using System.Diagnostics;
using ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport;
using ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport.Cip;

namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests.Differential;

/// <summary>One timed burst: every tag read once, concurrently.</summary>
/// <param name="Requests">Native only: <see cref="ConnectionDiagnostics.RequestsSent"/> delta over the pass (keep-alives included).</param>
/// <param name="TagFailures">Reads that ended with a tag-level status (a connection-level one aborts instead).</param>
/// <param name="Gc">Collections that ran during the pass, per generation (T21 review r1 M8: a client-side stall shows here).</param>
/// <param name="Rtt">Native only: round trip of each CIP exchange in the pass, from <see cref="CipConnection"/> (a slow
///     controller shows here; a slow pass with fast exchanges points at the client).</param>
internal sealed record LatencyPass(
    int Index, TimeSpan Wall, int? Requests, int TagFailures, GcDelta Gc = default, ConnectionDiagnostics.ExchangeStats? Rtt = null);

/// <summary>GC collections per generation over a window (gen0 counts include gen1/gen2 collections, as the runtime reports).</summary>
internal readonly record struct GcDelta(int Gen0, int Gen1, int Gen2)
{
    public static GcDelta Now() => new(GC.CollectionCount(0), GC.CollectionCount(1), GC.CollectionCount(2));
    public static GcDelta operator -(GcDelta a, GcDelta b) => new(a.Gen0 - b.Gen0, a.Gen1 - b.Gen1, a.Gen2 - b.Gen2);
    public override string ToString() => $"{Gen0}/{Gen1}/{Gen2}";
}

/// <summary>The outcome of the latency comparison.</summary>
internal sealed class LatencyResult
{
    public required DifferentialTarget Target { get; init; }

    /// <summary>The fixed set read every pass, in order (a name appears more than once only when <see cref="Repeated"/>).</summary>
    public required IReadOnlyList<SelectedTag> Tags { get; init; }
    public required int DistinctTags { get; init; }
    public required bool Repeated { get; init; }

    /// <summary>Names libplctag could not read at setup (tag-level status): dropped from BOTH transports' sets.</summary>
    public required IReadOnlyList<string> Dropped { get; init; }
    public required IReadOnlyList<LatencyPass> Libplctag { get; init; }
    public required IReadOnlyList<LatencyPass> Native { get; init; }
    public required int NativeForwardOpens { get; init; }

    /// <summary>Forward Closes the native phase sent / got a reply to, its anchor release included (review r1 M9).</summary>
    public required NativeCloses NativeForwardCloses { get; init; }

    /// <summary>TCP connections to the endpoint once the native phase's session was released and drained.</summary>
    public required int? ConnectionsAfterNative { get; init; }

    /// <summary>Native requests spent creating the runtimes (one read each, before any timed pass).</summary>
    public required int NativeSetupRequests { get; init; }
    public required List<string> Problems { get; init; }
}

/// <summary>
///     Task 21's poll-latency comparison, read-only and built on the differential's machinery: the same
///     endpoint parsing, the same anchors (one libplctag handle, one native lease), the same open-attempt budget,
///     the same connection barrier and the same stop-on-first-connection-failure rule.
///     <para>Order: the differential's run (its browse supplies the tags — no second listing), a barrier until its
///     native session is gone, every libplctag pass with every handle then disposed, a barrier until libplctag's
///     session is gone, then every native pass under one anchor lease. The two transports never overlap.</para>
///     <para>Per transport: create and read every tag once (untimed, paced by <c>AB_DIFF_PACE_MS</c>), then
///     <c>AB_LAT_PASSES</c> timed passes, each issuing all <c>AB_LAT_TAGS</c> reads at once (<c>Task.WhenAll</c>)
///     so the native shared scheduler can pack them into Multiple Service Packets as libplctag packs internally,
///     with <c>AB_LAT_PASS_GAP_MS</c> of quiet between passes.</para>
/// </summary>
internal static class PollLatencyRun
{
    private static readonly HashSet<AbCipDataType> Atomic =
    [
        AbCipDataType.Bool, AbCipDataType.SInt, AbCipDataType.Int, AbCipDataType.DInt, AbCipDataType.LInt,
        AbCipDataType.USInt, AbCipDataType.UInt, AbCipDataType.UDInt, AbCipDataType.ULInt,
        AbCipDataType.Real, AbCipDataType.LReal,
    ];

    /// <summary>
    ///     The fixed tag set: atomic, non-array scalars, from the differential's libplctag browse — or, when
    ///     <c>AB_DIFF_TAGS</c> is set, those of its names whose browsed type is an atomic scalar. When fewer
    ///     distinct tags exist than <c>AB_LAT_TAGS</c>, the set is REPEATED cyclically up to the count (each
    ///     repeat is its own runtime/handle on the same name) and reported as such — never silently.
    /// </summary>
    internal static (IReadOnlyList<SelectedTag> Tags, int Distinct, bool Repeated) PickTags(
        DifferentialTarget target, TransportObservations browsed)
    {
        var candidates = DifferentialRun.Select(target with { MaxTags = DifferentialTarget.Ceiling }, browsed)
            .Where(t => !t.IsArray && t.Type is { } type && Atomic.Contains(type))
            .DistinctBy(t => t.Name)
            .Take(target.LatencyTags)
            .ToList();
        if (candidates.Count == 0 || candidates.Count >= target.LatencyTags) return (candidates, candidates.Count, false);
        var repeated = Enumerable.Range(0, target.LatencyTags).Select(i => candidates[i % candidates.Count]).ToList();
        return (repeated, candidates.Count, true);
    }

    public static async Task<LatencyResult> ExecuteAsync(DifferentialTarget target, DifferentialResult differential, CancellationToken ct)
    {
        var (picked, distinct, repeated) = PickTags(target, differential.Libplctag);
        if (picked.Count == 0)
            throw new InvalidOperationException("The browse offered no atomic scalar tags to time; nothing was read.");

        // The differential's native session must be gone before libplctag connects.
        await DifferentialRun.WaitForSessionsToCloseAsync(
            target, differential.Addresses, differential.BaselineEndpoints, "the differential's native", ct).ConfigureAwait(false);

        // ---- libplctag: setup, passes, every handle disposed (anchor last). ----
        var dropped = new List<string>();
        var libFactory = AbCipTransportFactories.For(AbCipTransport.Libplctag).Tags;
        // Anchor on a tag the differential already read Ok through libplctag, so the anchor is never the refusal.
        var anchorTag = picked.FirstOrDefault(t => differential.Libplctag.Reads.TryGetValue(t.Name, out var o) && o.Succeeded)
                        ?? picked[0];
        var (libPasses, tags) = await DifferentialRun.WithLibplctagAnchorAsync("latency libplctag", target, anchorTag.Name, async () =>
        {
            var runtimes = new List<(SelectedTag Tag, IAbCipTagRuntime Runtime)>();
            try
            {
                foreach (var tag in picked)
                {
                    var rt = await CreateAsync("latency libplctag", target, libFactory, tag, ct).ConfigureAwait(false);
                    if (rt is null) { dropped.Add(tag.Name); continue; }
                    runtimes.Add((tag, rt));
                }
                var passes = await RunPassesAsync("latency libplctag", target, runtimes, countRequests: false, afterEach: null, ct)
                    .ConfigureAwait(false);
                return (passes, (IReadOnlyList<SelectedTag>)runtimes.Select(r => r.Tag).ToList());
            }
            finally
            {
                foreach (var (_, rt) in runtimes) rt.Dispose();
            }
        }, ct).ConfigureAwait(false);

        // ---- Barrier: libplctag's session must be gone before the native side connects. ----
        await DifferentialRun.WaitForSessionsToCloseAsync(
            target, differential.Addresses, differential.BaselineEndpoints, "libplctag", ct).ConfigureAwait(false);

        // ---- native: the same (post-drop) set, under one anchor lease. ----
        var problems = new List<string>();
        var nativeFactory = AbCipTransportFactories.For(AbCipTransport.Native).Tags;
        var ((nativePasses, setupRequests), opens, closes) = await DifferentialRun.WithNativeAnchorAsync("latency native", target, async checkOpens =>
        {
            var runtimes = new List<(SelectedTag Tag, IAbCipTagRuntime Runtime)>();
            try
            {
                var before = DeviceSessionPool.Shared.Diagnostics.RequestsSent;
                foreach (var tag in tags)
                {
                    var rt = await CreateAsync("latency native", target, nativeFactory, tag, ct).ConfigureAwait(false);
                    checkOpens($"setup of '{tag.Name}'");
                    if (rt is null) { problems.Add($"native could not read '{tag.Name}', which libplctag read"); continue; }
                    runtimes.Add((tag, rt));
                }
                var setup = DeviceSessionPool.Shared.Diagnostics.RequestsSent - before;
                var passes = await RunPassesAsync("latency native", target, runtimes, countRequests: true, checkOpens, ct)
                    .ConfigureAwait(false);
                return (passes, setup);
            }
            finally
            {
                foreach (var (_, rt) in runtimes) rt.Dispose();
            }
        }).ConfigureAwait(false);

        // ---- Barrier: the native session must be gone before the run reports (review r1 M9). ----
        var afterNative = await DifferentialRun.WaitForSessionsToCloseAsync(
            target, differential.Addresses, differential.BaselineEndpoints, "latency native", ct).ConfigureAwait(false);

        return new LatencyResult
        {
            Target = target,
            Tags = tags,
            DistinctTags = distinct,
            Repeated = repeated,
            Dropped = dropped,
            Libplctag = libPasses,
            Native = nativePasses,
            NativeForwardOpens = opens,
            NativeForwardCloses = closes,
            ConnectionsAfterNative = afterNative,
            NativeSetupRequests = setupRequests,
            Problems = problems,
        };
    }

    /// <summary>Create + first read of one tag. Null on a tag-level refusal; a connection-level failure aborts.</summary>
    private static async Task<IAbCipTagRuntime?> CreateAsync(
        string phase, DifferentialTarget target, IAbCipTagFactory factory, SelectedTag tag, CancellationToken ct)
    {
        var rt = factory.Create(target.Params(tag.Name, tag.ElementCount, tag.IsArray, tag.Type));
        try
        {
            await DifferentialRun.PaceAsync(target, ct).ConfigureAwait(false);
            await rt.InitializeAsync(ct).ConfigureAwait(false);
            if (rt.GetStatus() == (int)AbStatus.Ok) return rt;
        }
        catch (Exception ex) when (ex is not OperationCanceledException || !ct.IsCancellationRequested)
        {
            if (DifferentialRun.IsConnectionLevel(ex))
            {
                rt.Dispose();
                throw DifferentialRun.Abort(phase, $"setup of '{tag.Name}'", ex);
            }
        }
        catch
        {
            rt.Dispose();
            throw;
        }
        rt.Dispose();
        return null;
    }

    private static async Task<List<LatencyPass>> RunPassesAsync(
        string phase, DifferentialTarget target, List<(SelectedTag Tag, IAbCipTagRuntime Runtime)> runtimes,
        bool countRequests, Action<string>? afterEach, CancellationToken ct)
    {
        var passes = new List<LatencyPass>(target.LatencyPasses);
        for (var p = 1; p <= target.LatencyPasses; p++)
        {
            if (p > 1 && target.LatencyPassGapMs > 0) await Task.Delay(target.LatencyPassGapMs, ct).ConfigureAwait(false);

            var requestsBefore = DeviceSessionPool.Shared.Diagnostics.RequestsSent;
            DeviceSessionPool.Shared.Diagnostics.ResetExchangeStats();
            var gcBefore = GcDelta.Now();
            var clock = Stopwatch.StartNew();
            var outcomes = await Task.WhenAll(runtimes.Select(r => ReadOnceAsync(r.Runtime, ct))).ConfigureAwait(false);
            clock.Stop();
            var gc = GcDelta.Now() - gcBefore;
            var rtt = countRequests ? DeviceSessionPool.Shared.Diagnostics.ReadExchangeStats() : (ConnectionDiagnostics.ExchangeStats?)null;
            var requests = DeviceSessionPool.Shared.Diagnostics.RequestsSent - requestsBefore;

            var failures = 0;
            for (var i = 0; i < outcomes.Length; i++)
            {
                if (outcomes[i] is { } ex)
                {
                    if (DifferentialRun.IsConnectionLevel(ex))
                        throw DifferentialRun.Abort(phase, $"pass {p}, tag '{runtimes[i].Tag.Name}'", ex);
                    failures++;
                }
                else if (runtimes[i].Runtime.GetStatus() != (int)AbStatus.Ok)
                {
                    failures++;
                }
            }
            afterEach?.Invoke($"pass {p}");
            passes.Add(new LatencyPass(p, clock.Elapsed, countRequests ? requests : null, failures, gc, rtt));
        }
        return passes;
    }

    private static async Task<Exception?> ReadOnceAsync(IAbCipTagRuntime runtime, CancellationToken ct)
    {
        try
        {
            await runtime.ReadAsync(ct).ConfigureAwait(false);
            return null;
        }
        catch (Exception ex) when (ex is not OperationCanceledException || !ct.IsCancellationRequested)
        {
            return ex;
        }
    }

    /// <summary>Nearest-rank percentile (p in (0,100]) of the pass wall times, in milliseconds.</summary>
    internal static double Percentile(IEnumerable<TimeSpan> walls, double p)
    {
        var sorted = walls.Select(w => w.TotalMilliseconds).Order().ToList();
        if (sorted.Count == 0) throw new InvalidOperationException("No passes to take a percentile of.");
        var rank = (int)Math.Ceiling(p / 100.0 * sorted.Count);
        return sorted[Math.Clamp(rank, 1, sorted.Count) - 1];
    }
}