using ErsatzTV.Application.Artworks;
using ErsatzTV.Application.MediaCollections;
using ErsatzTV.Core;
using ErsatzTV.Core.Api.Channels;
using ErsatzTV.Core.Api.LibraryBrowse;
using ErsatzTV.Core.Domain;
using LanguageExt;
using MediatR;

namespace ErsatzTV.Application.Channels;

public class CreateAutoTunedChannelsHandler(ISender mediator)
    : IRequestHandler<CreateAutoTunedChannels, AutoTuneResult>
{
    private const string NumberTakenError = "Channel number must be unique";
    private const string DefaultGroup = "Auto-Tuned";

    public async Task<AutoTuneResult> Handle(
        CreateAutoTunedChannels request,
        CancellationToken cancellationToken)
    {
        string group = string.IsNullOrWhiteSpace(request.Group) ? DefaultGroup : request.Group.Trim();
        var outcomes = new List<AutoTuneChannelOutcome>();

        foreach (AutoTuneChannelSelection selection in request.Channels ?? [])
        {
            outcomes.Add(await CreateOne(request.TemplateId, group, selection, cancellationToken));
        }

        return new AutoTuneResult(outcomes);
    }

    private async Task<AutoTuneChannelOutcome> CreateOne(
        int templateId,
        string group,
        AutoTuneChannelSelection selection,
        CancellationToken cancellationToken)
    {
        string name = (selection.Name ?? string.Empty).Trim();
        if (name.Length is 0 or > 50)
        {
            return new AutoTuneChannelOutcome(name, AutoTuneOutcomeStatus.Failed, null, "Invalid channel name");
        }

        string query = AutoTuneAxisMap.GenerateQuery(selection.Axis, selection.Value);
        PlaybackOrder order = AutoTuneAxisMap.PlaybackOrderFor(selection.Axis);

        // 1. Create the smart collection that drives this channel.
        Either<BaseError, SmartCollectionViewModel> scResult =
            await mediator.Send(new CreateSmartCollection(query, name), cancellationToken);

        SmartCollectionViewModel smartCollection = null;
        foreach (BaseError error in scResult.LeftToSeq())
        {
            return new AutoTuneChannelOutcome(
                name, AutoTuneOutcomeStatus.Failed, null, $"Smart collection: {error.Value}");
        }

        foreach (SmartCollectionViewModel vm in scResult.RightToSeq())
        {
            smartCollection = vm;
        }

        // 2. Create the channel from a single-item lineup referencing the smart collection.
        var command = new CreateChannelFromLineup(
            name,
            selection.Number,
            group,
            string.Empty,
            ArtworkContentTypeModel.None,
            IsEnabled: true,
            ShowInEpg: true,
            templateId,
            new CreateChannelFromLineupAdvancedOptions(PlaybackOrder: order),
            [
                new CreateChannelFromLineupItem(
                    LibraryBrowseMediaType.SmartCollection,
                    CollectionType.SmartCollection,
                    CollectionId: null,
                    MultiCollectionId: null,
                    SmartCollectionId: smartCollection.Id,
                    RerunCollectionId: null,
                    MediaItemId: null,
                    PlaylistId: null)
            ]);

        Either<BaseError, CreateChannelFromLineupResponseModel> channelResult =
            await mediator.Send(command, cancellationToken);

        foreach (BaseError error in channelResult.LeftToSeq())
        {
            // Roll back the smart collection we just created so a retry of this
            // axis/value doesn't fail on SmartCollection-name uniqueness. Best-effort;
            // the primary outcome below is still Skipped/Failed regardless of the delete result.
            // Swallow any exception (not just an Either.Left) so a transient infra failure
            // during rollback never aborts this channel's outcome or the batch; the
            // orphaned SmartCollection is an acceptable degraded outcome.
            try
            {
                await mediator.Send(new DeleteSmartCollection(smartCollection.Id), cancellationToken);
            }
            catch (Exception)
            {
                // intentionally ignored; see comment above
            }

            AutoTuneOutcomeStatus status = error.Value.Contains(NumberTakenError, StringComparison.Ordinal)
                ? AutoTuneOutcomeStatus.Skipped
                : AutoTuneOutcomeStatus.Failed;
            return new AutoTuneChannelOutcome(name, status, null, error.Value);
        }

        int channelId = channelResult.Match(Left: _ => 0, Right: r => r.ChannelId);
        return new AutoTuneChannelOutcome(name, AutoTuneOutcomeStatus.Created, channelId, null);
    }
}