namespace ZB.MOM.WW.OtOpcUa.AdminUI.Hubs;

/// <summary>
///     Raises a multicast delegate one subscriber at a time, so a subscriber that throws cannot stop
///     delivery to the subscribers after it. The in-process stores and broadcasters raise their events on
///     the bridge actor's thread; a plain <c>handler?.Invoke(x)</c> stops at the first throwing handler (for
///     example a Blazor circuit whose renderer is mid-teardown), so the remaining panels miss the update and
///     the exception escapes into the bridge actor, which restarts it.
/// </summary>
internal static class SafeMulticast
{
    /// <summary>Invokes every subscriber of <paramref name="handler"/> with <paramref name="arg"/>, isolating failures.</summary>
    /// <typeparam name="T">The event payload type.</typeparam>
    /// <param name="handler">The captured multicast delegate; null means no subscribers.</param>
    /// <param name="arg">The payload passed to each subscriber.</param>
    /// <param name="onError">Optional sink for a subscriber's exception; it must not throw.</param>
    /// <returns>The number of subscribers that threw.</returns>
    public static int Invoke<T>(Action<T>? handler, T arg, Action<Exception>? onError = null)
    {
        if (handler is null) return 0;

        var failures = 0;
        foreach (var subscriber in handler.GetInvocationList())
        {
            try
            {
                ((Action<T>)subscriber)(arg);
            }
            catch (Exception ex)
            {
                failures++;
                try { onError?.Invoke(ex); }
                catch { /* the error sink must never take delivery down with it */ }
            }
        }

        return failures;
    }
}