SlowContactsSystem to SpeedModifierContactsSystem mini rework (#26110)

* rework

* update logic

Content.Shared/Movement/Systems/SpeedModifierContactsSystem.cs

@@ -0,0 +1,126 @@
+using Content.Shared.Movement.Components;
+using Robust.Shared.Physics.Components;
+using Robust.Shared.Physics.Events;
+using Robust.Shared.Physics.Systems;
+
+namespace Content.Shared.Movement.Systems;
+
+public sealed class SpeedModifierContactsSystem : EntitySystem
+{
+    [Dependency] private readonly SharedPhysicsSystem _physics = default!;
+    [Dependency] private readonly MovementSpeedModifierSystem _speedModifierSystem = default!;
+
+    // TODO full-game-save
+    // Either these need to be processed before a map is saved, or slowed/slowing entities need to update on init.
+    private HashSet<EntityUid> _toUpdate = new();
+    private HashSet<EntityUid> _toRemove = new();
+
+    public override void Initialize()
+    {
+        base.Initialize();
+        SubscribeLocalEvent<SpeedModifierContactsComponent, StartCollideEvent>(OnEntityEnter);
+        SubscribeLocalEvent<SpeedModifierContactsComponent, EndCollideEvent>(OnEntityExit);
+        SubscribeLocalEvent<SpeedModifiedByContactComponent, RefreshMovementSpeedModifiersEvent>(MovementSpeedCheck);
+        SubscribeLocalEvent<SpeedModifierContactsComponent, ComponentShutdown>(OnShutdown);
+
+        UpdatesAfter.Add(typeof(SharedPhysicsSystem));
+    }
+
+    public override void Update(float frameTime)
+    {
+        base.Update(frameTime);
+
+        _toRemove.Clear();
+
+        foreach (var ent in _toUpdate)
+        {
+            _speedModifierSystem.RefreshMovementSpeedModifiers(ent);
+        }
+
+        foreach (var ent in _toRemove)
+        {
+            RemComp<SpeedModifiedByContactComponent>(ent);
+        }
+
+        _toUpdate.Clear();
+    }
+
+    public void ChangeModifiers(EntityUid uid, float speed, SpeedModifierContactsComponent? component = null)
+    {
+        ChangeModifiers(uid, speed, speed, component);
+    }
+
+    public void ChangeModifiers(EntityUid uid, float walkSpeed, float sprintSpeed, SpeedModifierContactsComponent? component = null)
+    {
+        if (!Resolve(uid, ref component))
+        {
+            return;
+        }
+        component.WalkSpeedModifier = walkSpeed;
+        component.SprintSpeedModifier = sprintSpeed;
+        Dirty(component);
+        _toUpdate.UnionWith(_physics.GetContactingEntities(uid));
+    }
+
+    private void OnShutdown(EntityUid uid, SpeedModifierContactsComponent component, ComponentShutdown args)
+    {
+        if (!TryComp(uid, out PhysicsComponent? phys))
+            return;
+
+        // Note that the entity may not be getting deleted here. E.g., glue puddles.
+        _toUpdate.UnionWith(_physics.GetContactingEntities(uid, phys));
+    }
+
+    private void MovementSpeedCheck(EntityUid uid, SpeedModifiedByContactComponent component, RefreshMovementSpeedModifiersEvent args)
+    {
+        if (!EntityManager.TryGetComponent<PhysicsComponent>(uid, out var physicsComponent))
+            return;
+
+        var walkSpeed = 0.0f;
+        var sprintSpeed = 0.0f;
+
+        bool remove = true;
+        var entries = 0;
+        foreach (var ent in _physics.GetContactingEntities(uid, physicsComponent))
+        {
+            if (!TryComp<SpeedModifierContactsComponent>(ent, out var slowContactsComponent))
+                continue;
+
+            if (slowContactsComponent.IgnoreWhitelist != null && slowContactsComponent.IgnoreWhitelist.IsValid(uid))
+                continue;
+
+            walkSpeed += slowContactsComponent.WalkSpeedModifier;
+            sprintSpeed += slowContactsComponent.SprintSpeedModifier;
+            remove = false;
+            entries++;
+        }
+
+        if (entries > 0)
+        {
+            walkSpeed /= entries;
+            sprintSpeed /= entries;
+
+            args.ModifySpeed(walkSpeed, sprintSpeed);
+        }
+
+        // no longer colliding with anything
+        if (remove)
+            _toRemove.Add(uid);
+    }
+
+    private void OnEntityExit(EntityUid uid, SpeedModifierContactsComponent component, ref EndCollideEvent args)
+    {
+        var otherUid = args.OtherEntity;
+        _toUpdate.Add(otherUid);
+    }
+
+    private void OnEntityEnter(EntityUid uid, SpeedModifierContactsComponent component, ref StartCollideEvent args)
+    {
+        var otherUid = args.OtherEntity;
+        if (!HasComp<MovementSpeedModifierComponent>(otherUid))
+            return;
+
+        EnsureComp<SpeedModifiedByContactComponent>(otherUid);
+        _toUpdate.Add(otherUid);
+    }
+}