using Opc.Ua;

namespace ZB.MOM.WW.OtOpcUa.OpcUaServer;

/// <summary>
///     The Part 13 <see cref="AggregateConfiguration"/> processed reads are evaluated under, and the rule for a
///     client-supplied one in <c>ReadProcessedDetails</c>.
/// </summary>
/// <remarks>
///     <para>
///         The aggregate evaluators (<c>AggregateEvaluator</c> / <c>TimeWeightedAggregator</c> in
///         <c>Driver.Historian.Sql.Common</c>) are written against fixed settings, not parameterised: Uncertain time counts as
///         Good (<see cref="TreatUncertainAsBad"/> = false) in TimeAverage2 / Total2, while PercentGood / DurationGood count
///         Good time only and PercentBad / DurationBad Bad time only — Uncertain in neither (Part 13 §5.4.3.31-34, Mantis
///         0006166); the per-sample Average / Minimum /
///         Maximum / Range / *ActualTime / Count are defined by Part 13 over Good values whatever this setting, as the
///         SDK computes them under it; an interval is Good only when all of
///         it is (<see cref="PercentDataGood"/> = 100) and Bad only when none of it is non-Bad
///         (<see cref="PercentDataBad"/> = 100), otherwise <c>UncertainDataSubNormal</c>; the value past the last sample
///         is held (stepped, <see cref="UseSlopedExtrapolation"/> = false). Part 13's AggregateConfiguration defaults are
///         TreatUncertainAsBad = false, PercentDataBad = PercentDataGood = 100, UseSlopedExtrapolation = false (from the
///         spec as recalled, not re-read offline). The SDK matched these until Opc.Ua.Server 1.5.378.182, which flipped
///         <c>TreatUncertainAsBad</c> to true: that is a DELIBERATE DIVERGENCE we do not follow (consumers such as
///         ScadaBridge read these aggregates). <c>OtOpcUaSdkServer.CreateAggregateManager</c> pushes these values into
///         the SDK manager so live AggregateFilter subscriptions agree with history reads; a test pins both sides.
///     </para>
///     <para>
///         The live calculators are the application's frozen 1.5.378.182 copies (<c>Compatibility/Aggregates</c>), whose
///         <c>ComputeDurationGoodBad</c> counts Uncertain time as Good under <see cref="TreatUncertainAsBad"/> = false. That
///         made live PercentGood / DurationGood disagree with HistoryRead whenever Uncertain data was present. #809
///         (owner-approved 2026-11-11) overrides exactly those two (<c>GoodOnlyStatusAggregateCalculator</c>), so live and
///         HistoryRead now agree on them — pinned by
///         <c>SdkAggregateParityTests.Live_AggregateFilter_PercentGood_and_DurationGood_equal_HistoryRead_over_Uncertain_samples</c>.
///         Other known live-vs-HistoryRead differences (e.g. #821, an Uncertain first sample in a late-start interval) are
///         documented in <c>docs/Historian.md</c>.
///     </para>
///     <para>
///         A request asking for <c>UseServerCapabilitiesDefaults</c>, or spelling out exactly these values, is served;
///         any other configuration is refused per node with <c>BadAggregateConfigurationRejected</c> rather than silently
///         answered under settings the client did not ask for (it used to be ignored).
///     </para>
/// </remarks>
public static class ServerAggregateConfiguration
{
    /// <summary>Uncertain data is not treated as Bad.</summary>
    public const bool TreatUncertainAsBad = false;

    /// <summary>An interval is Bad only when 100 % of it is Bad.</summary>
    public const byte PercentDataBad = 100;

    /// <summary>An interval is Good only when 100 % of it is Good.</summary>
    public const byte PercentDataGood = 100;

    /// <summary>The value past the last sample is held (stepped), not sloped.</summary>
    public const bool UseSlopedExtrapolation = false;

    /// <summary>The server defaults as an <see cref="AggregateConfiguration"/> (explicit values, not "use defaults").</summary>
    public static AggregateConfiguration Defaults => new()
    {
        UseServerCapabilitiesDefaults = false,
        TreatUncertainAsBad = TreatUncertainAsBad,
        PercentDataBad = PercentDataBad,
        PercentDataGood = PercentDataGood,
        UseSlopedExtrapolation = UseSlopedExtrapolation,
    };

    /// <summary>
    ///     True when a processed read with <paramref name="requested"/> can be served: none supplied,
    ///     <c>UseServerCapabilitiesDefaults</c>, or every setting equal to the server's.
    /// </summary>
    /// <param name="requested">The request's configuration (may be null).</param>
    /// <returns>Whether to serve; false ⇒ <c>BadAggregateConfigurationRejected</c>.</returns>
    public static bool IsServable(AggregateConfiguration? requested) =>
        requested is null
        || requested.UseServerCapabilitiesDefaults
        || (requested.TreatUncertainAsBad == TreatUncertainAsBad
            && requested.PercentDataBad == PercentDataBad
            && requested.PercentDataGood == PercentDataGood
            && requested.UseSlopedExtrapolation == UseSlopedExtrapolation);
}