using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using ArchestrA.MxAccess;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.MxAccess;
using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Sta;

namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests;

[Trait("Category", "Unit")]
public sealed class MxAccessClientMonitorLoopTests
{
    /// <summary>
    ///     PR 6 low finding #1 — every $Heartbeat probe must RemoveItem the item handle it
    ///     allocated. Without that, the monitor leaks one handle per MonitorInterval seconds,
    ///     which over a 24h uptime becomes thousands of leaked MXAccess handles and can
    ///     eventually exhaust the runtime proxy's handle table.
    /// </summary>
    [Fact]
    public async Task Heartbeat_probe_calls_RemoveItem_for_every_AddItem()
    {
        using var pump = new StaPump("Monitor.Sta");
        await pump.WaitForStartedAsync();

        var proxy = new CountingProxy();
        var client = new MxAccessClient(pump, proxy, "probe-test", new MxAccessClientOptions
        {
            AutoReconnect = true,
            MonitorInterval = TimeSpan.FromMilliseconds(150),
            StaleThreshold = TimeSpan.FromMilliseconds(50),
        });

        await client.ConnectAsync();

        // Wait past StaleThreshold, then let several monitor cycles fire.
        await Task.Delay(700);

        client.Dispose();

        // One Heartbeat probe fires per monitor tick once the connection looks stale.
        proxy.HeartbeatAddCount.ShouldBeGreaterThan(1);
        // Every AddItem("$Heartbeat") must be matched by a RemoveItem on the same handle.
        proxy.HeartbeatAddCount.ShouldBe(proxy.HeartbeatRemoveCount);
        proxy.OutstandingHeartbeatHandles.ShouldBe(0);
    }

    /// <summary>
    ///     PR 6 low finding #2 — after reconnect, per-subscription replay failures must raise
    ///     SubscriptionReplayFailed so the backend can propagate the degradation, not get
    ///     silently eaten.
    /// </summary>
    [Fact]
    public async Task SubscriptionReplayFailed_fires_for_each_tag_that_fails_to_replay()
    {
        using var pump = new StaPump("Replay.Sta");
        await pump.WaitForStartedAsync();

        var proxy = new ReplayFailingProxy(failOnReplayForTags: new[] { "BadTag.A", "BadTag.B" });
        var client = new MxAccessClient(pump, proxy, "replay-test", new MxAccessClientOptions
        {
            AutoReconnect = true,
            MonitorInterval = TimeSpan.FromMilliseconds(120),
            StaleThreshold = TimeSpan.FromMilliseconds(50),
        });

        var failures = new ConcurrentBag<SubscriptionReplayFailedEventArgs>();
        client.SubscriptionReplayFailed += (_, e) => failures.Add(e);

        await client.ConnectAsync();
        await client.SubscribeAsync("GoodTag.X", (_, _) => { });
        await client.SubscribeAsync("BadTag.A", (_, _) => { });
        await client.SubscribeAsync("BadTag.B", (_, _) => { });

        proxy.TriggerProbeFailureOnNextCall();

        // Wait for the monitor loop to probe → fail → reconnect → replay.
        await Task.Delay(800);

        client.Dispose();

        failures.Count.ShouldBe(2);
        var names = new HashSet<string>();
        foreach (var f in failures) names.Add(f.TagReference);
        names.ShouldContain("BadTag.A");
        names.ShouldContain("BadTag.B");
    }

    // ----- test doubles -----

    private sealed class CountingProxy : IMxProxy
    {
        private int _next = 1;
        private readonly ConcurrentDictionary<int, string> _live = new();

        public int HeartbeatAddCount;
        public int HeartbeatRemoveCount;
        public int OutstandingHeartbeatHandles => _live.Count;

        public event MxDataChangeHandler? OnDataChange { add { } remove { } }
        public event MxWriteCompleteHandler? OnWriteComplete { add { } remove { } }

        public int Register(string _) => 42;
        public void Unregister(int _) { }

        public int AddItem(int _, string address)
        {
            var h = Interlocked.Increment(ref _next);
            _live[h] = address;
            if (address == "$Heartbeat") Interlocked.Increment(ref HeartbeatAddCount);
            return h;
        }

        public void RemoveItem(int _, int itemHandle)
        {
            if (_live.TryRemove(itemHandle, out var addr) && addr == "$Heartbeat")
                Interlocked.Increment(ref HeartbeatRemoveCount);
        }

        public void AdviseSupervisory(int _, int __) { }
        public void UnAdviseSupervisory(int _, int __) { }
        public void Write(int _, int __, object ___, int ____) { }
    }

    /// <summary>
    ///     Mock that lets us exercise the reconnect + replay path. TriggerProbeFailureOnNextCall
    ///     flips a one-shot flag so the very next AddItem("$Heartbeat") throws — that drives the
    ///     monitor loop into the reconnect-with-replay branch. During the replay, AddItem for the
    ///     tags listed in failOnReplayForTags throws so SubscriptionReplayFailed should fire once
    ///     per failing tag.
    /// </summary>
    private sealed class ReplayFailingProxy : IMxProxy
    {
        private int _next = 1;
        private readonly HashSet<string> _failOnReplay;
        private int _probeFailOnce;
        private readonly ConcurrentDictionary<string, bool> _replayedOnce = new(StringComparer.OrdinalIgnoreCase);

        public ReplayFailingProxy(IEnumerable<string> failOnReplayForTags)
        {
            _failOnReplay = new HashSet<string>(failOnReplayForTags, StringComparer.OrdinalIgnoreCase);
        }

        public void TriggerProbeFailureOnNextCall() => Interlocked.Exchange(ref _probeFailOnce, 1);

        public event MxDataChangeHandler? OnDataChange { add { } remove { } }
        public event MxWriteCompleteHandler? OnWriteComplete { add { } remove { } }

        public int Register(string _) => 42;
        public void Unregister(int _) { }

        public int AddItem(int _, string address)
        {
            if (address == "$Heartbeat" && Interlocked.Exchange(ref _probeFailOnce, 0) == 1)
                throw new InvalidOperationException("simulated probe failure");

            // Fail only on the *replay* AddItem for listed tags — not the initial subscribe.
            if (_failOnReplay.Contains(address) && _replayedOnce.ContainsKey(address))
                throw new InvalidOperationException($"simulated replay failure for {address}");

            if (_failOnReplay.Contains(address)) _replayedOnce[address] = true;
            return Interlocked.Increment(ref _next);
        }

        public void RemoveItem(int _, int __) { }
        public void AdviseSupervisory(int _, int __) { }
        public void UnAdviseSupervisory(int _, int __) { }
        public void Write(int _, int __, object ___, int ____) { }
    }
}