# 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.
# ==============================================================================
# pylint: disable=protected-access
"""Utils related to keras metrics.
"""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import functools
import weakref

from enum import Enum

from tensorflow.python.distribute import distribution_strategy_context
from tensorflow.python.framework import dtypes
from tensorflow.python.framework import ops
from tensorflow.python.keras.utils import tf_utils
from tensorflow.python.keras.utils.generic_utils import to_list
from tensorflow.python.keras.utils.losses_utils import squeeze_or_expand_dimensions
from tensorflow.python.ops import array_ops
from tensorflow.python.ops import check_ops
from tensorflow.python.ops import control_flow_ops
from tensorflow.python.ops import math_ops
from tensorflow.python.ops import nn_ops
from tensorflow.python.ops import weights_broadcast_ops
from tensorflow.python.util import tf_decorator

NEG_INF = -1e10


class Reduction(Enum):
  """Types of metrics reduction.

  Contains the following values:

  * `SUM`: Scalar sum of weighted values.
  * `SUM_OVER_BATCH_SIZE`: Scalar sum of weighted values divided by
        number of elements.
  * `WEIGHTED_MEAN`: Scalar sum of weighted values divided by sum of weights.
  """
  SUM = 'sum'
  SUM_OVER_BATCH_SIZE = 'sum_over_batch_size'
  WEIGHTED_MEAN = 'weighted_mean'


def update_state_wrapper(update_state_fn):
  """Decorator to wrap metric `update_state()` with `add_update()`.

  Args:
    update_state_fn: function that accumulates metric statistics.

  Returns:
    Decorated function that wraps `update_state_fn()` with `add_update()`.
  """

  def decorated(metric_obj, *args, **kwargs):
    """Decorated function with `add_update()`."""

    with tf_utils.graph_context_for_symbolic_tensors(*args, **kwargs):
      update_op = update_state_fn(*args, **kwargs)
    if update_op is not None:  # update_op will be None in eager execution.
      metric_obj.add_update(update_op, inputs=True)
    return update_op

  return tf_decorator.make_decorator(update_state_fn, decorated)


def result_wrapper(result_fn):
  """Decorator to wrap metric `result()` function in `merge_call()`.

  Result computation is an idempotent operation that simply calculates the
  metric value using the state variables.

  If metric state variables are distributed across replicas/devices and
  `result()` is requested from the context of one device - This function wraps
  `result()` in a distribution strategy `merge_call()`. With this,
  the metric state variables will be aggregated across devices.

  Args:
    result_fn: function that computes the metric result.

  Returns:
    Decorated function that wraps `result_fn()` in distribution strategy
    `merge_call()`.
  """

  def decorated(_, *args):
    """Decorated function with merge_call."""
    replica_context = distribution_strategy_context.get_replica_context()
    if replica_context is None:  # if in cross replica context already
      result_t = array_ops.identity(result_fn(*args))
    else:
      # TODO(psv): Test distribution of metrics using different distribution
      # strategies.

      # Creating a wrapper for merge_fn. merge_call invokes the given merge_fn
      # with distribution object as the first parameter. We create a wrapper
      # here so that the result function need not have that parameter.
      def merge_fn_wrapper(distribution, merge_fn, *args):
        # We will get `PerReplica` merge function. Taking the first one as all
        # are identical copies of the function that we had passed below.
        merged_result_fn = (
            distribution.experimental_local_results(merge_fn)[0](*args))

        # Wrapping result in identity so that control dependency between
        # update_op from `update_state` and result works in case result returns
        # a tensor.
        return array_ops.identity(merged_result_fn)

      # Wrapping result in merge_call. merge_call is used when we want to leave
      # replica mode and compute a value in cross replica mode.
      result_t = replica_context.merge_call(
          merge_fn_wrapper, args=(result_fn,) + args)
    return result_t

  return tf_decorator.make_decorator(result_fn, decorated)


def weakmethod(method):
  """Creates a weak reference to the bound method."""

  cls = method.im_class
  func = method.im_func
  instance_ref = weakref.ref(method.im_self)

  @functools.wraps(method)
  def inner(*args, **kwargs):
    return func.__get__(instance_ref(), cls)(*args, **kwargs)

  del method
  return inner


def assert_thresholds_range(thresholds):
  if thresholds is not None:
    invalid_thresholds = [t for t in thresholds if t is None or t < 0 or t > 1]
    if invalid_thresholds:
      raise ValueError(
          'Threshold values must be in [0, 1]. Invalid values: {}'.format(
              invalid_thresholds))


def parse_init_thresholds(thresholds, default_threshold=0.5):
  if thresholds is not None:
    assert_thresholds_range(to_list(thresholds))
  thresholds = to_list(default_threshold if thresholds is None else thresholds)
  return thresholds


class ConfusionMatrix(Enum):
  TRUE_POSITIVES = 'tp'
  FALSE_POSITIVES = 'fp'
  TRUE_NEGATIVES = 'tn'
  FALSE_NEGATIVES = 'fn'


class AUCCurve(Enum):
  """Type of AUC Curve (ROC or PR)."""
  ROC = 'ROC'
  PR = 'PR'

  @staticmethod
  def from_str(key):
    if key in ('pr', 'PR'):
      return AUCCurve.PR
    elif key in ('roc', 'ROC'):
      return AUCCurve.ROC
    else:
      raise ValueError('Invalid AUC curve value "%s".' % key)


class AUCSummationMethod(Enum):
  """Type of AUC summation method.

  https://en.wikipedia.org/wiki/Riemann_sum)

  Contains the following values:
  * 'interpolation': Applies mid-point summation scheme for `ROC` curve. For
    `PR` curve, interpolates (true/false) positives but not the ratio that is
    precision (see Davis & Goadrich 2006 for details).
  * 'minoring': Applies left summation for increasing intervals and right
    summation for decreasing intervals.
  * 'majoring': Applies right summation for increasing intervals and left
    summation for decreasing intervals.
  """
  INTERPOLATION = 'interpolation'
  MAJORING = 'majoring'
  MINORING = 'minoring'

  @staticmethod
  def from_str(key):
    if key in ('interpolation', 'Interpolation'):
      return AUCSummationMethod.INTERPOLATION
    elif key in ('majoring', 'Majoring'):
      return AUCSummationMethod.MAJORING
    elif key in ('minoring', 'Minoring'):
      return AUCSummationMethod.MINORING
    else:
      raise ValueError('Invalid AUC summation method value "%s".' % key)


def update_confusion_matrix_variables(variables_to_update,
                                      y_true,
                                      y_pred,
                                      thresholds,
                                      top_k=None,
                                      class_id=None,
                                      sample_weight=None):
  """Returns op to update the given confusion matrix variables.

  For every pair of values in y_true and y_pred:

  true_positive: y_true == True and y_pred > thresholds
  false_negatives: y_true == True and y_pred <= thresholds
  true_negatives: y_true == False and y_pred <= thresholds
  false_positive: y_true == False and y_pred > thresholds

  The results will be weighted and added together. When multiple thresholds are
  provided, we will repeat the same for every threshold.

  For estimation of these metrics over a stream of data, the function creates an
  `update_op` operation that updates the given variables.

  If `sample_weight` is `None`, weights default to 1.
  Use weights of 0 to mask values.

  Args:
    variables_to_update: Dictionary with 'tp', 'fn', 'tn', 'fp' as valid keys
      and corresponding variables to update as values.
    y_true: A `Tensor` whose shape matches `y_pred`. Will be cast to `bool`.
    y_pred: A floating point `Tensor` of arbitrary shape and whose values are in
      the range `[0, 1]`.
    thresholds: A float value or a python list or tuple of float thresholds in
      `[0, 1]`, or NEG_INF (used when top_k is set).
    top_k: Optional int, indicates that the positive labels should be limited to
      the top k predictions.
    class_id: Optional int, limits the prediction and labels to the class
      specified by this argument.
    sample_weight: Optional `Tensor` whose rank is either 0, or the same rank as
      `y_true`, and must be broadcastable to `y_true` (i.e., all dimensions must
      be either `1`, or the same as the corresponding `y_true` dimension).

  Returns:
    Update op.

  Raises:
    ValueError: If `y_pred` and `y_true` have mismatched shapes, or if
      `sample_weight` is not `None` and its shape doesn't match `y_pred`, or if
      `variables_to_update` contains invalid keys.
  """
  if variables_to_update is None:
    return
  y_true = math_ops.cast(y_true, dtype=dtypes.float32)
  y_pred = math_ops.cast(y_pred, dtype=dtypes.float32)
  y_pred.shape.assert_is_compatible_with(y_true.shape)

  if not any(
      key for key in variables_to_update if key in list(ConfusionMatrix)):
    raise ValueError(
        'Please provide at least one valid confusion matrix '
        'variable to update. Valid variable key options are: "{}". '
        'Received: "{}"'.format(
            list(ConfusionMatrix), variables_to_update.keys()))

  invalid_keys = [
      key for key in variables_to_update if key not in list(ConfusionMatrix)
  ]
  if invalid_keys:
    raise ValueError(
        'Invalid keys: {}. Valid variable key options are: "{}"'.format(
            invalid_keys, list(ConfusionMatrix)))

  with ops.control_dependencies([
      check_ops.assert_greater_equal(
          y_pred,
          math_ops.cast(0.0, dtype=y_pred.dtype),
          message='predictions must be >= 0'),
      check_ops.assert_less_equal(
          y_pred,
          math_ops.cast(1.0, dtype=y_pred.dtype),
          message='predictions must be <= 1')
  ]):
    y_pred, y_true, sample_weight = squeeze_or_expand_dimensions(
        y_pred, y_true, sample_weight)

  if top_k is not None:
    y_pred = _filter_top_k(y_pred, top_k)
  if class_id is not None:
    y_true = y_true[..., class_id]
    y_pred = y_pred[..., class_id]

  thresholds = to_list(thresholds)
  num_thresholds = len(thresholds)
  num_predictions = array_ops.size(y_pred)

  # Reshape predictions and labels.
  predictions_2d = array_ops.reshape(y_pred, [1, -1])
  labels_2d = array_ops.reshape(
      math_ops.cast(y_true, dtype=dtypes.bool), [1, -1])

  # Tile the thresholds for every prediction.
  thresh_tiled = array_ops.tile(
      array_ops.expand_dims(array_ops.constant(thresholds), 1),
      array_ops.stack([1, num_predictions]))

  # Tile the predictions for every threshold.
  preds_tiled = array_ops.tile(predictions_2d, [num_thresholds, 1])

  # Compare predictions and threshold.
  pred_is_pos = math_ops.greater(preds_tiled, thresh_tiled)

  # Tile labels by number of thresholds
  label_is_pos = array_ops.tile(labels_2d, [num_thresholds, 1])

  if sample_weight is not None:
    weights = weights_broadcast_ops.broadcast_weights(
        math_ops.cast(sample_weight, dtype=dtypes.float32), y_pred)
    weights_tiled = array_ops.tile(
        array_ops.reshape(weights, [1, -1]), [num_thresholds, 1])
  else:
    weights_tiled = None

  update_ops = []

  def weighted_assign_add(label, pred, weights, var):
    label_and_pred = math_ops.cast(
        math_ops.logical_and(label, pred), dtype=dtypes.float32)
    if weights is not None:
      label_and_pred *= weights
    return var.assign_add(math_ops.reduce_sum(label_and_pred, 1))

  loop_vars = {
      ConfusionMatrix.TRUE_POSITIVES: (label_is_pos, pred_is_pos),
  }
  update_tn = ConfusionMatrix.TRUE_NEGATIVES in variables_to_update
  update_fp = ConfusionMatrix.FALSE_POSITIVES in variables_to_update
  update_fn = ConfusionMatrix.FALSE_NEGATIVES in variables_to_update

  if update_fn or update_tn:
    pred_is_neg = math_ops.logical_not(pred_is_pos)
    loop_vars[ConfusionMatrix.FALSE_NEGATIVES] = (label_is_pos, pred_is_neg)

  if update_fp or update_tn:
    label_is_neg = math_ops.logical_not(label_is_pos)
    loop_vars[ConfusionMatrix.FALSE_POSITIVES] = (label_is_neg, pred_is_pos)
    if update_tn:
      loop_vars[ConfusionMatrix.TRUE_NEGATIVES] = (label_is_neg, pred_is_neg)

  for matrix_cond, (label, pred) in loop_vars.items():
    if matrix_cond in variables_to_update:
      update_ops.append(
          weighted_assign_add(label, pred, weights_tiled,
                              variables_to_update[matrix_cond]))
  return control_flow_ops.group(update_ops)


def _filter_top_k(x, k):
  """Filters top-k values in the last dim of x and set the rest to NEG_INF.

  Used for computing top-k prediction values in dense labels (which has the same
  shape as predictions) for recall and precision top-k metrics.

  Args:
    x: tensor with any dimensions.
    k: the number of values to keep.

  Returns:
    tensor with same shape and dtype as x.
  """
  _, top_k_idx = nn_ops.top_k(x, k, sorted=False)
  top_k_mask = math_ops.reduce_sum(
      array_ops.one_hot(top_k_idx, x.shape[-1], axis=-1), axis=-2)
  return x * top_k_mask + NEG_INF * (1 - top_k_mask)