using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
using Google.Protobuf.Collections;
using ZB.MOM.WW.MxGateway.Contracts.Proto;
using ZB.MOM.WW.MxGateway.Worker.MxAccess;

namespace ZB.MOM.WW.MxGateway.Worker.Tests.MxAccess;

/// <summary>
///     Unit tests for <see cref="MxAccessWriteCompletionCache"/>. The cache is
///     consumed by the write command executor's bounded pump-wait so a
///     WriteSecured/WriteSecured2 reply can carry the correlated
///     OnWriteComplete outcome; its version-baseline contract is exercised in
///     isolation here before the STA / COM plumbing gets layered on top.
/// </summary>
public sealed class MxAccessWriteCompletionCacheTests
{
    /// <summary>Verifies that Record bumps the version per key and keys stay isolated.</summary>
    [Fact]
    public void Record_IncrementsVersionPerKey()
    {
        MxAccessWriteCompletionCache cache = new();

        Assert.Equal(0UL, cache.CurrentVersion(7, 21));

        cache.Record(7, 21, BuildStatuses(detail: 100));
        Assert.Equal(1UL, cache.CurrentVersion(7, 21));

        cache.Record(7, 21, BuildStatuses(detail: 200));
        Assert.Equal(2UL, cache.CurrentVersion(7, 21));

        cache.Record(7, 22, BuildStatuses(detail: 300));
        Assert.Equal(1UL, cache.CurrentVersion(7, 22));
        Assert.Equal(2UL, cache.CurrentVersion(7, 21));
    }

    /// <summary>Verifies that a completion newer than the baseline is returned with its status rows.</summary>
    [Fact]
    public void TryWaitForCompletion_WhenCompletionNewerThanBaseline_ReturnsStatuses()
    {
        MxAccessWriteCompletionCache cache = new();
        cache.Record(7, 21, BuildStatuses(detail: 4321));

        bool found = cache.TryWaitForCompletion(
            7,
            21,
            sinceVersion: 0UL,
            deadlineUtc: DateTime.UtcNow.AddSeconds(5),
            pumpStep: static () => { },
            out RepeatedField<MxStatusProxy> statuses);

        Assert.True(found);
        MxStatusProxy row = Assert.Single(statuses);
        Assert.Equal(4321, row.Detail);
        Assert.Equal(MxStatusCategory.Ok, row.Category);
    }

    /// <summary>
    ///     Verifies that a completion recorded before the baseline was captured is
    ///     never misattributed to the waiting write: only a strictly newer version
    ///     satisfies the wait, so a stale row times the wait out.
    /// </summary>
    [Fact]
    public void TryWaitForCompletion_WhenOnlyStaleCompletion_TimesOut()
    {
        MxAccessWriteCompletionCache cache = new();
        cache.Record(7, 21, BuildStatuses(detail: 4321));
        ulong baseline = cache.CurrentVersion(7, 21);

        bool found = cache.TryWaitForCompletion(
            7,
            21,
            sinceVersion: baseline,
            deadlineUtc: DateTime.UtcNow.AddMilliseconds(50),
            pumpStep: static () => { },
            out RepeatedField<MxStatusProxy> statuses);

        Assert.False(found);
        Assert.Empty(statuses);
    }

    /// <summary>
    ///     Verifies the pump loop is what lets a completion land: the completion is
    ///     recorded from inside a later pump step (standing in for the STA
    ///     dispatching the OnWriteComplete message) and the wait then succeeds.
    /// </summary>
    [Fact]
    public void TryWaitForCompletion_InvokesPumpStepEachIteration()
    {
        MxAccessWriteCompletionCache cache = new();
        int pumpCalls = 0;

        bool found = cache.TryWaitForCompletion(
            7,
            21,
            sinceVersion: 0UL,
            deadlineUtc: DateTime.UtcNow.AddSeconds(5),
            pumpStep: () =>
            {
                pumpCalls++;
                if (pumpCalls == 2)
                {
                    cache.Record(7, 21, BuildStatuses(detail: 55));
                }
            },
            out RepeatedField<MxStatusProxy> statuses);

        Assert.True(found);
        Assert.True(pumpCalls >= 2);
        Assert.Equal(55, Assert.Single(statuses).Detail);
    }

    /// <summary>
    ///     Verifies the wait slice stays bounded no matter what poll interval the
    ///     caller asks for: with a 10 s interval and a 3 s deadline, a completion
    ///     recorded 50 ms in is still returned in time, because every slice is
    ///     capped at the 50 ms fallback tick. The blind <c>Thread.Sleep</c> this
    ///     replaced would have slept the full interval — on the STA, 10 s with no
    ///     Windows messages dispatched — and then reported a timeout.
    /// </summary>
    /// <remarks>
    ///     Scope: this proves the cadence bound, not the signal path. The clamp
    ///     alone would satisfy it, so it stays green if the <c>Record</c>-side
    ///     <c>Set()</c> is deleted. <c>StaWaitHelperTests</c> owns the signal
    ///     path, where a five-second wait with no clamp in play makes the handle
    ///     the only thing that can end it early.
    /// </remarks>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task TryWaitForCompletion_CompletesWithinDeadline_WhenPollIntervalExceedsTheFallbackTick()
    {
        MxAccessWriteCompletionCache cache = new();
        using ManualResetEventSlim waitEntered = new(false);

        Task recorder = Task.Run(async () =>
        {
            // Handshake so the completion cannot land before the wait starts —
            // otherwise the first check would satisfy it and prove nothing.
            waitEntered.Wait(TimeSpan.FromSeconds(5));
            await Task.Delay(50, CancellationToken.None);
            cache.Record(7, 21, BuildStatuses(detail: 8080));
        });

        Stopwatch elapsed = Stopwatch.StartNew();
        bool found = cache.TryWaitForCompletion(
            7,
            21,
            sinceVersion: 0UL,
            deadlineUtc: DateTime.UtcNow.AddSeconds(3),
            pumpStep: () => waitEntered.Set(),
            out RepeatedField<MxStatusProxy> statuses,
            pollIntervalMs: 10_000);
        elapsed.Stop();
        await recorder;

        Assert.True(found);
        Assert.Equal(8080, Assert.Single(statuses).Detail);
        Assert.True(
            elapsed.Elapsed < TimeSpan.FromSeconds(2),
            $"The wait should have re-checked within the fallback tick, not slept out the poll interval; took {elapsed.ElapsedMilliseconds} ms.");
    }

    /// <summary>Verifies that Record stores an independent clone of the caller's rows.</summary>
    [Fact]
    public void Record_ClonesStatuses()
    {
        MxAccessWriteCompletionCache cache = new();
        RepeatedField<MxStatusProxy> callerRows = BuildStatuses(detail: 77);

        cache.Record(7, 21, callerRows);
        callerRows[0].Detail = 999;
        callerRows.Add(new MxStatusProxy());

        Assert.True(cache.TryWaitForCompletion(
            7,
            21,
            sinceVersion: 0UL,
            deadlineUtc: DateTime.UtcNow.AddSeconds(5),
            pumpStep: static () => { },
            out RepeatedField<MxStatusProxy> statuses));
        Assert.Equal(77, Assert.Single(statuses).Detail);
    }

    /// <summary>Verifies that Remove forgets only the given handle pair.</summary>
    [Fact]
    public void Remove_ForgetsOnlyThatHandlePair()
    {
        MxAccessWriteCompletionCache cache = new();
        cache.Record(7, 21, BuildStatuses(detail: 1));
        cache.Record(7, 22, BuildStatuses(detail: 2));

        cache.Remove(7, 21);
        cache.Remove(7, 99); // unknown pair is a no-op

        Assert.Equal(1, cache.Count);
        Assert.Equal(0UL, cache.CurrentVersion(7, 21));
        Assert.Equal(1UL, cache.CurrentVersion(7, 22));
    }

    /// <summary>Verifies that RemoveServer forgets every pair of that server and no other.</summary>
    [Fact]
    public void RemoveServer_ForgetsOnlyThatServersPairs()
    {
        MxAccessWriteCompletionCache cache = new();
        cache.Record(7, 21, BuildStatuses(detail: 1));
        cache.Record(7, -5, BuildStatuses(detail: 2));
        cache.Record(8, 21, BuildStatuses(detail: 3));
        cache.Record(-7, 21, BuildStatuses(detail: 4));

        cache.RemoveServer(7);

        Assert.Equal(2, cache.Count);
        Assert.Equal(1UL, cache.CurrentVersion(8, 21));
        Assert.Equal(1UL, cache.CurrentVersion(-7, 21));
    }

    private static RepeatedField<MxStatusProxy> BuildStatuses(int detail)
    {
        return new RepeatedField<MxStatusProxy>
        {
            new MxStatusProxy
            {
                Success = 1,
                Category = MxStatusCategory.Ok,
                Detail = detail,
            },
        };
    }
}