using System; using System.Collections.Generic; using System.Linq; using System.Reflection; using ErsatzTV.Core.Domain; using ErsatzTV.Core.Interfaces.Scheduling; using LanguageExt; using static LanguageExt.Prelude; namespace ErsatzTV.Core.Scheduling { public class ShuffledMediaCollectionEnumerator : IMediaCollectionEnumerator { private readonly int _mediaItemCount; private readonly IList _mediaItems; private Random _random; private IList _shuffled; public ShuffledMediaCollectionEnumerator( IList mediaItems, CollectionEnumeratorState state) { _mediaItemCount = mediaItems.Sum(i => 1 + Optional(i.Additional).Flatten().Count()); _mediaItems = mediaItems; if (state.Index >= _mediaItems.Count) { state.Index = 0; state.Seed = new Random(state.Seed).Next(); } _random = new Random(state.Seed); _shuffled = Shuffle(_mediaItems, _random); State = new CollectionEnumeratorState { Seed = state.Seed }; while (State.Index < state.Index) { MoveNext(); } } public CollectionEnumeratorState State { get; } public Option Current => _shuffled.Any() ? _shuffled[State.Index % _mediaItemCount] : None; public void MoveNext() { if ((State.Index + 1) % _shuffled.Count == 0) { Option tail = Current; State.Index = 0; 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; } public Option Peek(int offset) { if ((State.Index + offset) % _mediaItemCount == 0) { IList shuffled; Option 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); do { int newSeed = randomCopy.Next(); randomCopy = new Random(newSeed); shuffled = Shuffle(_mediaItems, randomCopy); } while (_mediaItems.Count > 1 && shuffled[0] == tail); return shuffled.Any() ? shuffled[0] : None; } return _shuffled.Any() ? _shuffled[(State.Index + offset) % _mediaItemCount] : None; } private IList Shuffle(IEnumerable list, Random random) { GroupedMediaItem[] copy = list.ToArray(); int n = copy.Length; while (n > 1) { n--; int k = random.Next(n + 1); (copy[k], copy[n]) = (copy[n], copy[k]); } return GroupedMediaItem.FlattenGroups(copy, _mediaItemCount); } } }