"""
Cron utilities for handling day-of-week conversion
"""
import re


def convert_unix_to_iso_dayofweek(cron_expr: str) -> str:
    """
    Convert Unix cron day-of-week numbering (0=Sunday) to ISO numbering (0=Monday)

    Unix cron standard:
    0 = Sunday, 1 = Monday, 2 = Tuesday, 3 = Wednesday, 4 = Thursday, 5 = Friday, 6 = Saturday

    ISO standard (used by APScheduler):
    0 = Monday, 1 = Tuesday, 2 = Wednesday, 3 = Thursday, 4 = Friday, 5 = Saturday, 6 = Sunday

    Conversion mapping:
    Unix -> ISO
    0 (Sun) -> 6
    1 (Mon) -> 0
    2 (Tue) -> 1
    3 (Wed) -> 2
    4 (Thu) -> 3
    5 (Fri) -> 4
    6 (Sat) -> 5

    Args:
        cron_expr: 5-field cron expression (e.g., "30 12 * * 3")

    Returns:
        Converted cron expression with ISO day-of-week numbering
    """
    parts = cron_expr.strip().split()

    # Must be 5 fields
    if len(parts) != 5:
        return cron_expr

    minute, hour, day, month, weekday = parts

    # If weekday field contains only letters (day names), no conversion needed
    if weekday.replace(',', '').replace('-', '').isalpha():
        return cron_expr

    # If weekday is *, no conversion needed
    if weekday == '*':
        return cron_expr

    # Convert numeric day-of-week from Unix to ISO
    def convert_day(day_str: str) -> str:
        """Convert a single day number or range"""
        # Unix to ISO mapping
        unix_to_iso = {
            '0': '6',  # Sun -> 6
            '1': '0',  # Mon -> 0
            '2': '1',  # Tue -> 1
            '3': '2',  # Wed -> 2
            '4': '3',  # Thu -> 3
            '5': '4',  # Fri -> 4
            '6': '5',  # Sat -> 5
        }

        # Handle ranges like "1-5"
        if '-' in day_str:
            start, end = day_str.split('-')
            if start in unix_to_iso and end in unix_to_iso:
                return f"{unix_to_iso[start]}-{unix_to_iso[end]}"

        # Handle single numbers
        return unix_to_iso.get(day_str, day_str)

    # Handle comma-separated days like "1,3,5"
    if ',' in weekday:
        converted_days = [convert_day(d.strip()) for d in weekday.split(',')]
        weekday = ','.join(converted_days)
    else:
        weekday = convert_day(weekday)

    # Reconstruct cron expression
    return f"{minute} {hour} {day} {month} {weekday}"