"""Download the exact public sample used by tutorial revision 1. Python 3.10+."""
import argparse
import hashlib
from pathlib import Path
import urllib.request

URL = 'https://historicaldata.net/file/options_sample_2022H2.zip'
SHA256 = '8517b069f4d41e44f950dc79a3cdab694359b0fae91664190011e39dd8e48b76'

def digest(path):
    h = hashlib.sha256()
    with path.open('rb') as f:
        while chunk := f.read(1024 * 1024):
            h.update(chunk)
    return h.hexdigest()

def download(path):
    if path.exists():
        if digest(path) != SHA256:
            raise ValueError('Existing file differs from tutorial sample. Choose another output path.')
        return
    part = path.with_suffix(path.suffix + '.part')
    # Exclusive creation never overwrites an existing download or user file.
    with part.open('xb') as out, urllib.request.urlopen(URL, timeout=90) as response:
        while chunk := response.read(1024 * 1024):
            out.write(chunk)
    if digest(part) != SHA256:
        raise ValueError('Sample version changed or download is incomplete. Kept .part for inspection.')
    part.rename(path)

if __name__ == '__main__':
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('--output', type=Path, default=Path('options_sample_2022H2.zip'))
    args = parser.parse_args()
    download(args.output)
    print('Verified SHA-256 ' + SHA256)