using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using Jellyfin.Data.Enums;
using Jellyfin.Database.Implementations.Entities;
using MediaBrowser.Controller.Entities;
using MediaBrowser.Controller.Entities.Movies;
using MediaBrowser.Controller.Library;
using Microsoft.Extensions.Logging;

namespace Jellyfin.Plugin.CinemaTrailers4Jellyfins.Services
{
    public class TrailerIntroProvider : IIntroProvider
    {
        private static readonly Random _rng = new();

        // Per-user set of trailer IDs already shown in the current cycle.
        // Resets automatically once every trailer in the active pool has been seen.
        private static readonly ConcurrentDictionary<Guid, HashSet<Guid>> _seenByUser = new();
        private static readonly object _seenLock = new();

        private readonly ILibraryManager _libraryManager;
        private readonly ILogger<TrailerIntroProvider> _logger;

        public string Name => "CinemaTrailers4Jellyfins";

        public TrailerIntroProvider(ILibraryManager libraryManager, ILogger<TrailerIntroProvider> logger)
        {
            _libraryManager = libraryManager;
            _logger = logger;
        }

        public Task<IEnumerable<IntroInfo>> GetIntros(BaseItem item, User user)
        {
            var config = Plugin.Instance?.Configuration;
            if (config == null || config.TrailersPerMovie <= 0)
                return Task.FromResult(Enumerable.Empty<IntroInfo>());

            if (item is not Movie)
                return Task.FromResult(Enumerable.Empty<IntroInfo>());

            var outputFolder = config.DownloadFolder?.TrimEnd(
                Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar);
            if (string.IsNullOrEmpty(outputFolder))
                return Task.FromResult(Enumerable.Empty<IntroInfo>());

            // Break recursion: don't inject intros before items from our own output folder
            // (covers both the fake-movie files and their trailer extras).
            if (item.Path?.StartsWith(outputFolder, StringComparison.OrdinalIgnoreCase) == true)
                return Task.FromResult(Enumerable.Empty<IntroInfo>());

            // Server-scoped query so hidden libraries don't block trailer discovery.
            var pairs = _libraryManager
                .GetItemList(new InternalItemsQuery
                {
                    IncludeItemTypes = new[] { BaseItemKind.Movie },
                    Recursive = true,
                })
                .OfType<Movie>()
                .Where(m =>
                    m.Path?.StartsWith(outputFolder, StringComparison.OrdinalIgnoreCase) == true
                    && m.LocalTrailers.Count > 0)
                .SelectMany(m => m.LocalTrailers.Select(t => (Movie: m, Trailer: t)))
                .ToList();

            if (pairs.Count == 0)
            {
                _logger.LogDebug(
                    "|CinemaTrailers4Jellyfins| No indexed trailers in {Folder}. "
                    + "Ensure the output folder is added as a Jellyfin Movies library and scanned.",
                    outputFolder);
                return Task.FromResult(Enumerable.Empty<IntroInfo>());
            }

            // Apply enabled filters. If nothing survives, fall back to the full pool.
            var filtered = ApplyFilters(pairs, item, config);
            var pool = filtered.Count > 0 ? filtered : pairs;

            // Prefer unseen trailers within the pool; reset the cycle when all have been shown.
            pool = ApplyAvoidRepeats(pool, user.Id, config.AvoidRepeats);

            var selected = pool
                .OrderBy(_ => _rng.Next())
                .Take(config.TrailersPerMovie)
                .ToList();

            if (config.AvoidRepeats)
                MarkSeen(user.Id, selected.Select(p => p.Trailer.Id));

            var intros = selected.Select(p => new IntroInfo { ItemId = p.Trailer.Id, Path = p.Trailer.Path });
            return Task.FromResult<IEnumerable<IntroInfo>>(intros.ToList());
        }

        private static List<(Movie Movie, BaseItem Trailer)> ApplyFilters(
            List<(Movie Movie, BaseItem Trailer)> pairs,
            BaseItem feature,
            Configuration.PluginConfiguration config)
        {
            var result = pairs;

            if (config.FilterByGenre && feature.Genres.Length > 0)
            {
                var featureGenres = new HashSet<string>(feature.Genres, StringComparer.OrdinalIgnoreCase);
                result = result
                    .Where(p => p.Movie.Genres.Any(g => featureGenres.Contains(g)))
                    .ToList();
            }

            if (config.FilterByRating)
            {
                result = result
                    .Where(p =>
                        // Unrated trailer: no restriction — include it.
                        p.Movie.InheritedParentalRatingValue == null
                        // Unrated feature: can't determine a ceiling — include everything.
                        || feature.InheritedParentalRatingValue == null
                        // Trailer rating must be at most the feature's rating.
                        || p.Movie.InheritedParentalRatingValue <= feature.InheritedParentalRatingValue)
                    .ToList();
            }

            return result;
        }

        private static List<(Movie Movie, BaseItem Trailer)> ApplyAvoidRepeats(
            List<(Movie Movie, BaseItem Trailer)> pool,
            Guid userId,
            bool enabled)
        {
            if (!enabled)
                return pool;

            lock (_seenLock)
            {
                var seen = _seenByUser.GetOrAdd(userId, _ => new HashSet<Guid>());
                var unseen = pool.Where(p => !seen.Contains(p.Trailer.Id)).ToList();

                if (unseen.Count > 0)
                    return unseen;

                // All trailers in this pool have been seen — reset the cycle.
                foreach (var p in pool)
                    seen.Remove(p.Trailer.Id);

                return pool.ToList();
            }
        }

        private static void MarkSeen(Guid userId, IEnumerable<Guid> trailerIds)
        {
            lock (_seenLock)
            {
                var seen = _seenByUser.GetOrAdd(userId, _ => new HashSet<Guid>());
                foreach (var id in trailerIds)
                    seen.Add(id);
            }
        }
    }
}