namespace SeaHaven.Services.Helpers
{
    public enum WorkOrderAdvancedSearchDatePreset
    {
        ThisWeek,
        LastWeek,
        ThisMonth,
        Last3Months,
        NextWeek,
        NextMonth,
        Custom
    }

    public record WorkOrderSearchDateRange(DateOnly From, DateOnly To);

    public static class WorkOrderSearchDateRangeResolver
    {
        // Widest windows the frontend sends for "every week": the no-range search
        // (ADVANCED_SEARCH_ALL_WEEKS_FROM/TO, 2000-01-01..2099-12-31) and the pinned
        // Unassigned queue (UNASSIGNED_QUEUE_DATE_FROM/TO, 1970-01-01..2099-12-31).
        private static readonly DateOnly AllWeeksFrom = new(2000, 1, 1);
        private static readonly DateOnly AllWeeksTo = new(2099, 12, 31);

        /// <summary>
        /// Whether a board search adds open undated rows to its date range (SH-391).
        /// An explicit <paramref name="includeDateless"/> wins. When it is omitted,
        /// as by clients that predate the flag, a search with no date input or with
        /// an all-weeks Custom window still returns undated rows, as before SH-391:
        /// those requests mean "no range selected". Any other range is strict.
        /// </summary>
        public static bool ResolveIncludeDateless(
            bool? includeDateless,
            WorkOrderAdvancedSearchDatePreset? preset,
            DateOnly? dateFrom,
            DateOnly? dateTo)
        {
            if (includeDateless.HasValue)
                return includeDateless.Value;

            if (!preset.HasValue && !dateFrom.HasValue && !dateTo.HasValue)
                return true;

            return preset == WorkOrderAdvancedSearchDatePreset.Custom
                && dateFrom <= AllWeeksFrom
                && dateTo >= AllWeeksTo;
        }

        public static WorkOrderSearchDateRange Resolve(
            WorkOrderAdvancedSearchDatePreset? preset,
            DateOnly? dateFrom,
            DateOnly? dateTo,
            DateOnly? referenceDate = null)
        {
            var today = referenceDate ?? DateOnly.FromDateTime(DateTime.UtcNow);
            var resolvedPreset = preset ?? WorkOrderAdvancedSearchDatePreset.ThisWeek;

            if (resolvedPreset == WorkOrderAdvancedSearchDatePreset.Custom)
            {
                if (!dateFrom.HasValue || !dateTo.HasValue)
                    throw new ArgumentException("dateFrom and dateTo are required when datePreset is custom.");

                if (dateTo.Value < dateFrom.Value)
                    throw new ArgumentException("dateTo must be on or after dateFrom.");

                return new WorkOrderSearchDateRange(dateFrom.Value, dateTo.Value);
            }

            return resolvedPreset switch
            {
                WorkOrderAdvancedSearchDatePreset.ThisWeek => ThisIsoWeek(today),
                WorkOrderAdvancedSearchDatePreset.LastWeek => LastIsoWeek(today),
                WorkOrderAdvancedSearchDatePreset.ThisMonth => ThisMonth(today),
                WorkOrderAdvancedSearchDatePreset.Last3Months => Last3Months(today),
                WorkOrderAdvancedSearchDatePreset.NextWeek => NextIsoWeek(today),
                WorkOrderAdvancedSearchDatePreset.NextMonth => NextMonth(today),
                _ => ThisIsoWeek(today)
            };
        }

        public static DateOnly GetIsoWeekStart(DateOnly date)
        {
            var diff = (7 + (date.DayOfWeek - DayOfWeek.Monday)) % 7;
            return date.AddDays(-diff);
        }

        private static WorkOrderSearchDateRange ThisIsoWeek(DateOnly today)
        {
            var start = GetIsoWeekStart(today);
            return new WorkOrderSearchDateRange(start, start.AddDays(4));
        }

        private static WorkOrderSearchDateRange LastIsoWeek(DateOnly today)
        {
            var start = GetIsoWeekStart(today).AddDays(-7);
            return new WorkOrderSearchDateRange(start, start.AddDays(4));
        }

        private static WorkOrderSearchDateRange NextIsoWeek(DateOnly today)
        {
            var start = GetIsoWeekStart(today).AddDays(7);
            return new WorkOrderSearchDateRange(start, start.AddDays(4));
        }

        private static WorkOrderSearchDateRange ThisMonth(DateOnly today)
        {
            var start = new DateOnly(today.Year, today.Month, 1);
            var end = start.AddMonths(1).AddDays(-1);
            return new WorkOrderSearchDateRange(start, end);
        }

        private static WorkOrderSearchDateRange NextMonth(DateOnly today)
        {
            var start = new DateOnly(today.Year, today.Month, 1).AddMonths(1);
            var end = start.AddMonths(1).AddDays(-1);
            return new WorkOrderSearchDateRange(start, end);
        }

        private static WorkOrderSearchDateRange Last3Months(DateOnly today)
        {
            var end = today;
            var start = today.AddMonths(-3);
            return new WorkOrderSearchDateRange(start, end);
        }
    }
}