From 4b510f64484449e58f11c775c2b8790ce0440ae8 Mon Sep 17 00:00:00 2001
From: ig <ig ig@devnullmail.com>
Date: Thu, 4 May 2023 09:42:57 +0200
Subject: [PATCH] add GroupUntil extension

---
 csharp/Lib/Utils/EnumerableUtils.cs | 43 +++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/csharp/Lib/Utils/EnumerableUtils.cs b/csharp/Lib/Utils/EnumerableUtils.cs
index 609258c37..6811c7e30 100644
--- a/csharp/Lib/Utils/EnumerableUtils.cs
+++ b/csharp/Lib/Utils/EnumerableUtils.cs
@@ -68,6 +68,8 @@ public static class EnumerableUtils
     // }
 
 
+    
+  
     public static Queue<T> ToQueue<T>(this IEnumerable<T> ts)
     {
         var q = new Queue<T>();
@@ -141,6 +143,7 @@ public static class EnumerableUtils
         }
     }
 
+    
     public static IEnumerable<(T left, T right)> Pairwise<T>(this IEnumerable<T> ts, T seed)
     {
         using var e = ts.GetEnumerator();
@@ -363,6 +366,46 @@ public static class EnumerableUtils
     }
 
 
+
+    
+
+    [SuppressMessage("ReSharper", "AccessToDisposedClosure")]
+    public static IEnumerable<IEnumerable<T>> GroupUntil<T>(this IEnumerable<T> sequence, Func<T, T, Boolean> splitBetween)
+    {
+        using var e = sequence.GetEnumerator();
+        
+        if(!e.MoveNext())
+            yield break;  // empty sequence
+
+		var moreInSeq   = false;
+        var moreInGroup = false;
+
+        do
+        {
+            yield return GetGroup();
+            while (moreInGroup)
+                MoveNext();
+        }
+        while (moreInSeq);
+
+        void MoveNext()
+        {
+            var prev = e.Current; 
+            moreInSeq = e.MoveNext();
+            moreInGroup = moreInSeq && !splitBetween(prev, e.Current);
+        }
+
+        IEnumerable<T> GetGroup()
+        {
+            do
+            {
+                yield return e.Current;
+				MoveNext();
+            }
+            while (moreInGroup);
+        }
+    }
+
     public static IEnumerable<T> NotNull<T>(this IEnumerable<T?> ts)
     {
         return ts.Where(t => t != null)!;