# Copyright 2019, The TensorFlow Authors.
#
# 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 CNN on MNIST with vectorized DP-SGD optimizer."""

from absl import app
from absl import flags
from absl import logging
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.rdp_accountant import compute_rdp
from tensorflow_privacy.privacy.analysis.rdp_accountant import get_privacy_spent
from tensorflow_privacy.privacy.optimizers import dp_optimizer_vectorized

flags.DEFINE_boolean(
    'dpsgd', True, 'If True, train with DP-SGD. If False, '
    'train with vanilla SGD.')
flags.DEFINE_float('learning_rate', .15, 'Learning rate for training')
flags.DEFINE_float('noise_multiplier', 1.1,
                   'Ratio of the standard deviation to the clipping norm')
flags.DEFINE_float('l2_norm_clip', 1.0, 'Clipping norm')
flags.DEFINE_integer('batch_size', 200, 'Batch size')
flags.DEFINE_integer('epochs', 60, 'Number of epochs')
flags.DEFINE_integer(
    'microbatches', 200, 'Number of microbatches '
    '(must evenly divide batch_size)')
flags.DEFINE_string('model_dir', None, 'Model directory')

FLAGS = flags.FLAGS

NUM_TRAIN_EXAMPLES = 60000

GradientDescentOptimizer = tf.compat.v1.train.GradientDescentOptimizer


def compute_epsilon(steps):
  """Computes epsilon value for given hyperparameters."""
  if FLAGS.noise_multiplier == 0.0:
    return float('inf')
  orders = [1 + x / 10. for x in range(1, 100)] + list(range(12, 64))
  sampling_probability = FLAGS.batch_size / NUM_TRAIN_EXAMPLES
  rdp = compute_rdp(
      q=sampling_probability,
      noise_multiplier=FLAGS.noise_multiplier,
      steps=steps,
      orders=orders)
  # Delta is set to approximate 1 / (number of training points).
  return get_privacy_spent(orders, rdp, target_delta=1e-5)[0]


def cnn_model_fn(features, labels, mode):
  """Model function for a CNN."""

  # Define CNN architecture using tf.keras.layers.
  input_layer = tf.reshape(features['x'], [-1, 28, 28, 1])
  y = tf.keras.layers.Conv2D(
      16, 8, strides=2, padding='same', activation='relu').apply(input_layer)
  y = tf.keras.layers.MaxPool2D(2, 1).apply(y)
  y = tf.keras.layers.Conv2D(
      32, 4, strides=2, padding='valid', activation='relu').apply(y)
  y = tf.keras.layers.MaxPool2D(2, 1).apply(y)
  y = tf.keras.layers.Flatten().apply(y)
  y = tf.keras.layers.Dense(32, activation='relu').apply(y)
  logits = tf.keras.layers.Dense(10).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(input_tensor=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.compat.v1.train.Optimizer should be wrappable in differentially
      # private counterparts by calling dp_optimizer.optimizer_from_args().
      optimizer = dp_optimizer_vectorized.VectorizedDPSGD(
          l2_norm_clip=FLAGS.l2_norm_clip,
          noise_multiplier=FLAGS.noise_multiplier,
          num_microbatches=FLAGS.microbatches,
          learning_rate=FLAGS.learning_rate)
      opt_loss = vector_loss
    else:
      optimizer = GradientDescentOptimizer(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).
  elif mode == tf_estimator.ModeKeys.EVAL:
    eval_metric_ops = {
        'accuracy':
            tf.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)


def load_mnist():
  """Loads MNIST and preprocesses to combine training and validation data."""
  train, test = tf.keras.datasets.mnist.load_data()
  train_data, train_labels = train
  test_data, test_labels = test

  train_data = np.array(train_data, dtype=np.float32) / 255
  test_data = np.array(test_data, dtype=np.float32) / 255

  train_labels = np.array(train_labels, dtype=np.int32)
  test_labels = np.array(test_labels, dtype=np.int32)

  assert train_data.min() == 0.
  assert train_data.max() == 1.
  assert test_data.min() == 0.
  assert test_data.max() == 1.
  assert train_labels.ndim == 1
  assert test_labels.ndim == 1

  return train_data, train_labels, test_data, test_labels


def main(unused_argv):
  logger = tf.get_logger()
  logger.set_level(logging.INFO)

  if FLAGS.dpsgd and FLAGS.batch_size % FLAGS.microbatches != 0:
    raise ValueError('Number of microbatches should divide evenly batch_size')

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

  # Instantiate the tf.Estimator.
  mnist_classifier = tf_estimator.Estimator(
      model_fn=cnn_model_fn, model_dir=FLAGS.model_dir)

  # Create tf.Estimator input functions for the training and test data.
  train_input_fn = tf_compat_v1_estimator.inputs.numpy_input_fn(
      x={'x': train_data},
      y=train_labels,
      batch_size=FLAGS.batch_size,
      num_epochs=FLAGS.epochs,
      shuffle=True)
  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_TRAIN_EXAMPLES // FLAGS.batch_size
  for epoch in range(1, FLAGS.epochs + 1):
    # Train the model for one epoch.
    mnist_classifier.train(input_fn=train_input_fn, steps=steps_per_epoch)

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

    # Compute the privacy budget expended.
    if FLAGS.dpsgd:
      eps = compute_epsilon(epoch * NUM_TRAIN_EXAMPLES // FLAGS.batch_size)
      print('For delta=1e-5, the current epsilon is: %.2f' % eps)
    else:
      print('Trained with vanilla non-private SGD optimizer')


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