Refactor ElkSharp routing sources into partial modules

src/__Libraries/StellaOps.ElkSharp/ElkEdgeRoutingGeometry.cs

@@ -190,6 +190,70 @@ internal static class ElkEdgeRoutingGeometry
         return "bottom";
     }
 
+    internal static string ResolveBoundaryApproachSide(
+        ElkPoint boundaryPoint,
+        ElkPoint adjacentPoint,
+        ElkPositionedNode node)
+    {
+        if (!ElkShapeBoundaries.IsGatewayShape(node))
+        {
+            return ResolveBoundarySide(boundaryPoint, node);
+        }
+
+        var deltaX = boundaryPoint.X - adjacentPoint.X;
+        var deltaY = boundaryPoint.Y - adjacentPoint.Y;
+        var absDx = Math.Abs(deltaX);
+        var absDy = Math.Abs(deltaY);
+        if (absDx <= CoordinateTolerance && absDy > CoordinateTolerance)
+        {
+            return deltaY >= 0d ? "top" : "bottom";
+        }
+
+        if (absDy <= CoordinateTolerance && absDx > CoordinateTolerance)
+        {
+            return deltaX >= 0d ? "left" : "right";
+        }
+
+        if (absDx > absDy * 1.25d)
+        {
+            return deltaX >= 0d ? "left" : "right";
+        }
+
+        if (absDy > absDx * 1.25d)
+        {
+            return deltaY >= 0d ? "top" : "bottom";
+        }
+
+        return ResolveBoundarySide(boundaryPoint, node);
+    }
+
+    internal static double ComputeParallelOverlapLength(
+        ElkPoint a1,
+        ElkPoint a2,
+        ElkPoint b1,
+        ElkPoint b2)
+    {
+        if (IsHorizontal(a1, a2) && IsHorizontal(b1, b2))
+        {
+            return OverlapLength(
+                Math.Min(a1.X, a2.X),
+                Math.Max(a1.X, a2.X),
+                Math.Min(b1.X, b2.X),
+                Math.Max(b1.X, b2.X));
+        }
+
+        if (IsVertical(a1, a2) && IsVertical(b1, b2))
+        {
+            return OverlapLength(
+                Math.Min(a1.Y, a2.Y),
+                Math.Max(a1.Y, a2.Y),
+                Math.Min(b1.Y, b2.Y),
+                Math.Max(b1.Y, b2.Y));
+        }
+
+        return 0d;
+    }
+
     internal static bool AreCollinearAndOverlapping(ElkPoint a1, ElkPoint a2, ElkPoint b1, ElkPoint b2)
     {
         if (IsHorizontal(a1, a2) && IsHorizontal(b1, b2) && Math.Abs(a1.Y - b1.Y) <= CoordinateTolerance)