Happy ISO Week Date New Year!

#!/usr/bin/env python3
"""Produce a Markdown table for the ISO week-date calendar."""

# Christopher Phan
# 2025-W52
# SPDX-License-Identifier: MIT

import datetime
import string
import sys


def iso_table(year: int) -> str:
    """Produce a Markdown table for the ISO week-date calendar."""
    outstr = "| ISO week date | ISO Gregorian |\n"
    outstr += "|:--------------|:--------------|\n"
    jan_1 = datetime.date(year, 1, 1)
    # If Jan 1 is a Thursday, or is Wednesday of a leap year, there is 53 weeks.
    # Otherwise 52 weeks:
    if jan_1.isoweekday() == 4 or (
        jan_1.isoweekday() == 3 and (year % 400 == 0 or year % 4 == 0 and year % 100)
    ):
        num_weeks = 53
    else:
        num_weeks = 52
    for week in range(num_weeks):
        d = datetime.date.fromisocalendar(year, week + 1, 1)
        outstr += f"| {year}-W{week+1:02d}-1    | {d:%Y-%m-%d}    |\n"
    return outstr


if __name__ == "__main__":
    if len(sys.argv) > 1 and (
        # strip out any non-digit characters from the first argument
        year_str := "".join(k if k in string.digits else "" for k in sys.argv[1])
    ):
        year = int(year_str)
    else:
        year = datetime.date.today().year
    print(iso_table(year))