from datetime import date


def months_before(d, n):
    """Return a date on the 1st of the month n months before d."""
    m = (d.month - 1 - n) % 12 + 1
    y = d.year + (d.month - 1 - n) // 12
    return date(y, m, 1)


def pruning_status(plant, today=None):
    """
    Returns one of: 'overdue', 'due_this_month', 'upcoming', 'no_schedule'.

    Checks the most recent past pruning month within 12 months. If it was
    not logged the plant is overdue. Uses a 12-month rolling window so
    December is correctly caught when checked in January.
    """
    if today is None:
        today = date.today()

    months = plant.pruning_months or []
    if not months:
        return 'no_schedule'

    logs = plant.pruning_logs.all()
    logged = {(log.pruned_on.year, log.pruned_on.month) for log in logs}

    # Check if this month is scheduled
    if today.month in months:
        if (today.year, today.month) not in logged:
            return 'due_this_month'
        else:
            # This month is scheduled and already logged -> upcoming
            return 'upcoming'

    # Look for any scheduled month in the past 12 months (excluding this month, which we handled above).
    # Stop at the first scheduled month we encounter going backwards.
    for i in range(1, 13):
        past = months_before(today, i)
        if past.month in months:
            # Found a past scheduled month
            if (past.year, past.month) not in logged:
                # Determine if this past month represents an actual overdue condition
                if past.year == today.year:
                    # Same year, past month -> overdue
                    return 'overdue'
                else:
                    # Previous year. It's overdue if:
                    # - past.month < today.month (e.g., Aug 2025 when today >= Aug)
                    # - OR wrap-around: today is early (1-3) and past.month >= some threshold
                    if past.month < today.month:
                        return 'overdue'
                    # Wrap-around when today is early and we're looking at previous year
                    # Consider any month in previous year as overdue if today is Jan-Mar
                    elif today.month <= 3:
                        return 'overdue'
            return 'upcoming'

    # No past scheduled month found
    return 'upcoming'