using Opc.Ua;

namespace ZB.MOM.WW.OtOpcUa.OpcUaServer.IntegrationTests;

/// <summary>
///     Stalls condition-event delivery at one of the node manager's notifiers (Gitea #855): every condition event whose walk
///     reaches that notifier suspends there until <see cref="Release"/>, without blocking the reporter or holding the node
///     manager's <c>Lock</c> — so the condition's later events are deferred, as they were behind a full SDK channel before
///     folder items were delivered per item.
/// </summary>
/// <remarks>
///     The pre-#855 tests produced deferral by holding a folder item's server-side <c>MonitoredItem</c> lock, which parked
///     the SDK's per-node delivery task. Folder items are now queued synchronously by the reporter (as Server-object items
///     always were), so holding an item lock would block the reporter instead; this goes through the node manager's test
///     probe (<see cref="OtOpcUaNodeManager.NotifierDeliveryStall"/>). The probe is consulted only at a notifier that has
///     event items (the hop the per-item delivery serves), so the stalled notifier must carry at least one.
/// </remarks>
internal sealed class NotifierStall : IDisposable
{
    private readonly OtOpcUaNodeManager _nm;
    private readonly TaskCompletionSource _released = new(TaskCreationOptions.RunContinuationsAsynchronously);
    private readonly Func<NodeState, Task?> _probe;

    private NotifierStall(OtOpcUaNodeManager nm, string notifierId)
    {
        _nm = nm;
        _probe = node => !_released.Task.IsCompleted && node.NodeId.IdentifierAsString == notifierId ? _released.Task : null;
        nm.NotifierDeliveryStall = _probe;
    }

    /// <summary>Starts stalling delivery at the notifier whose NodeId identifier is <paramref name="notifierId"/>.</summary>
    public static NotifierStall Hold(OtOpcUaNodeManager nm, string notifierId) => new(nm, notifierId);

    /// <summary>Lets every stalled walk continue (on pool threads, off <c>Lock</c>).</summary>
    public void Release() => _released.TrySetResult();

    public void Dispose()
    {
        Release();
        if (ReferenceEquals(_nm.NotifierDeliveryStall, _probe)) _nm.NotifierDeliveryStall = null;
    }
}