make yaml playout count an expression (#2102)

CHANGELOG.md

@@ -54,6 +54,14 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
     - `count / 2` will start in the middle of the content
     - `random` will start at a random point in the content
     - `2` (similar to before this change) will skip the first two items in the content
+- YAML playout: make `count` an expression
+    - The following parameters can be used:
+        - `count`: the total number of items in the content
+        - `random`: a random number between zero and (count - 1)
+    - For example:
+        - `count / 2` will play half of the items in the content
+        - `random % 4 + 1` will play between 1 and 4 items
+        - `2` (similar to before this change) will play exactly two items
 
 ### Changed
 - Allow `Other Video` libraries and `Image` libraries to use the same folders

ErsatzTV.Core/Scheduling/PlaylistEnumerator.cs

@@ -46,6 +46,8 @@ public class PlaylistEnumerator : IMediaCollectionEnumerator
 
     public int Count => throw new NotSupportedException("Count isn't used for playlist enumeration");
 
+    public int CountForRandom => _allMediaItemIds.Count;
+
     public Option<TimeSpan> MinimumDuration { get; private set; }
 
     public void MoveNext()

ErsatzTV.Core/Scheduling/YamlScheduling/Handlers/YamlPlayoutCountHandler.cs

@@ -28,7 +28,30 @@ public class YamlPlayoutCountHandler(EnumeratorCache enumeratorCache) : YamlPlay
 
         foreach (IMediaCollectionEnumerator enumerator in maybeEnumerator)
         {
-            for (var i = 0; i < count.Count; i++)
+            var random = new Random(context.Playout.Seed + context.InstructionIndex);
+            int enumeratorCount = enumerator is PlaylistEnumerator playlistEnumerator
+                ? playlistEnumerator.CountForRandom
+                : enumerator.Count;
+            var expression = new NCalc.Expression(count.Count);
+            expression.EvaluateParameter += (name, e) =>
+            {
+                e.Result = name switch
+                {
+                    "count" => enumeratorCount,
+                    "random" => random.Next() % enumeratorCount,
+                    _ => e.Result
+                };
+            };
+
+            object expressionResult = expression.Evaluate();
+            int countValue = expressionResult switch
+            {
+                double doubleResult => (int)Math.Floor(doubleResult),
+                int intResult => intResult,
+                _ => 0
+            };
+
+            for (var i = 0; i < countValue; i++)
             {
                 foreach (MediaItem mediaItem in enumerator.Current)
                 {

ErsatzTV.Core/Scheduling/YamlScheduling/Handlers/YamlPlayoutSkipItemsHandler.cs

@@ -27,13 +27,17 @@ public class YamlPlayoutSkipItemsHandler(EnumeratorCache enumeratorCache) : IYam
 
         foreach (IMediaCollectionEnumerator enumerator in maybeEnumerator)
         {
+            var random = new Random(context.Playout.Seed + context.InstructionIndex);
+            int enumeratorCount = enumerator is PlaylistEnumerator playlistEnumerator
+                ? playlistEnumerator.CountForRandom
+                : enumerator.Count;
             var expression = new NCalc.Expression(skipItems.SkipItems);
             expression.EvaluateParameter += (name, e) =>
             {
                 e.Result = name switch
                 {
-                    "count" => enumerator.Count,
-                    "random" => new Random().Next() % enumerator.Count,
+                    "count" => enumeratorCount,
+                    "random" => random.Next() % enumeratorCount,
                     _ => e.Result
                 };
             };

ErsatzTV.Core/Scheduling/YamlScheduling/Models/YamlPlayoutCountInstruction.cs

@@ -2,5 +2,5 @@ namespace ErsatzTV.Core.Scheduling.YamlScheduling.Models;
 
 public class YamlPlayoutCountInstruction : YamlPlayoutInstruction
 {
-    public int Count { get; set; }
+    public string Count { get; set; }
 }