Mousetraps (#8440)

Co-authored-by: Kara <lunarautomaton6@gmail.com>

Content.Server/Mousetrap/MousetrapSystem.cs

@@ -0,0 +1,82 @@
+using Content.Server.Damage.Systems;
+using Content.Server.Explosion.EntitySystems;
+using Content.Shared.Interaction.Events;
+using Content.Shared.Inventory;
+using Content.Shared.Mousetrap;
+using Content.Shared.StepTrigger;
+
+namespace Content.Server.Mousetrap;
+
+public sealed class MousetrapSystem : EntitySystem
+{
+    [Dependency] private readonly InventorySystem _inventorySystem = default!;
+    [Dependency] private readonly TriggerSystem _triggerSystem = default!;
+
+    public override void Initialize()
+    {
+        SubscribeLocalEvent<MousetrapComponent, UseInHandEvent>(OnUseInHand);
+        SubscribeLocalEvent<MousetrapComponent, BeforeDamageOnTriggerEvent>(BeforeDamageOnTrigger);
+        SubscribeLocalEvent<MousetrapComponent, StepTriggerAttemptEvent>(OnStepTriggerAttempt);
+        SubscribeLocalEvent<MousetrapComponent, StepTriggeredEvent>(OnStepTrigger);
+    }
+
+    private void OnUseInHand(EntityUid uid, MousetrapComponent component, UseInHandEvent args)
+    {
+        component.IsActive = !component.IsActive;
+
+        UpdateVisuals(uid);
+    }
+
+    private void OnStepTriggerAttempt(EntityUid uid, MousetrapComponent component, ref StepTriggerAttemptEvent args)
+    {
+        args.Continue = component.IsActive;
+    }
+
+    private void BeforeDamageOnTrigger(EntityUid uid, MousetrapComponent component, BeforeDamageOnTriggerEvent args)
+    {
+        foreach (var slot in component.IgnoreDamageIfSlotFilled)
+        {
+            if (!_inventorySystem.TryGetSlotContainer(args.Tripper, slot, out var container, out _))
+            {
+                continue;
+            }
+
+            // This also means that wearing slippers won't
+            // hurt the entity.
+            if (container.ContainedEntity != null)
+            {
+                args.Damage *= 0;
+                return;
+            }
+        }
+
+        if (TryComp(args.Tripper, out PhysicsComponent? physics))
+        {
+            // The idea here is inverse,
+            // Small - big damage,
+            // Large - small damage
+            // yes i punched numbers into a calculator until the graph looked right
+            var scaledDamage = -50 * Math.Atan(physics.Mass - component.MassBalance) + (25 * Math.PI);
+            args.Damage *= scaledDamage;
+        }
+    }
+
+    private void OnStepTrigger(EntityUid uid, MousetrapComponent component, ref StepTriggeredEvent args)
+    {
+        component.IsActive = false;
+        _triggerSystem.Trigger(uid);
+
+        UpdateVisuals(uid);
+    }
+
+    private void UpdateVisuals(EntityUid uid, MousetrapComponent? mousetrap = null, AppearanceComponent? appearance = null)
+    {
+        if (!Resolve(uid, ref mousetrap, ref appearance, false))
+        {
+            return;
+        }
+
+        appearance.SetData(MousetrapVisuals.Visual,
+            mousetrap.IsActive ? MousetrapVisuals.Armed : MousetrapVisuals.Unarmed);
+    }
+}