using System.Threading.Channels;
using Google.Protobuf.WellKnownTypes;
using ZB.MOM.WW.MxGateway.Contracts.Proto;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Config;
using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Runtime;

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

/// <summary>
///     End-to-end tests for <see cref="GalaxyDriver"/>'s ISubscribable wiring +
///     <see cref="EventPump"/>. The fake subscriber replays a controlled stream of
///     <see cref="MxEvent"/>s; the test asserts the driver's <c>OnDataChange</c> fans
///     out per registered subscription.
/// </summary>
public sealed class GalaxyDriverSubscribeTests
{
    private static GalaxyDriverOptions Opts() => new(
        new GalaxyGatewayOptions("https://mxgw.test:5001", "key"),
        new GalaxyMxAccessOptions("OtOpcUa-A"),
        new GalaxyRepositoryOptions(),
        new GalaxyReconnectOptions());

    internal sealed class FakeSubscriber : IGalaxySubscriber
    {
        private int _nextHandle = 1;
        private readonly Channel<MxEvent> _events = Channel.CreateUnbounded<MxEvent>();

        /// <summary>Gets the mapping of tag references to subscription handles.</summary>
        public Dictionary<string, int> Map { get; } = new();

        /// <summary>Gets the list of unsubscribed handles.</summary>
        public List<int> UnsubscribedHandles { get; } = [];

        /// <summary>Gets the list of buffered intervals called.</summary>
        public List<int> BufferedIntervalsCalled { get; } = [];

        /// <summary>Gets or sets a function to decide whether to accept a subscription.</summary>
        public Func<string, bool> Decide { get; set; } = _ => true;

        /// <summary>Subscribes to bulk updates for the specified tag references.</summary>
        /// <param name="fullReferences">The tag references to subscribe to.</param>
        /// <param name="bufferedUpdateIntervalMs">The buffered update interval in milliseconds.</param>
        /// <param name="cancellationToken">Cancellation token for the operation.</param>
        /// <returns>A list of subscription results.</returns>
        public Task<IReadOnlyList<SubscribeResult>> SubscribeBulkAsync(
            IReadOnlyList<string> fullReferences, int bufferedUpdateIntervalMs, CancellationToken cancellationToken)
        {
            BufferedIntervalsCalled.Add(bufferedUpdateIntervalMs);
            var results = new List<SubscribeResult>(fullReferences.Count);
            foreach (var fullRef in fullReferences)
            {
                if (Decide(fullRef))
                {
                    var handle = Interlocked.Increment(ref _nextHandle);
                    Map[fullRef] = handle;
                    results.Add(new SubscribeResult
                    {
                        TagAddress = fullRef,
                        ItemHandle = handle,
                        WasSuccessful = true,
                    });
                }
                else
                {
                    results.Add(new SubscribeResult
                    {
                        TagAddress = fullRef,
                        ItemHandle = 0,
                        WasSuccessful = false,
                        ErrorMessage = "rejected by fake",
                    });
                }
            }
            return Task.FromResult<IReadOnlyList<SubscribeResult>>(results);
        }

        /// <summary>Unsubscribes from bulk updates for the specified item handles.</summary>
        /// <param name="itemHandles">The handles to unsubscribe.</param>
        /// <param name="cancellationToken">Cancellation token for the operation.</param>
        /// <returns>A completed task.</returns>
        public Task UnsubscribeBulkAsync(IReadOnlyList<int> itemHandles, CancellationToken cancellationToken)
        {
            UnsubscribedHandles.AddRange(itemHandles);
            return Task.CompletedTask;
        }

        /// <summary>Streams events asynchronously.</summary>
        /// <param name="cancellationToken">Cancellation token for the operation.</param>
        /// <returns>An async enumerable of MX events.</returns>
        public IAsyncEnumerable<MxEvent> StreamEventsAsync(CancellationToken cancellationToken)
            => _events.Reader.ReadAllAsync(cancellationToken);

        /// <summary>Emits a data change event asynchronously.</summary>
        /// <param name="itemHandle">The handle of the item that changed.</param>
        /// <param name="value">The new value.</param>
        /// <param name="quality">The quality of the value.</param>
        /// <returns>A value task representing the asynchronous emission.</returns>
        public ValueTask EmitOnDataChangeAsync(int itemHandle, double value, byte quality = 192) =>
            _events.Writer.WriteAsync(new MxEvent
            {
                Family = MxEventFamily.OnDataChange,
                ItemHandle = itemHandle,
                Value = new MxValue { DoubleValue = value },
                Quality = quality,
                SourceTimestamp = Timestamp.FromDateTime(DateTime.UtcNow),
            });

        /// <summary>Completes the event stream.</summary>
        public void CompleteEvents() => _events.Writer.Complete();
    }

    /// <summary>Verifies subscription allocates a handle and dispatches value changes.</summary>
    [Fact]
    public async Task SubscribeAsync_AllocatesHandle_AndDispatchesValueChange()
    {
        var subscriber = new FakeSubscriber();
        using var driver = new GalaxyDriver(
            "g", Opts(), hierarchySource: null, dataReader: null, dataWriter: null, subscriber: subscriber);

        var captured = new List<DataChangeEventArgs>();
        driver.OnDataChange += (_, args) => captured.Add(args);

        var handle = await driver.SubscribeAsync(["Tank.Level"], TimeSpan.FromSeconds(1), CancellationToken.None);

        var itemHandle = subscriber.Map["Tank.Level"];
        await subscriber.EmitOnDataChangeAsync(itemHandle, 42.0);

        await WaitForAsync(() => captured.Count >= 1);
        captured.Count.ShouldBe(1);
        captured[0].SubscriptionHandle.ShouldBe(handle);
        captured[0].FullReference.ShouldBe("Tank.Level");
        ((double)captured[0].Snapshot.Value!).ShouldBe(42.0);
    }

    /// <summary>Verifies two subscriptions for the same tag each receive updates.</summary>
    [Fact]
    public async Task SubscribeAsync_TwoSubscriptions_SameTag_FanOutOnePerSubscription()
    {
        var subscriber = new FakeSubscriber();
        using var driver = new GalaxyDriver(
            "g", Opts(), hierarchySource: null, dataReader: null, dataWriter: null, subscriber: subscriber);

        var captured = new List<DataChangeEventArgs>();
        driver.OnDataChange += (_, args) => captured.Add(args);

        var handle1 = await driver.SubscribeAsync(["A"], TimeSpan.FromSeconds(1), CancellationToken.None);
        var handle2 = await driver.SubscribeAsync(["A"], TimeSpan.FromSeconds(1), CancellationToken.None);

        // Both subscriptions resolved the same FullRef. The fake gives each its own
        // itemHandle (Map["A"] gets overwritten), so we use the latest mapping for the
        // second subscription's expected delivery; the first subscription's binding
        // points at an item handle the gateway fake hasn't emitted on. To exercise the
        // fan-out, register both subs against the SAME handle (matches the gw's "one
        // handle per (server, tag) pair" pattern in production where SubscribeBulk
        // returns the existing handle for an already-AddItem'd tag).
        subscriber.Map["A"].ShouldBeGreaterThan(0);
        // Synthesize an event against handle 2 (which is also tracked under sub 2).
        // Fan-out for the same tag is best validated at the registry level — the
        // SubscriptionRegistryTests cover the multi-sub-same-handle case directly.
        await subscriber.EmitOnDataChangeAsync(subscriber.Map["A"], 7.0);

        await WaitForAsync(() => captured.Count >= 1);

        // At least one delivery — depending on which subscription owns the handle,
        // either handle1 or handle2 receives. The fan-out invariant (a single handle
        // delivers to every subscription that registered it) is pinned in
        // SubscriptionRegistryTests; here we just confirm the wiring works.
        captured.ShouldNotBeEmpty();
        captured[0].SubscriptionHandle.DiagnosticId.ShouldStartWith("galaxy-sub-");
        // Either handle1 or handle2 must match the captured handle's id.
        var captured0Id = ((GalaxySubscriptionHandle)captured[0].SubscriptionHandle).SubscriptionId;
        var allowed = new[] {
            ((GalaxySubscriptionHandle)handle1).SubscriptionId,
            ((GalaxySubscriptionHandle)handle2).SubscriptionId,
        };
        allowed.ShouldContain(captured0Id);
    }

    /// <summary>Verifies failed subscriptions do not dispatch events.</summary>
    [Fact]
    public async Task SubscribeAsync_FailedTag_DoesNotDispatchEvents()
    {
        var subscriber = new FakeSubscriber { Decide = tag => tag != "Bad" };
        using var driver = new GalaxyDriver(
            "g", Opts(), hierarchySource: null, dataReader: null, dataWriter: null, subscriber: subscriber);

        var captured = new List<DataChangeEventArgs>();
        driver.OnDataChange += (_, args) => captured.Add(args);

        await driver.SubscribeAsync(["Good", "Bad"], TimeSpan.FromSeconds(1), CancellationToken.None);

        // Good has an itemHandle; Bad doesn't (item handle 0). An event with handle 0
        // must NOT be dispatched (no subscribers registered against it).
        await subscriber.EmitOnDataChangeAsync(itemHandle: 0, value: 999.0);
        await Task.Delay(50); // give the pump a chance

        captured.ShouldBeEmpty();
    }

    /// <summary>Verifies unsubscribe removes registration and calls gateway unsubscribe.</summary>
    [Fact]
    public async Task UnsubscribeAsync_RemovesRegistration_AndCallsGwUnsubscribe()
    {
        var subscriber = new FakeSubscriber();
        using var driver = new GalaxyDriver(
            "g", Opts(), hierarchySource: null, dataReader: null, dataWriter: null, subscriber: subscriber);

        var handle = await driver.SubscribeAsync(["X"], TimeSpan.FromSeconds(1), CancellationToken.None);
        var itemHandle = subscriber.Map["X"];

        await driver.UnsubscribeAsync(handle, CancellationToken.None);

        subscriber.UnsubscribedHandles.ShouldContain(itemHandle);

        // Subsequent events for the dropped handle don't dispatch.
        var captured = new List<DataChangeEventArgs>();
        driver.OnDataChange += (_, args) => captured.Add(args);
        await subscriber.EmitOnDataChangeAsync(itemHandle, 11.0);
        await Task.Delay(50);
        captured.ShouldBeEmpty();
    }

    /// <summary>Verifies unsubscribing with an unknown handle is handled.</summary>
    [Fact]
    public async Task UnsubscribeAsync_UnknownHandle_NoOp()
    {
        var subscriber = new FakeSubscriber();
        using var driver = new GalaxyDriver(
            "g", Opts(), hierarchySource: null, dataReader: null, dataWriter: null, subscriber: subscriber);

        // Handle issued by a different driver shape — must throw (it's a programming
        // error, not a recoverable runtime condition).
        var foreignHandle = new ForeignHandle();
        await Should.ThrowAsync<ArgumentException>(() =>
            driver.UnsubscribeAsync(foreignHandle, CancellationToken.None));
    }

    /// <summary>Verifies subscription without a subscriber throws.</summary>
    [Fact]
    public async Task SubscribeAsync_NoSubscriber_Throws()
    {
        using var driver = new GalaxyDriver("g", Opts());
        var ex = await Should.ThrowAsync<NotSupportedException>(() =>
            driver.SubscribeAsync(["x"], TimeSpan.FromSeconds(1), CancellationToken.None));
        ex.Message.ShouldContain("GalaxyDriver.SubscribeAsync requires");
    }

    /// <summary>Verifies subscription falls back to configured interval when zero is passed.</summary>
    [Fact]
    public async Task SubscribeAsync_FallsBackToConfiguredInterval_WhenCallerPassesZero()
    {
        // PR 6.3 — when the caller doesn't set a publishing interval (TimeSpan.Zero),
        // the driver substitutes MxAccess.PublishingIntervalMs from its options.
        var subscriber = new FakeSubscriber();
        var opts = new GalaxyDriverOptions(
            new GalaxyGatewayOptions("https://mxgw.test:5001", "key"),
            new GalaxyMxAccessOptions("OtOpcUa-A", PublishingIntervalMs: 750),
            new GalaxyRepositoryOptions(),
            new GalaxyReconnectOptions());
        using var driver = new GalaxyDriver(
            "g", opts, hierarchySource: null, dataReader: null, dataWriter: null, subscriber: subscriber);

        await driver.SubscribeAsync(["Tag.A"], TimeSpan.Zero, CancellationToken.None);

        subscriber.BufferedIntervalsCalled.ShouldHaveSingleItem().ShouldBe(750);
    }

    /// <summary>Verifies subscription respects caller's interval when non-zero.</summary>
    [Fact]
    public async Task SubscribeAsync_RespectsCallerInterval_WhenNonZero()
    {
        // The caller's publishingInterval wins when explicitly set — the configured
        // option only applies as a fallback for "no-preference" callers.
        var subscriber = new FakeSubscriber();
        var opts = new GalaxyDriverOptions(
            new GalaxyGatewayOptions("https://mxgw.test:5001", "key"),
            new GalaxyMxAccessOptions("OtOpcUa-A", PublishingIntervalMs: 750),
            new GalaxyRepositoryOptions(),
            new GalaxyReconnectOptions());
        using var driver = new GalaxyDriver(
            "g", opts, hierarchySource: null, dataReader: null, dataWriter: null, subscriber: subscriber);

        await driver.SubscribeAsync(["Tag.A"], TimeSpan.FromMilliseconds(250), CancellationToken.None);

        subscriber.BufferedIntervalsCalled.ShouldHaveSingleItem().ShouldBe(250);
    }

    /// <summary>Verifies subscription with empty tag list returns handle without calling gateway.</summary>
    [Fact]
    public async Task SubscribeAsync_EmptyTagList_ReturnsHandleWithoutCallingGw()
    {
        var subscriber = new FakeSubscriber();
        using var driver = new GalaxyDriver(
            "g", Opts(), hierarchySource: null, dataReader: null, dataWriter: null, subscriber: subscriber);

        var handle = await driver.SubscribeAsync([], TimeSpan.FromSeconds(1), CancellationToken.None);
        handle.ShouldNotBeNull();
        subscriber.Map.ShouldBeEmpty();
    }

    /// <summary>A subscription handle from a foreign source.</summary>
    private sealed class ForeignHandle : ISubscriptionHandle
    {
        /// <summary>Gets the diagnostic identifier for this handle.</summary>
        public string DiagnosticId => "foreign-x";
    }

    private static async Task WaitForAsync(Func<bool> predicate, int timeoutMs = 1000)
    {
        var deadline = DateTime.UtcNow.AddMilliseconds(timeoutMs);
        while (DateTime.UtcNow < deadline)
        {
            if (predicate()) return;
            await Task.Delay(10);
        }
        predicate().ShouldBeTrue("Predicate did not become true within timeout.");
    }
}