# Copyright 2020 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.
# =============================================================================
"""Training a deep NN on IMDB reviews with differentially private Adam optimizer."""

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

from absl import app
from absl import flags

from keras.preprocessing import sequence
import numpy as np
import tensorflow as tf

from tensorflow import estimator as tf_estimator
from tensorflow.compat.v1 import estimator as tf_compat_v1_estimator
from tensorflow_privacy.privacy.analysis.gdp_accountant import compute_eps_poisson
from tensorflow_privacy.privacy.analysis.gdp_accountant import compute_mu_poisson
from tensorflow_privacy.privacy.optimizers import dp_optimizer

#### FLAGS
FLAGS = flags.FLAGS
flags.DEFINE_boolean(
    'dpsgd', True, 'If True, train with DP-SGD. If False, '
    'train with vanilla SGD.')
flags.DEFINE_float('learning_rate', 0.02, 'Learning rate for training')
flags.DEFINE_float('noise_multiplier', 0.56,
                   'Ratio of the standard deviation to the clipping norm')
flags.DEFINE_float('l2_norm_clip', 1, 'Clipping norm')
flags.DEFINE_integer('epochs', 25, 'Number of epochs')
flags.DEFINE_integer('max_mu', 2, 'GDP upper limit')
flags.DEFINE_string('model_dir', None, 'Model directory')

sampling_batch = 512
microbatches = 512

max_features = 10000
maxlen = 256
num_examples = 25000


def nn_model_fn(features, labels, mode):
  """Define NN architecture using tf.keras.layers."""
  input_layer = tf.reshape(features['x'], [-1, maxlen])
  y = tf.keras.layers.Embedding(max_features, 16).apply(input_layer)
  y = tf.keras.layers.GlobalAveragePooling1D().apply(y)
  y = tf.keras.layers.Dense(16, activation='relu').apply(y)
  logits = tf.keras.layers.Dense(2).apply(y)

  # Calculate loss as a vector (to support microbatches in DP-SGD).
  vector_loss = tf.nn.sparse_softmax_cross_entropy_with_logits(
      labels=labels, logits=logits)
  # Define mean of loss across minibatch (for reporting through tf.Estimator).
  scalar_loss = tf.reduce_mean(vector_loss)

  # Configure the training op (for TRAIN mode).
  if mode == tf_estimator.ModeKeys.TRAIN:
    if FLAGS.dpsgd:
      # Use DP version of GradientDescentOptimizer. Other optimizers are
      # available in dp_optimizer. Most optimizers inheriting from
      # tf.train.Optimizer should be wrappable in differentially private
      # counterparts by calling dp_optimizer.optimizer_from_args().
      optimizer = dp_optimizer.DPAdamGaussianOptimizer(
          l2_norm_clip=FLAGS.l2_norm_clip,
          noise_multiplier=FLAGS.noise_multiplier,
          num_microbatches=microbatches,
          learning_rate=FLAGS.learning_rate)
      opt_loss = vector_loss
    else:
      optimizer = tf.compat.v1.train.AdamOptimizer(
          learning_rate=FLAGS.learning_rate)
      opt_loss = scalar_loss

    global_step = tf.compat.v1.train.get_global_step()
    train_op = optimizer.minimize(loss=opt_loss, global_step=global_step)
    # In the following, we pass the mean of the loss (scalar_loss) rather than
    # the vector_loss because tf.estimator requires a scalar loss. This is only
    # used for evaluation and debugging by tf.estimator. The actual loss being
    # minimized is opt_loss defined above and passed to optimizer.minimize().
    return tf_estimator.EstimatorSpec(
        mode=mode, loss=scalar_loss, train_op=train_op)

  # Add evaluation metrics (for EVAL mode).
  if mode == tf_estimator.ModeKeys.EVAL:
    eval_metric_ops = {
        'accuracy':
            tf.compat.v1.metrics.accuracy(
                labels=labels, predictions=tf.argmax(input=logits, axis=1))
    }
    return tf_estimator.EstimatorSpec(
        mode=mode, loss=scalar_loss, eval_metric_ops=eval_metric_ops)
  return None


def load_imdb():
  """Load IMDB movie reviews data."""
  (train_data, train_labels), (test_data,
                               test_labels) = tf.keras.datasets.imdb.load_data(
                                   num_words=max_features)

  train_data = sequence.pad_sequences(
      train_data, maxlen=maxlen).astype('float32')
  test_data = sequence.pad_sequences(test_data, maxlen=maxlen).astype('float32')
  return train_data, train_labels, test_data, test_labels


def main(unused_argv):
  tf.compat.v1.logging.set_verbosity(3)

  # Load training and test data.
  train_data, train_labels, test_data, test_labels = load_imdb()

  # Instantiate the tf.Estimator.
  imdb_classifier = tf_estimator.Estimator(
      model_fn=nn_model_fn, model_dir=FLAGS.model_dir)

  # Create tf.Estimator input functions for the training and test data.
  eval_input_fn = tf_compat_v1_estimator.inputs.numpy_input_fn(
      x={'x': test_data}, y=test_labels, num_epochs=1, shuffle=False)

  # Training loop.
  steps_per_epoch = num_examples // sampling_batch
  test_accuracy_list = []

  for epoch in range(1, FLAGS.epochs + 1):
    for _ in range(steps_per_epoch):
      whether = np.random.random_sample(num_examples) > (
          1 - sampling_batch / num_examples)
      subsampling = [i for i in np.arange(num_examples) if whether[i]]
      global microbatches
      microbatches = len(subsampling)

      train_input_fn = tf_compat_v1_estimator.inputs.numpy_input_fn(
          x={'x': train_data[subsampling]},
          y=train_labels[subsampling],
          batch_size=len(subsampling),
          num_epochs=1,
          shuffle=False)
      # Train the model for one step.
      imdb_classifier.train(input_fn=train_input_fn, steps=1)

    # Evaluate the model and print results
    eval_results = imdb_classifier.evaluate(input_fn=eval_input_fn)
    test_accuracy = eval_results['accuracy']
    test_accuracy_list.append(test_accuracy)
    print('Test accuracy after %d epochs is: %.3f' % (epoch, test_accuracy))

    # Compute the privacy budget expended so far.
    if FLAGS.dpsgd:
      eps = compute_eps_poisson(epoch, FLAGS.noise_multiplier, num_examples,
                                sampling_batch, 1e-5)
      mu = compute_mu_poisson(epoch, FLAGS.noise_multiplier, num_examples,
                              sampling_batch)
      print('For delta=1e-5, the current epsilon is: %.2f' % eps)
      print('For delta=1e-5, the current mu is: %.2f' % mu)

      if mu > FLAGS.max_mu:
        break
    else:
      print('Trained with vanilla non-private SGD optimizer')


if __name__ == '__main__':
  app.run(main)
