Add polygon shape

StructureHelperCommon/Models/Shapes/Logics/PolygonCalculator.cs

@@ -0,0 +1,77 @@
+using System;
+
+namespace StructureHelperCommon.Models.Shapes
+{
+    public class PolygonCalculator : IPolygonCalculator
+    {
+        public double GetPerimeter(IPolygonShape polygon)
+        {
+            if (polygon.Vertices.Count < 2)
+                return 0;
+
+            double perimeter = 0;
+
+            for (int i = 0; i < polygon.Vertices.Count - 1; i++)
+            {
+                perimeter += Distance(polygon.Vertices[i].Point, polygon.Vertices[i + 1].Point);
+            }
+
+            if (polygon.IsClosed && polygon.Vertices.Count > 2)
+            {
+                perimeter += Distance(polygon.Vertices[^1].Point, polygon.Vertices[0].Point);
+            }
+
+            return perimeter;
+        }
+
+        public double GetArea(IPolygonShape polygon)
+        {
+            if (!polygon.IsClosed || polygon.Vertices.Count < 3)
+                return 0;
+
+            // Shoelace formula
+            double sum = 0;
+            for (int i = 0; i < polygon.Vertices.Count; i++)
+            {
+                var p1 = polygon.Vertices[i].Point;
+                var p2 = polygon.Vertices[(i + 1) % polygon.Vertices.Count].Point;
+                sum += (p1.X * p2.Y - p2.X * p1.Y);
+            }
+
+            return Math.Abs(sum) / 2.0;
+        }
+
+        public bool ContainsPoint(IPolygonShape polygon, IPoint2D point)
+        {
+            if (!polygon.IsClosed || polygon.Vertices.Count < 3)
+                return false;
+
+            // Ray casting algorithm
+            bool inside = false;
+            int j = polygon.Vertices.Count - 1;
+
+            for (int i = 0; i < polygon.Vertices.Count; i++)
+            {
+                var pi = polygon.Vertices[i].Point;
+                var pj = polygon.Vertices[j].Point;
+
+                if (((pi.Y > point.Y) != (pj.Y > point.Y)) &&
+                    (point.X < (pj.X - pi.X) * (point.Y - pi.Y) / (pj.Y - pi.Y) + pi.X))
+                {
+                    inside = !inside;
+                }
+                j = i;
+            }
+
+            return inside;
+        }
+
+        private double Distance(IPoint2D p1, IPoint2D p2)
+        {
+            double dx = p2.X - p1.X;
+            double dy = p2.Y - p1.Y;
+            return Math.Sqrt(dx * dx + dy * dy);
+        }
+    }
+
+}