using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Runtime;

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

/// <summary>
///     Tests for <see cref="SubscriptionRegistry"/> — the bookkeeping the EventPump
///     uses to fan one OnDataChange event out to every driver subscription that
///     observes the changed item handle.
/// </summary>
public sealed class SubscriptionRegistryTests
{
    [Fact]
    public void NextSubscriptionId_IsMonotonic()
    {
        var registry = new SubscriptionRegistryAccess();
        registry.NextSubscriptionId().ShouldBe(1);
        registry.NextSubscriptionId().ShouldBe(2);
        registry.NextSubscriptionId().ShouldBe(3);
    }

    [Fact]
    public void Register_OneSubscription_OneTag_ResolvesSingleSubscriber()
    {
        var registry = new SubscriptionRegistryAccess();
        registry.Register(42, [new TagBindingAccess("Tank.Level", 100)]);

        var subs = registry.ResolveSubscribers(100);
        subs.Count.ShouldBe(1);
        subs[0].SubscriptionId.ShouldBe(42);
        subs[0].FullReference.ShouldBe("Tank.Level");
    }

    [Fact]
    public void Register_TwoSubscriptions_SameTag_FanOutToBoth()
    {
        var registry = new SubscriptionRegistryAccess();
        registry.Register(1, [new TagBindingAccess("Tank.Level", 100)]);
        registry.Register(2, [new TagBindingAccess("Tank.Level", 100)]);

        var subs = registry.ResolveSubscribers(100);
        subs.Count.ShouldBe(2);
        subs.Select(s => s.SubscriptionId).OrderBy(x => x).ShouldBe(new[] { 1L, 2L });
    }

    [Fact]
    public void Register_FailedItemHandle_NotIndexedForFanOut()
    {
        var registry = new SubscriptionRegistryAccess();
        registry.Register(1, [
            new TagBindingAccess("Good", 100),
            new TagBindingAccess("Bad", 0),  // gw rejected this tag
        ]);

        registry.ResolveSubscribers(100).Count.ShouldBe(1);
        registry.ResolveSubscribers(0).ShouldBeEmpty();
    }

    [Fact]
    public void Remove_DropsAllBindings_AndReturnsThemForUnsubscribe()
    {
        var registry = new SubscriptionRegistryAccess();
        registry.Register(1, [
            new TagBindingAccess("A", 100),
            new TagBindingAccess("B", 200),
        ]);

        var removed = registry.Remove(1);

        removed.ShouldNotBeNull();
        removed!.Count.ShouldBe(2);
        registry.ResolveSubscribers(100).ShouldBeEmpty();
        registry.ResolveSubscribers(200).ShouldBeEmpty();
    }

    [Fact]
    public void Remove_OneOfTwoSubscriptions_LeavesOtherIntact()
    {
        var registry = new SubscriptionRegistryAccess();
        registry.Register(1, [new TagBindingAccess("A", 100)]);
        registry.Register(2, [new TagBindingAccess("A", 100)]);

        registry.Remove(1);

        var subs = registry.ResolveSubscribers(100);
        subs.Count.ShouldBe(1);
        subs[0].SubscriptionId.ShouldBe(2);
    }

    [Fact]
    public void Remove_UnknownSubscription_IsNullSentinel()
    {
        var registry = new SubscriptionRegistryAccess();
        registry.Remove(999).ShouldBeNull();
    }

    [Fact]
    public void TrackedCounts_ReflectAdditionsAndRemovals()
    {
        var registry = new SubscriptionRegistryAccess();
        registry.TrackedSubscriptionCount.ShouldBe(0);

        registry.Register(1, [new TagBindingAccess("A", 100)]);
        registry.Register(2, [new TagBindingAccess("A", 100), new TagBindingAccess("B", 200)]);
        registry.TrackedSubscriptionCount.ShouldBe(2);
        registry.TrackedItemHandleCount.ShouldBe(2);

        registry.Remove(1);
        registry.TrackedSubscriptionCount.ShouldBe(1);
        registry.TrackedItemHandleCount.ShouldBe(2); // sub 2 still observes both handles

        registry.Remove(2);
        registry.TrackedSubscriptionCount.ShouldBe(0);
        registry.TrackedItemHandleCount.ShouldBe(0);
    }

    // Internal types are accessed via friend assembly (InternalsVisibleTo); these
    // wrapper aliases keep the test code readable.
    private sealed class SubscriptionRegistryAccess
    {
        private readonly SubscriptionRegistry _inner = new();
        public int TrackedSubscriptionCount => _inner.TrackedSubscriptionCount;
        public int TrackedItemHandleCount => _inner.TrackedItemHandleCount;
        public long NextSubscriptionId() => _inner.NextSubscriptionId();
        public void Register(long id, IReadOnlyList<TagBindingAccess> bindings)
            => _inner.Register(id, [.. bindings.Select(b => new TagBinding(b.FullReference, b.ItemHandle))]);
        public IReadOnlyList<TagBindingAccess>? Remove(long id)
        {
            var removed = _inner.Remove(id);
            return removed is null ? null : [.. removed.Select(b => new TagBindingAccess(b.FullReference, b.ItemHandle))];
        }
        public IReadOnlyList<(long SubscriptionId, string FullReference)> ResolveSubscribers(int handle)
            => _inner.ResolveSubscribers(handle);
    }
    private sealed record TagBindingAccess(string FullReference, int ItemHandle);
}