ErsatzTV/ErsatzTV.Core/Scheduling/PlayoutBuilder.cs

using ErsatzTV.Core.Domain;
using ErsatzTV.Core.Interfaces.Repositories;
using ErsatzTV.Core.Interfaces.Scheduling;
using LanguageExt.UnsafeValueAccess;
using Microsoft.Extensions.Logging;
using Map = LanguageExt.Map;

namespace ErsatzTV.Core.Scheduling;

// TODO: these tests fail on days when offset changes
// because the change happens during the playout
public class PlayoutBuilder : IPlayoutBuilder
{
    private static readonly Random Random = new();
    private readonly IArtistRepository _artistRepository;
    private readonly ILogger<PlayoutBuilder> _logger;
    private readonly IConfigElementRepository _configElementRepository;
    private readonly IMediaCollectionRepository _mediaCollectionRepository;
    private readonly ITelevisionRepository _televisionRepository;

    public PlayoutBuilder(
        IConfigElementRepository configElementRepository,
        IMediaCollectionRepository mediaCollectionRepository,
        ITelevisionRepository televisionRepository,
        IArtistRepository artistRepository,
        ILogger<PlayoutBuilder> logger)
    {
        _configElementRepository = configElementRepository;
        _mediaCollectionRepository = mediaCollectionRepository;
        _televisionRepository = televisionRepository;
        _artistRepository = artistRepository;
        _logger = logger;
    }

    public async Task<Playout> Build(Playout playout, PlayoutBuildMode mode)
    {
        foreach (PlayoutParameters parameters in await Validate(playout))
        {
            // for testing purposes
            // if (mode == PlayoutBuildMode.Reset)
            // {
            //     return await Build(playout, mode, parameters with { Start = parameters.Start.AddDays(-2) });
            // }

            return await Build(playout, mode, parameters);
        }

        return playout;
    }

    private Task<Playout> Build(Playout playout, PlayoutBuildMode mode, PlayoutParameters parameters) =>
        mode switch
        {
            PlayoutBuildMode.Refresh => RefreshPlayout(playout, parameters),
            PlayoutBuildMode.Reset => ResetPlayout(playout, parameters),
            _ => ContinuePlayout(playout, parameters)
        };

    internal async Task<Playout> Build(
        Playout playout,
        PlayoutBuildMode mode,
        DateTimeOffset start,
        DateTimeOffset finish)
    {
        foreach (PlayoutParameters parameters in await Validate(playout))
        {
            return await Build(playout, mode, parameters with { Start = start, Finish = finish });
        }

        return playout;
    }

    private async Task<Playout> RefreshPlayout(Playout playout, PlayoutParameters parameters)
    {
        _logger.LogDebug(
            "Refreshing playout {PlayoutId} for channel {ChannelNumber} - {ChannelName}",
            playout.Id,
            playout.Channel.Number,
            playout.Channel.Name);

        playout.Items.Clear();
        playout.Anchor = null;

        // foreach (PlayoutProgramScheduleAnchor anchor in playout.ProgramScheduleAnchors)
        // {
        //     anchor.Playout = null;
        //     anchor.Collection = null;
        //     anchor.ProgramSchedule = null;
        // }

        // _logger.LogDebug("All anchors: {@Anchors}", playout.ProgramScheduleAnchors);

        // remove null anchor date ("continue" anchors)
        playout.ProgramScheduleAnchors.RemoveAll(a => a.AnchorDate is null);

        // _logger.LogDebug("Checkpoint anchors: {@Anchors}", playout.ProgramScheduleAnchors);

        // remove old checkpoints
        playout.ProgramScheduleAnchors.RemoveAll(
            a => a.AnchorDateOffset.IfNone(SystemTime.MaxValueUtc) < parameters.Start.Date);

        // remove new checkpoints
        playout.ProgramScheduleAnchors.RemoveAll(
            a => a.AnchorDateOffset.IfNone(SystemTime.MinValueUtc).Date > parameters.Start.Date);

        // _logger.LogDebug("Remaining anchors: {@Anchors}", playout.ProgramScheduleAnchors);

        var allAnchors = playout.ProgramScheduleAnchors.ToList();

        var collectionIds = playout.ProgramScheduleAnchors.Map(a => Optional(a.CollectionId)).Somes().ToHashSet();

        var multiCollectionIds =
            playout.ProgramScheduleAnchors.Map(a => Optional(a.MultiCollectionId)).Somes().ToHashSet();

        var smartCollectionIds =
            playout.ProgramScheduleAnchors.Map(a => Optional(a.SmartCollectionId)).Somes().ToHashSet();

        var mediaItemIds = playout.ProgramScheduleAnchors.Map(a => Optional(a.MediaItemId)).Somes().ToHashSet();

        playout.ProgramScheduleAnchors.Clear();

        foreach (int collectionId in collectionIds)
        {
            PlayoutProgramScheduleAnchor minAnchor = allAnchors.Filter(a => a.CollectionId == collectionId)
                .MinBy(a => a.AnchorDateOffset.IfNone(DateTimeOffset.MaxValue).Ticks);
            playout.ProgramScheduleAnchors.Add(minAnchor);
        }

        foreach (int multiCollectionId in multiCollectionIds)
        {
            PlayoutProgramScheduleAnchor minAnchor = allAnchors.Filter(a => a.MultiCollectionId == multiCollectionId)
                .MinBy(a => a.AnchorDateOffset.IfNone(DateTimeOffset.MaxValue).Ticks);
            playout.ProgramScheduleAnchors.Add(minAnchor);
        }

        foreach (int smartCollectionId in smartCollectionIds)
        {
            PlayoutProgramScheduleAnchor minAnchor = allAnchors.Filter(a => a.SmartCollectionId == smartCollectionId)
                .MinBy(a => a.AnchorDateOffset.IfNone(DateTimeOffset.MaxValue).Ticks);
            playout.ProgramScheduleAnchors.Add(minAnchor);
        }

        foreach (int mediaItemId in mediaItemIds)
        {
            PlayoutProgramScheduleAnchor minAnchor = allAnchors.Filter(a => a.MediaItemId == mediaItemId)
                .MinBy(a => a.AnchorDateOffset.IfNone(DateTimeOffset.MaxValue).Ticks);
            playout.ProgramScheduleAnchors.Add(minAnchor);
        }

        // _logger.LogDebug("Oldest anchors for each collection: {@Anchors}", playout.ProgramScheduleAnchors);

        // convert checkpoints to non-checkpoints
        // foreach (PlayoutProgramScheduleAnchor anchor in playout.ProgramScheduleAnchors)
        // {
        //     anchor.AnchorDate = null;
        // }

        // _logger.LogDebug("Final anchors: {@Anchors}", playout.ProgramScheduleAnchors);

        Option<DateTime> maybeAnchorDate = playout.ProgramScheduleAnchors
            .Map(a => Optional(a.AnchorDate))
            .Somes()
            .HeadOrNone();

        foreach (DateTime anchorDate in maybeAnchorDate)
        {
            playout.Anchor = new PlayoutAnchor
            {
                NextStart = anchorDate
            };
        }

        return await BuildPlayoutItems(
            playout,
            parameters.Start,
            parameters.Finish,
            parameters.CollectionMediaItems);
    }

    private async Task<Playout> ResetPlayout(Playout playout, PlayoutParameters parameters)
    {
        _logger.LogDebug(
            "Resetting playout {PlayoutId} for channel {ChannelNumber} - {ChannelName}",
            playout.Id,
            playout.Channel.Number,
            playout.Channel.Name);

        playout.Items.Clear();
        playout.Anchor = null;
        playout.ProgramScheduleAnchors.Clear();

        await BuildPlayoutItems(
            playout,
            parameters.Start,
            parameters.Finish,
            parameters.CollectionMediaItems);

        return playout;
    }

    private async Task<Playout> ContinuePlayout(Playout playout, PlayoutParameters parameters)
    {
        _logger.LogDebug(
            "Building playout {PlayoutId} for channel {ChannelNumber} - {ChannelName}",
            playout.Id,
            playout.Channel.Number,
            playout.Channel.Name);

        await BuildPlayoutItems(
            playout,
            parameters.Start,
            parameters.Finish,
            parameters.CollectionMediaItems);

        return playout;
    }

    private async Task<Option<PlayoutParameters>> Validate(Playout playout)
    {
        Map<CollectionKey, List<MediaItem>> collectionMediaItems = await GetCollectionMediaItems(playout);
        if (!collectionMediaItems.Any())
        {
            _logger.LogWarning(
                "Playout {Playout} schedule {Schedule} has no items",
                playout.Channel.Name,
                playout.ProgramSchedule.Name);

            return None;
        }

        Option<CollectionKey> maybeEmptyCollection = await CheckForEmptyCollections(collectionMediaItems);
        foreach (CollectionKey emptyCollection in maybeEmptyCollection)
        {
            Option<string> maybeName = await _mediaCollectionRepository.GetNameFromKey(emptyCollection);
            if (maybeName.IsSome)
            {
                foreach (string name in maybeName)
                {
                    _logger.LogError(
                        "Unable to rebuild playout; {CollectionType} {CollectionName} has no valid items!",
                        emptyCollection.CollectionType,
                        name);
                }
            }
            else
            {
                _logger.LogError(
                    "Unable to rebuild playout; collection {@CollectionKey} has no valid items!",
                    emptyCollection);
            }

            return None;
        }

        playout.Items ??= new List<PlayoutItem>();
        playout.ProgramScheduleAnchors ??= new List<PlayoutProgramScheduleAnchor>();

        Option<int> daysToBuild = await _configElementRepository.GetValue<int>(ConfigElementKey.PlayoutDaysToBuild);

        DateTimeOffset now = DateTimeOffset.Now;
        
        return new PlayoutParameters(
            now,
            now.AddDays(await daysToBuild.IfNoneAsync(2)),
            collectionMediaItems);
    }

    private async Task<Playout> BuildPlayoutItems(
        Playout playout,
        DateTimeOffset playoutStart,
        DateTimeOffset playoutFinish,
        Map<CollectionKey, List<MediaItem>> collectionMediaItems)
    {
        DateTimeOffset trimBefore = playoutStart.AddHours(-4);
        DateTimeOffset trimAfter = playoutFinish;

        DateTimeOffset start = playoutStart;
        DateTimeOffset finish = playoutStart.Date.AddDays(1);

        // _logger.LogDebug(
        //     "Trim before: {TrimBefore}, Start: {Start}, Finish: {Finish}, PlayoutFinish: {PlayoutFinish}",
        //     trimBefore,
        //     start,
        //     finish,
        //     playoutFinish);

        // build each day with "continue" anchors
        while (finish < playoutFinish)
        {
            // _logger.LogDebug("Building playout from {Start} to {Finish}", start, finish);
            playout = await BuildPlayoutItems(playout, start, finish, collectionMediaItems, true);

            start = playout.Anchor.NextStartOffset;
            finish = finish.AddDays(1);
        }

        if (start < playoutFinish)
        {
            // build one final time without continue anchors
            // _logger.LogDebug("Building final playout from {Start} to {Finish}", start, playoutFinish);
            playout = await BuildPlayoutItems(
                playout,
                start,
                playoutFinish,
                collectionMediaItems,
                false);
        }

        // remove any items outside the desired range
        playout.Items.RemoveAll(old => old.FinishOffset < trimBefore || old.StartOffset > trimAfter);

        return playout;
    }

    private async Task<Playout> BuildPlayoutItems(
        Playout playout,
        DateTimeOffset playoutStart,
        DateTimeOffset playoutFinish,
        Map<CollectionKey, List<MediaItem>> collectionMediaItems,
        bool saveAnchorDate)
    {
        var sortedScheduleItems = playout.ProgramSchedule.Items.OrderBy(i => i.Index).ToList();
        CollectionEnumeratorState scheduleItemsEnumeratorState =
            playout.Anchor?.ScheduleItemsEnumeratorState ?? new CollectionEnumeratorState
                { Seed = Random.Next(), Index = 0 };
        IScheduleItemsEnumerator scheduleItemsEnumerator = playout.ProgramSchedule.ShuffleScheduleItems
            ? new ShuffledScheduleItemsEnumerator(playout.ProgramSchedule.Items, scheduleItemsEnumeratorState)
            : new OrderedScheduleItemsEnumerator(playout.ProgramSchedule.Items, scheduleItemsEnumeratorState);
        var collectionEnumerators = new Dictionary<CollectionKey, IMediaCollectionEnumerator>();
        foreach ((CollectionKey collectionKey, List<MediaItem> mediaItems) in collectionMediaItems)
        {
            // use configured playback order for primary collection, shuffle for filler
            Option<ProgramScheduleItem> maybeScheduleItem = sortedScheduleItems
                .FirstOrDefault(item => CollectionKey.ForScheduleItem(item) == collectionKey);
            PlaybackOrder playbackOrder = maybeScheduleItem
                .Match(item => item.PlaybackOrder, () => PlaybackOrder.Shuffle);
            IMediaCollectionEnumerator enumerator =
                await GetMediaCollectionEnumerator(playout, collectionKey, mediaItems, playbackOrder);
            collectionEnumerators.Add(collectionKey, enumerator);
        }

        // find start anchor
        PlayoutAnchor startAnchor = FindStartAnchor(playout, playoutStart, scheduleItemsEnumerator);

        // start at the previously-decided time
        DateTimeOffset currentTime = startAnchor.NextStartOffset.ToLocalTime();
        // _logger.LogDebug(
        //     "Starting playout ({PlayoutId}) for channel {ChannelNumber} - {ChannelName} at {StartTime}",
        //     playout.Id,
        //     playout.Channel.Number,
        //     playout.Channel.Name,
        //     currentTime);

        // removing any items scheduled past the start anchor
        // this could happen if the app was closed after scheduling items
        // but before saving the anchor
        int removed = playout.Items.RemoveAll(pi => pi.StartOffset >= currentTime);
        if (removed > 0)
        {
            _logger.LogWarning("Removed {Count} schedule items beyond current start anchor", removed);
        }

        // start with the previously-decided schedule item
        // start with the previous multiple/duration states
        var playoutBuilderState = new PlayoutBuilderState(
            scheduleItemsEnumerator,
            Optional(startAnchor.MultipleRemaining),
            startAnchor.DurationFinishOffset,
            startAnchor.InFlood,
            startAnchor.InDurationFiller,
            startAnchor.NextGuideGroup,
            currentTime);

        var schedulerOne = new PlayoutModeSchedulerOne(_logger);
        var schedulerMultiple = new PlayoutModeSchedulerMultiple(collectionMediaItems, _logger);
        var schedulerDuration = new PlayoutModeSchedulerDuration(_logger);
        var schedulerFlood = new PlayoutModeSchedulerFlood(_logger);

        // loop until we're done filling the desired amount of time
        while (playoutBuilderState.CurrentTime < playoutFinish)
        {
            // get the schedule item out of the sorted list
            ProgramScheduleItem scheduleItem = playoutBuilderState.ScheduleItemsEnumerator.Current;

            ProgramScheduleItem nextScheduleItem = playoutBuilderState.ScheduleItemsEnumerator.Peek(1);

            Tuple<PlayoutBuilderState, List<PlayoutItem>> result = scheduleItem switch
            {
                ProgramScheduleItemMultiple multiple => schedulerMultiple.Schedule(
                    playoutBuilderState,
                    collectionEnumerators,
                    multiple,
                    nextScheduleItem,
                    playoutFinish),
                ProgramScheduleItemDuration duration => schedulerDuration.Schedule(
                    playoutBuilderState,
                    collectionEnumerators,
                    duration,
                    nextScheduleItem,
                    playoutFinish),
                ProgramScheduleItemFlood flood => schedulerFlood.Schedule(
                    playoutBuilderState,
                    collectionEnumerators,
                    flood,
                    nextScheduleItem,
                    playoutFinish),
                ProgramScheduleItemOne one => schedulerOne.Schedule(
                    playoutBuilderState,
                    collectionEnumerators,
                    one,
                    nextScheduleItem,
                    playoutFinish),
                _ => throw new ArgumentOutOfRangeException(nameof(scheduleItem))
            };

            (PlayoutBuilderState nextState, List<PlayoutItem> playoutItems) = result;

            foreach (PlayoutItem playoutItem in playoutItems)
            {
                playout.Items.Add(playoutItem);
            }

            playoutBuilderState = nextState;
        }

        // once more to get playout anchor
        ProgramScheduleItem anchorScheduleItem = playoutBuilderState.ScheduleItemsEnumerator.Current;

        if (playout.Items.Any())
        {
            DateTimeOffset maxStartTime = playout.Items.Max(i => i.FinishOffset);
            if (maxStartTime < playoutBuilderState.CurrentTime)
            {
                playoutBuilderState = playoutBuilderState with { CurrentTime = maxStartTime };
            }
        }

        playout.Anchor = new PlayoutAnchor
        {
            ScheduleItemsEnumeratorState = playoutBuilderState.ScheduleItemsEnumerator.State,
            NextStart = PlayoutModeSchedulerBase<ProgramScheduleItem>
                .GetStartTimeAfter(playoutBuilderState, anchorScheduleItem)
                .UtcDateTime,
            InFlood = playoutBuilderState.InFlood,
            InDurationFiller = playoutBuilderState.InDurationFiller,
            NextGuideGroup = playoutBuilderState.NextGuideGroup
        };

        foreach (int multipleRemaining in playoutBuilderState.MultipleRemaining)
        {
            playout.Anchor.MultipleRemaining = multipleRemaining;
        }

        foreach (DateTimeOffset durationFinish in playoutBuilderState.DurationFinish)
        {
            playout.Anchor.DurationFinish = durationFinish.UtcDateTime;
        }

        // build program schedule anchors
        playout.ProgramScheduleAnchors = BuildProgramScheduleAnchors(playout, collectionEnumerators, saveAnchorDate);

        return playout;
    }

    private async Task<Map<CollectionKey, List<MediaItem>>> GetCollectionMediaItems(Playout playout)
    {
        var collectionKeys = playout.ProgramSchedule.Items
            .SelectMany(CollectionKeysForItem)
            .Distinct()
            .ToList();

        IEnumerable<Tuple<CollectionKey, List<MediaItem>>> tuples = await collectionKeys.Map(
            async collectionKey => Tuple(
                collectionKey,
                await MediaItemsForCollection.Collect(
                    _mediaCollectionRepository,
                    _televisionRepository,
                    _artistRepository,
                    collectionKey))).SequenceParallel();

        return Map.createRange(tuples);
    }

    private async Task<Option<CollectionKey>> CheckForEmptyCollections(
        Map<CollectionKey, List<MediaItem>> collectionMediaItems)
    {
        foreach ((CollectionKey _, List<MediaItem> items) in collectionMediaItems)
        {
            var zeroItems = new List<MediaItem>();
            // var missingItems = new List<MediaItem>();

            foreach (MediaItem item in items)
            {
                bool isZero = item switch
                {
                    Movie m => await m.MediaVersions.Map(v => v.Duration).HeadOrNone()
                        .IfNoneAsync(TimeSpan.Zero) == TimeSpan.Zero,
                    Episode e => await e.MediaVersions.Map(v => v.Duration).HeadOrNone()
                        .IfNoneAsync(TimeSpan.Zero) == TimeSpan.Zero,
                    MusicVideo mv => await mv.MediaVersions.Map(v => v.Duration).HeadOrNone()
                        .IfNoneAsync(TimeSpan.Zero) == TimeSpan.Zero,
                    OtherVideo ov => await ov.MediaVersions.Map(v => v.Duration).HeadOrNone()
                        .IfNoneAsync(TimeSpan.Zero) == TimeSpan.Zero,
                    Song s => await s.MediaVersions.Map(v => v.Duration).HeadOrNone()
                        .IfNoneAsync(TimeSpan.Zero) == TimeSpan.Zero,
                    _ => true
                };

                // if (item.State == MediaItemState.FileNotFound)
                // {
                //     _logger.LogWarning(
                //         "Skipping media item that does not exist on disk  {MediaItem} - {MediaItemTitle} - {Path}",
                //         item.Id,
                //         DisplayTitle(item),
                //         item.GetHeadVersion().MediaFiles.Head().Path);
                //
                //     missingItems.Add(item);
                // }
                // else
                if (isZero)
                {
                    _logger.LogWarning(
                        "Skipping media item with zero duration {MediaItem} - {MediaItemTitle}",
                        item.Id,
                        DisplayTitle(item));

                    zeroItems.Add(item);
                }
            }

            // items.RemoveAll(missingItems.Contains);
            items.RemoveAll(zeroItems.Contains);
        }

        return collectionMediaItems.Find(c => !c.Value.Any()).Map(c => c.Key);
    }

    private static PlayoutAnchor FindStartAnchor(
        Playout playout,
        DateTimeOffset start,
        IScheduleItemsEnumerator enumerator) =>
        Optional(playout.Anchor).IfNone(
            () =>
            {
                ProgramScheduleItem schedule = enumerator.Current;
                switch (schedule.StartType)
                {
                    case StartType.Fixed:
                        return new PlayoutAnchor
                        {
                            ScheduleItemsEnumeratorState = enumerator.State,
                            NextStart = (start - start.TimeOfDay).UtcDateTime +
                                        schedule.StartTime.GetValueOrDefault()
                        };
                    case StartType.Dynamic:
                    default:
                        return new PlayoutAnchor
                        {
                            ScheduleItemsEnumeratorState = enumerator.State,
                            NextStart = (start - start.TimeOfDay).UtcDateTime
                        };
                }
            });

    private static List<PlayoutProgramScheduleAnchor> BuildProgramScheduleAnchors(
        Playout playout,
        Dictionary<CollectionKey, IMediaCollectionEnumerator> collectionEnumerators,
        bool saveAnchorDate)
    {
        var result = new List<PlayoutProgramScheduleAnchor>();

        foreach (CollectionKey collectionKey in collectionEnumerators.Keys)
        {
            Option<PlayoutProgramScheduleAnchor> maybeExisting = playout.ProgramScheduleAnchors.FirstOrDefault(
                a => a.CollectionType == collectionKey.CollectionType
                     && a.CollectionId == collectionKey.CollectionId
                     && a.MediaItemId == collectionKey.MediaItemId
                     && a.AnchorDate is null);

            var maybeEnumeratorState = collectionEnumerators.GroupBy(e => e.Key, e => e.Value.State).ToDictionary(
                mcs => mcs.Key,
                mcs => mcs.Head());

            PlayoutProgramScheduleAnchor scheduleAnchor = maybeExisting.Match(
                existing =>
                {
                    existing.EnumeratorState = maybeEnumeratorState[collectionKey];
                    return existing;
                },
                () => new PlayoutProgramScheduleAnchor
                {
                    Playout = playout,
                    PlayoutId = playout.Id,
                    ProgramSchedule = playout.ProgramSchedule,
                    ProgramScheduleId = playout.ProgramScheduleId,
                    CollectionType = collectionKey.CollectionType,
                    CollectionId = collectionKey.CollectionId,
                    MultiCollectionId = collectionKey.MultiCollectionId,
                    SmartCollectionId = collectionKey.SmartCollectionId,
                    MediaItemId = collectionKey.MediaItemId,
                    EnumeratorState = maybeEnumeratorState[collectionKey]
                });

            if (saveAnchorDate)
            {
                scheduleAnchor.AnchorDate = playout.Anchor?.NextStart;
            }

            result.Add(scheduleAnchor);
        }

        foreach (PlayoutProgramScheduleAnchor continueAnchor in playout.ProgramScheduleAnchors.Where(
                     a => a.AnchorDate is not null))
        {
            result.Add(continueAnchor);
        }

        return result;
    }

    private async Task<IMediaCollectionEnumerator> GetMediaCollectionEnumerator(
        Playout playout,
        CollectionKey collectionKey,
        List<MediaItem> mediaItems,
        PlaybackOrder playbackOrder)
    {
        Option<PlayoutProgramScheduleAnchor> maybeAnchor = playout.ProgramScheduleAnchors.FirstOrDefault(
            a => a.ProgramScheduleId == playout.ProgramScheduleId
                 && a.CollectionType == collectionKey.CollectionType
                 && a.CollectionId == collectionKey.CollectionId
                 && a.MultiCollectionId == collectionKey.MultiCollectionId
                 && a.SmartCollectionId == collectionKey.SmartCollectionId
                 && a.MediaItemId == collectionKey.MediaItemId);

        CollectionEnumeratorState state = maybeAnchor.Match(
            anchor => anchor.EnumeratorState ??
                      (anchor.EnumeratorState = new CollectionEnumeratorState { Seed = Random.Next(), Index = 0 }),
            () => new CollectionEnumeratorState { Seed = Random.Next(), Index = 0 });

        if (await _mediaCollectionRepository.IsCustomPlaybackOrder(collectionKey.CollectionId ?? 0))
        {
            Option<Collection> collectionWithItems =
                await _mediaCollectionRepository.GetCollectionWithCollectionItemsUntracked(
                    collectionKey.CollectionId ?? 0);

            if (collectionKey.CollectionType == ProgramScheduleItemCollectionType.Collection &&
                collectionWithItems.IsSome)
            {
                return new CustomOrderCollectionEnumerator(
                    collectionWithItems.ValueUnsafe(),
                    mediaItems,
                    state);
            }
        }

        switch (playbackOrder)
        {
            case PlaybackOrder.Chronological:
                return new ChronologicalMediaCollectionEnumerator(mediaItems, state);
            case PlaybackOrder.Random:
                return new RandomizedMediaCollectionEnumerator(mediaItems, state);
            case PlaybackOrder.Shuffle:
                return new ShuffledMediaCollectionEnumerator(
                    await GetGroupedMediaItemsForShuffle(playout, mediaItems, collectionKey),
                    state);
            case PlaybackOrder.ShuffleInOrder:
                return new ShuffleInOrderCollectionEnumerator(
                    await GetCollectionItemsForShuffleInOrder(collectionKey),
                    state);
            default:
                // TODO: handle this error case differently?
                return new RandomizedMediaCollectionEnumerator(mediaItems, state);
        }
    }

    private async Task<List<GroupedMediaItem>> GetGroupedMediaItemsForShuffle(
        Playout playout,
        List<MediaItem> mediaItems,
        CollectionKey collectionKey)
    {
        if (collectionKey.MultiCollectionId != null)
        {
            List<CollectionWithItems> collections = await _mediaCollectionRepository
                .GetMultiCollectionCollections(collectionKey.MultiCollectionId.Value);

            return MultiCollectionGrouper.GroupMediaItems(collections);
        }

        return playout.ProgramSchedule.KeepMultiPartEpisodesTogether
            ? MultiPartEpisodeGrouper.GroupMediaItems(
                mediaItems,
                playout.ProgramSchedule.TreatCollectionsAsShows)
            : mediaItems.Map(mi => new GroupedMediaItem(mi, null)).ToList();
    }

    private async Task<List<CollectionWithItems>> GetCollectionItemsForShuffleInOrder(CollectionKey collectionKey)
    {
        List<CollectionWithItems> result;

        if (collectionKey.MultiCollectionId != null)
        {
            result = await _mediaCollectionRepository.GetMultiCollectionCollections(
                collectionKey.MultiCollectionId.Value);
        }
        else
        {
            result = await _mediaCollectionRepository.GetFakeMultiCollectionCollections(
                collectionKey.CollectionId,
                collectionKey.SmartCollectionId);
        }

        return result;
    }

    internal static string DisplayTitle(MediaItem mediaItem)
    {
        switch (mediaItem)
        {
            case Episode e:
                string showTitle = e.Season.Show.ShowMetadata.HeadOrNone()
                    .Map(sm => $"{sm.Title} - ").IfNone(string.Empty);
                return e.EpisodeMetadata.HeadOrNone()
                    .Map(em => $"{showTitle}s{e.Season.SeasonNumber:00}e{em.EpisodeNumber:00} - {em.Title}")
                    .IfNone("[unknown episode]");
            case Movie m:
                return m.MovieMetadata.HeadOrNone().Match(mm => mm.Title ?? string.Empty, () => "[unknown movie]");
            case MusicVideo mv:
                string artistName = mv.Artist.ArtistMetadata.HeadOrNone()
                    .Map(am => $"{am.Title} - ").IfNone(string.Empty);
                return mv.MusicVideoMetadata.HeadOrNone()
                    .Map(mvm => $"{artistName}{mvm.Title}")
                    .IfNone("[unknown music video]");
            case OtherVideo ov:
                return ov.OtherVideoMetadata.HeadOrNone().Match(
                    ovm => ovm.Title ?? string.Empty,
                    () => "[unknown video]");
            case Song s:
                return s.SongMetadata.HeadOrNone().Match(
                    sm => sm.Title ?? string.Empty,
                    () => "[unknown song]");
            default:
                return string.Empty;
        }
    }

    private static List<CollectionKey> CollectionKeysForItem(ProgramScheduleItem item)
    {
        var result = new List<CollectionKey>
        {
            CollectionKey.ForScheduleItem(item)
        };

        if (item.PreRollFiller != null)
        {
            result.Add(CollectionKey.ForFillerPreset(item.PreRollFiller));
        }

        if (item.MidRollFiller != null)
        {
            result.Add(CollectionKey.ForFillerPreset(item.MidRollFiller));
        }

        if (item.PostRollFiller != null)
        {
            result.Add(CollectionKey.ForFillerPreset(item.PostRollFiller));
        }

        if (item.TailFiller != null)
        {
            result.Add(CollectionKey.ForFillerPreset(item.TailFiller));
        }

        if (item.FallbackFiller != null)
        {
            result.Add(CollectionKey.ForFillerPreset(item.FallbackFiller));
        }

        return result;
    }
}