From 76446e0d696e52e30def0df850f5cb9da01015aa Mon Sep 17 00:00:00 2001
From: Jason Dove <jason@jasondove.me>
Date: Mon, 15 Mar 2021 11:28:07 +0000
Subject: [PATCH] prevent repeated playout items when reshuffling (#80)

---
 .../Scheduling/ShuffledContentTests.cs        | 48 +++++++++++++++++++
 .../ShuffledMediaCollectionEnumerator.cs      | 18 +++++--
 2 files changed, 61 insertions(+), 5 deletions(-)

diff --git a/ErsatzTV.Core.Tests/Scheduling/ShuffledContentTests.cs b/ErsatzTV.Core.Tests/Scheduling/ShuffledContentTests.cs
index 9240de89f..3784f3d97 100644
--- a/ErsatzTV.Core.Tests/Scheduling/ShuffledContentTests.cs
+++ b/ErsatzTV.Core.Tests/Scheduling/ShuffledContentTests.cs
@@ -15,6 +15,54 @@ namespace ErsatzTV.Core.Tests.Scheduling
         // this seed will produce (shuffle) 1-10 in order
         private const int MagicSeed = 670596;
 
+        [Test]
+        public void Episodes_Should_Not_Duplicate_When_Reshuffling()
+        {
+            List<MediaItem> contents = Episodes(10);
+
+            // normally returns 10 5 7 4 3 6 2 8 9 1 1 (note duplicate 1 at end)
+            var state = new CollectionEnumeratorState { Seed = 8 };
+
+            var shuffledContent = new ShuffledMediaCollectionEnumerator(contents, state);
+
+            var list = new List<int>();
+            for (var i = 1; i <= 1000; i++)
+            {
+                shuffledContent.Current.IsSome.Should().BeTrue();
+                shuffledContent.Current.Do(x => list.Add(x.Id));
+                shuffledContent.MoveNext();
+            }
+
+            for (var i = 0; i < list.Count - 1; i++)
+            {
+                if (list[i] == list[i + 1])
+                {
+                    Assert.Fail("List contains duplicate items");
+                }
+            }
+        }
+
+        [Test]
+        [Timeout(2000)]
+        public void Duplicate_Check_Should_Ignore_Single_Item()
+        {
+            List<MediaItem> contents = Episodes(1);
+
+            var state = new CollectionEnumeratorState();
+
+            var shuffledContent = new ShuffledMediaCollectionEnumerator(contents, state);
+
+            var list = new List<int>();
+            for (var i = 1; i <= 10; i++)
+            {
+                shuffledContent.Current.IsSome.Should().BeTrue();
+                shuffledContent.Current.Do(x => list.Add(x.Id));
+                shuffledContent.MoveNext();
+            }
+
+            list.Should().Equal(1, 1, 1, 1, 1, 1, 1, 1, 1, 1);
+        }
+
         [Test]
         public void Episodes_Should_Shuffle()
         {
diff --git a/ErsatzTV.Core/Scheduling/ShuffledMediaCollectionEnumerator.cs b/ErsatzTV.Core/Scheduling/ShuffledMediaCollectionEnumerator.cs
index d51ca9fb1..e45d4f049 100644
--- a/ErsatzTV.Core/Scheduling/ShuffledMediaCollectionEnumerator.cs
+++ b/ErsatzTV.Core/Scheduling/ShuffledMediaCollectionEnumerator.cs
@@ -34,13 +34,21 @@ namespace ErsatzTV.Core.Scheduling
 
         public void MoveNext()
         {
-            State.Index++;
-            if (State.Index % _shuffled.Count == 0)
+            if ((State.Index + 1) % _shuffled.Count == 0)
             {
+                Option<MediaItem> tail = Current;
+
                 State.Index = 0;
-                State.Seed = _random.Next();
-                _random = new Random(State.Seed);
-                _shuffled = Shuffle(_mediaItems, _random);
+                do
+                {
+                    State.Seed = _random.Next();
+                    _random = new Random(State.Seed);
+                    _shuffled = Shuffle(_mediaItems, _random);
+                } while (_mediaItems.Count > 1 && Current == tail);
+            }
+            else
+            {
+                State.Index++;
             }
 
             State.Index %= _shuffled.Count;