Add a crew monitoring server (#7542)

Content.Server/DeviceNetwork/Systems/StationLimitedNetworkSystem.cs

@@ -0,0 +1,68 @@
+using Content.Server.DeviceNetwork.Components;
+using Content.Server.Station.Systems;
+using JetBrains.Annotations;
+using Robust.Shared.Map;
+
+namespace Content.Server.DeviceNetwork.Systems
+{
+    /// <summary>
+    /// This system requires the StationLimitedNetworkComponent to be on the the sending entity as well as the receiving entity
+    /// </summary>
+    [UsedImplicitly]
+    public sealed class StationLimitedNetworkSystem : EntitySystem
+    {
+        [Dependency] private readonly StationSystem _stationSystem = default!;
+        public override void Initialize()
+        {
+            base.Initialize();
+            SubscribeLocalEvent<StationLimitedNetworkComponent, MapInitEvent>(OnMapInit);
+            SubscribeLocalEvent<StationLimitedNetworkComponent, BeforePacketSentEvent>(OnBeforePacketSent);
+        }
+
+        /// <summary>
+        /// Sets the station id the device is limited to.
+        /// </summary>
+        public void SetStation(EntityUid uid, EntityUid? stationId, StationLimitedNetworkComponent? component = null)
+        {
+            if (!Resolve(uid, ref component))
+                return;
+
+            component.StationId = stationId;
+        }
+
+        /// <summary>
+        /// Set the station id to the one the entity is on when the station limited component is added
+        /// </summary>
+        private void OnMapInit(EntityUid uid, StationLimitedNetworkComponent networkComponent, MapInitEvent args)
+        {
+            networkComponent.StationId = _stationSystem.GetOwningStation(uid);
+        }
+
+        /// <summary>
+        /// Checks if both devices are limited to the same station
+        /// </summary>
+        private void OnBeforePacketSent(EntityUid uid, StationLimitedNetworkComponent component, BeforePacketSentEvent args)
+        {
+            if (!CheckStationId(args.Sender, component.AllowNonStationPackets, component.StationId))
+            {
+                args.Cancel();
+            }
+        }
+
+        /// <summary>
+        /// Compares the station IDs of the sending and receiving network components.
+        /// Returns false if either of them doesn't have a station ID or if their station ID isn't equal.
+        /// Returns true even when the sending entity isn't tied to a station if `allowNonStationPackets` is set to true.
+        /// </summary>
+        private bool CheckStationId(EntityUid senderUid, bool allowNonStationPackets, EntityUid? receiverStationId, StationLimitedNetworkComponent? sender = null)
+        {
+            if (!receiverStationId.HasValue)
+                return false;
+
+            if (!Resolve(senderUid, ref sender, false))
+                return allowNonStationPackets;
+
+            return sender.StationId == receiverStationId;
+        }
+    }
+}