namespace SeaHaven.Services.Helpers
{
    public static class WorkOrderOperationalWeek
    {
        public static DateOnly GetMondayOfWeek(DateOnly date)
        {
            var daysFromMonday = ((int)date.DayOfWeek + 6) % 7;
            return date.AddDays(-daysFromMonday);
        }

        public static DateOnly GetPreviousOperationalWeekStart(DateTime utcNow)
            => GetMondayOfWeek(DateOnly.FromDateTime(utcNow)).AddDays(-7);

        public static DateOnly GetOperationalWeekEnd(DateOnly weekStartMonday)
            => weekStartMonday.AddDays(4);

        public static string BuildWeekCorrelationId(DateOnly sourceWeekStart)
            => $"week:{sourceWeekStart:yyyy-MM-dd}";

        /// <summary>
        /// Returns a validation error message when the week window is invalid; otherwise null.
        /// </summary>
        public static string? ValidateWeekWindow(DateOnly weekStart, DateOnly weekEnd)
        {
            if (weekEnd < weekStart)
                return "weekEnd must be on or after weekStart.";

            var spanDays = weekEnd.DayNumber - weekStart.DayNumber;
            if (spanDays > 6)
                return "Week window cannot exceed 7 days.";

            return null;
        }
    }
}