feat: add FillScore struct with lexicographic comparison

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

OpenNest.Engine/FillScore.cs

@@ -0,0 +1,125 @@
+using System.Collections.Generic;
+using System.Linq;
+using OpenNest.Geometry;
+using OpenNest.Math;
+
+namespace OpenNest
+{
+    public readonly struct FillScore : System.IComparable<FillScore>
+    {
+        /// <summary>
+        /// Minimum short-side dimension for a remnant to be considered usable.
+        /// </summary>
+        public const double MinRemnantDimension = 12.0;
+
+        public int Count { get; }
+
+        /// <summary>
+        /// Area of the largest remnant whose short side >= MinRemnantDimension.
+        /// Zero if no usable remnant exists.
+        /// </summary>
+        public double UsableRemnantArea { get; }
+
+        /// <summary>
+        /// Total part area / bounding box area of all placed parts.
+        /// </summary>
+        public double Density { get; }
+
+        public FillScore(int count, double usableRemnantArea, double density)
+        {
+            Count = count;
+            UsableRemnantArea = usableRemnantArea;
+            Density = density;
+        }
+
+        /// <summary>
+        /// Computes a fill score from placed parts and the work area they were placed in.
+        /// </summary>
+        public static FillScore Compute(List<Part> parts, Box workArea)
+        {
+            if (parts == null || parts.Count == 0)
+                return default;
+
+            var totalPartArea = 0.0;
+
+            foreach (var part in parts)
+                totalPartArea += part.BaseDrawing.Area;
+
+            var bbox = ((IEnumerable<IBoundable>)parts).GetBoundingBox();
+            var bboxArea = bbox.Area();
+            var density = bboxArea > 0 ? totalPartArea / bboxArea : 0;
+
+            var usableRemnantArea = ComputeUsableRemnantArea(parts, workArea);
+
+            return new FillScore(parts.Count, usableRemnantArea, density);
+        }
+
+        /// <summary>
+        /// Finds the largest usable remnant (short side >= MinRemnantDimension)
+        /// by checking right and top edge strips between placed parts and the work area boundary.
+        /// </summary>
+        private static double ComputeUsableRemnantArea(List<Part> parts, Box workArea)
+        {
+            var maxRight = double.MinValue;
+            var maxTop = double.MinValue;
+
+            foreach (var part in parts)
+            {
+                var bb = part.BoundingBox;
+
+                if (bb.Right > maxRight)
+                    maxRight = bb.Right;
+
+                if (bb.Top > maxTop)
+                    maxTop = bb.Top;
+            }
+
+            var largest = 0.0;
+
+            // Right strip
+            if (maxRight < workArea.Right)
+            {
+                var width = workArea.Right - maxRight;
+                var height = workArea.Height;
+
+                if (System.Math.Min(width, height) >= MinRemnantDimension)
+                    largest = System.Math.Max(largest, width * height);
+            }
+
+            // Top strip
+            if (maxTop < workArea.Top)
+            {
+                var width = workArea.Width;
+                var height = workArea.Top - maxTop;
+
+                if (System.Math.Min(width, height) >= MinRemnantDimension)
+                    largest = System.Math.Max(largest, width * height);
+            }
+
+            return largest;
+        }
+
+        /// <summary>
+        /// Lexicographic comparison: count, then usable remnant area, then density.
+        /// </summary>
+        public int CompareTo(FillScore other)
+        {
+            var c = Count.CompareTo(other.Count);
+
+            if (c != 0)
+                return c;
+
+            c = UsableRemnantArea.CompareTo(other.UsableRemnantArea);
+
+            if (c != 0)
+                return c;
+
+            return Density.CompareTo(other.Density);
+        }
+
+        public static bool operator >(FillScore a, FillScore b) => a.CompareTo(b) > 0;
+        public static bool operator <(FillScore a, FillScore b) => a.CompareTo(b) < 0;
+        public static bool operator >=(FillScore a, FillScore b) => a.CompareTo(b) >= 0;
+        public static bool operator <=(FillScore a, FillScore b) => a.CompareTo(b) <= 0;
+    }
+}