using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Channels;
using System.Threading.Tasks;
using FluentAssertions;
using Xunit;
using ZB.MOM.WW.LmxProxy.Host.Domain;
using ZB.MOM.WW.LmxProxy.Host.Subscriptions;

namespace ZB.MOM.WW.LmxProxy.Host.Tests.Subscriptions
{
    public class SubscriptionManagerTests
    {
        /// <summary>Fake IScadaClient for testing (no COM dependency).</summary>
        private class FakeScadaClient : IScadaClient
        {
            public bool IsConnected => true;
            public ConnectionState ConnectionState => ConnectionState.Connected;
            public event EventHandler<ConnectionStateChangedEventArgs>? ConnectionStateChanged;
            public Task ConnectAsync(CancellationToken ct = default) => Task.CompletedTask;
            public Task DisconnectAsync(CancellationToken ct = default) => Task.CompletedTask;
            public Task<Vtq> ReadAsync(string address, CancellationToken ct = default) =>
                Task.FromResult(Vtq.Good(42.0));
            public Task<IReadOnlyDictionary<string, Vtq>> ReadBatchAsync(IEnumerable<string> addresses, CancellationToken ct = default) =>
                Task.FromResult<IReadOnlyDictionary<string, Vtq>>(new Dictionary<string, Vtq>());
            public Task WriteAsync(string address, object value, CancellationToken ct = default) => Task.CompletedTask;
            public Task WriteBatchAsync(IReadOnlyDictionary<string, object> values, CancellationToken ct = default) => Task.CompletedTask;
            public Task<(bool flagReached, int elapsedMs)> WriteBatchAndWaitAsync(
                IReadOnlyDictionary<string, object> values, string flagTag, object flagValue,
                int timeoutMs, int pollIntervalMs, CancellationToken ct = default) =>
                Task.FromResult((false, 0));
            public Task<IAsyncDisposable> SubscribeAsync(IEnumerable<string> addresses, Action<string, Vtq> callback, CancellationToken ct = default) =>
                Task.FromResult<IAsyncDisposable>(new FakeSubscriptionHandle());
            public ValueTask DisposeAsync() => default;

            // Suppress unused event warning
            internal void FireEvent() => ConnectionStateChanged?.Invoke(this, null!);

            private class FakeSubscriptionHandle : IAsyncDisposable
            {
                public ValueTask DisposeAsync() => default;
            }
        }

        [Fact]
        public void Subscribe_ReturnsChannelReader()
        {
            using var sm = new SubscriptionManager(new FakeScadaClient());
            using var cts = new CancellationTokenSource();
            var reader = sm.Subscribe("client1", new[] { "Tag1", "Tag2" }, cts.Token);
            reader.Should().NotBeNull();
        }

        [Fact]
        public async Task OnTagValueChanged_FansOutToSubscribedClients()
        {
            using var sm = new SubscriptionManager(new FakeScadaClient());
            using var cts = new CancellationTokenSource();
            var reader = sm.Subscribe("client1", new[] { "Motor.Speed" }, cts.Token);

            var vtq = Vtq.Good(42.0);
            sm.OnTagValueChanged("Motor.Speed", vtq);

            var result = await reader.ReadAsync(cts.Token);
            result.address.Should().Be("Motor.Speed");
            result.vtq.Value.Should().Be(42.0);
            result.vtq.Quality.Should().Be(Quality.Good);
        }

        [Fact]
        public async Task OnTagValueChanged_MultipleClients_BothReceive()
        {
            using var sm = new SubscriptionManager(new FakeScadaClient());
            using var cts = new CancellationTokenSource();
            var reader1 = sm.Subscribe("client1", new[] { "Motor.Speed" }, cts.Token);
            var reader2 = sm.Subscribe("client2", new[] { "Motor.Speed" }, cts.Token);

            sm.OnTagValueChanged("Motor.Speed", Vtq.Good(99.0));

            var r1 = await reader1.ReadAsync(cts.Token);
            var r2 = await reader2.ReadAsync(cts.Token);
            r1.vtq.Value.Should().Be(99.0);
            r2.vtq.Value.Should().Be(99.0);
        }

        [Fact]
        public void OnTagValueChanged_NonSubscribedTag_NoDelivery()
        {
            using var sm = new SubscriptionManager(new FakeScadaClient());
            using var cts = new CancellationTokenSource();
            var reader = sm.Subscribe("client1", new[] { "Motor.Speed" }, cts.Token);

            sm.OnTagValueChanged("Motor.Torque", Vtq.Good(10.0));

            // Channel should be empty
            reader.TryRead(out _).Should().BeFalse();
        }

        [Fact]
        public void UnsubscribeClient_CompletesChannel()
        {
            using var sm = new SubscriptionManager(new FakeScadaClient());
            using var cts = new CancellationTokenSource();
            var reader = sm.Subscribe("client1", new[] { "Motor.Speed" }, cts.Token);

            sm.UnsubscribeClient("client1");

            // Channel should be completed
            reader.Completion.IsCompleted.Should().BeTrue();
        }

        [Fact]
        public void UnsubscribeClient_RemovesFromTagSubscriptions()
        {
            using var sm = new SubscriptionManager(new FakeScadaClient());
            using var cts = new CancellationTokenSource();
            sm.Subscribe("client1", new[] { "Motor.Speed" }, cts.Token);

            sm.UnsubscribeClient("client1");

            var stats = sm.GetStats();
            stats.TotalClients.Should().Be(0);
            stats.TotalTags.Should().Be(0);
        }

        [Fact]
        public void RefCounting_LastClientUnsubscribeRemovesTag()
        {
            using var sm = new SubscriptionManager(new FakeScadaClient());
            using var cts = new CancellationTokenSource();
            sm.Subscribe("client1", new[] { "Motor.Speed" }, cts.Token);
            sm.Subscribe("client2", new[] { "Motor.Speed" }, cts.Token);

            sm.GetStats().TotalTags.Should().Be(1);

            sm.UnsubscribeClient("client1");
            sm.GetStats().TotalTags.Should().Be(1); // client2 still subscribed

            sm.UnsubscribeClient("client2");
            sm.GetStats().TotalTags.Should().Be(0); // last client gone
        }

        [Fact]
        public void NotifyDisconnection_SendsBadQualityToAll()
        {
            using var sm = new SubscriptionManager(new FakeScadaClient());
            using var cts = new CancellationTokenSource();
            var reader = sm.Subscribe("client1", new[] { "Motor.Speed", "Motor.Torque" }, cts.Token);

            sm.NotifyDisconnection();

            // Should receive 2 bad quality messages
            reader.TryRead(out var r1).Should().BeTrue();
            r1.vtq.Quality.Should().Be(Quality.Bad_NotConnected);
            reader.TryRead(out var r2).Should().BeTrue();
            r2.vtq.Quality.Should().Be(Quality.Bad_NotConnected);
        }

        [Fact]
        public void Backpressure_DropOldest_DropsWhenFull()
        {
            using var sm = new SubscriptionManager(new FakeScadaClient(), channelCapacity: 3);
            using var cts = new CancellationTokenSource();
            var reader = sm.Subscribe("client1", new[] { "Motor.Speed" }, cts.Token);

            // Fill the channel beyond capacity
            for (int i = 0; i < 10; i++)
            {
                sm.OnTagValueChanged("Motor.Speed", Vtq.Good((double)i));
            }

            // Should have exactly 3 messages (capacity limit)
            int count = 0;
            while (reader.TryRead(out _)) count++;
            count.Should().Be(3);
        }

        [Fact]
        public void GetStats_ReturnsCorrectCounts()
        {
            using var sm = new SubscriptionManager(new FakeScadaClient());
            using var cts = new CancellationTokenSource();
            sm.Subscribe("c1", new[] { "Tag1", "Tag2" }, cts.Token);
            sm.Subscribe("c2", new[] { "Tag2", "Tag3" }, cts.Token);

            var stats = sm.GetStats();
            stats.TotalClients.Should().Be(2);
            stats.TotalTags.Should().Be(3); // Tag1, Tag2, Tag3
            stats.ActiveSubscriptions.Should().Be(4); // c1:Tag1, c1:Tag2, c2:Tag2, c2:Tag3
        }
    }
}