Highlight active item slot and activate when shortcut key is pressed

src/engine/gameplay/CombatLogic.ts

@@ -51,3 +51,46 @@ export function traceProjectile(
         hitActorId
     };
 }
+
+/**
+ * Finds the closest visible enemy to a given position.
+ */
+export function getClosestVisibleEnemy(
+    world: World,
+    origin: Vec2,
+    seenTiles: Set<string> | boolean[] | Uint8Array, // Support various visibility structures
+    width?: number // Required if seenTiles is a flat array
+): Vec2 | null {
+    let closestDistSq = Infinity;
+    let closestPos: Vec2 | null = null;
+    
+    // Helper to check visibility
+    const isVisible = (x: number, y: number) => {
+        if (Array.isArray(seenTiles) || seenTiles instanceof Uint8Array || seenTiles instanceof Int8Array) {
+            // Flat array
+            if (!width) return false;
+            return (seenTiles as any)[y * width + x]; 
+        } else {
+            // Set<string>
+            return (seenTiles as Set<string>).has(`${x},${y}`);
+        }
+    };
+
+    for (const actor of world.actors.values()) {
+        if (actor.category !== "combatant" || actor.isPlayer) continue;
+        
+        // Check visibility
+        if (!isVisible(actor.pos.x, actor.pos.y)) continue;
+
+        const dx = actor.pos.x - origin.x;
+        const dy = actor.pos.y - origin.y;
+        const distSq = dx*dx + dy*dy;
+
+        if (distSq < closestDistSq) {
+            closestDistSq = distSq;
+            closestPos = { x: actor.pos.x, y: actor.pos.y };
+        }
+    }
+
+    return closestPos;
+}