using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Options;
using ZB.MOM.WW.ScadaBridge.Communication.Grpc;

namespace ZB.MOM.WW.ScadaBridge.Communication.Tests.Grpc;

/// <summary>
/// ScadaBridge#67: <see cref="SiteStreamGrpcClientFactory"/> evicts (and disposes) clients whose
/// <c>(site, endpoint)</c> has gone unused for <see cref="CommunicationOptions.GrpcClientIdleTtl"/>,
/// so a renamed or removed address does not leave its channel resident for the life of the process.
/// </summary>
public class SiteStreamGrpcClientFactoryIdleEvictionTests
{
    private static readonly TimeSpan Ttl = TimeSpan.FromMinutes(10);

    /// <summary>Test clock: only advances when told to.</summary>
    private sealed class ManualTimeProvider : TimeProvider
    {
        private long _ticks = TimeSpan.FromHours(1).Ticks;
        public override long TimestampFrequency => TimeSpan.TicksPerSecond;
        public override long GetTimestamp() => Interlocked.Read(ref _ticks);
        public void Advance(TimeSpan by) => Interlocked.Add(ref _ticks, by.Ticks);
    }

    private sealed class TrackingClient(string endpoint) : SiteStreamGrpcClient(endpoint)
    {
        public int DisposeCount;
        public override void Dispose() { Interlocked.Increment(ref DisposeCount); base.Dispose(); }
        public override ValueTask DisposeAsync() { Interlocked.Increment(ref DisposeCount); return base.DisposeAsync(); }
    }

    private sealed class Factory(ManualTimeProvider clock, TimeSpan ttl) : SiteStreamGrpcClientFactory(
        NullLoggerFactory.Instance,
        Options.Create(new CommunicationOptions { GrpcClientIdleTtl = ttl }),
        pskProvider: null,
        clock)
    {
        public int Created;
        protected override SiteStreamGrpcClient CreateClient(string siteIdentifier, string grpcEndpoint)
        {
            Interlocked.Increment(ref Created);
            return new TrackingClient(grpcEndpoint);
        }
    }

    /// <summary>An unused client is disposed and removed once the TTL elapses; a fresh one is created on next use.</summary>
    [Fact]
    public void IdleClient_IsEvictedAndDisposed_ThenRecreatedOnDemand()
    {
        var clock = new ManualTimeProvider();
        using var factory = new Factory(clock, Ttl);
        var old = (TrackingClient)factory.GetOrCreate("site-a", "http://old:5100");

        clock.Advance(Ttl + TimeSpan.FromSeconds(1));
        Assert.Equal(1, factory.EvictIdle());

        Assert.Equal(1, old.DisposeCount);
        Assert.Null(factory.TryGet("site-a", "http://old:5100"));
        var fresh = factory.GetOrCreate("site-a", "http://old:5100");
        Assert.NotSame(old, fresh);
    }

    /// <summary>A client used within the TTL survives the sweep - and using it resets the idle clock.</summary>
    [Fact]
    public void RecentlyUsedClient_IsNotEvicted()
    {
        var clock = new ManualTimeProvider();
        using var factory = new Factory(clock, Ttl);
        var kept = (TrackingClient)factory.GetOrCreate("site-a", "http://a:5100");
        var idle = (TrackingClient)factory.GetOrCreate("site-a", "http://b:5100");

        clock.Advance(TimeSpan.FromMinutes(8));
        Assert.Same(kept, factory.GetOrCreate("site-a", "http://a:5100")); // touch
        clock.Advance(TimeSpan.FromMinutes(8));

        Assert.Equal(1, factory.EvictIdle());
        Assert.Equal(0, kept.DisposeCount);
        Assert.Equal(1, idle.DisposeCount);
        Assert.Same(kept, factory.TryGet("site-a", "http://a:5100"));
    }

    /// <summary>A client with a live subscription is never evicted, however long since it was handed out.</summary>
    [Fact]
    public void ClientWithActiveSubscription_IsNotEvicted()
    {
        var clock = new ManualTimeProvider();
        using var factory = new Factory(clock, Ttl);
        var busy = (TrackingClient)factory.GetOrCreate("site-a", "http://a:5100");
        using var cts = new CancellationTokenSource();
        busy.RegisterSubscription("corr-1", cts);

        clock.Advance(Ttl * 3);

        Assert.Equal(0, factory.EvictIdle());
        Assert.Equal(0, busy.DisposeCount);

        // Once the subscription is gone it becomes evictable again.
        busy.Unsubscribe("corr-1");
        Assert.Equal(1, factory.EvictIdle());
        Assert.Equal(1, busy.DisposeCount);
    }

    /// <summary>A zero TTL disables idle eviction entirely.</summary>
    [Fact]
    public void ZeroTtl_DisablesEviction()
    {
        var clock = new ManualTimeProvider();
        using var factory = new Factory(clock, TimeSpan.Zero);
        var client = (TrackingClient)factory.GetOrCreate("site-a", "http://a:5100");

        clock.Advance(TimeSpan.FromDays(30));

        Assert.Equal(0, factory.EvictIdle());
        Assert.Equal(0, client.DisposeCount);
    }

    /// <summary>Hand-out racing the sweep never throws and never returns null; evicted entries are re-created.</summary>
    [Fact]
    public async Task ConcurrentGetOrCreateAndEviction_IsThreadSafe()
    {
        var clock = new ManualTimeProvider();
        using var factory = new Factory(clock, TimeSpan.FromSeconds(1));
        var stop = false;

        var evictor = Task.Run(() =>
        {
            while (!Volatile.Read(ref stop))
            {
                clock.Advance(TimeSpan.FromSeconds(2));
                factory.EvictIdle();
            }
        });
        var getters = Enumerable.Range(0, 4).Select(_ => Task.Run(() =>
        {
            for (var i = 0; i < 20_000; i++)
            {
                Assert.NotNull(factory.GetOrCreate("site-a", "http://a:5100"));
                factory.TryGet("site-a", "http://a:5100");
            }
        })).ToArray();

        await Task.WhenAll(getters);
        Volatile.Write(ref stop, true);
        await evictor;

        Assert.True(factory.Created >= 1);
    }

    /// <summary>The validator rejects a negative idle TTL and accepts zero.</summary>
    [Fact]
    public void Validator_RejectsNegativeIdleTtl()
    {
        var validator = new CommunicationOptionsValidator();
        var bad = validator.Validate(null, new CommunicationOptions { GrpcClientIdleTtl = TimeSpan.FromSeconds(-1) });
        var zero = validator.Validate(null, new CommunicationOptions { GrpcClientIdleTtl = TimeSpan.Zero });

        Assert.True(bad.Failed);
        Assert.Contains("GrpcClientIdleTtl", string.Join(" ", bad.Failures!));
        Assert.DoesNotContain("GrpcClientIdleTtl", string.Join(" ", zero.Failures ?? []));
    }
}