ScadaBridge/tests/ZB.MOM.WW.ScadaBridge.DataConnectionLayer.Tests/Adapters/FakeMxGatewayClient.cs

using ZB.MOM.WW.ScadaBridge.DataConnectionLayer.Adapters;

namespace ZB.MOM.WW.ScadaBridge.DataConnectionLayer.Tests.Adapters;

/// <summary>
/// In-memory fake <see cref="IMxGatewayClient"/> for adapter unit tests. Lets tests
/// drive the event loop (push updates / fault the stream) and stub read/write/browse.
/// </summary>
public sealed class FakeMxGatewayClient : IMxGatewayClient, IMxGatewayClientFactory
{
    public MxGatewayConnectionOptions? ConnectedWith;
    public readonly List<string> Subscribed = new();
    public readonly List<string> Unsubscribed = new();
    public readonly TaskCompletionSource EventLoopGate = new(TaskCreationOptions.RunContinuationsAsynchronously);
    public Action<MxValueUpdate>? OnUpdate;
    public Func<IReadOnlyList<string>, IReadOnlyList<MxReadOutcome>>? ReadHandler;
    public Func<IReadOnlyList<(string TagPath, object? Value)>, IReadOnlyList<MxWriteOutcome>>? WriteHandler;
    public Func<string?, (IReadOnlyList<MxBrowseChild>, bool)>? BrowseHandler;
    private int _nextHandle;

    public IMxGatewayClient Create() => this;

    public Task ConnectAsync(MxGatewayConnectionOptions o, CancellationToken ct = default)
    {
        ConnectedWith = o;
        return Task.CompletedTask;
    }

    public Task DisconnectAsync(CancellationToken ct = default) => Task.CompletedTask;

    public Task<string> SubscribeAsync(string tag, CancellationToken ct = default)
    {
        var id = (++_nextHandle).ToString();
        Subscribed.Add(tag);
        return Task.FromResult(id);
    }

    public Task UnsubscribeAsync(string id, CancellationToken ct = default)
    {
        Unsubscribed.Add(id);
        return Task.CompletedTask;
    }

    public Task<IReadOnlyList<MxReadOutcome>> ReadAsync(IReadOnlyList<string> tags, CancellationToken ct = default)
        => Task.FromResult(ReadHandler!(tags));

    public Task<IReadOnlyList<MxWriteOutcome>> WriteAsync(IReadOnlyList<(string TagPath, object? Value)> w, CancellationToken ct = default)
        => Task.FromResult(WriteHandler!(w));

    public Task<(IReadOnlyList<MxBrowseChild> Children, bool Truncated)> BrowseChildrenAsync(string? p, CancellationToken ct = default)
        => Task.FromResult(BrowseHandler!(p));

    public async Task RunEventLoopAsync(Action<MxValueUpdate> onUpdate, CancellationToken ct = default)
    {
        OnUpdate = onUpdate;
        using var reg = ct.Register(() => EventLoopGate.TrySetResult());
        await EventLoopGate.Task;          // test completes this to end the loop…
        ct.ThrowIfCancellationRequested(); // …or FaultEventLoop() faults it to simulate a stream break
    }

    public ValueTask DisposeAsync() => ValueTask.CompletedTask;

    /// <summary>Simulate a stream break so the adapter raises Disconnected.</summary>
    public void FaultEventLoop() => EventLoopGate.TrySetException(new Exception("stream broke"));
}