# Copyright 2021 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.
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"""Evaluation for Bert2Bert."""

import os
# Import libraries
from absl import logging
import numpy as np
import tensorflow as tf

from official.nlp.nhnet import input_pipeline
from official.nlp.nhnet import models
from official.nlp.transformer import metrics as metrics_v2
from official.nlp.transformer.utils import metrics


def rouge_l_fscore(logits, labels):
  """ROUGE scores computation between labels and predictions.

  This is an approximate ROUGE scoring method since we do not glue word pieces
  or decode the ids and tokenize the output.

  Args:
    logits: tensor, model predictions
    labels: tensor, gold output.

  Returns:
    rouge_l_fscore: approx rouge-l f1 score.
  """
  predictions = np.argmax(logits, axis=-1)
  rouge_l_f_score = metrics.rouge_l_sentence_level(predictions, labels)
  return rouge_l_f_score


def rouge_2_fscore(logits, labels):
  """ROUGE-2 F1 score computation between labels and predictions.

  This is an approximate ROUGE scoring method since we do not glue word pieces
  or decode the ids and tokenize the output.

  Args:
    logits: tensor, model predictions
    labels: tensor, gold output.

  Returns:
    rouge2_fscore: approx rouge-2 f1 score.
  """
  predictions = np.argmax(logits, axis=-1)
  rouge_2_f_score = metrics.rouge_n(predictions, labels)
  return rouge_2_f_score


def bleu_score(logits, labels):
  """Approximate BLEU score computation between labels and predictions.

  An approximate BLEU scoring method since we do not glue word pieces or
  decode the ids and tokenize the output. By default, we use ngram order of 4
  and use brevity penalty. Also, this does not have beam search.

  Args:
    logits: Tensor of size [batch_size, length_logits, vocab_size]
    labels: Tensor of size [batch-size, length_labels]

  Returns:
    bleu: int, approx bleu score
  """
  predictions = np.argmax(logits, axis=-1)
  bleu = metrics.compute_bleu(labels, predictions)
  return bleu


def continuous_eval(strategy,
                    params,
                    model_type,
                    eval_file_pattern=None,
                    batch_size=4,
                    eval_steps=None,
                    model_dir=None,
                    timeout=3000):
  """Continuously evaluate checkpoints on testing data."""
  test_dataset = input_pipeline.get_input_dataset(
      eval_file_pattern,
      batch_size=batch_size,
      params=params,
      is_training=False,
      strategy=strategy)

  with strategy.scope():
    model = models.create_model(model_type, params)
    metric_layer = metrics_v2.MetricLayer(params.vocab_size)
    eval_summary_writer = tf.summary.create_file_writer(
        os.path.join(model_dir, "summaries/eval"))
    global_step = tf.Variable(
        0,
        trainable=False,
        dtype=tf.int64,
        aggregation=tf.VariableAggregation.ONLY_FIRST_REPLICA,
        shape=[])

  @tf.function
  def test_step(inputs):
    """Calculates evaluation metrics on distributed devices."""

    def _test_step_fn(inputs):
      """Replicated accuracy calculation."""
      targets = models.remove_sos_from_seq(inputs["target_ids"],
                                           params.pad_token_id)

      # Using ground truth sequences as targets to calculate logits for accuracy
      # and perplexity metrics.
      logits, _, _ = model(inputs, training=False, mode="train")
      metric_layer([logits, targets])

      # Get logits from top beam search results for bleu and rouge metrics.
      logits = model(inputs, training=False, mode="eval")

      return targets, logits

    outputs = strategy.run(_test_step_fn, args=(inputs,))

    return tf.nest.map_structure(strategy.experimental_local_results, outputs)

  metrics_and_funcs = [
      (tf.keras.metrics.Mean("bleu", dtype=tf.float32), bleu_score),
      (tf.keras.metrics.Mean("rouge_2_fscore",
                             dtype=tf.float32), rouge_2_fscore),
      (tf.keras.metrics.Mean("rouge_l_fscore",
                             dtype=tf.float32), rouge_l_fscore),
  ]
  eval_results = {}
  for latest_checkpoint in tf.train.checkpoints_iterator(
      model_dir, timeout=timeout):
    checkpoint = tf.train.Checkpoint(model=model, global_step=global_step)
    checkpoint.restore(latest_checkpoint).expect_partial()
    logging.info("Loaded checkpoint %s", latest_checkpoint)

    for i, inputs in enumerate(test_dataset):
      if eval_steps and i >= eval_steps:
        break
      outputs = test_step(inputs)
      for metric, func in metrics_and_funcs:
        for targets, logits in zip(outputs[0], outputs[1]):
          metric.update_state(func(logits.numpy(), targets.numpy()))

    with eval_summary_writer.as_default():
      step = global_step.numpy()
      for metric, _ in metrics_and_funcs:
        eval_results[metric.name] = metric.result().numpy().astype(float)
        tf.summary.scalar(
            metric.name,
            eval_results[metric.name],
            step=step)
      for metric in metric_layer.metrics:
        eval_results[metric.name] = metric.result().numpy().astype(float)
        tf.summary.scalar(
            metric.name,
            eval_results[metric.name],
            step=step)
      logging.info("Step %d Metrics= %s", step, str(eval_results))
      eval_summary_writer.flush()

    # Resets metrics.
    for metric, _ in metrics_and_funcs:
      metric.reset_states()
    for metric in metric_layer.metrics:
      metric.reset_states()
  return eval_results
