# Copyright 2022 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,
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"""Loads dataset for the dual encoder (retrieval) task."""
import functools
import itertools
from typing import Iterable, Mapping, Optional, Tuple

import dataclasses
import tensorflow as tf
import tensorflow_hub as hub

from official.core import config_definitions as cfg
from official.core import input_reader
from official.nlp.data import data_loader
from official.nlp.data import data_loader_factory
from official.nlp.modeling import layers


@dataclasses.dataclass
class DualEncoderDataConfig(cfg.DataConfig):
  """Data config for dual encoder task (tasks/dual_encoder)."""
  # Either set `input_path`...
  input_path: str = ''
  # ...or `tfds_name` and `tfds_split` to specify input.
  tfds_name: str = ''
  tfds_split: str = ''
  global_batch_size: int = 32
  # Either build preprocessing with Python code by specifying these values...
  vocab_file: str = ''
  lower_case: bool = True
  # ...or load preprocessing from a SavedModel at this location.
  preprocessing_hub_module_url: str = ''

  left_text_fields: Tuple[str] = ('left_input',)
  right_text_fields: Tuple[str] = ('right_input',)
  is_training: bool = True
  seq_length: int = 128


@data_loader_factory.register_data_loader_cls(DualEncoderDataConfig)
class DualEncoderDataLoader(data_loader.DataLoader):
  """A class to load dataset for dual encoder task (tasks/dual_encoder)."""

  def __init__(self, params):
    if bool(params.tfds_name) == bool(params.input_path):
      raise ValueError('Must specify either `tfds_name` and `tfds_split` '
                       'or `input_path`.')
    if bool(params.vocab_file) == bool(params.preprocessing_hub_module_url):
      raise ValueError('Must specify exactly one of vocab_file (with matching '
                       'lower_case flag) or preprocessing_hub_module_url.')
    self._params = params
    self._seq_length = params.seq_length
    self._left_text_fields = params.left_text_fields
    self._right_text_fields = params.right_text_fields

    if params.preprocessing_hub_module_url:
      preprocessing_hub_module = hub.load(params.preprocessing_hub_module_url)
      self._tokenizer = preprocessing_hub_module.tokenize
      self._pack_inputs = functools.partial(
          preprocessing_hub_module.bert_pack_inputs,
          seq_length=params.seq_length)
    else:
      self._tokenizer = layers.BertTokenizer(
          vocab_file=params.vocab_file, lower_case=params.lower_case)
      self._pack_inputs = layers.BertPackInputs(
          seq_length=params.seq_length,
          special_tokens_dict=self._tokenizer.get_special_tokens_dict())

  def _decode(self, record: tf.Tensor):
    """Decodes a serialized tf.Example."""
    name_to_features = {
        x: tf.io.FixedLenFeature([], tf.string)
        for x in itertools.chain(
            *[self._left_text_fields, self._right_text_fields])
    }
    example = tf.io.parse_single_example(record, name_to_features)

    # tf.Example only supports tf.int64, but the TPU only supports tf.int32.
    # So cast all int64 to int32.
    for name in example:
      t = example[name]
      if t.dtype == tf.int64:
        t = tf.cast(t, tf.int32)
      example[name] = t

    return example

  def _bert_tokenize(
      self, record: Mapping[str, tf.Tensor],
      text_fields: Iterable[str]) -> Tuple[tf.Tensor, tf.Tensor, tf.Tensor]:
    """Tokenize the input in text_fields using BERT tokenizer.

    Args:
      record: A tfexample record contains the features.
      text_fields: A list of fields to be tokenzied.

    Returns:
      The tokenized features in a tuple of (input_word_ids, input_mask,
      input_type_ids).
    """
    segments_text = [record[x] for x in text_fields]
    segments_tokens = [self._tokenizer(s) for s in segments_text]
    segments = [tf.cast(x.merge_dims(1, 2), tf.int32) for x in segments_tokens]
    return self._pack_inputs(segments)

  def _bert_preprocess(
      self, record: Mapping[str, tf.Tensor]) -> Mapping[str, tf.Tensor]:
    """Perform the bert word piece tokenization for left and right inputs."""

    def _switch_prefix(string, old, new):
      if string.startswith(old): return new + string[len(old):]
      raise ValueError('Expected {} to start with {}'.format(string, old))

    def _switch_key_prefix(d, old, new):
      return {_switch_prefix(key, old, new): value for key, value in d.items()}

    model_inputs = _switch_key_prefix(
        self._bert_tokenize(record, self._left_text_fields),
        'input_', 'left_')
    model_inputs.update(_switch_key_prefix(
        self._bert_tokenize(record, self._right_text_fields),
        'input_', 'right_'))
    return model_inputs

  def load(self, input_context: Optional[tf.distribute.InputContext] = None):
    """Returns a tf.dataset.Dataset."""
    reader = input_reader.InputReader(
        params=self._params,
        # Skip `decoder_fn` for tfds input.
        decoder_fn=self._decode if self._params.input_path else None,
        dataset_fn=tf.data.TFRecordDataset,
        postprocess_fn=self._bert_preprocess)
    return reader.read(input_context)
