#!/usr/bin/env python3

import argparse
import re
from datetime import datetime

updated_pattern = r"<updated>(?P<datetime>.{25})</updated>"
datetime_pattern = "%Y-%m-%dT%H:%M:%S%z"


def get_post_datetimes(feed):
    regex = re.compile(updated_pattern)

    datetimes = list()
    first_skipped = False

    for match in regex.finditer(feed):
        # Skip first found datetime, as this is what we want to replace.
        if not first_skipped:
            first_skipped = True
            continue
        dt = datetime.strptime(match.group("datetime"), datetime_pattern)
        datetimes.append(dt)

    return datetimes


def main():
    parser = argparse.ArgumentParser(
        description="Patch the updated date field on an Atom feed."
    )

    parser.add_argument(
        "--file", "-f", type=str, required=True, help="Path to the Atom feed file."
    )

    args = parser.parse_args()
    with open(args.file, "r") as f:
        feed = f.read()

    datetimes = get_post_datetimes(feed)
    newest_datetime = max(datetimes)

    print(
        re.sub(
            updated_pattern,
            f"<updated>{newest_datetime.strftime(datetime_pattern)}</updated>",
            feed,
            count=1,
        ),
        end="",
    )


if __name__ == "__main__":
    main()