"""
This is a copy of the official evaluation script for SQuAD version 2.0.
Modified by XLNet authors to update `find_best_threshold` scripts for SQuAD V2.0

In addition to basic functionality, we also compute additional statistics and
plot precision-recall curves if an additional na_prob.json file is provided.
This file is expected to map question ID's to the model's predicted probability
that a question is unanswerable.
"""
import collections
import re
import string


def normalize_answer(s: str):
    """
    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_tokens(s: str):
    if not s: 
        return []
    return normalize_answer(s).split()

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

def compute_f1(a_gold: str, a_pred: str):
    gold_toks = get_tokens(a_gold)
    pred_toks = get_tokens(a_pred)
    common: collections.Counter = 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
