using Serilog;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
using ZB.MOM.WW.OtOpcUa.Core.Scripting;

namespace ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms.Tests;

/// <summary>
///     Review R05:1 / R05:12 / R05:3 — the engine's value cache is pruned on every reload (it used to keep
///     every path ever referenced, forever), is no longer written after Dispose, and Dispose's in-flight
///     drain is bounded (a hung store no longer hangs host shutdown).
/// </summary>
[Trait("Category", "Unit")]
public sealed class ScriptedAlarmEngineLifecycleTests
{
    private static ScriptedAlarmDefinition Alarm(string id, string predicate) =>
        new(AlarmId: id, EquipmentPath: "Plant/Line1/Reactor", AlarmName: id, Kind: AlarmKind.AlarmCondition,
            Severity: AlarmSeverity.High, MessageTemplate: "condition", PredicateScriptSource: predicate);

    private static ScriptedAlarmEngine Build(FakeUpstream up, IAlarmStateStore? store = null)
    {
        var logger = new LoggerConfiguration().CreateLogger();
        return new ScriptedAlarmEngine(up, store ?? new InMemoryAlarmStateStore(), new ScriptLoggerFactory(logger), logger);
    }

    [Fact]
    public async Task Reload_prunes_value_cache_entries_for_paths_the_new_alarm_set_no_longer_references()
    {
        var up = new FakeUpstream();
        up.Set("Temp", 50);
        up.Set("Pressure", 5);
        using var eng = Build(up);
        var ct = TestContext.Current.CancellationToken;

        await eng.LoadAsync(
            [Alarm("a", """return (int)ctx.GetTag("Temp").Value > 100 || (int)ctx.GetTag("Pressure").Value > 10;""")], ct);
        eng.ValueCacheCountForTest.ShouldBe(2);

        // The redeploy drops Pressure from every predicate: its entry must go with it.
        await eng.LoadAsync([Alarm("a", """return (int)ctx.GetTag("Temp").Value > 100;""")], ct);
        eng.ValueCacheCountForTest.ShouldBe(1);
        eng.ValueCacheContainsForTest("Pressure").ShouldBeFalse();
        eng.ValueCacheContainsForTest("Temp").ShouldBeTrue();
    }

    [Fact]
    public async Task A_push_after_Dispose_does_not_write_the_value_cache()
    {
        var up = new FakeUpstream();
        up.Set("Temp", 50);
        var eng = Build(up);
        await eng.LoadAsync([Alarm("a", """return (int)ctx.GetTag("Temp").Value > 100;""")],
            TestContext.Current.CancellationToken);
        eng.Dispose();
        eng.ValueCacheCountForTest.ShouldBe(1);

        eng.OnUpstreamChange("Late", new DataValueSnapshot(1, 0u, DateTime.UtcNow, DateTime.UtcNow));

        eng.ValueCacheContainsForTest("Late").ShouldBeFalse("a disposed engine must not grow its cache");
    }

    [Fact]
    public async Task Dispose_gives_up_on_a_store_that_never_returns_after_the_drain_bound_and_cancels_it()
    {
        var up = new FakeUpstream();
        up.Set("Temp", 50);
        var store = new NeverReturningSaveStore();
        var eng = Build(up, store);
        eng.DisposeDrainTimeout = TimeSpan.FromMilliseconds(300);
        await eng.LoadAsync([Alarm("A", """return (int)ctx.GetTag("Temp").Value > 100;""")],
            TestContext.Current.CancellationToken);

        store.BlockNext = true;
        up.Push("Temp", 150); // Activated → SaveAsync → blocks forever (until cancelled)
        await WaitForAsync(() => store.SaveInProgress);

        var sw = System.Diagnostics.Stopwatch.StartNew();
        eng.Dispose();
        sw.Stop();

        sw.Elapsed.ShouldBeLessThan(TimeSpan.FromSeconds(5), "the drain is bounded; a hung store cannot hang shutdown");
        await WaitForAsync(() => store.ObservedCancellation, timeoutMs: 2000);
        store.ObservedCancellation.ShouldBeTrue("the in-flight save was cancelled through the engine's shutdown token");
        eng.ShutdownCtsDisposedForTest.ShouldBeTrue("the cancelled save completed inside the grace, so the CTS is released");
    }

    [Fact]
    public async Task Dispose_still_waits_for_a_save_that_completes_inside_the_bound()
    {
        // Positive control for the bound: a save that finishes promptly is drained, not cut off.
        var up = new FakeUpstream();
        up.Set("Temp", 50);
        var store = new NeverReturningSaveStore { ReleaseAfter = TimeSpan.FromMilliseconds(100) };
        var eng = Build(up, store);
        eng.DisposeDrainTimeout = TimeSpan.FromSeconds(5);
        await eng.LoadAsync([Alarm("A", """return (int)ctx.GetTag("Temp").Value > 100;""")],
            TestContext.Current.CancellationToken);

        store.BlockNext = true;
        up.Push("Temp", 150);
        await WaitForAsync(() => store.SaveInProgress);

        eng.Dispose();

        store.SaveInProgress.ShouldBeFalse();
        store.ObservedCancellation.ShouldBeFalse("a save that completes within the bound is never cancelled");
        store.Saved.ShouldContain("A");
        eng.ShutdownCtsDisposedForTest.ShouldBeTrue("every background task completed, so the shutdown CTS is disposed");
        Should.NotThrow(() => eng.OnUpstreamChange("Temp", new DataValueSnapshot(1, 0u, DateTime.UtcNow, DateTime.UtcNow)));
    }

    private static async Task WaitForAsync(Func<bool> cond, int timeoutMs = 5000)
    {
        var deadline = DateTime.UtcNow.AddMilliseconds(timeoutMs);
        while (DateTime.UtcNow < deadline)
        {
            if (cond()) return;
            await Task.Delay(20);
        }
        throw new TimeoutException("Condition did not become true in time");
    }

    /// <summary>A store whose next SaveAsync blocks until cancelled (or until <see cref="ReleaseAfter"/>).</summary>
    private sealed class NeverReturningSaveStore : IAlarmStateStore
    {
        private readonly InMemoryAlarmStateStore _inner = new();
        public volatile bool BlockNext;
        public volatile bool SaveInProgress;
        public volatile bool ObservedCancellation;
        public TimeSpan? ReleaseAfter { get; set; }
        public List<string> Saved { get; } = [];

        public Task<AlarmConditionState?> LoadAsync(string alarmId, CancellationToken ct) => _inner.LoadAsync(alarmId, ct);
        public Task<IReadOnlyList<AlarmConditionState>> LoadAllAsync(CancellationToken ct) => _inner.LoadAllAsync(ct);
        public Task RemoveAsync(string alarmId, CancellationToken ct) => _inner.RemoveAsync(alarmId, ct);

        public async Task SaveAsync(AlarmConditionState state, CancellationToken ct)
        {
            if (BlockNext)
            {
                BlockNext = false;
                SaveInProgress = true;
                try
                {
                    await Task.Delay(ReleaseAfter ?? Timeout.InfiniteTimeSpan, ct).ConfigureAwait(false);
                }
                catch (OperationCanceledException)
                {
                    ObservedCancellation = true;
                    throw;
                }
                finally
                {
                    SaveInProgress = false;
                }
            }
            lock (Saved) Saved.Add(state.AlarmId);
            await _inner.SaveAsync(state, ct).ConfigureAwait(false);
        }
    }
}