Reimplement AdjacentPairs as a composition of RepeatFirst and Edges

Plugin/EnumerableExtensions/Edges.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Collections.Generic;
+
+namespace Kethane.EnumerableExtensions
+{
+    public static class EdgesEx
+    {
+        public static IEnumerable<Pair<T>> Edges<T>(this IEnumerable<T> sequence)
+        {
+            if (sequence == null) { throw new ArgumentNullException("sequence"); }
+            return edgesImpl(sequence);
+        }
+
+        public static IEnumerable<Pair<T>> EdgesCircular<T>(this IEnumerable<T> sequence)
+        {
+            return sequence.RepeatFirstOrEmpty().Edges();
+        }
+
+        private static IEnumerable<Pair<T>> edgesImpl<T>(IEnumerable<T> sequence)
+        {
+            using (var enumerator = sequence.GetEnumerator())
+            {
+                if (!enumerator.MoveNext()) { yield break; }
+                T previous = enumerator.Current;
+                while (enumerator.MoveNext())
+                {
+                    T current = enumerator.Current;
+                    yield return new Pair<T>(previous, current);
+                    previous = current;
+                }
+            }
+        }
+    }
+}

Plugin/EnumerableExtensions/Repeat.cs

@@ -0,0 +1,42 @@
+using System;
+using System.Collections.Generic;
+
+namespace Kethane.EnumerableExtensions
+{
+    public static class Repeat
+    {
+        public static IEnumerable<T> RepeatFirst<T>(this IEnumerable<T> sequence)
+        {
+            if (sequence == null) { throw new ArgumentNullException("sequence"); }
+            return repeatFirstImpl(sequence, true);
+        }
+
+        public static IEnumerable<T> RepeatFirstOrEmpty<T>(this IEnumerable<T> sequence)
+        {
+            if (sequence == null) { throw new ArgumentNullException("sequence"); }
+            return repeatFirstImpl(sequence, false);
+        }
+
+        private static IEnumerable<T> repeatFirstImpl<T>(IEnumerable<T> sequence, bool throwOnEmpty)
+        {
+            using (var enumerator = sequence.GetEnumerator())
+            {
+                if (!enumerator.MoveNext())
+                {
+                    if (throwOnEmpty) { throw new InvalidOperationException("Sequence is empty"); }
+                    yield break;
+                }
+
+                T first = enumerator.Current;
+                yield return first;
+
+                while (enumerator.MoveNext())
+                {
+                    yield return enumerator.Current;
+                }
+
+                yield return first;
+            }
+        }
+    }
+}

Plugin/GeodesicGrid/BoundsMap.cs

@@ -29,7 +29,7 @@ public BoundsMap(Func<Cell, float> heightAt, int level)
             {
                 maxs[triangle.Index] = triangle.GetVertices(level).Max(heightAt);
 
-                var min = Mathf.Sqrt(triangle.GetVertices(level).AdjacentPairs().Min(e => (e.First.Position * heightAt(e.First) + e.Second.Position * heightAt(e.Second)).sqrMagnitude)) / 2;
+                var min = Mathf.Sqrt(triangle.GetVertices(level).EdgesCircular().Min(e => (e.First.Position * heightAt(e.First) + e.Second.Position * heightAt(e.Second)).sqrMagnitude)) / 2;
                 mins[triangle.Index] = Math.Min(min, triangle.GetVertices(level).Min(heightAt));
             }
 

Plugin/GeodesicGrid/Cell.cs

@@ -140,14 +140,14 @@ public Vector3 Position
         public IEnumerable<Vector3> GetVertices(int level)
         {
             var position = this.Position;
-            return this.GetNeighbors(level).Select(c => c.Position).AdjacentPairs().Select(p => (position + p.First + p.Second).normalized);
+            return this.GetNeighbors(level).Select(c => c.Position).EdgesCircular().Select(p => (position + p.First + p.Second).normalized);
         }
 
         public IEnumerable<Vector3> GetVertices(int level, Func<Cell, float> heightAt)
         {
             var position = this.Position;
             var height = heightAt(this);
-            foreach (var pair in this.GetNeighbors(level).AdjacentPairs())
+            foreach (var pair in this.GetNeighbors(level).EdgesCircular())
             {
                 yield return (position + pair.First.Position + pair.Second.Position).normalized * (height + heightAt(pair.First) + heightAt(pair.Second)) / 3;
             }

Plugin/GeodesicGrid/Triangle.cs

@@ -180,7 +180,7 @@ private static bool intersectsCell(Ray ray, Triangle triangle, int level, float
                 if ((radius >= min) && triangleContains(triangle, level, ray.origin)) { return true; }
             }
 
-            return triangle.GetVertices(level).Select(c => c.Position).AdjacentPairs().Any(p => intersectsFace(ray, p.Second, p.First, min, max));
+            return triangle.GetVertices(level).Select(c => c.Position).EdgesCircular().Any(p => intersectsFace(ray, p.Second, p.First, min, max));
         }
 
         private static bool triangleContains(Triangle triangle, int level, Vector3 line)

Plugin/Kethane.csproj

@@ -46,9 +46,11 @@
     </Reference>
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="EnumerableExtensions\Edges.cs" />
     <Compile Include="EnumerableExtensions\AppendPrepend.cs" />
     <Compile Include="EnumerableExtensions\MinMaxBy.cs" />
     <Compile Include="EnumerableExtensions\Pair.cs" />
+    <Compile Include="EnumerableExtensions\Repeat.cs" />
     <Compile Include="EnumerableExtensions\ReverseComparer.cs" />
     <Compile Include="GeodesicGrid\BoundsMap.cs" />
     <Compile Include="GeodesicGrid\Cell.cs" />
@@ -63,7 +65,6 @@
     <Compile Include="InstallCleanup.cs" />
     <Compile Include="IWindowToggle.cs" />
     <Compile Include="LegacyResourceGenerator.cs" />
-    <Compile Include="EnumerableExtensions\EnumerableExtensions.cs" />
     <Compile Include="HeatSinkAnimator.cs" />
     <Compile Include="IResourceGenerator.cs" />
     <Compile Include="IDetectorAnimator.cs" />