NPC refactor (#10122)

Co-authored-by: metalgearsloth <metalgearsloth@gmail.com>

Content.Server/NPC/Pathfinding/PathfindingSystem.Simplifier.cs

@@ -0,0 +1,53 @@
+using Robust.Shared.Map;
+
+namespace Content.Server.NPC.Pathfinding;
+
+public sealed partial class PathfindingSystem
+{
+    // TODO: Re-use the existing simplifier. Because the pathfinding API sucks I just copy-pasted for now.
+    public static List<TileRef> Simplify(List<TileRef> vertices, float tolerance = 0)
+    {
+        if (vertices.Count <= 3)
+            return vertices;
+
+        var simplified = new List<TileRef>();
+
+        for (var i = 0; i < vertices.Count; i++)
+        {
+            // No wraparound for negative sooooo
+            var prev = vertices[i == 0 ? vertices.Count - 1 : i - 1];
+            var current = vertices[i];
+            var next = vertices[(i + 1) % vertices.Count];
+
+            // If they collinear, continue
+            if (IsCollinear(in prev, in current, in next, tolerance))
+                continue;
+
+            simplified.Add(current);
+        }
+
+        // Farseer didn't seem to handle straight lines and nuked all points
+        if (simplified.Count == 0)
+        {
+            simplified.Add(vertices[0]);
+            simplified.Add(vertices[^1]);
+        }
+
+        return simplified;
+    }
+
+    private static bool IsCollinear(in TileRef prev, in TileRef current, in TileRef next, float tolerance)
+    {
+        return FloatInRange(Area(in prev, in current, in next), -tolerance, tolerance);
+    }
+
+    private static float Area(in TileRef a, in TileRef b, in TileRef c)
+    {
+        return a.X * (b.Y - c.Y) + b.X * (c.Y - a.Y) + c.X * (a.Y - b.Y);
+    }
+
+    private static bool FloatInRange(float value, float min, float max)
+    {
+        return (value >= min && value <= max);
+    }
+}