fix filler playout crash (#517)

CHANGELOG.md

@@ -12,6 +12,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Properly split song genre tags
 - Properly display all songs that have an identical album and title
 - Fix channel logo and watermark uploads
+- Fix regression introduced with `v0.2.4-alpha` that caused some filler edge cases to crash the playout builder
 
 ### Added
 - Add song genres to search index

ErsatzTV.Core.Tests/Scheduling/ShuffledMediaCollectionEnumeratorTests.cs

@@ -0,0 +1,90 @@
+using System.Collections.Generic;
+using ErsatzTV.Core.Domain;
+using ErsatzTV.Core.Scheduling;
+using FluentAssertions;
+using LanguageExt;
+using LanguageExt.UnsafeValueAccess;
+using NUnit.Framework;
+
+namespace ErsatzTV.Core.Tests.Scheduling
+{
+    [TestFixture]
+    public class ShuffledMediaCollectionEnumeratorTests
+    {
+        private readonly List<GroupedMediaItem> _mediaItems = new()
+        {
+            new GroupedMediaItem(new MediaItem { Id = 1 }, new List<MediaItem>()),
+            new GroupedMediaItem(new MediaItem { Id = 2 }, new List<MediaItem>()),
+            new GroupedMediaItem(new MediaItem { Id = 3 }, new List<MediaItem>())
+        };
+        
+        [Test]
+        public void Peek_Zero_Should_Match_Current()
+        {
+            var state = new CollectionEnumeratorState { Index = 0, Seed = 0 };
+            var enumerator = new ShuffledMediaCollectionEnumerator(_mediaItems, state);
+
+            Option<MediaItem> peek = enumerator.Peek(0);
+            Option<MediaItem> current = enumerator.Current;
+
+            peek.IsSome.Should().BeTrue();
+            current.IsSome.Should().BeTrue();
+            peek.ValueUnsafe().Id.Should().Be(1);
+            current.ValueUnsafe().Id.Should().Be(1);
+        }
+        
+        [Test]
+        public void Peek_One_Should_Match_Next()
+        {
+            var state = new CollectionEnumeratorState { Index = 0, Seed = 0 };
+            var enumerator = new ShuffledMediaCollectionEnumerator(_mediaItems, state);
+
+            Option<MediaItem> peek = enumerator.Peek(1);
+
+            enumerator.MoveNext();
+            Option<MediaItem> next = enumerator.Current;
+
+            peek.IsSome.Should().BeTrue();
+            next.IsSome.Should().BeTrue();
+            peek.ValueUnsafe().Id.Should().Be(2);
+            next.ValueUnsafe().Id.Should().Be(2);
+        }
+        
+        [Test]
+        public void Peek_Two_Should_Match_NextNext()
+        {
+            var state = new CollectionEnumeratorState { Index = 0, Seed = 0 };
+            var enumerator = new ShuffledMediaCollectionEnumerator(_mediaItems, state);
+
+            Option<MediaItem> peek = enumerator.Peek(2);
+
+            enumerator.MoveNext();
+            enumerator.MoveNext();
+            Option<MediaItem> next = enumerator.Current;
+
+            peek.IsSome.Should().BeTrue();
+            next.IsSome.Should().BeTrue();
+            peek.ValueUnsafe().Id.Should().Be(3);
+            next.ValueUnsafe().Id.Should().Be(3);
+        }
+        
+        [Test]
+        public void Peek_Three_Should_Match_NextNextNext()
+        {
+            var state = new CollectionEnumeratorState { Index = 0, Seed = 0 };
+            var enumerator = new ShuffledMediaCollectionEnumerator(_mediaItems, state);
+
+            Option<MediaItem> peek = enumerator.Peek(3);
+
+            enumerator.MoveNext();
+            enumerator.MoveNext();
+            enumerator.MoveNext();
+            Option<MediaItem> next = enumerator.Current;
+
+            peek.IsSome.Should().BeTrue();
+            next.IsSome.Should().BeTrue();
+            peek.ValueUnsafe().Id.Should().Be(2);
+            next.ValueUnsafe().Id.Should().Be(2);
+        }
+    }
+}

ErsatzTV.Core/Scheduling/CloneableRandom.cs

@@ -0,0 +1,41 @@
+using System;
+
+namespace ErsatzTV.Core.Scheduling
+{
+    public class CloneableRandom
+    {
+        private readonly int _seed;
+        private readonly Random _random;
+        private int _count;
+        
+        public CloneableRandom(int seed)
+        {
+            _seed = seed;
+            _random = new Random(_seed);
+        }
+
+        public CloneableRandom Clone()
+        {
+            var clone = new CloneableRandom(_seed);
+            
+            for (var i = 0; i < _count; i++)
+            {
+                clone.Next();
+            }
+
+            return clone;
+        }
+
+        public int Next()
+        {
+            _count++;
+            return _random.Next();
+        }
+
+        public int Next(int maxValue)
+        {
+            _count++;
+            return _random.Next(maxValue);
+        }
+    }
+}

ErsatzTV.Core/Scheduling/ShuffledMediaCollectionEnumerator.cs

@@ -1,7 +1,6 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using System.Reflection;
 using ErsatzTV.Core.Domain;
 using ErsatzTV.Core.Interfaces.Scheduling;
 using LanguageExt;
@@ -13,7 +12,7 @@ namespace ErsatzTV.Core.Scheduling
     {
         private readonly int _mediaItemCount;
         private readonly IList<GroupedMediaItem> _mediaItems;
-        private Random _random;
+        private CloneableRandom _random;
         private IList<MediaItem> _shuffled;
 
         public ShuffledMediaCollectionEnumerator(
@@ -29,7 +28,7 @@ namespace ErsatzTV.Core.Scheduling
                 state.Seed = new Random(state.Seed).Next();
             }
 
-            _random = new Random(state.Seed);
+            _random = new CloneableRandom(state.Seed);
             _shuffled = Shuffle(_mediaItems, _random);
 
             State = new CollectionEnumeratorState { Seed = state.Seed };
@@ -45,7 +44,7 @@ namespace ErsatzTV.Core.Scheduling
 
         public void MoveNext()
         {
-            if ((State.Index + 1) % _shuffled.Count == 0)
+            if ((State.Index + 1) % _mediaItemCount == 0)
             {
                 Option<MediaItem> tail = Current;
 
@@ -53,7 +52,7 @@ namespace ErsatzTV.Core.Scheduling
                 do
                 {
                     State.Seed = _random.Next();
-                    _random = new Random(State.Seed);
+                    _random = new CloneableRandom(State.Seed);
                     _shuffled = Shuffle(_mediaItems, _random);
                 } while (_mediaItems.Count > 1 && Current == tail);
             }
@@ -62,29 +61,28 @@ namespace ErsatzTV.Core.Scheduling
                 State.Index++;
             }
 
-            State.Index %= _shuffled.Count;
+            State.Index %= _mediaItemCount;
         }
 
         public Option<MediaItem> Peek(int offset)
         {
+            if (offset == 0)
+            {
+                return Current;
+            }
+
             if ((State.Index + offset) % _mediaItemCount == 0)
             {
                 IList<MediaItem> shuffled;
                 Option<MediaItem> tail = Current;
 
                 // clone the random
-                var randomCopy = new Random();
-                FieldInfo seedArrayInfo = typeof(Random).GetField(
-                    "_seedArray",
-                    BindingFlags.NonPublic | BindingFlags.Instance);
-                var seedArray = seedArrayInfo.GetValue(_random) as int[];
-                int[] seedArrayCopy = seedArray.ToArray();
-                seedArrayInfo.SetValue(randomCopy, seedArrayCopy);
+                CloneableRandom randomCopy = _random.Clone();
                 
                 do
                 {
                     int newSeed = randomCopy.Next();
-                    randomCopy = new Random(newSeed);
+                    randomCopy = new CloneableRandom(newSeed);
                     shuffled = Shuffle(_mediaItems, randomCopy);
                 } while (_mediaItems.Count > 1 && shuffled[0] == tail);
 
@@ -94,7 +92,7 @@ namespace ErsatzTV.Core.Scheduling
             return _shuffled.Any() ? _shuffled[(State.Index + offset) % _mediaItemCount] : None;
         }
 
-        private IList<MediaItem> Shuffle(IEnumerable<GroupedMediaItem> list, Random random)
+        private IList<MediaItem> Shuffle(IEnumerable<GroupedMediaItem> list, CloneableRandom random)
         {
             GroupedMediaItem[] copy = list.ToArray();