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.Entities.TV;
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();

        // Per-user date of the last episode that received trailers, so only the
        // first episode a user watches each day gets them.
        private static readonly ConcurrentDictionary<Guid, DateTime> _lastEpisodeTrailerDateByUser = 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)
                return Task.FromResult(Enumerable.Empty<IntroInfo>());

            var trailersEnabled = config.TrailersPerMovie > 0;
            var preRollEnabled = !string.IsNullOrEmpty(config.TrailerPreRollLibraryId);
            var featurePreRollEnabled = !string.IsNullOrEmpty(config.FeaturePreRollLibraryId);

            _logger.LogInformation(
                "|CinemaTrailers4Jellyfins| GetIntros called for {Type} '{Name}' (Path={Path}). "
                + "trailersEnabled={Trailers} preRollEnabled={PreRoll} featurePreRollEnabled={FeaturePreRoll}",
                item.GetType().Name,
                item.Name,
                item.Path,
                trailersEnabled,
                preRollEnabled,
                featurePreRollEnabled);

            if (!trailersEnabled && !preRollEnabled && !featurePreRollEnabled)
                return Task.FromResult(Enumerable.Empty<IntroInfo>());

            // The item used for genre/rating filtering. For episodes this is the
            // parent series, since episodes rarely carry their own genre metadata.
            BaseItem feature;
            bool isEpisode;

            switch (item)
            {
                case Movie:
                    feature = item;
                    isEpisode = false;
                    break;

                case Episode episode:
                    if (!config.TrailersForEpisodes)
                    {
                        _logger.LogInformation("|CinemaTrailers4Jellyfins| Skipping: TrailersForEpisodes is disabled.");
                        return Task.FromResult(Enumerable.Empty<IntroInfo>());
                    }

                    if (!IsFirstEpisodeOfDay(user.Id))
                    {
                        _logger.LogInformation("|CinemaTrailers4Jellyfins| Skipping: not the first episode of the day for this user.");
                        return Task.FromResult(Enumerable.Empty<IntroInfo>());
                    }

                    feature = episode.Series ?? (BaseItem)episode;
                    isEpisode = true;
                    break;

                default:
                    _logger.LogInformation("|CinemaTrailers4Jellyfins| Skipping: item type {Type} is not a Movie or Episode.", item.GetType().Name);
                    return Task.FromResult(Enumerable.Empty<IntroInfo>());
            }

            var outputFolder = config.DownloadFolder?.TrimEnd(
                Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar);

            // Break recursion: don't inject intros before items from our own output folder
            // (covers both the fake-movie files and their trailer extras).
            if (!string.IsNullOrEmpty(outputFolder)
                && item.Path?.StartsWith(outputFolder, StringComparison.OrdinalIgnoreCase) == true)
            {
                _logger.LogInformation("|CinemaTrailers4Jellyfins| Skipping: item path is inside the output folder ({Folder}).", outputFolder);
                return Task.FromResult(Enumerable.Empty<IntroInfo>());
            }

            var intros = new List<IntroInfo>();

            if (preRollEnabled)
            {
                var preRoll = GetRandomLibraryMovieIntro("Trailer Pre-Roll", config.TrailerPreRollLibraryId, item.Id);
                if (preRoll != null)
                    intros.Add(preRoll);
            }

            if (trailersEnabled && !string.IsNullOrEmpty(outputFolder))
            {
                // 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
                        // Keep TV show trailers for episodes and movie trailers for movies separate.
                        && m.Tags.Contains(TrailerTags.TvShow, StringComparer.OrdinalIgnoreCase) == isEpisode)
                    .SelectMany(m => m.LocalTrailers.Select(t => (Movie: m, Trailer: t)))
                    .ToList();

                if (pairs.Count == 0)
                {
                    _logger.LogDebug(
                        "|CinemaTrailers4Jellyfins| No indexed {Kind} trailers in {Folder}. "
                        + "Ensure the output folder is added as a Jellyfin Movies library and scanned.",
                        isEpisode ? "TV show" : "movie",
                        outputFolder);
                }
                else
                {
                    // Apply enabled filters. If nothing survives, fall back to the full pool.
                    var filtered = ApplyFilters(pairs, feature, 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));

                    intros.AddRange(selected.Select(p => new IntroInfo { ItemId = p.Trailer.Id, Path = p.Trailer.Path }));
                }
            }

            if (featurePreRollEnabled)
            {
                var featureRoll = GetRandomLibraryMovieIntro("Feature Pre-Roll", config.FeaturePreRollLibraryId, item.Id);
                if (featureRoll != null)
                    intros.Add(featureRoll);
            }

            _logger.LogInformation(
                "|CinemaTrailers4Jellyfins| Returning {Count} intro(s): {Paths}",
                intros.Count,
                string.Join(", ", intros.Select(i => i.Path)));

            return Task.FromResult<IEnumerable<IntroInfo>>(intros);
        }

        /// <summary>
        /// Picks a random Movie from the given Jellyfin library (VirtualFolder ItemId) to use as a
        /// pre-roll/post-roll bumper, excluding the item currently being played.
        /// </summary>
        private IntroInfo? GetRandomLibraryMovieIntro(string label, string libraryId, Guid excludeId)
        {
            if (!Guid.TryParse(libraryId, out var parsedId))
            {
                _logger.LogWarning(
                    "|CinemaTrailers4Jellyfins| {Label} library ID '{LibraryId}' is not a valid GUID — check the plugin settings.",
                    label,
                    libraryId);
                return null;
            }

            if (_libraryManager.GetItemById(parsedId) is not Folder folder)
            {
                _logger.LogWarning(
                    "|CinemaTrailers4Jellyfins| {Label} library {LibraryId} could not be found.",
                    label,
                    parsedId);
                return null;
            }

            var movies = folder.GetRecursiveChildren()
                .OfType<Movie>()
                .Where(m => m.Id != excludeId)
                .ToList();

            if (movies.Count == 0)
            {
                _logger.LogInformation(
                    "|CinemaTrailers4Jellyfins| {Label} library {LibraryId} has no eligible Movie items. "
                    + "Ensure the library has been scanned and contains at least one other Movie.",
                    label,
                    parsedId);
                return null;
            }

            var movie = movies[_rng.Next(movies.Count)];
            _logger.LogInformation(
                "|CinemaTrailers4Jellyfins| {Label}: picked '{Title}' ({Path}).",
                label,
                movie.Name,
                movie.Path);
            return new IntroInfo { ItemId = movie.Id, Path = movie.Path };
        }

        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();
            }
        }

        /// <summary>
        /// Returns true (and records today's date) only the first time this is called
        /// for a given user on a given day.
        /// </summary>
        private static bool IsFirstEpisodeOfDay(Guid userId)
        {
            var today = DateTime.Now.Date;
            var isFirst = false;

            _lastEpisodeTrailerDateByUser.AddOrUpdate(
                userId,
                _ =>
                {
                    isFirst = true;
                    return today;
                },
                (_, lastDate) =>
                {
                    if (lastDate < today)
                    {
                        isFirst = true;
                        return today;
                    }

                    return lastDate;
                });

            return isFirst;
        }

        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);
            }
        }
    }
}