shoc-backend/SeaHaven.Services/Helpers/SlaResponseWindows.cs

namespace SeaHaven.Services.Helpers
{
    public enum SlaState
    {
        OnTrack,
        /// <summary>At least half of the response window has elapsed.</summary>
        AtRisk,
        /// <summary>The whole response window has elapsed: the response deadline was missed.</summary>
        Breached
    }

    /// <summary>Where one work order stands against its SEV response window.</summary>
    public sealed record SlaClock(int Severity, DateTime StartedAt, DateTime DeadlineAt, int PercentElapsed, SlaState State);

    /// <summary>
    /// Respond deadlines from the client's SEV table, the same values the severity badge tooltip shows.
    /// They apply to Reactive and Emergency work orders with a severity, and the clock starts when the
    /// work order is created, never at its scheduled date. The table's "next day if after hours" note
    /// is not modelled: the clock always counts the plain hours.
    /// </summary>
    public static class SlaResponseWindows
    {
        public static readonly IReadOnlyDictionary<int, TimeSpan> Respond = new Dictionary<int, TimeSpan>
        {
            [1] = TimeSpan.FromHours(2),
            [2] = TimeSpan.FromHours(4),
            [3] = TimeSpan.FromHours(8),
            [4] = TimeSpan.FromHours(24),
            [5] = TimeSpan.FromHours(72)
        };

        /// <summary>The latest creation time at which a work order of this level has used half its window.</summary>
        public static DateTime AtRiskCreatedAtOrBefore(int severity, DateTime now) => now - Respond[severity] / 2;

        /// <summary>The latest creation time at which a work order of this level has missed its deadline.</summary>
        public static DateTime BreachedCreatedAtOrBefore(int severity, DateTime now) => now - Respond[severity];

        /// <summary>Null when the severity is not a SEV 1–5 level.</summary>
        public static SlaClock? Evaluate(string? severity, DateTime createdAt, DateTime now)
        {
            var level = WorkOrderSeverityRules.ParseLevel(severity);
            if (level is not int sev)
                return null;

            var window = Respond[sev];
            var startedAt = DateTime.SpecifyKind(createdAt, DateTimeKind.Utc);
            var elapsed = now - startedAt;
            var state = elapsed >= window
                ? SlaState.Breached
                : elapsed >= window / 2 ? SlaState.AtRisk : SlaState.OnTrack;
            var percent = (int)Math.Floor(Math.Max(elapsed.Ticks, 0) * 100d / window.Ticks);
            return new SlaClock(sev, startedAt, startedAt + window, percent, state);
        }
    }
}