Make ghost component ECS (#4159)

* Make ghost component ECS

* Remove players and locations properties from ghost component

* Address reviews

* One more doc

* Fix client ghost component state method error

Content.Client/Ghost/GhostSystem.cs

@@ -0,0 +1,117 @@
+using Content.Client.HUD;
+using Content.Shared.Ghost;
+using JetBrains.Annotations;
+using Robust.Client.GameObjects;
+using Robust.Client.Player;
+using Robust.Shared.GameObjects;
+using Robust.Shared.IoC;
+
+namespace Content.Client.Ghost
+{
+    [UsedImplicitly]
+    public class GhostSystem : SharedGhostSystem
+    {
+        [Dependency] private readonly IPlayerManager _playerManager = default!;
+        [Dependency] private readonly IGameHud _gameHud = default!;
+
+        private bool _ghostVisibility;
+
+        private bool GhostVisibility
+        {
+            get => _ghostVisibility;
+            set
+            {
+                if (_ghostVisibility == value)
+                {
+                    return;
+                }
+
+                _ghostVisibility = value;
+
+                foreach (var ghost in ComponentManager.GetAllComponents(typeof(GhostComponent), true))
+                {
+                    if (ghost.Owner.TryGetComponent(out SpriteComponent? sprite))
+                    {
+                        sprite.Visible = value;
+                    }
+                }
+            }
+        }
+
+        public override void Initialize()
+        {
+            base.Initialize();
+
+            SubscribeLocalEvent<GhostComponent, ComponentInit>(OnGhostInit);
+            SubscribeLocalEvent<GhostComponent, ComponentRemove>(OnGhostRemove);
+
+            SubscribeLocalEvent<GhostComponent, PlayerAttachedEvent>(OnGhostPlayerAttach);
+            SubscribeLocalEvent<GhostComponent, PlayerDetachedEvent>(OnGhostPlayerDetach);
+
+            SubscribeNetworkEvent<GhostWarpsResponseEvent>(OnGhostWarpsResponse);
+        }
+
+        private void OnGhostInit(EntityUid uid, GhostComponent component, ComponentInit args)
+        {
+            if (component.Owner.TryGetComponent(out SpriteComponent? sprite))
+            {
+                sprite.Visible = GhostVisibility;
+            }
+        }
+
+        private void OnGhostRemove(EntityUid uid, GhostComponent component, ComponentRemove args)
+        {
+            component.Gui?.Dispose();
+
+            // PlayerDetachedMsg might not fire due to deletion order so...
+            if (component.IsAttached)
+            {
+                GhostVisibility = false;
+            }
+        }
+
+        private void OnGhostPlayerAttach(EntityUid uid, GhostComponent component, PlayerAttachedEvent playerAttachedEvent)
+        {
+            if (component.Gui == null)
+            {
+                component.Gui = new GhostGui(component, EntityManager.EntityNetManager!);
+                component.Gui.Update();
+            }
+            else
+            {
+                component.Gui.Orphan();
+            }
+
+            _gameHud.HandsContainer.AddChild(component.Gui);
+            GhostVisibility = true;
+            component.IsAttached = true;
+        }
+
+        private void OnGhostPlayerDetach(EntityUid uid, GhostComponent component, PlayerDetachedEvent args)
+        {
+            component.Gui?.Parent?.RemoveChild(component.Gui);
+            GhostVisibility = false;
+            component.IsAttached = false;
+        }
+
+        private void OnGhostWarpsResponse(GhostWarpsResponseEvent msg)
+        {
+            var entity = _playerManager.LocalPlayer?.ControlledEntity;
+
+            if (entity == null ||
+                !entity.TryGetComponent(out GhostComponent? ghost))
+            {
+                return;
+            }
+
+            var window = ghost.Gui?.TargetWindow;
+
+            if (window != null)
+            {
+                window.Locations = msg.Locations;
+                window.Players = msg.Players;
+                window.Populate();
+            }
+        }
+    }
+}