using System.Collections.Frozen;
using ZB.MOM.WW.HistorianGateway.Contracts.Grpc;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;

namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway.Mapping;

/// <summary>
/// Maps the driver-agnostic <see cref="HistoryAggregateType"/> (OPC UA Part 13 aggregate) onto the
/// gateway's native <see cref="RetrievalMode"/>.
/// </summary>
/// <remarks>
/// <para>
/// Served: <see cref="HistoryAggregateType.TimeAverage"/> → <see cref="RetrievalMode.TimeWeightedAverage"/>,
/// Minimum → <see cref="RetrievalMode.MinimumWithTime"/>, Maximum → <see cref="RetrievalMode.MaximumWithTime"/>,
/// Total → <see cref="RetrievalMode.Integral"/>.
/// </para>
/// <para>
/// Deliberately NOT served (#679): <see cref="HistoryAggregateType.Average"/> (OPC UA Average is the arithmetic mean;
/// AVEVA's modes include no arithmetic mean — only the time-weighted one, which is TimeAverage) and
/// <see cref="HistoryAggregateType.Count"/> (AVEVA <c>Counter</c> is a rollover-counter increase, not a sample count).
/// Both surface as <c>BadAggregateNotSupported</c> rather than returning a different statistic under the requested name.
/// </para>
/// </remarks>
internal static class AggregateModeMapper
{
    /// <summary>
    ///     The aggregates the gateway serves — every defined member <see cref="TryMap"/> maps, derived from it so the
    ///     advertised set and the dispatch can never disagree. <see cref="GatewayHistorianDataSource.SupportedAggregates"/>
    ///     returns it (#682); it is the ONLY declaration of the gateway's served set.
    /// </summary>
    public static readonly IReadOnlySet<HistoryAggregateType> Served =
        Enum.GetValues<HistoryAggregateType>().Where(a => TryMap(a) is not null).ToFrozenSet();

    /// <summary>Maps an aggregate function to the gateway retrieval mode.</summary>
    /// <param name="aggregate">The driver-agnostic aggregate function.</param>
    /// <returns>The matching gateway <see cref="RetrievalMode"/>.</returns>
    /// <exception cref="HistoryAggregateNotSupportedException">A defined member the gateway has no retrieval mode for.</exception>
    /// <exception cref="ArgumentOutOfRangeException">An undefined enum value.</exception>
    public static RetrievalMode ToRetrievalMode(HistoryAggregateType aggregate)
    {
        if (TryMap(aggregate) is { } mode) return mode;

        // Part 13 aggregates the gateway has no retrieval mode for (#285) — an UNDEFINED enum value is a
        // programming error, but a defined-yet-unserved member is a normal client request the server
        // answers with BadAggregateNotSupported.
        if (Enum.IsDefined(aggregate)) throw new HistoryAggregateNotSupportedException(aggregate);
        throw new ArgumentOutOfRangeException(
            nameof(aggregate), aggregate, "Unmapped HistoryAggregateType — add a RetrievalMode mapping.");
    }

    /// <summary>The single mapping table: the retrieval mode for a served aggregate, or null.</summary>
    private static RetrievalMode? TryMap(HistoryAggregateType aggregate) => aggregate switch
    {
        HistoryAggregateType.TimeAverage => RetrievalMode.TimeWeightedAverage,
        HistoryAggregateType.Minimum => RetrievalMode.MinimumWithTime,
        HistoryAggregateType.Maximum => RetrievalMode.MaximumWithTime,
        HistoryAggregateType.Total => RetrievalMode.Integral,
        _ => null,
    };
}