feat: add SpikeGrooveSplit implementation

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

OpenNest.Core/Splitting/SpikeGrooveSplit.cs

@@ -0,0 +1,105 @@
+using System.Collections.Generic;
+using OpenNest.Geometry;
+
+namespace OpenNest;
+
+/// <summary>
+/// Generates interlocking spike/V-groove pairs along the split edge.
+/// Spikes protrude from the positive side into the negative side.
+/// V-grooves on the negative side receive the spikes for self-alignment during welding.
+/// </summary>
+public class SpikeGrooveSplit : ISplitFeature
+{
+    public string Name => "Spike / V-Groove";
+
+    public SplitFeatureResult GenerateFeatures(SplitLine line, double extentStart, double extentEnd, SplitParameters parameters)
+    {
+        var extent = extentEnd - extentStart;
+        var pairCount = parameters.SpikePairCount;
+        var depth = parameters.SpikeDepth;
+        var angleRad = OpenNest.Math.Angle.ToRadians(parameters.SpikeAngle / 2);
+        var halfWidth = depth * System.Math.Tan(angleRad);
+
+        var isVertical = line.Axis == CutOffAxis.Vertical;
+        var pos = line.Position;
+
+        // Place pairs evenly: one near each end, with margin
+        var margin = extent * 0.15;
+        var pairPositions = new List<double>();
+        if (pairCount == 1)
+        {
+            pairPositions.Add(extentStart + extent / 2);
+        }
+        else
+        {
+            var usable = extent - 2 * margin;
+            for (var i = 0; i < pairCount; i++)
+                pairPositions.Add(extentStart + margin + usable * i / (pairCount - 1));
+        }
+
+        var negEntities = BuildGrooveSide(pairPositions, halfWidth, depth, extentStart, extentEnd, pos, isVertical);
+        var posEntities = BuildSpikeSide(pairPositions, halfWidth, depth, extentStart, extentEnd, pos, isVertical);
+
+        return new SplitFeatureResult(negEntities, posEntities);
+    }
+
+    private static List<Entity> BuildGrooveSide(List<double> pairPositions, double halfWidth, double depth,
+        double extentStart, double extentEnd, double pos, bool isVertical)
+    {
+        var entities = new List<Entity>();
+        var cursor = extentStart;
+
+        foreach (var center in pairPositions)
+        {
+            var grooveStart = center - halfWidth;
+            var grooveEnd = center + halfWidth;
+
+            if (grooveStart > cursor + OpenNest.Math.Tolerance.Epsilon)
+                entities.Add(MakeLine(pos, cursor, pos, grooveStart, isVertical));
+
+            entities.Add(MakeLine(pos, grooveStart, pos - depth, center, isVertical));
+            entities.Add(MakeLine(pos - depth, center, pos, grooveEnd, isVertical));
+
+            cursor = grooveEnd;
+        }
+
+        if (extentEnd > cursor + OpenNest.Math.Tolerance.Epsilon)
+            entities.Add(MakeLine(pos, cursor, pos, extentEnd, isVertical));
+
+        return entities;
+    }
+
+    private static List<Entity> BuildSpikeSide(List<double> pairPositions, double halfWidth, double depth,
+        double extentStart, double extentEnd, double pos, bool isVertical)
+    {
+        var entities = new List<Entity>();
+        var cursor = extentEnd;
+
+        for (var i = pairPositions.Count - 1; i >= 0; i--)
+        {
+            var center = pairPositions[i];
+            var spikeEnd = center + halfWidth;
+            var spikeStart = center - halfWidth;
+
+            if (cursor > spikeEnd + OpenNest.Math.Tolerance.Epsilon)
+                entities.Add(MakeLine(pos, cursor, pos, spikeEnd, isVertical));
+
+            entities.Add(MakeLine(pos, spikeEnd, pos - depth, center, isVertical));
+            entities.Add(MakeLine(pos - depth, center, pos, spikeStart, isVertical));
+
+            cursor = spikeStart;
+        }
+
+        if (cursor > extentStart + OpenNest.Math.Tolerance.Epsilon)
+            entities.Add(MakeLine(pos, cursor, pos, extentStart, isVertical));
+
+        return entities;
+    }
+
+    private static Line MakeLine(double splitAxis1, double along1, double splitAxis2, double along2, bool isVertical)
+    {
+        return isVertical
+            ? new Line(new Vector(splitAxis1, along1), new Vector(splitAxis2, along2))
+            : new Line(new Vector(along1, splitAxis1), new Vector(along2, splitAxis2));
+    }
+}

OpenNest.Tests/Splitting/SplitFeatureTests.cs

@@ -93,4 +93,44 @@ public class SplitFeatureTests
     {
         Assert.Equal("Straight", new StraightSplit().Name);
     }
+
+    [Fact]
+    public void SpikeGrooveSplit_Vertical_TwoPairs_SpikesOnPositiveSide()
+    {
+        var feature = new SpikeGrooveSplit();
+        var line = new SplitLine(50.0, CutOffAxis.Vertical);
+        var parameters = new SplitParameters
+        {
+            Type = SplitType.SpikeGroove,
+            SpikeDepth = 1.0,
+            SpikeAngle = 60.0,
+            SpikePairCount = 2
+        };
+
+        var result = feature.GenerateFeatures(line, 0.0, 100.0, parameters);
+
+        // Both sides should have multiple entities (straight segments + spike/groove geometry)
+        Assert.True(result.NegativeSideEdge.Count > 1, "Negative side should have groove geometry");
+        Assert.True(result.PositiveSideEdge.Count > 1, "Positive side should have spike geometry");
+
+        // All entities should be lines
+        Assert.All(result.NegativeSideEdge, e => Assert.IsType<Line>(e));
+        Assert.All(result.PositiveSideEdge, e => Assert.IsType<Line>(e));
+
+        // Spikes protrude in negative-X direction (into the negative side's territory)
+        var posLines = result.PositiveSideEdge.Cast<Line>().ToList();
+        var minX = posLines.Min(l => System.Math.Min(l.StartPoint.X, l.EndPoint.X));
+        Assert.True(minX < 50.0, "Spikes should protrude past the split line");
+
+        // Grooves indent in the positive-X direction (into positive side's territory)
+        var negLines = result.NegativeSideEdge.Cast<Line>().ToList();
+        var maxX = negLines.Max(l => System.Math.Max(l.StartPoint.X, l.EndPoint.X));
+        Assert.True(maxX <= 50.0, "Grooves should not protrude past the split line");
+    }
+
+    [Fact]
+    public void SpikeGrooveSplit_Name()
+    {
+        Assert.Equal("Spike / V-Groove", new SpikeGrooveSplit().Name);
+    }
 }