acdream/src/AcDream.Core/Plugins/WorldEvents.cs

// src/AcDream.Core/Plugins/WorldEvents.cs
using AcDream.Plugin.Abstractions;

namespace AcDream.Core.Plugins;

public sealed class WorldEvents : IEvents
{
    private readonly object _lock = new();
    private readonly List<WorldEntitySnapshot> _alreadySpawned = new();
    private Action<WorldEntitySnapshot>? _subscribers;

    /// <summary>
    /// Called by the host as each entity is hydrated into the world. Records the
    /// snapshot for later replay and dispatches to current subscribers.
    /// </summary>
    public void FireEntitySpawned(WorldEntitySnapshot snapshot)
    {
        Action<WorldEntitySnapshot>? toNotify;
        lock (_lock)
        {
            _alreadySpawned.Add(snapshot);
            toNotify = _subscribers;
        }

        if (toNotify is null) return;
        foreach (Action<WorldEntitySnapshot> handler in toNotify.GetInvocationList())
        {
            try { handler(snapshot); }
            catch { /* plugin errors don't propagate out of event dispatch */ }
        }
    }

    public event Action<WorldEntitySnapshot> EntitySpawned
    {
        add
        {
            WorldEntitySnapshot[] replay;
            lock (_lock)
            {
                _subscribers += value;
                replay = _alreadySpawned.ToArray();
            }
            // Replay outside the lock to avoid deadlock if a handler re-enters.
            foreach (var s in replay)
            {
                try { value(s); }
                catch { /* plugin errors don't propagate out of += */ }
            }
        }
        remove
        {
            lock (_lock)
                _subscribers -= value;
        }
    }
}