namespace ZB.MOM.WW.OtOpcUa.Commons.OpcUa;

/// <summary>
/// Late-binding adapter that accepts and retains the latest requested ServiceLevel until
/// the SDK publisher is available. Binding synchronously replays that request, including zero.
/// </summary>
/// <remarks>
/// Publishing and binding are serialized through the synchronous inner call. Inner publishers
/// must not call back into this adapter. Acceptance while unbound is not an SDK write confirmation.
/// A failed call retains both the requested level and the installed publisher for later recovery.
/// </remarks>
public sealed class DeferredServiceLevelPublisher : IServiceLevelPublisher
{
    private readonly object _gate = new();
    private IServiceLevelPublisher? _inner;
    private byte? _latest;

    /// <summary>Bind and replay the latest request, or unbind while retaining that request.</summary>
    /// <param name="inner">The publisher implementation to use, or null to unbind.</param>
    public void SetInner(IServiceLevelPublisher? inner)
    {
        lock (_gate)
        {
            _inner = inner;
            if (_latest is { } latest) _inner?.Publish(latest);
        }
    }

    /// <inheritdoc />
    public void Publish(byte serviceLevel)
    {
        lock (_gate)
        {
            _latest = serviceLevel;
            _inner?.Publish(serviceLevel);
        }
    }
}