Remove IStartCollide from flammable (#4314)

I ported some stuff to be ECS but didn't feel like porting the rest, sue me.

Content.Server/Atmos/Components/FlammableComponent.cs

@@ -18,24 +18,22 @@ using Robust.Server.GameObjects;
 using Robust.Shared.GameObjects;
 using Robust.Shared.Localization;
 using Robust.Shared.Physics;
-using Robust.Shared.Physics.Collision;
-using Robust.Shared.Physics.Dynamics;
 using Robust.Shared.Serialization.Manager.Attributes;
 using Robust.Shared.ViewVariables;
 
 namespace Content.Server.Atmos.Components
 {
     [RegisterComponent]
-    public class FlammableComponent : SharedFlammableComponent, IStartCollide, IFireAct, IInteractUsing
+    public class FlammableComponent : SharedFlammableComponent, IFireAct, IInteractUsing
     {
         private bool _resisting = false;
         private readonly List<EntityUid> _collided = new();
 
         [ViewVariables(VVAccess.ReadWrite)]
-        public bool OnFire { get; private set; }
+        public bool OnFire { get; set; }
 
         [ViewVariables(VVAccess.ReadWrite)]
-        public float FireStacks { get; private set; }
+        public float FireStacks { get; set; }
 
         [ViewVariables(VVAccess.ReadWrite)]
         [DataField("fireSpread")]
@@ -45,17 +43,6 @@ namespace Content.Server.Atmos.Components
         [DataField("canResistFire")]
         public bool CanResistFire { get; private set; } = false;
 
-        public void Ignite()
-        {
-            if (FireStacks > 0 && !OnFire)
-            {
-                OnFire = true;
-
-            }
-
-            UpdateAppearance();
-        }
-
         public void Extinguish()
         {
             if (!OnFire) return;
@@ -145,37 +132,7 @@ namespace Content.Server.Atmos.Components
             }
         }
 
-        void IStartCollide.CollideWith(Fixture ourFixture, Fixture otherFixture, in Manifold manifold)
+        public void UpdateAppearance()
-        {
-            if (!otherFixture.Body.Owner.TryGetComponent(out FlammableComponent? otherFlammable))
-                return;
-
-            if (!FireSpread || !otherFlammable.FireSpread)
-                return;
-
-            if (OnFire)
-            {
-                if (otherFlammable.OnFire)
-                {
-                    var fireSplit = (FireStacks + otherFlammable.FireStacks) / 2;
-                    FireStacks = fireSplit;
-                    otherFlammable.FireStacks = fireSplit;
-                }
-                else
-                {
-                    FireStacks /= 2;
-                    otherFlammable.FireStacks += FireStacks;
-                    otherFlammable.Ignite();
-                }
-            } else if (otherFlammable.OnFire)
-            {
-                otherFlammable.FireStacks /= 2;
-                FireStacks += otherFlammable.FireStacks;
-                Ignite();
-            }
-        }
-
-        private void UpdateAppearance()
         {
             if (Owner.Deleted || !Owner.TryGetComponent(out AppearanceComponent? appearanceComponent)) return;
             appearanceComponent.SetData(FireVisuals.OnFire, OnFire);
@@ -185,7 +142,7 @@ namespace Content.Server.Atmos.Components
         public void FireAct(float temperature, float volume)
         {
             AdjustFireStacks(3);
-            Ignite();
+            EntitySystem.Get<FlammableSystem>().Ignite(this);
         }
 
         // This needs some improvements...
@@ -212,7 +169,7 @@ namespace Content.Server.Atmos.Components
             {
                 if (hotItem.IsCurrentlyHot())
                 {
-                    Ignite();
+                    EntitySystem.Get<FlammableSystem>().Ignite(this);
                     return true;
                 }
             }

Content.Server/Atmos/EntitySystems/FlammableSystem.cs

@@ -0,0 +1,56 @@
+using Content.Server.Atmos.Components;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Physics.Dynamics;
+
+namespace Content.Server.Atmos.EntitySystems
+{
+    internal sealed class FlammableSystem : EntitySystem
+    {
+        // TODO: Port the rest of Flammable.
+        public override void Initialize()
+        {
+            base.Initialize();
+            SubscribeLocalEvent<FlammableComponent, StartCollideEvent>(HandleCollide);
+        }
+
+        private void HandleCollide(EntityUid uid, FlammableComponent component, StartCollideEvent args)
+        {
+            if (!args.OtherFixture.Body.Owner.TryGetComponent(out FlammableComponent? otherFlammable))
+                return;
+
+            if (!component.FireSpread || !otherFlammable.FireSpread)
+                return;
+
+            if (component.OnFire)
+            {
+                if (otherFlammable.OnFire)
+                {
+                    var fireSplit = (component.FireStacks + otherFlammable.FireStacks) / 2;
+                    component.FireStacks = fireSplit;
+                    otherFlammable.FireStacks = fireSplit;
+                }
+                else
+                {
+                    component.FireStacks /= 2;
+                    otherFlammable.FireStacks += component.FireStacks;
+                    Ignite(otherFlammable);
+                }
+            } else if (otherFlammable.OnFire)
+            {
+                otherFlammable.FireStacks /= 2;
+                component.FireStacks += otherFlammable.FireStacks;
+                Ignite(component);
+            }
+        }
+
+        internal void Ignite(FlammableComponent component)
+        {
+            if (component.FireStacks > 0 && !component.OnFire)
+            {
+                component.OnFire = true;
+            }
+
+            component.UpdateAppearance();
+        }
+    }
+}