""" Utility classes and functions used by qa.torch_models (forked from the simpletransformers library) """

from __future__ import absolute_import, division, print_function

import json
import logging
import math
import collections
from io import open
import re
import string

from tqdm import tqdm

# from torch.utils.data import DataLoader, RandomSampler, SequentialSampler, TensorDataset

# from transformers.tokenization_bert import BasicTokenizer, whitespace_tokenize
from transformers import BertTokenizer


def whitespace_tokenize(s):
    return s.split()

# from transformers import get_linear_schedule_with_warmup
# from tensorboardX import SummaryWriter


logger = logging.getLogger(__name__)


class InputExample(object):
    """
    A single training/test example.
    For examples without an answer, the start and end position are -1.
    """

    def __init__(
        self,
        qas_id,
        question_text,
        doc_tokens,
        orig_answer_text=None,
        start_position=None,
        end_position=None,
        is_impossible=None,
    ):
        self.qas_id = qas_id
        self.question_text = question_text
        self.doc_tokens = doc_tokens
        self.orig_answer_text = orig_answer_text
        self.start_position = start_position
        self.end_position = end_position
        self.is_impossible = is_impossible

    def __str__(self):
        return self.__repr__()

    def __repr__(self):
        s = ""
        s += "qas_id: %s" % (self.qas_id)
        s += ", question_text: %s" % (self.question_text)
        s += ", doc_tokens: [%s]" % (" ".join(self.doc_tokens))
        if self.start_position:
            s += ", start_position: %d" % (self.start_position)
        if self.end_position:
            s += ", end_position: %d" % (self.end_position)
        if self.is_impossible:
            s += ", is_impossible: %r" % (self.is_impossible)
        return s


def to_list(tensor):
    return tensor.detach().cpu().tolist()


class InputFeatures(object):
    """A single set of features of data."""

    def __init__(
        self,
        unique_id,
        example_index,
        doc_span_index,
        tokens,
        token_to_orig_map,
        token_is_max_context,
        input_ids,
        input_mask,
        segment_ids,
        cls_index,
        p_mask,
        paragraph_len,
        start_position=None,
        end_position=None,
        is_impossible=None,
    ):
        self.unique_id = unique_id
        self.example_index = example_index
        self.doc_span_index = doc_span_index
        self.tokens = tokens
        self.token_to_orig_map = token_to_orig_map
        self.token_is_max_context = token_is_max_context
        self.input_ids = input_ids
        self.input_mask = input_mask
        self.segment_ids = segment_ids
        self.cls_index = cls_index
        self.p_mask = p_mask
        self.paragraph_len = paragraph_len
        self.start_position = start_position
        self.end_position = end_position
        self.is_impossible = is_impossible


def get_examples(examples_to_process, is_training=True, version_2_with_negative=True):
    if not isinstance(examples_to_process, list):
        raise TypeError("Input should be a list of examples.")

    def is_whitespace(c):
        if c == " " or c == "\t" or c == "\r" or c == "\n" or ord(c) == 0x202F:
            return True
        return False

    examples = []
    for paragraph in examples_to_process:
        paragraph_text = paragraph["context"]
        doc_tokens = []
        char_to_word_offset = []
        prev_is_whitespace = True
        for c in paragraph_text:
            if is_whitespace(c):
                prev_is_whitespace = True
            else:
                if prev_is_whitespace:
                    doc_tokens.append(c)
                else:
                    doc_tokens[-1] += c
                prev_is_whitespace = False
            char_to_word_offset.append(len(doc_tokens) - 1)

        for qa in paragraph["qas"]:
            qas_id = qa["id"]
            question_text = qa["question"]
            start_position = None
            end_position = None
            orig_answer_text = None
            is_impossible = qa.get("is_impossible")
            if is_training:
                if version_2_with_negative:
                    is_impossible = qa["is_impossible"]
                if (len(qa["answers"]) != 1) and (not is_impossible):
                    raise ValueError(
                        "For training, each question should have exactly 1 answer."
                    )
                if not is_impossible:
                    answer = qa["answers"][0]
                    orig_answer_text = answer["text"]
                    answer_offset = answer["answer_start"]
                    answer_length = len(orig_answer_text)
                    start_position = char_to_word_offset[answer_offset]
                    end_position = char_to_word_offset[
                        answer_offset + answer_length - 1
                    ]
                    # Only add answers where the text can be exactly recovered from the
                    # document. If this CAN'T happen it's likely due to weird Unicode
                    # stuff so we will just skip the example.
                    #
                    # Note that this means for training mode, every example is NOT
                    # guaranteed to be preserved.
                    actual_text = " ".join(
                        doc_tokens[start_position: (end_position + 1)]
                    )
                    cleaned_answer_text = " ".join(
                        whitespace_tokenize(orig_answer_text)
                    )
                    if actual_text.find(cleaned_answer_text) == -1:
                        logger.warning(
                            "Could not find answer: '%s' vs. '%s'",
                            actual_text,
                            cleaned_answer_text,
                        )
                        continue
                else:
                    start_position = -1
                    end_position = -1
                    orig_answer_text = ""

            example = InputExample(
                qas_id=qas_id,
                question_text=question_text,
                doc_tokens=doc_tokens,
                orig_answer_text=orig_answer_text,
                start_position=start_position,
                end_position=end_position,
                is_impossible=is_impossible,
            )
            examples.append(example)
    return examples


def convert_examples_to_features(
    examples,
    tokenizer,
    max_seq_length,
    doc_stride,
    max_query_length,
    is_training,
    cls_token_at_end=False,
    cls_token="[CLS]",
    sep_token="[SEP]",
    pad_token=0,
    sequence_a_segment_id=0,
    sequence_b_segment_id=1,
    cls_token_segment_id=0,
    pad_token_segment_id=0,
    mask_padding_with_zero=True,
    sequence_a_is_doc=False,
    silent=False,
):
    """Loads a data file into a list of `InputBatch`s."""

    unique_id = 1000000000
    # cnt_pos, cnt_neg = 0, 0
    # max_N, max_M = 1024, 1024
    # f = np.zeros((max_N, max_M), dtype=np.float32)

    features = []
    for (example_index, example) in enumerate(tqdm(examples, disable=silent)):

        # if example_index % 100 == 0:
        #     logger.info('Converting %s/%s pos %s neg %s', example_index, len(examples), cnt_pos, cnt_neg)

        query_tokens = tokenizer.tokenize(example.question_text)

        if len(query_tokens) > max_query_length:
            query_tokens = query_tokens[0:max_query_length]

        tok_to_orig_index = []
        orig_to_tok_index = []
        all_doc_tokens = []
        for (i, token) in enumerate(example.doc_tokens):
            orig_to_tok_index.append(len(all_doc_tokens))
            sub_tokens = tokenizer.tokenize(token)
            for sub_token in sub_tokens:
                tok_to_orig_index.append(i)
                all_doc_tokens.append(sub_token)

        tok_start_position = None
        tok_end_position = None
        if is_training and example.is_impossible:
            tok_start_position = -1
            tok_end_position = -1
        if is_training and not example.is_impossible:
            tok_start_position = orig_to_tok_index[example.start_position]
            if example.end_position < len(example.doc_tokens) - 1:
                tok_end_position = orig_to_tok_index[example.end_position + 1] - 1
            else:
                tok_end_position = len(all_doc_tokens) - 1
            (tok_start_position, tok_end_position) = _improve_answer_span(
                all_doc_tokens,
                tok_start_position,
                tok_end_position,
                tokenizer,
                example.orig_answer_text,
            )

        # The -3 accounts for [CLS], [SEP] and [SEP]
        max_tokens_for_doc = max_seq_length - len(query_tokens) - 3

        # We can have documents that are longer than the maximum sequence length.
        # To deal with this we do a sliding window approach, where we take chunks
        # of the up to our max length with a stride of `doc_stride`.
        _DocSpan = collections.namedtuple(  # pylint: disable=invalid-name
            "DocSpan", ["start", "length"]
        )
        doc_spans = []
        start_offset = 0
        while start_offset < len(all_doc_tokens):
            length = len(all_doc_tokens) - start_offset
            if length > max_tokens_for_doc:
                length = max_tokens_for_doc
            doc_spans.append(_DocSpan(start=start_offset, length=length))
            if start_offset + length == len(all_doc_tokens):
                break
            start_offset += min(length, doc_stride)

        for (doc_span_index, doc_span) in enumerate(doc_spans):
            tokens = []
            token_to_orig_map = {}
            token_is_max_context = {}
            segment_ids = []

            # p_mask: mask with 1 for token than cannot be in the answer (0 for token which can be in an answer)
            # Original TF implem also keep the classification token (set to 0) (not sure why...)
            p_mask = []

            # CLS token at the beginning
            if not cls_token_at_end:
                tokens.append(cls_token)
                segment_ids.append(cls_token_segment_id)
                p_mask.append(0)
                cls_index = 0

            # XLNet: P SEP Q SEP CLS
            # Others: CLS Q SEP P SEP
            if not sequence_a_is_doc:
                # Query
                tokens += query_tokens
                segment_ids += [sequence_a_segment_id] * len(query_tokens)
                p_mask += [1] * len(query_tokens)

                # SEP token
                tokens.append(sep_token)
                segment_ids.append(sequence_a_segment_id)
                p_mask.append(1)

            # Paragraph
            for i in range(doc_span.length):
                split_token_index = doc_span.start + i
                token_to_orig_map[len(tokens)] = tok_to_orig_index[split_token_index]

                is_max_context = _check_is_max_context(
                    doc_spans, doc_span_index, split_token_index
                )
                token_is_max_context[len(tokens)] = is_max_context
                tokens.append(all_doc_tokens[split_token_index])
                if not sequence_a_is_doc:
                    segment_ids.append(sequence_b_segment_id)
                else:
                    segment_ids.append(sequence_a_segment_id)
                p_mask.append(0)
            paragraph_len = doc_span.length

            if sequence_a_is_doc:
                # SEP token
                tokens.append(sep_token)
                segment_ids.append(sequence_a_segment_id)
                p_mask.append(1)

                tokens += query_tokens
                segment_ids += [sequence_b_segment_id] * len(query_tokens)
                p_mask += [1] * len(query_tokens)

            # SEP token
            tokens.append(sep_token)
            segment_ids.append(sequence_b_segment_id)
            p_mask.append(1)

            # CLS token at the end
            if cls_token_at_end:
                tokens.append(cls_token)
                segment_ids.append(cls_token_segment_id)
                p_mask.append(0)
                cls_index = len(tokens) - 1  # Index of classification token

            input_ids = tokenizer.convert_tokens_to_ids(tokens)

            # The mask has 1 for real tokens and 0 for padding tokens. Only real
            # tokens are attended to.
            input_mask = [1 if mask_padding_with_zero else 0] * len(input_ids)

            # Zero-pad up to the sequence length.
            while len(input_ids) < max_seq_length:
                input_ids.append(pad_token)
                input_mask.append(0 if mask_padding_with_zero else 1)
                segment_ids.append(pad_token_segment_id)
                p_mask.append(1)

            assert len(input_ids) == max_seq_length
            assert len(input_mask) == max_seq_length
            assert len(segment_ids) == max_seq_length

            span_is_impossible = example.is_impossible
            start_position = None
            end_position = None
            if is_training and not span_is_impossible:
                # For training, if our document chunk does not contain an annotation
                # we throw it out, since there is nothing to predict.
                doc_start = doc_span.start
                doc_end = doc_span.start + doc_span.length - 1
                out_of_span = False
                if not (
                    tok_start_position >= doc_start and tok_end_position <= doc_end
                ):
                    out_of_span = True
                if out_of_span:
                    start_position = 0
                    end_position = 0
                    span_is_impossible = True
                else:
                    if sequence_a_is_doc:
                        doc_offset = 0
                    else:
                        doc_offset = len(query_tokens) + 2
                    start_position = tok_start_position - doc_start + doc_offset
                    end_position = tok_end_position - doc_start + doc_offset

            if is_training and span_is_impossible:
                start_position = cls_index
                end_position = cls_index

            if example_index < 20:
                logger.info("*** Example ***")
                logger.info("unique_id: %s" % (unique_id))
                logger.info("example_index: %s" % (example_index))
                logger.info("doc_span_index: %s" % (doc_span_index))
                logger.info("tokens: %s" % " ".join(tokens))
                logger.info(
                    "token_to_orig_map: %s"
                    % " ".join(
                        ["%d:%d" % (x, y) for (x, y) in token_to_orig_map.items()]
                    )
                )
                logger.info(
                    "token_is_max_context: %s"
                    % " ".join(
                        ["%d:%s" % (x, y) for (x, y) in token_is_max_context.items()]
                    )
                )
                logger.info("input_ids: %s" % " ".join([str(x) for x in input_ids]))
                logger.info("input_mask: %s" % " ".join([str(x) for x in input_mask]))
                logger.info("segment_ids: %s" % " ".join([str(x) for x in segment_ids]))
                if is_training and span_is_impossible:
                    logger.info("impossible example")
                if is_training and not span_is_impossible:
                    answer_text = " ".join(tokens[start_position: (end_position + 1)])
                    logger.info("start_position: %d" % (start_position))
                    logger.info("end_position: %d" % (end_position))
                    logger.info("answer: %s" % (answer_text))

            features.append(
                InputFeatures(
                    unique_id=unique_id,
                    example_index=example_index,
                    doc_span_index=doc_span_index,
                    tokens=tokens,
                    token_to_orig_map=token_to_orig_map,
                    token_is_max_context=token_is_max_context,
                    input_ids=input_ids,
                    input_mask=input_mask,
                    segment_ids=segment_ids,
                    cls_index=cls_index,
                    p_mask=p_mask,
                    paragraph_len=paragraph_len,
                    start_position=start_position,
                    end_position=end_position,
                    is_impossible=span_is_impossible,
                )
            )
            unique_id += 1

    return features


def _improve_answer_span(
    doc_tokens, input_start, input_end, tokenizer, orig_answer_text
):
    """Returns tokenized answer spans that better match the annotated answer."""

    # The SQuAD annotations are character based. We first project them to
    # whitespace-tokenized words. But then after WordPiece tokenization, we can
    # often find a "better match". For example:
    #
    #   Question: What year was John Smith born?
    #   Context: The leader was John Smith (1895-1943).
    #   Answer: 1895
    #
    # The original whitespace-tokenized answer will be "(1895-1943).". However
    # after tokenization, our tokens will be "( 1895 - 1943 ) .". So we can match
    # the exact answer, 1895.
    #
    # However, this is not always possible. Consider the following:
    #
    #   Question: What country is the top exporter of electornics?
    #   Context: The Japanese electronics industry is the lagest in the world.
    #   Answer: Japan
    #
    # In this case, the annotator chose "Japan" as a character sub-span of
    # the word "Japanese". Since our WordPiece tokenizer does not split
    # "Japanese", we just use "Japanese" as the annotation. This is fairly rare
    # in SQuAD, but does happen.
    tok_answer_text = " ".join(tokenizer.tokenize(orig_answer_text))

    for new_start in range(input_start, input_end + 1):
        for new_end in range(input_end, new_start - 1, -1):
            text_span = " ".join(doc_tokens[new_start: (new_end + 1)])
            if text_span == tok_answer_text:
                return (new_start, new_end)

    return (input_start, input_end)


def _check_is_max_context(doc_spans, cur_span_index, position):
    """Check if this is the 'max context' doc span for the token."""

    # Because of the sliding window approach taken to scoring documents, a single
    # token can appear in multiple documents. E.g.
    #  Doc: the man went to the store and bought a gallon of milk
    #  Span A: the man went to the
    #  Span B: to the store and bought
    #  Span C: and bought a gallon of
    #  ...
    #
    # Now the word 'bought' will have two scores from spans B and C. We only
    # want to consider the score with "maximum context", which we define as
    # the *minimum* of its left and right context (the *sum* of left and
    # right context will always be the same, of course).
    #
    # In the example the maximum context for 'bought' would be span C since
    # it has 1 left context and 3 right context, while span B has 4 left context
    # and 0 right context.
    best_score = None
    best_span_index = None
    for (span_index, doc_span) in enumerate(doc_spans):
        end = doc_span.start + doc_span.length - 1
        if position < doc_span.start:
            continue
        if position > end:
            continue
        num_left_context = position - doc_span.start
        num_right_context = end - position
        score = min(num_left_context, num_right_context) + 0.01 * doc_span.length
        if best_score is None or score > best_score:
            best_score = score
            best_span_index = span_index

    return cur_span_index == best_span_index


RawResult = collections.namedtuple(
    "RawResult", ("unique_id", "start_logits", "end_logits")
)


def write_predictions(
    all_examples,
    all_features,
    all_results,
    n_best_size,
    max_answer_length,
    do_lower_case,
    output_prediction_file,
    output_nbest_file,
    output_null_log_odds_file,
    verbose_logging,
    version_2_with_negative,
    null_score_diff_threshold,
):
    """Write final predictions to the json file and log-odds of null if needed."""
    logger.info("Writing predictions to: %s" % (output_prediction_file))
    logger.info("Writing nbest to: %s" % (output_nbest_file))

    example_index_to_features = collections.defaultdict(list)
    for feature in all_features:
        example_index_to_features[feature.example_index].append(feature)

    unique_id_to_result = {}
    for result in all_results:
        unique_id_to_result[result.unique_id] = result

    _PrelimPrediction = collections.namedtuple(  # pylint: disable=invalid-name
        "PrelimPrediction",
        ["feature_index", "start_index", "end_index", "start_logit", "end_logit"],
    )

    all_predictions = collections.OrderedDict()
    all_nbest_json = collections.OrderedDict()
    scores_diff_json = collections.OrderedDict()

    for (example_index, example) in enumerate(all_examples):
        features = example_index_to_features[example_index]

        prelim_predictions = []
        # keep track of the minimum score of null start+end of position 0
        score_null = 1000000  # large and positive
        min_null_feature_index = 0  # the paragraph slice with min null score
        null_start_logit = 0  # the start logit at the slice with min null score
        null_end_logit = 0  # the end logit at the slice with min null score
        for (feature_index, feature) in enumerate(features):
            result = unique_id_to_result[feature.unique_id]
            start_indexes = _get_best_indexes(result.start_logits, n_best_size)
            end_indexes = _get_best_indexes(result.end_logits, n_best_size)
            # if we could have irrelevant answers, get the min score of irrelevant
            if version_2_with_negative:
                feature_null_score = result.start_logits[0] + result.end_logits[0]
                if feature_null_score < score_null:
                    score_null = feature_null_score
                    min_null_feature_index = feature_index
                    null_start_logit = result.start_logits[0]
                    null_end_logit = result.end_logits[0]
            for start_index in start_indexes:
                for end_index in end_indexes:
                    # We could hypothetically create invalid predictions, e.g., predict
                    # that the start of the span is in the question. We throw out all
                    # invalid predictions.
                    if start_index >= len(feature.tokens):
                        continue
                    if end_index >= len(feature.tokens):
                        continue
                    if start_index not in feature.token_to_orig_map:
                        continue
                    if end_index not in feature.token_to_orig_map:
                        continue
                    if not feature.token_is_max_context.get(start_index, False):
                        continue
                    if end_index < start_index:
                        continue
                    length = end_index - start_index + 1
                    if length > max_answer_length:
                        continue
                    prelim_predictions.append(
                        _PrelimPrediction(
                            feature_index=feature_index,
                            start_index=start_index,
                            end_index=end_index,
                            start_logit=result.start_logits[start_index],
                            end_logit=result.end_logits[end_index],
                        )
                    )
        if version_2_with_negative:
            prelim_predictions.append(
                _PrelimPrediction(
                    feature_index=min_null_feature_index,
                    start_index=0,
                    end_index=0,
                    start_logit=null_start_logit,
                    end_logit=null_end_logit,
                )
            )
        prelim_predictions = sorted(
            prelim_predictions,
            key=lambda x: (x.start_logit + x.end_logit),
            reverse=True,
        )

        _NbestPrediction = collections.namedtuple(  # pylint: disable=invalid-name
            "NbestPrediction", ["text", "start_logit", "end_logit"]
        )

        seen_predictions = {}
        nbest = []
        for pred in prelim_predictions:
            if len(nbest) >= n_best_size:
                break
            feature = features[pred.feature_index]
            if pred.start_index > 0:  # this is a non-null prediction
                tok_tokens = feature.tokens[pred.start_index: (pred.end_index + 1)]
                orig_doc_start = feature.token_to_orig_map[pred.start_index]
                orig_doc_end = feature.token_to_orig_map[pred.end_index]
                orig_tokens = example.doc_tokens[orig_doc_start: (orig_doc_end + 1)]
                tok_text = " ".join(tok_tokens)

                # De-tokenize WordPieces that have been split off.
                tok_text = tok_text.replace(" ##", "")
                tok_text = tok_text.replace("##", "")

                # Clean whitespace
                tok_text = tok_text.strip()
                tok_text = " ".join(tok_text.split())
                orig_text = " ".join(orig_tokens)

                final_text = get_final_text(
                    tok_text, orig_text, do_lower_case, verbose_logging
                )
                if final_text in seen_predictions:
                    continue

                seen_predictions[final_text] = True
            else:
                final_text = ""
                seen_predictions[final_text] = True

            nbest.append(
                _NbestPrediction(
                    text=final_text,
                    start_logit=pred.start_logit,
                    end_logit=pred.end_logit,
                )
            )
        # if we didn't include the empty option in the n-best, include it
        if version_2_with_negative:
            if "" not in seen_predictions:
                nbest.append(
                    _NbestPrediction(
                        text="", start_logit=null_start_logit, end_logit=null_end_logit
                    )
                )

            # In very rare edge cases we could only have single null prediction.
            # So we just create a nonce prediction in this case to avoid failure.
            if len(nbest) == 1:
                nbest.insert(
                    0, _NbestPrediction(text="empty", start_logit=0.0, end_logit=0.0)
                )

        # In very rare edge cases we could have no valid predictions. So we
        # just create a nonce prediction in this case to avoid failure.
        if not nbest:
            nbest.append(_NbestPrediction(text="empty", start_logit=0.0, end_logit=0.0))

        assert len(nbest) >= 1

        total_scores = []
        best_non_null_entry = None
        for entry in nbest:
            total_scores.append(entry.start_logit + entry.end_logit)
            if not best_non_null_entry:
                if entry.text:
                    best_non_null_entry = entry

        probs = _compute_softmax(total_scores)

        nbest_json = []
        for (i, entry) in enumerate(nbest):
            output = collections.OrderedDict()
            output["text"] = entry.text
            output["probability"] = probs[i]
            output["start_logit"] = entry.start_logit
            output["end_logit"] = entry.end_logit
            nbest_json.append(output)

        assert len(nbest_json) >= 1

        if not version_2_with_negative:
            all_predictions[example.qas_id] = nbest_json[0]["text"]
        else:
            # predict "" iff the null score - the score of best non-null > threshold
            score_diff = (
                score_null - best_non_null_entry.start_logit - (best_non_null_entry.end_logit)
            )
            scores_diff_json[example.qas_id] = score_diff
            if score_diff > null_score_diff_threshold:
                all_predictions[example.qas_id] = ""
            else:
                all_predictions[example.qas_id] = best_non_null_entry.text
        all_nbest_json[example.qas_id] = nbest_json

    with open(output_prediction_file, "w") as writer:
        writer.write(json.dumps(all_predictions, indent=4) + "\n")

    with open(output_nbest_file, "w") as writer:
        writer.write(json.dumps(all_nbest_json, indent=4) + "\n")

    if version_2_with_negative:
        with open(output_null_log_odds_file, "w") as writer:
            writer.write(json.dumps(scores_diff_json, indent=4) + "\n")

    return all_predictions, all_nbest_json, scores_diff_json


# For XLNet (and XLM which uses the same head)
RawResultExtended = collections.namedtuple(
    "RawResultExtended",
    [
        "unique_id",
        "start_top_log_probs",
        "start_top_index",
        "end_top_log_probs",
        "end_top_index",
        "cls_logits",
    ],
)


def write_predictions_extended(
    all_examples,
    all_features,
    all_results,
    n_best_size,
    max_answer_length,
    output_prediction_file,
    output_nbest_file,
    output_null_log_odds_file,
    orig_data_file,
    start_n_top,
    end_n_top,
    version_2_with_negative,
    tokenizer,
    verbose_logging,
):
    """ XLNet write prediction logic (more complex than Bert's).
                    Write final predictions to the json file and log-odds of null if needed.
                    Requires utils_squad_evaluate.py
    """
    _PrelimPrediction = collections.namedtuple(  # pylint: disable=invalid-name
        "PrelimPrediction",
        ["feature_index", "start_index", "end_index", "start_log_prob", "end_log_prob"],
    )

    _NbestPrediction = collections.namedtuple(  # pylint: disable=invalid-name
        "NbestPrediction", ["text", "start_log_prob", "end_log_prob"]
    )

    logger.info("Writing predictions to: %s", output_prediction_file)
    # logger.info("Writing nbest to: %s" % (output_nbest_file))

    example_index_to_features = collections.defaultdict(list)
    for feature in all_features:
        example_index_to_features[feature.example_index].append(feature)

    unique_id_to_result = {}
    for result in all_results:
        unique_id_to_result[result.unique_id] = result

    all_predictions = collections.OrderedDict()
    all_nbest_json = collections.OrderedDict()
    scores_diff_json = collections.OrderedDict()

    for (example_index, example) in enumerate(all_examples):
        features = example_index_to_features[example_index]

        prelim_predictions = []
        # keep track of the minimum score of null start+end of position 0
        score_null = 1000000  # large and positive

        for (feature_index, feature) in enumerate(features):
            result = unique_id_to_result[feature.unique_id]

            cur_null_score = result.cls_logits

            # if we could have irrelevant answers, get the min score of irrelevant
            score_null = min(score_null, cur_null_score)

            for i in range(start_n_top):
                for j in range(end_n_top):
                    start_log_prob = result.start_top_log_probs[i]
                    start_index = result.start_top_index[i]

                    j_index = i * end_n_top + j

                    end_log_prob = result.end_top_log_probs[j_index]
                    end_index = result.end_top_index[j_index]

                    # We could hypothetically create invalid predictions, e.g., predict
                    # that the start of the span is in the question. We throw out all
                    # invalid predictions.
                    if start_index >= feature.paragraph_len - 1:
                        continue
                    if end_index >= feature.paragraph_len - 1:
                        continue

                    if not feature.token_is_max_context.get(start_index, False):
                        continue
                    if end_index < start_index:
                        continue
                    length = end_index - start_index + 1
                    if length > max_answer_length:
                        continue

                    prelim_predictions.append(
                        _PrelimPrediction(
                            feature_index=feature_index,
                            start_index=start_index,
                            end_index=end_index,
                            start_log_prob=start_log_prob,
                            end_log_prob=end_log_prob,
                        )
                    )

        prelim_predictions = sorted(
            prelim_predictions,
            key=lambda x: (x.start_log_prob + x.end_log_prob),
            reverse=True,
        )

        seen_predictions = {}
        nbest = []
        for pred in prelim_predictions:
            if len(nbest) >= n_best_size:
                break
            feature = features[pred.feature_index]

            # XLNet un-tokenizer
            # Let's keep it simple for now and see if we need all this later.
            #
            # tok_start_to_orig_index = feature.tok_start_to_orig_index
            # tok_end_to_orig_index = feature.tok_end_to_orig_index
            # start_orig_pos = tok_start_to_orig_index[pred.start_index]
            # end_orig_pos = tok_end_to_orig_index[pred.end_index]
            # paragraph_text = example.paragraph_text
            # final_text = paragraph_text[start_orig_pos: end_orig_pos + 1].strip()

            # Previously used Bert untokenizer
            tok_tokens = feature.tokens[pred.start_index: (pred.end_index + 1)]
            orig_doc_start = feature.token_to_orig_map[pred.start_index]
            orig_doc_end = feature.token_to_orig_map[pred.end_index]
            orig_tokens = example.doc_tokens[orig_doc_start: (orig_doc_end + 1)]
            tok_text = tokenizer.convert_tokens_to_string(tok_tokens)

            # Clean whitespace
            tok_text = tok_text.strip()
            tok_text = " ".join(tok_text.split())
            orig_text = " ".join(orig_tokens)

            final_text = get_final_text(tok_text, orig_text, False, verbose_logging)

            if final_text in seen_predictions:
                continue

            seen_predictions[final_text] = True

            nbest.append(
                _NbestPrediction(
                    text=final_text,
                    start_log_prob=pred.start_log_prob,
                    end_log_prob=pred.end_log_prob,
                )
            )

        # In very rare edge cases we could have no valid predictions. So we
        # just create a nonce prediction in this case to avoid failure.
        if not nbest:
            nbest.append(
                _NbestPrediction(text="", start_log_prob=-1e6, end_log_prob=-1e6)
            )

        total_scores = []
        best_non_null_entry = None
        for entry in nbest:
            total_scores.append(entry.start_log_prob + entry.end_log_prob)
            if not best_non_null_entry:
                best_non_null_entry = entry

        probs = _compute_softmax(total_scores)

        nbest_json = []
        for (i, entry) in enumerate(nbest):
            output = collections.OrderedDict()
            output["text"] = entry.text
            output["probability"] = probs[i]
            output["start_log_prob"] = entry.start_log_prob
            output["end_log_prob"] = entry.end_log_prob
            nbest_json.append(output)

        assert len(nbest_json) >= 1
        assert best_non_null_entry is not None

        score_diff = score_null
        scores_diff_json[example.qas_id] = score_diff
        # note: always predict best_non_null_entry
        # and the evaluation script will search for the best threshold
        all_predictions[example.qas_id] = best_non_null_entry.text

        all_nbest_json[example.qas_id] = nbest_json

    with open(output_prediction_file, "w") as writer:
        writer.write(json.dumps(all_predictions, indent=4) + "\n")

    with open(output_nbest_file, "w") as writer:
        writer.write(json.dumps(all_nbest_json, indent=4) + "\n")

    if version_2_with_negative:
        with open(output_null_log_odds_file, "w") as writer:
            writer.write(json.dumps(scores_diff_json, indent=4) + "\n")

    if isinstance(orig_data_file, str):
        with open(orig_data_file, "r", encoding="utf-8") as reader:
            orig_data = json.load(reader)
    else:
        orig_data = orig_data_file

    qid_to_has_ans = make_qid_to_has_ans(orig_data)
    exact_raw, f1_raw = get_raw_scores(orig_data, all_predictions)
    out_eval = {}

    find_all_best_thresh_v2(
        out_eval, all_predictions, exact_raw, f1_raw, scores_diff_json, qid_to_has_ans
    )

    return all_predictions, all_nbest_json, scores_diff_json


def get_best_predictions(
    all_examples,
    all_features,
    all_results,
    n_best_size,
    max_answer_length,
    do_lower_case,
    verbose_logging,
    version_2_with_negative,
    null_score_diff_threshold,
):

    example_index_to_features = collections.defaultdict(list)
    for feature in all_features:
        example_index_to_features[feature.example_index].append(feature)

    unique_id_to_result = {}
    for result in all_results:
        unique_id_to_result[result.unique_id] = result

    _PrelimPrediction = collections.namedtuple(  # pylint: disable=invalid-name
        "PrelimPrediction",
        ["feature_index", "start_index", "end_index", "start_logit", "end_logit"],
    )

    all_predictions = collections.OrderedDict()
    all_nbest_json = collections.OrderedDict()
    scores_diff_json = collections.OrderedDict()

    for (example_index, example) in enumerate(all_examples):
        features = example_index_to_features[example_index]

        prelim_predictions = []
        # keep track of the minimum score of null start+end of position 0
        score_null = 1000000  # large and positive
        min_null_feature_index = 0  # the paragraph slice with min null score
        null_start_logit = 0  # the start logit at the slice with min null score
        null_end_logit = 0  # the end logit at the slice with min null score
        for (feature_index, feature) in enumerate(features):
            result = unique_id_to_result[feature.unique_id]
            start_indexes = _get_best_indexes(result.start_logits, n_best_size)
            end_indexes = _get_best_indexes(result.end_logits, n_best_size)
            # if we could have irrelevant answers, get the min score of irrelevant
            if version_2_with_negative:
                feature_null_score = result.start_logits[0] + result.end_logits[0]
                if feature_null_score < score_null:
                    score_null = feature_null_score
                    min_null_feature_index = feature_index
                    null_start_logit = result.start_logits[0]
                    null_end_logit = result.end_logits[0]
            for start_index in start_indexes:
                for end_index in end_indexes:
                    # We could hypothetically create invalid predictions, e.g., predict
                    # that the start of the span is in the question. We throw out all
                    # invalid predictions.
                    if start_index >= len(feature.tokens):
                        continue
                    if end_index >= len(feature.tokens):
                        continue
                    if start_index not in feature.token_to_orig_map:
                        continue
                    if end_index not in feature.token_to_orig_map:
                        continue
                    if not feature.token_is_max_context.get(start_index, False):
                        continue
                    if end_index < start_index:
                        continue
                    length = end_index - start_index + 1
                    if length > max_answer_length:
                        continue
                    prelim_predictions.append(
                        _PrelimPrediction(
                            feature_index=feature_index,
                            start_index=start_index,
                            end_index=end_index,
                            start_logit=result.start_logits[start_index],
                            end_logit=result.end_logits[end_index],
                        )
                    )
        if version_2_with_negative:
            prelim_predictions.append(
                _PrelimPrediction(
                    feature_index=min_null_feature_index,
                    start_index=0,
                    end_index=0,
                    start_logit=null_start_logit,
                    end_logit=null_end_logit,
                )
            )
        prelim_predictions = sorted(
            prelim_predictions,
            key=lambda x: (x.start_logit + x.end_logit),
            reverse=True,
        )

        _NbestPrediction = collections.namedtuple(  # pylint: disable=invalid-name
            "NbestPrediction", ["text", "start_logit", "end_logit"]
        )

        seen_predictions = {}
        nbest = []
        for pred in prelim_predictions:
            if len(nbest) >= n_best_size:
                break
            feature = features[pred.feature_index]
            if pred.start_index > 0:  # this is a non-null prediction
                tok_tokens = feature.tokens[pred.start_index: (pred.end_index + 1)]
                orig_doc_start = feature.token_to_orig_map[pred.start_index]
                orig_doc_end = feature.token_to_orig_map[pred.end_index]
                orig_tokens = example.doc_tokens[orig_doc_start: (orig_doc_end + 1)]
                tok_text = " ".join(tok_tokens)

                # De-tokenize WordPieces that have been split off.
                tok_text = tok_text.replace(" ##", "")
                tok_text = tok_text.replace("##", "")

                # Clean whitespace
                tok_text = tok_text.strip()
                tok_text = " ".join(tok_text.split())
                orig_text = " ".join(orig_tokens)

                final_text = get_final_text(
                    tok_text, orig_text, do_lower_case, verbose_logging
                )
                if final_text in seen_predictions:
                    continue

                seen_predictions[final_text] = True
            else:
                final_text = ""
                seen_predictions[final_text] = True

            nbest.append(
                _NbestPrediction(
                    text=final_text,
                    start_logit=pred.start_logit,
                    end_logit=pred.end_logit,
                )
            )
        # if we didn't include the empty option in the n-best, include it
        if version_2_with_negative:
            if "" not in seen_predictions:
                nbest.append(
                    _NbestPrediction(
                        text="", start_logit=null_start_logit, end_logit=null_end_logit
                    )
                )

            # In very rare edge cases we could only have single null prediction.
            # So we just create a nonce prediction in this case to avoid failure.
            if len(nbest) == 1:
                nbest.insert(
                    0, _NbestPrediction(text="empty", start_logit=0.0, end_logit=0.0)
                )

        # In very rare edge cases we could have no valid predictions. So we
        # just create a nonce prediction in this case to avoid failure.
        if not nbest:
            nbest.append(_NbestPrediction(text="empty", start_logit=0.0, end_logit=0.0))

        assert len(nbest) >= 1

        total_scores = []
        best_non_null_entry = None
        for entry in nbest:
            total_scores.append(entry.start_logit + entry.end_logit)
            if not best_non_null_entry:
                if entry.text:
                    best_non_null_entry = entry

        probs = _compute_softmax(total_scores)

        nbest_json = []
        for (i, entry) in enumerate(nbest):
            output = collections.OrderedDict()
            output["text"] = entry.text
            output["probability"] = probs[i]
            output["start_logit"] = entry.start_logit
            output["end_logit"] = entry.end_logit
            nbest_json.append(output)

        assert len(nbest_json) >= 1

        if not version_2_with_negative:
            all_predictions[example.qas_id] = nbest_json[0]["text"]
        else:
            # predict "" iff the null score - the score of best non-null > threshold
            score_diff = (
                score_null - best_non_null_entry.start_logit - (best_non_null_entry.end_logit)
            )
            scores_diff_json[example.qas_id] = score_diff
            if score_diff > null_score_diff_threshold:
                all_predictions[example.qas_id] = ""
            else:
                all_predictions[example.qas_id] = best_non_null_entry.text
        all_nbest_json[example.qas_id] = nbest_json

    all_best = [
        {"id": id, "answer": answers[0]["text"], "probability": answers[0]["probability"]}
        for id, answers in all_nbest_json.items()
    ]
    return all_best


def get_best_predictions_extended(
    all_examples,
    all_features,
    all_results,
    n_best_size,
    max_answer_length,
    start_n_top,
    end_n_top,
    version_2_with_negative,
    tokenizer,
    verbose_logging,
):
    """ XLNet write prediction logic (more complex than Bert's).
                    Write final predictions to the json file and log-odds of null if needed.
                    Requires utils_squad_evaluate.py
    """
    _PrelimPrediction = collections.namedtuple(  # pylint: disable=invalid-name
        "PrelimPrediction",
        ["feature_index", "start_index", "end_index", "start_log_prob", "end_log_prob"],
    )

    _NbestPrediction = collections.namedtuple(  # pylint: disable=invalid-name
        "NbestPrediction", ["text", "start_log_prob", "end_log_prob"]
    )

    example_index_to_features = collections.defaultdict(list)
    for feature in all_features:
        example_index_to_features[feature.example_index].append(feature)

    unique_id_to_result = {}
    for result in all_results:
        unique_id_to_result[result.unique_id] = result

    all_predictions = collections.OrderedDict()
    all_nbest_json = collections.OrderedDict()
    scores_diff_json = collections.OrderedDict()

    for (example_index, example) in enumerate(all_examples):
        features = example_index_to_features[example_index]

        prelim_predictions = []
        # keep track of the minimum score of null start+end of position 0
        score_null = 1000000  # large and positive

        for (feature_index, feature) in enumerate(features):
            result = unique_id_to_result[feature.unique_id]

            cur_null_score = result.cls_logits

            # if we could have irrelevant answers, get the min score of irrelevant
            score_null = min(score_null, cur_null_score)

            for i in range(start_n_top):
                for j in range(end_n_top):
                    start_log_prob = result.start_top_log_probs[i]
                    start_index = result.start_top_index[i]

                    j_index = i * end_n_top + j

                    end_log_prob = result.end_top_log_probs[j_index]
                    end_index = result.end_top_index[j_index]

                    # We could hypothetically create invalid predictions, e.g., predict
                    # that the start of the span is in the question. We throw out all
                    # invalid predictions.
                    if start_index >= feature.paragraph_len - 1:
                        continue
                    if end_index >= feature.paragraph_len - 1:
                        continue

                    if not feature.token_is_max_context.get(start_index, False):
                        continue
                    if end_index < start_index:
                        continue
                    length = end_index - start_index + 1
                    if length > max_answer_length:
                        continue

                    prelim_predictions.append(
                        _PrelimPrediction(
                            feature_index=feature_index,
                            start_index=start_index,
                            end_index=end_index,
                            start_log_prob=start_log_prob,
                            end_log_prob=end_log_prob,
                        )
                    )

        prelim_predictions = sorted(
            prelim_predictions,
            key=lambda x: (x.start_log_prob + x.end_log_prob),
            reverse=True,
        )

        seen_predictions = {}
        nbest = []
        for pred in prelim_predictions:
            if len(nbest) >= n_best_size:
                break
            feature = features[pred.feature_index]

            # XLNet un-tokenizer
            # Let's keep it simple for now and see if we need all this later.
            #
            # tok_start_to_orig_index = feature.tok_start_to_orig_index
            # tok_end_to_orig_index = feature.tok_end_to_orig_index
            # start_orig_pos = tok_start_to_orig_index[pred.start_index]
            # end_orig_pos = tok_end_to_orig_index[pred.end_index]
            # paragraph_text = example.paragraph_text
            # final_text = paragraph_text[start_orig_pos: end_orig_pos + 1].strip()

            # Previously used Bert untokenizer
            tok_tokens = feature.tokens[pred.start_index: (pred.end_index + 1)]
            orig_doc_start = feature.token_to_orig_map[pred.start_index]
            orig_doc_end = feature.token_to_orig_map[pred.end_index]
            orig_tokens = example.doc_tokens[orig_doc_start: (orig_doc_end + 1)]
            tok_text = tokenizer.convert_tokens_to_string(tok_tokens)

            # Clean whitespace
            tok_text = tok_text.strip()
            tok_text = " ".join(tok_text.split())
            orig_text = " ".join(orig_tokens)

            final_text = get_final_text(
                tok_text, orig_text, tokenizer.do_lower_case, verbose_logging
            )

            if final_text in seen_predictions:
                continue

            seen_predictions[final_text] = True

            nbest.append(
                _NbestPrediction(
                    text=final_text,
                    start_log_prob=pred.start_log_prob,
                    end_log_prob=pred.end_log_prob,
                )
            )

        # In very rare edge cases we could have no valid predictions. So we
        # just create a nonce prediction in this case to avoid failure.
        if not nbest:
            nbest.append(
                _NbestPrediction(text="", start_log_prob=-1e6, end_log_prob=-1e6)
            )

        total_scores = []
        best_non_null_entry = None
        for entry in nbest:
            total_scores.append(entry.start_log_prob + entry.end_log_prob)
            if not best_non_null_entry:
                best_non_null_entry = entry

        probs = _compute_softmax(total_scores)

        nbest_json = []
        for (i, entry) in enumerate(nbest):
            output = collections.OrderedDict()
            output["text"] = entry.text
            output["probability"] = probs[i]
            output["start_log_prob"] = entry.start_log_prob
            output["end_log_prob"] = entry.end_log_prob
            nbest_json.append(output)

        assert len(nbest_json) >= 1
        assert best_non_null_entry is not None

        score_diff = score_null
        scores_diff_json[example.qas_id] = score_diff
        # note(zhiliny): always predict best_non_null_entry
        # and the evaluation script will search for the best threshold
        all_predictions[example.qas_id] = best_non_null_entry.text

        all_nbest_json[example.qas_id] = nbest_json

        all_best = [
            {"id": id, "answer": answers[0]["text"]}
            for id, answers in all_nbest_json.items()
        ]
    return all_best


def find_all_best_thresh_v2(
    main_eval, preds, exact_raw, f1_raw, na_probs, qid_to_has_ans
):
    best_exact, exact_thresh, has_ans_exact = find_best_thresh_v2(
        preds, exact_raw, na_probs, qid_to_has_ans
    )
    best_f1, f1_thresh, has_ans_f1 = find_best_thresh_v2(
        preds, f1_raw, na_probs, qid_to_has_ans
    )
    main_eval["best_exact"] = best_exact
    main_eval["best_exact_thresh"] = exact_thresh
    main_eval["best_f1"] = best_f1
    main_eval["best_f1_thresh"] = f1_thresh
    main_eval["has_ans_exact"] = has_ans_exact
    main_eval["has_ans_f1"] = has_ans_f1


def find_best_thresh_v2(preds, scores, na_probs, qid_to_has_ans):
    num_no_ans = sum(1 for k in qid_to_has_ans if not qid_to_has_ans[k])
    cur_score = num_no_ans
    best_score = cur_score
    best_thresh = 0.0
    qid_list = sorted(na_probs, key=lambda k: na_probs[k])
    for i, qid in enumerate(qid_list):
        if qid not in scores:
            continue
        if qid_to_has_ans[qid]:
            diff = scores[qid]
        else:
            if preds[qid]:
                diff = -1
            else:
                diff = 0
        cur_score += diff
        if cur_score > best_score:
            best_score = cur_score
            best_thresh = na_probs[qid]

    has_ans_score, has_ans_cnt = 0, 0
    for qid in qid_list:
        if not qid_to_has_ans[qid]:
            continue
        has_ans_cnt += 1

        if qid not in scores:
            continue
        has_ans_score += scores[qid]

    return (
        100.0 * best_score / len(scores),
        best_thresh,
        1.0 * has_ans_score / has_ans_cnt,
    )


def make_qid_to_has_ans(dataset):
    qid_to_has_ans = {}
    for p in dataset:
        for qa in p["qas"]:
            qid_to_has_ans[qa["id"]] = bool(qa["answers"])
    return qid_to_has_ans


def get_raw_scores(dataset, preds):
    exact_scores = {}
    f1_scores = {}
    for p in dataset:
        for qa in p["qas"]:
            qid = qa["id"]
            gold_answers = [
                a["text"] for a in qa["answers"] if normalize_answer(a["text"])
            ]
            if not gold_answers:
                # For unanswerable questions, only correct answer is empty string
                gold_answers = [""]
            if qid not in preds:
                logger.warning("Missing prediction for %s" % qid)
                continue
            a_pred = preds[qid]
            # Take max over all gold answers
            exact_scores[qid] = max(compute_exact(a, a_pred) for a in gold_answers)
            f1_scores[qid] = max(compute_f1(a, a_pred) for a in gold_answers)
    return exact_scores, f1_scores


def compute_exact(a_gold, a_pred):
    return int(normalize_answer(a_gold) == normalize_answer(a_pred))


def compute_f1(a_gold, a_pred):
    gold_toks = get_tokens(a_gold)
    pred_toks = get_tokens(a_pred)
    common = collections.Counter(gold_toks) & collections.Counter(pred_toks)
    num_same = sum(common.values())
    if len(gold_toks) == 0 or len(pred_toks) == 0:
        # If either is no-answer, then F1 is 1 if they agree, 0 otherwise
        return int(gold_toks == pred_toks)
    if num_same == 0:
        return 0
    precision = 1.0 * num_same / len(pred_toks)
    recall = 1.0 * num_same / len(gold_toks)
    f1 = (2 * precision * recall) / (precision + recall)
    return f1


def get_tokens(s):
    if not s:
        return []
    return normalize_answer(s).split()


def normalize_answer(s):
    """Lower text and remove punctuation, articles and extra whitespace."""

    def remove_articles(text):
        regex = re.compile(r"\b(a|an|the)\b", re.UNICODE)
        return re.sub(regex, " ", text)

    def white_space_fix(text):
        return " ".join(text.split())

    def remove_punc(text):
        exclude = set(string.punctuation)
        return "".join(ch for ch in text if ch not in exclude)

    def lower(text):
        return text.lower()

    return white_space_fix(remove_articles(remove_punc(lower(s))))


def get_final_text(pred_text, orig_text, do_lower_case, verbose_logging=False):
    """Project the tokenized prediction back to the original text."""

    # When we created the data, we kept track of the alignment between original
    # (whitespace tokenized) tokens and our WordPiece tokenized tokens. So
    # now `orig_text` contains the span of our original text corresponding to the
    # span that we predicted.
    #
    # However, `orig_text` may contain extra characters that we don't want in
    # our prediction.
    #
    # For example, let's say:
    #   pred_text = steve smith
    #   orig_text = Steve Smith's
    #
    # We don't want to return `orig_text` because it contains the extra "'s".
    #
    # We don't want to return `pred_text` because it's already been normalized
    # (the SQuAD eval script also does punctuation stripping/lower casing but
    # our tokenizer does additional normalization like stripping accent
    # characters).
    #
    # What we really want to return is "Steve Smith".
    #
    # Therefore, we have to apply a semi-complicated alignment heuristic between
    # `pred_text` and `orig_text` to get a character-to-character alignment. This
    # can fail in certain cases in which case we just return `orig_text`.

    def _strip_spaces(text):
        ns_chars = []
        ns_to_s_map = collections.OrderedDict()
        for (i, c) in enumerate(text):
            if c == " ":
                continue
            ns_to_s_map[len(ns_chars)] = i
            ns_chars.append(c)
        ns_text = "".join(ns_chars)
        return (ns_text, ns_to_s_map)

    # We first tokenize `orig_text`, strip whitespace from the result
    # and `pred_text`, and check if they are the same length. If they are
    # NOT the same length, the heuristic has failed. If they are the same
    # length, we assume the characters are one-to-one aligned.
    tokenizer = BertTokenizer(do_lower_case=do_lower_case)

    tok_text = " ".join(tokenizer.tokenize(orig_text))

    start_position = tok_text.find(pred_text)
    if start_position == -1:
        if verbose_logging:
            logger.info("Unable to find text: '%s' in '%s'" % (pred_text, orig_text))
        return orig_text
    end_position = start_position + len(pred_text) - 1

    (orig_ns_text, orig_ns_to_s_map) = _strip_spaces(orig_text)
    (tok_ns_text, tok_ns_to_s_map) = _strip_spaces(tok_text)

    if len(orig_ns_text) != len(tok_ns_text):
        if verbose_logging:
            logger.info(
                "Length not equal after stripping spaces: '%s' vs '%s'",
                orig_ns_text,
                tok_ns_text,
            )
        return orig_text

    # We then project the characters in `pred_text` back to `orig_text` using
    # the character-to-character alignment.
    tok_s_to_ns_map = {}
    for (i, tok_index) in tok_ns_to_s_map.items():
        tok_s_to_ns_map[tok_index] = i

    orig_start_position = None
    if start_position in tok_s_to_ns_map:
        ns_start_position = tok_s_to_ns_map[start_position]
        if ns_start_position in orig_ns_to_s_map:
            orig_start_position = orig_ns_to_s_map[ns_start_position]

    if orig_start_position is None:
        if verbose_logging:
            logger.info("Couldn't map start position")
        return orig_text

    orig_end_position = None
    if end_position in tok_s_to_ns_map:
        ns_end_position = tok_s_to_ns_map[end_position]
        if ns_end_position in orig_ns_to_s_map:
            orig_end_position = orig_ns_to_s_map[ns_end_position]

    if orig_end_position is None:
        if verbose_logging:
            logger.info("Couldn't map end position")
        return orig_text

    output_text = orig_text[orig_start_position: (orig_end_position + 1)]
    return output_text


def _get_best_indexes(logits, n_best_size):
    """Get the n-best logits from a list."""
    index_and_score = sorted(enumerate(logits), key=lambda x: x[1], reverse=True)

    best_indexes = []
    for i in range(len(index_and_score)):
        if i >= n_best_size:
            break
        best_indexes.append(index_and_score[i][0])
    return best_indexes


def _compute_softmax(scores):
    """Compute softmax probability over raw logits."""
    if not scores:
        return []

    max_score = None
    for score in scores:
        if max_score is None or score > max_score:
            max_score = score

    exp_scores = []
    total_sum = 0.0
    for score in scores:
        x = math.exp(score - max_score)
        exp_scores.append(x)
        total_sum += x

    probs = []
    for score in exp_scores:
        probs.append(score / total_sum)
    return probs


def build_examples(to_predict):
    """
    Builds a list of dicts in input data format from a list of contexts and qas.
    """
    examples = []

    for row in to_predict:
        context = row["context"]
        for qa in row["qas"]:
            qa["answers"] = [{"text": " ", "answer_start": 0}]
            qa["is_impossible"]: False
        example = {"context": context, "qas": row["qas"]}
        examples.append(example)

    return examples
