RobustToolbox/Robust.Server/GameObjects/EntitySystems/ViewSubscriberSystem.cs

using Robust.Shared.GameObjects;
using Robust.Shared.Player;

namespace Robust.Server.GameObjects
{
    /// <summary>
    ///     Entity System that handles subscribing and unsubscribing to PVS views.
    /// </summary>
    public sealed class ViewSubscriberSystem : EntitySystem
    {
        public override void Initialize()
        {
            base.Initialize();

            SubscribeLocalEvent<ViewSubscriberComponent, ComponentShutdown>(OnViewSubscriberShutdown);
        }

        /// <summary>
        ///     Subscribes the session to get PVS updates from the point of view of the specified entity.
        /// </summary>
        public void AddViewSubscriber(EntityUid uid, ICommonSession session)
        {
            // If the entity doesn't have the component, it will be added.
            var viewSubscriber = EntityManager.EnsureComponent<ViewSubscriberComponent>(uid);

            if (viewSubscriber.SubscribedSessions.Contains(session))
                return; // Already subscribed, do nothing else.

            viewSubscriber.SubscribedSessions.Add(session);
            session.ViewSubscriptions.Add(uid);

            RaiseLocalEvent(uid, new ViewSubscriberAddedEvent(uid, session), true);
        }

        /// <summary>
        ///     Unsubscribes the session from getting PVS updates from the point of view of the specified entity.
        /// </summary>
        public void RemoveViewSubscriber(EntityUid uid, ICommonSession session)
        {
            if(!EntityManager.TryGetComponent(uid, out ViewSubscriberComponent? viewSubscriber))
                return; // Entity didn't have any subscriptions, do nothing.

            if (!viewSubscriber.SubscribedSessions.Remove(session))
                return; // Session wasn't subscribed, do nothing.

            session.ViewSubscriptions.Remove(uid);
            RaiseLocalEvent(uid, new ViewSubscriberRemovedEvent(uid, session), true);
        }

        private void OnViewSubscriberShutdown(EntityUid uid, ViewSubscriberComponent component, ComponentShutdown _)
        {
            foreach (var session in component.SubscribedSessions)
            {
                session.ViewSubscriptions.Remove(uid);
            }
        }
    }

    /// <summary>
    ///     Raised when a session subscribes to an entity's PVS view.
    /// </summary>
    public sealed class ViewSubscriberAddedEvent : EntityEventArgs
    {
        public EntityUid View { get; }
        public ICommonSession Subscriber { get; }

        public ViewSubscriberAddedEvent(EntityUid view, ICommonSession subscriber)
        {
            View = view;
            Subscriber = subscriber;
        }
    }

    /// <summary>
    ///     Raised when a session is unsubscribed from an entity's PVS view.
    ///     Not raised when sessions are unsubscribed due to the component being removed.
    /// </summary>
    public sealed class ViewSubscriberRemovedEvent : EntityEventArgs
    {
        public EntityUid View { get; }
        public ICommonSession Subscriber { get; }

        public ViewSubscriberRemovedEvent(EntityUid view, ICommonSession subscriber)
        {
            View = view;
            Subscriber = subscriber;
        }
    }
}