using System;
using System.Collections.Generic;
using System.Threading;
using Jellyfin.Data.Enums;
using MediaBrowser.Controller.Library;
using MediaBrowser.Controller.Session;
using MediaBrowser.Controller.SyncPlay;
using MediaBrowser.Controller.SyncPlay.Requests;
using MediaBrowser.Model.SyncPlay;
using Microsoft.Extensions.Logging;

namespace Emby.Server.Implementations.SyncPlay
{
    /// <summary>
    /// Class SyncPlayManager.
    /// </summary>
    public class SyncPlayManager : ISyncPlayManager, IDisposable
    {
        /// <summary>
        /// The logger.
        /// </summary>
        private readonly ILogger<SyncPlayManager> _logger;

        /// <summary>
        /// The logger factory.
        /// </summary>
        private readonly ILoggerFactory _loggerFactory;

        /// <summary>
        /// The user manager.
        /// </summary>
        private readonly IUserManager _userManager;

        /// <summary>
        /// The session manager.
        /// </summary>
        private readonly ISessionManager _sessionManager;

        /// <summary>
        /// The library manager.
        /// </summary>
        private readonly ILibraryManager _libraryManager;

        /// <summary>
        /// The map between sessions and groups.
        /// </summary>
        private readonly Dictionary<string, IGroupController> _sessionToGroupMap =
            new Dictionary<string, IGroupController>(StringComparer.OrdinalIgnoreCase);

        /// <summary>
        /// The groups.
        /// </summary>
        private readonly Dictionary<Guid, IGroupController> _groups =
            new Dictionary<Guid, IGroupController>();

        /// <summary>
        /// Lock used for accessing any group.
        /// </summary>
        /// <remarks>
        /// Always lock before <see cref="_mapsLock"/> and before locking on any <see cref="IGroupController"/>.
        /// </remarks>
        private readonly object _groupsLock = new object();

        /// <summary>
        /// Lock used for accessing the session-to-group map.
        /// </summary>
        /// <remarks>
        /// Always lock after <see cref="_groupsLock"/> and before locking on any <see cref="IGroupController"/>.
        /// </remarks>
        private readonly object _mapsLock = new object();

        private bool _disposed = false;

        /// <summary>
        /// Initializes a new instance of the <see cref="SyncPlayManager" /> class.
        /// </summary>
        /// <param name="loggerFactory">The logger factory.</param>
        /// <param name="userManager">The user manager.</param>
        /// <param name="sessionManager">The session manager.</param>
        /// <param name="libraryManager">The library manager.</param>
        public SyncPlayManager(
            ILoggerFactory loggerFactory,
            IUserManager userManager,
            ISessionManager sessionManager,
            ILibraryManager libraryManager)
        {
            _loggerFactory = loggerFactory;
            _userManager = userManager;
            _sessionManager = sessionManager;
            _libraryManager = libraryManager;
            _logger = loggerFactory.CreateLogger<SyncPlayManager>();
            _sessionManager.SessionStarted += OnSessionManagerSessionStarted;
        }

        /// <inheritdoc />
        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        /// <inheritdoc />
        public void NewGroup(SessionInfo session, NewGroupRequest request, CancellationToken cancellationToken)
        {
            // Locking required to access list of groups.
            lock (_groupsLock)
            {
                // Locking required as session-to-group map will be edited.
                // Locking the group is not required as it is not visible yet.
                lock (_mapsLock)
                {
                    if (IsSessionInGroup(session))
                    {
                        var leaveGroupRequest = new LeaveGroupRequest();
                        LeaveGroup(session, leaveGroupRequest, cancellationToken);
                    }

                    var group = new GroupController(_loggerFactory, _userManager, _sessionManager, _libraryManager);
                    _groups[group.GroupId] = group;

                    AddSessionToGroup(session, group);
                    group.CreateGroup(session, request, cancellationToken);
                }
            }
        }

        /// <inheritdoc />
        public void JoinGroup(SessionInfo session, JoinGroupRequest request, CancellationToken cancellationToken)
        {
            var user = _userManager.GetUserById(session.UserId);

            // Locking required to access list of groups.
            lock (_groupsLock)
            {
                _groups.TryGetValue(request.GroupId, out IGroupController group);

                if (group == null)
                {
                    _logger.LogWarning("Session {SessionId} tried to join group {GroupId} that does not exist.", session.Id, request.GroupId);

                    var error = new GroupUpdate<string>(Guid.Empty, GroupUpdateType.GroupDoesNotExist, string.Empty);
                    _sessionManager.SendSyncPlayGroupUpdate(session, error, CancellationToken.None);
                    return;
                }

                // Locking required as session-to-group map will be edited.
                lock (_mapsLock)
                {
                    // Group lock required to let other requests end first.
                    lock (group)
                    {
                        if (!group.HasAccessToPlayQueue(user))
                        {
                            _logger.LogWarning("Session {SessionId} tried to join group {GroupId} but does not have access to some content of the playing queue.", session.Id, group.GroupId.ToString());

                            var error = new GroupUpdate<string>(group.GroupId, GroupUpdateType.LibraryAccessDenied, string.Empty);
                            _sessionManager.SendSyncPlayGroupUpdate(session, error, CancellationToken.None);
                            return;
                        }

                        if (IsSessionInGroup(session))
                        {
                            if (FindJoinedGroupId(session).Equals(request.GroupId))
                            {
                                group.SessionRestore(session, request, cancellationToken);
                                return;
                            }

                            var leaveGroupRequest = new LeaveGroupRequest();
                            LeaveGroup(session, leaveGroupRequest, cancellationToken);
                        }

                        AddSessionToGroup(session, group);
                        group.SessionJoin(session, request, cancellationToken);
                    }
                }
            }
        }

        /// <inheritdoc />
        public void LeaveGroup(SessionInfo session, LeaveGroupRequest request, CancellationToken cancellationToken)
        {
            // Locking required to access list of groups.
            lock (_groupsLock)
            {
                // Locking required as session-to-group map will be edited.
                lock (_mapsLock)
                {
                    var group = FindJoinedGroup(session);
                    if (group == null)
                    {
                        _logger.LogWarning("Session {SessionId} does not belong to any group.", session.Id);

                        var error = new GroupUpdate<string>(Guid.Empty, GroupUpdateType.NotInGroup, string.Empty);
                        _sessionManager.SendSyncPlayGroupUpdate(session, error, CancellationToken.None);
                        return;
                    }

                    // Group lock required to let other requests end first.
                    lock (group)
                    {
                        RemoveSessionFromGroup(session, group);
                        group.SessionLeave(session, request, cancellationToken);

                        if (group.IsGroupEmpty())
                        {
                            _logger.LogInformation("Group {GroupId} is empty, removing it.", group.GroupId);
                            _groups.Remove(group.GroupId, out _);
                        }
                    }
                }
            }
        }

        /// <inheritdoc />
        public List<GroupInfoDto> ListGroups(SessionInfo session, ListGroupsRequest request)
        {
            var user = _userManager.GetUserById(session.UserId);
            List<GroupInfoDto> list = new List<GroupInfoDto>();

            // Locking required to access list of groups.
            lock (_groupsLock)
            {
                foreach (var group in _groups.Values)
                {
                    // Locking required as group is not thread-safe.
                    lock (group)
                    {
                        if (group.HasAccessToPlayQueue(user))
                        {
                            list.Add(group.GetInfo());
                        }
                    }
                }
            }

            return list;
        }

        /// <inheritdoc />
        public void HandleRequest(SessionInfo session, IGroupPlaybackRequest request, CancellationToken cancellationToken)
        {
            IGroupController group;
            lock (_mapsLock)
            {
                group = FindJoinedGroup(session);
            }

            if (group == null)
            {
                _logger.LogWarning("Session {SessionId} does not belong to any group.", session.Id);

                var error = new GroupUpdate<string>(Guid.Empty, GroupUpdateType.NotInGroup, string.Empty);
                _sessionManager.SendSyncPlayGroupUpdate(session, error, CancellationToken.None);
                return;
            }

            // Group lock required as GroupController is not thread-safe.
            lock (group)
            {
                group.HandleRequest(session, request, cancellationToken);
            }
        }

        /// <summary>
        /// Releases unmanaged and optionally managed resources.
        /// </summary>
        /// <param name="disposing"><c>true</c> to release both managed and unmanaged resources; <c>false</c> to release only unmanaged resources.</param>
        protected virtual void Dispose(bool disposing)
        {
            if (_disposed)
            {
                return;
            }

            _sessionManager.SessionStarted -= OnSessionManagerSessionStarted;
            _disposed = true;
        }

        private void OnSessionManagerSessionStarted(object sender, SessionEventArgs e)
        {
            var session = e.SessionInfo;

            Guid groupId = Guid.Empty;
            lock (_mapsLock)
            {
                groupId = FindJoinedGroupId(session);
            }

            if (groupId.Equals(Guid.Empty))
            {
                return;
            }

            var request = new JoinGroupRequest(groupId);
            JoinGroup(session, request, CancellationToken.None);
        }

        /// <summary>
        /// Checks if a given session has joined a group.
        /// </summary>
        /// <remarks>
        /// Method is not thread-safe, external locking on <see cref="_mapsLock"/> is required.
        /// </remarks>
        /// <param name="session">The session.</param>
        /// <returns><c>true</c> if the session has joined a group, <c>false</c> otherwise.</returns>
        private bool IsSessionInGroup(SessionInfo session)
        {
            return _sessionToGroupMap.ContainsKey(session.Id);
        }

        /// <summary>
        /// Gets the group joined by the given session, if any.
        /// </summary>
        /// <remarks>
        /// Method is not thread-safe, external locking on <see cref="_mapsLock"/> is required.
        /// </remarks>
        /// <param name="session">The session.</param>
        /// <returns>The group.</returns>
        private IGroupController FindJoinedGroup(SessionInfo session)
        {
            _sessionToGroupMap.TryGetValue(session.Id, out var group);
            return group;
        }

        /// <summary>
        /// Gets the group identifier joined by the given session, if any.
        /// </summary>
        /// <remarks>
        /// Method is not thread-safe, external locking on <see cref="_mapsLock"/> is required.
        /// </remarks>
        /// <param name="session">The session.</param>
        /// <returns>The group identifier if the session has joined a group, an empty identifier otherwise.</returns>
        private Guid FindJoinedGroupId(SessionInfo session)
        {
            return FindJoinedGroup(session)?.GroupId ?? Guid.Empty;
        }

        /// <summary>
        /// Maps a session to a group.
        /// </summary>
        /// <remarks>
        /// Method is not thread-safe, external locking on <see cref="_mapsLock"/> is required.
        /// </remarks>
        /// <param name="session">The session.</param>
        /// <param name="group">The group.</param>
        /// <exception cref="InvalidOperationException">Thrown when the user is in another group already.</exception>
        private void AddSessionToGroup(SessionInfo session, IGroupController group)
        {
            if (session == null)
            {
                throw new InvalidOperationException("Session is null!");
            }

            if (IsSessionInGroup(session))
            {
                throw new InvalidOperationException("Session in other group already!");
            }

            _sessionToGroupMap[session.Id] = group ?? throw new InvalidOperationException("Group is null!");
        }

        /// <summary>
        /// Unmaps a session from a group.
        /// </summary>
        /// <remarks>
        /// Method is not thread-safe, external locking on <see cref="_mapsLock"/> is required.
        /// </remarks>
        /// <param name="session">The session.</param>
        /// <param name="group">The group.</param>
        /// <exception cref="InvalidOperationException">Thrown when the user is not found in the specified group.</exception>
        private void RemoveSessionFromGroup(SessionInfo session, IGroupController group)
        {
            if (session == null)
            {
                throw new InvalidOperationException("Session is null!");
            }

            if (group == null)
            {
                throw new InvalidOperationException("Group is null!");
            }

            if (!IsSessionInGroup(session))
            {
                throw new InvalidOperationException("Session not in any group!");
            }

            _sessionToGroupMap.Remove(session.Id, out var tempGroup);
            if (!tempGroup.GroupId.Equals(group.GroupId))
            {
                throw new InvalidOperationException("Session was in wrong group!");
            }
        }
    }
}