import argparse
import os

from preprocess import word_tokenize
from nltk.translate.bleu_score import corpus_bleu


def get_args():
    parser = argparse.ArgumentParser(description='Command-line script for BLEU scoring.')
    parser.add_argument('--system', required=True, help='system output')
    parser.add_argument('--reference', required=True, help='references')
    parser.add_argument('--orders', nargs='+', type=int, default=[1, 2, 3, 4], help='n-grams for calculating BLEU scores')
    parser.add_argument('--ignore-case', action='store_true', help='case-insensitive scoring')
    return parser.parse_args()


def readlines(filename, ignore_case=False, wrapped=False):
    lines = []
    with open(filename) as file:
        for line in file.readlines():
            line = line.rstrip()
            if ignore_case:
                line = line.lower()
            line = word_tokenize(line)
            lines.append([line] if wrapped else line)
    return lines


def main(args):
    assert os.path.exists(args.system), "System output file {} does not exist".format(args.system)
    assert os.path.exists(args.reference), "Reference file {} does not exist".format(args.reference)

    scores = {}
    reference = readlines(args.reference, wrapped=True)
    system = readlines(args.system)
    for order in args.orders:
        scores[order] = corpus_bleu(reference, system, weights=(1.0 / order,) * order)
    print(', '.join('BLEU{} = {:.4f}'.format(order, 100 * score) for order, score in scores.items()))


if __name__ == '__main__':
    args = get_args()
    main(args)