    # Create a train op under the grad_debugger context.
    with grad_debugger:
      train_op = tf.train.GradientDescentOptimizer(z)

    # Now we can reflect through grad_debugger to get the gradient tensor
    # with respect to y.
    y_grad = grad_debugger.gradient_tensor(y)
    ```

    Args:
      input_tensor: the input `tf.Tensor` object whose related gradient tensors
        are to be reigstered with this `GradientsDebugger` instance when they
        are created, e.g., during @{tf.gradients} calls or the construction
        of optimization (training) op that uses @{tf.gradients}.

    Returns:
      A forwarded identity of `input_tensor`, as a `tf.Tensor`.

    Raises:
      ValueError: If an op with name that duplicates the gradient-debugging op
        already exists in the graph (highly unlikely).
    """
    # TODO(cais): Allow overriding gradient.
    # TODO(cais): Implement value_stack.
    grad_debug_op_name = _tensor_to_grad_debug_op_name(input_tensor, self._uuid)
    # pylint: disable=protected-access
    debug_grad_identity = gen_array_ops._debug_gradient_identity(
        input_tensor, name=grad_debug_op_name)
    # pylint: enable=protected-access
    if debug_grad_identity.op.name != grad_debug_op_name:
      raise ValueError(
          "The graph already contains an op named %s" % grad_debug_op_name)
    return debug_grad_identity

  def watch_gradients_by_tensors(self, graph, tensors):
    """Watch gradient tensors by x-tensor(s).

    The side effect of this method is that when gradient tensor(s) are created
    with respect to the any paths that include the `x_tensor`s, the gradient
    tensor(s) with repsect to the tensor will be registered with this
    this `GradientsDebugger` instance and can later be retrieved, with the
    methods `gradient_tensor` and `gradient_tensors`.

    Unlike the method `identify_gradient`, this method is used to retrieve
    gradient tensors after the construction of the forward subgraph has
    completed (but before the construction of the backward subgraph).

    This method is the same as `watch_gradients_by_x_tensor_names` except that
    the tensors are specified by the Python `tf.Tensor` or `tf.Variable`
    objects, instead by name patterns.

    Example:

    ```python
    x = tf.Variable(1.0)
    y = tf.add(x, x, name="y")
    z = tf.square(debug_y)

    # Create a train op under the grad_debugger context.
    grad_debugger = tf_debug.GradientsDebugger()
    with grad_debugger.watch_gradients_by_tensors(y):
      train_op = tf.train.GradientDescentOptimizer(z)

    # Now we can reflect through grad_debugger to get the gradient tensor
    # with respect to y.
    y_grad = grad_debugger.gradient_tensor(y)
    # or
    y_grad = grad_debugger.gradient_tensor("y:0")
    ```

    Args:
      graph: the `tf.Graph` to watch the gradients on.
      tensors: a `tf.Tensor` or `tf.Variable` object, or a list of such objects.

    Returns:
      The GradientsDebugger instance itself.
    """

    if not isinstance(tensors, list):
      tensors = [tensors]

    tensor_name_regex = []
    for tensor in tensors:
      tensor_name_regex.append(re.escape(tensor.name) + "$")
    tensor_name_regex = "(" + "|".join(tensor_name_regex) + ")"
    return self.watch_gradients_by_tensor_names(graph, tensor_name_regex)

  def watch_gradients_by_tensor_names(self, graph, tensor_name_regex):
    """Watch gradient tensors by name(s) of the x-tensor(s).

    The side effect of this method is that when gradient tensor(s) are created
    with respect to the x-tensors, the gradient tensor(s) will be registered
    with this `GradientsDebugger` instance and can later be retrieved.

    Unlike the `identify_gradient` method, this method is used after the
    construction of the forward graph has completed. Unlike the
    `watch_gradients_by_tensor` method, this method does not use handles to the
    tensors of interest; it uses their names.

    This method is the same as `watch_gradients_by_tensors` except that the
    x-tensors are specified by name patterns, instead of `tf.Tensor` or
    `tf.Variable` objects.

    Example:

    ```python
    x = tf.Variable(1.0, name="x")
    y = tf.add(x, x, name="y")
    z = tf.square(debug_y)

    # Create a train op under the grad_debugger context.
    grad_debugger = tf_debug.GradientsDebugger()
    with grad_debugger.watch_gradients_by_tensor_names(r"(x|y):0$"):
      train_op = tf.train.GradientDescentOptimizer(z)

    # Now we can reflect through grad_debugger to get the gradient tensor
    # with respect to x and y.
    x_grad = grad_debugger.gradient_tensor("x:0")
    y_grad = grad_debugger.gradient_tensor("y:0")
    ```

    Args:
      graph: the `tf.Graph` to watch the gradients on.
      tensor_name_regex: the regular-expression pattern of the name(s) of the
        x-tensor(s) to watch. x-tensor refers to the tensors on the denominator
        of the differentiation.

    Returns:
      The GradientsDebugger instance itself.
    """
    tensor_name_pattern = re.compile(tensor_name_regex)

    # pylint: disable=protected-access
    with graph.as_default():
      for op in graph.get_operations():
        for output in op.outputs:
          if tensor_name_pattern.match(output.name):
            debug_op = self.identify_gradient(output)

            for consumer in output.consumers():
              if consumer == debug_op.op:
                continue

              # Locate the slot index of the original input.
              input_slots = []
              for i, consumer_input in enumerate(consumer._inputs):
                if consumer_input == output:
                  input_slots.append(i)

              for slot in input_slots:
                consumer._inputs[slot] = debug_op
                debug_op._consumers.append(consumer)

            del output._consumers[:]
            output._consumers.append(debug_op.op)
    # pylint: enable=protected-access

    return self

  def _check_same_graph(self, tensor):
    if self._graph is None:
      self._graph = tensor.graph
    elif self._graph != tensor.graph:
      raise ValueError(
          "The graph of the value (%s) is not the same as the graph %s" %
          (tensor.graph, self._graph))

  def register_gradient_tensor(self,
                               x_tensor_name,
                               gradient_tensor):
    """Register the gradient tensor for an x-tensor.

    Args:
      x_tensor_name: (`str`) the name of the the independent `tf.Tensor`, i.e.,
        the tensor on the denominator of the differentiation.
      gradient_tensor: the gradient `tf.Tensor`.
    """
    if len(_gradient_debuggers) == 1 or self._is_active_context:
      self._check_same_graph(gradient_tensor)
      self._gradient_tensors[x_tensor_name] = gradient_tensor

  def gradient_tensor(self, x_tensor):
    """Get the gradient tensor of an x-tensor.

    Args:
      x_tensor: (`tf.Tensor`, `tf.Variable` or `str`) The x-tensor object or its
        name. x-tensor refers to the independent `tf.Tensor`, i.e., the tensor
        on the denominator of the differentiation.

    Returns:
      If found, the gradient tensor.

    Raises:
      TypeError: If `x_tensor` is not a `tf.Tensor`, `tf.Variable` or `str`.
      LookupError: If the `x_tensor` has not been registered with a gradient
        tensor.
    """
    x_tensor_name = self._get_tensor_name(x_tensor)
    if x_tensor_name not in self._gradient_tensors:
      raise LookupError(
          "This GradientsDebugger has not received any gradient tensor for "
          "x-tensor %s" % x_tensor_name)
    return self._gradient_tensors[x_tensor_name]

  def gradient_tensors(self):
    """Get the gradient tensors that this object is aware of.

    Returns:
      A dict mapping x-tensor names to gradient tensor objects. x-tensor refers
      to the tensors on the denominator of the differentation.
    """
    return self._gradient_tensors

  def _get_tensor_name(self, tensor):
    if isinstance(tensor, (ops.Tensor, variables.Variable)):
      return tensor.name
    elif  isinstance(tensor, six.string_types):
      return tensor
    else:
      raise TypeError(
          "x_tensor must be a str or tf.Tensor or tf.Variable, "
          "but instead has type %s" % type(tensor))


def clear_gradient_debuggers():
  """Clear all globally registered gradient debuggers."""
  _gradient_debuggers.clear()


@ops.RegisterGradient("DebugGradientIdentity")
def _identify_gradient_grad(op, dy):
  """Gradient function for the DebugIdentity op."""
  # TODO(cais): Allow overriding gradient.
  grad_debugger_uuid, orig_tensor_name = _parse_grad_debug_op_name(op.name)
  grad_debugger = _gradient_debuggers[grad_debugger_uuid]
  grad_debugger.register_gradient_tensor(orig_tensor_name, dy)
  return dy


def gradient_values_from_dump(grad_debugger, x_tensor, dump):
  """Find gradient values from a `DebugDumpDir` object.

  Args:
    grad_debugger: the `tf_debug.GradientsDebugger` instance to be used.
    x_tensor: (`tf.Tensor`, `tf.Variable` or `str`) The x-tensor object or its
      name. x-tensor refers to the independent `tf.Tensor`, i.e., the tensor
      on the denominator of the differentiation.
    dump: A `tfdbg.DebugDumpDir` object.

  Returns:
    If this `GradientsDebugger` instance has the gradient tensor of `x_tensor`
      registered: a list of `numpy.ndarray` representing the value of the
      gradient tensor from `dump`. The list could be empty, if the gradient
      tensor is not executed in the `tf.Session.run()` call that generated
      the `dump`. The list could also contain multiple values of the gradient
      tensor, e.g., if gradient tensor is computed repeatedly in a
      `tf.while_loop` during the run that generated the `dump`.

  Raises:
    LookupError: If this `GradientsDebugger` instance does not have the
      gradient tensor of `x_tensor` registered.
    ValueError: If this `GradientsDebugger` has a `tf.Graph` object that
      does not match the `tf.Graph` object of the `dump`.
    TypeError: If `x_tensor` is not a `tf.Tensor`, `tf.Variable` or `str`.
  """
  # TODO(cais): Use this method in LocalCLIDebugWrapperSession to present the
  # gradient tensors to the TFDBG CLI.

  # If possible, verify that the Python graph of the dump and that of this
  # GradientsDebugger match.
  if (dump.python_graph and grad_debugger.graph and
      dump.python_graph != grad_debugger.graph):
    raise ValueError(
        "This GradientsDebugger instance has a graph (%s) that differs from "
        "the graph of the DebugDumpDir object (%s)." %
        (grad_debugger.graph, dump.python_graph))

  gradient_tensor = grad_debugger.gradient_tensor(x_tensor)
  node_name, output_slot = debug_data.parse_node_or_tensor_name(
      gradient_tensor.name)

  try:
    return dump.get_tensors(node_name, output_slot, "DebugIdentity")
  except debug_data.WatchKeyDoesNotExistInDebugDumpDirError:
    return []
