// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.

#nullable enable

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using osu.Framework.Allocation;
using osu.Framework.Bindables;
using osu.Game.Beatmaps;
using osu.Game.Online.API;
using osu.Game.Online.API.Requests.Responses;
using osu.Game.Online.Multiplayer;
using osu.Game.Online.Multiplayer.MatchTypes.TeamVersus;
using osu.Game.Online.Rooms;
using osu.Game.Rulesets.Mods;
using APIUser = osu.Game.Online.API.Requests.Responses.APIUser;

namespace osu.Game.Tests.Visual.Multiplayer
{
    /// <summary>
    /// A <see cref="MultiplayerClient"/> for use in multiplayer test scenes. Should generally not be used by itself outside of a <see cref="MultiplayerTestScene"/>.
    /// </summary>
    public class TestMultiplayerClient : MultiplayerClient
    {
        public override IBindable<bool> IsConnected => isConnected;
        private readonly Bindable<bool> isConnected = new Bindable<bool>(true);

        public new Room? APIRoom => base.APIRoom;

        public Action<MultiplayerRoom>? RoomSetupAction;

        [Resolved]
        private IAPIProvider api { get; set; } = null!;

        [Resolved]
        private BeatmapManager beatmaps { get; set; } = null!;

        private readonly TestMultiplayerRoomManager roomManager;

        /// <summary>
        /// Guaranteed up-to-date playlist.
        /// </summary>
        private List<MultiplayerPlaylistItem> serverSidePlaylist = new List<MultiplayerPlaylistItem>();

        private MultiplayerPlaylistItem? currentItem => Room?.Playlist[currentIndex];
        private int currentIndex;

        public TestMultiplayerClient(TestMultiplayerRoomManager roomManager)
        {
            this.roomManager = roomManager;
        }

        public void Connect() => isConnected.Value = true;

        public void Disconnect() => isConnected.Value = false;

        public MultiplayerRoomUser AddUser(APIUser user, bool markAsPlaying = false)
        {
            var roomUser = new MultiplayerRoomUser(user.Id) { User = user };

            addUser(roomUser);

            if (markAsPlaying)
                PlayingUserIds.Add(user.Id);

            return roomUser;
        }

        public void TestAddUnresolvedUser() => addUser(new MultiplayerRoomUser(TestUserLookupCache.UNRESOLVED_USER_ID));

        private void addUser(MultiplayerRoomUser user)
        {
            ((IMultiplayerClient)this).UserJoined(user).Wait();

            // We want the user to be immediately available for testing, so force a scheduler update to run the update-bound continuation.
            Scheduler.Update();

            switch (Room?.MatchState)
            {
                case TeamVersusRoomState teamVersus:
                    Debug.Assert(Room != null);

                    // simulate the server's automatic assignment of users to teams on join.
                    // the "best" team is the one with the least users on it.
                    int bestTeam = teamVersus.Teams
                                             .Select(team => (teamID: team.ID, userCount: Room.Users.Count(u => (u.MatchState as TeamVersusUserState)?.TeamID == team.ID)))
                                             .OrderBy(pair => pair.userCount)
                                             .First().teamID;
                    ((IMultiplayerClient)this).MatchUserStateChanged(user.UserID, new TeamVersusUserState { TeamID = bestTeam }).Wait();
                    break;
            }
        }

        public void RemoveUser(APIUser user)
        {
            Debug.Assert(Room != null);
            ((IMultiplayerClient)this).UserLeft(new MultiplayerRoomUser(user.Id));

            Schedule(() =>
            {
                if (Room.Users.Any())
                    TransferHost(Room.Users.First().UserID);
            });
        }

        public void ChangeRoomState(MultiplayerRoomState newState)
        {
            Debug.Assert(Room != null);
            ((IMultiplayerClient)this).RoomStateChanged(newState);
        }

        public void ChangeUserState(int userId, MultiplayerUserState newState)
        {
            Debug.Assert(Room != null);
            ((IMultiplayerClient)this).UserStateChanged(userId, newState);

            Schedule(() =>
            {
                switch (Room.State)
                {
                    case MultiplayerRoomState.WaitingForLoad:
                        if (Room.Users.All(u => u.State != MultiplayerUserState.WaitingForLoad))
                        {
                            foreach (var u in Room.Users.Where(u => u.State == MultiplayerUserState.Loaded))
                                ChangeUserState(u.UserID, MultiplayerUserState.Playing);

                            ((IMultiplayerClient)this).MatchStarted();

                            ChangeRoomState(MultiplayerRoomState.Playing);
                        }

                        break;

                    case MultiplayerRoomState.Playing:
                        if (Room.Users.All(u => u.State != MultiplayerUserState.Playing))
                        {
                            foreach (var u in Room.Users.Where(u => u.State == MultiplayerUserState.FinishedPlay))
                                ChangeUserState(u.UserID, MultiplayerUserState.Results);
                            ChangeRoomState(MultiplayerRoomState.Open);

                            ((IMultiplayerClient)this).ResultsReady();

                            FinishCurrentItem().Wait();
                        }

                        break;
                }
            });
        }

        public void ChangeUserBeatmapAvailability(int userId, BeatmapAvailability newBeatmapAvailability)
        {
            Debug.Assert(Room != null);

            ((IMultiplayerClient)this).UserBeatmapAvailabilityChanged(userId, newBeatmapAvailability);
        }

        protected override async Task<MultiplayerRoom> JoinRoom(long roomId, string? password = null)
        {
            var apiRoom = roomManager.ServerSideRooms.Single(r => r.RoomID.Value == roomId);

            if (password != apiRoom.Password.Value)
                throw new InvalidOperationException("Invalid password.");

            serverSidePlaylist.Clear();
            serverSidePlaylist.AddRange(apiRoom.Playlist.Select(item => new MultiplayerPlaylistItem(item)));

            var localUser = new MultiplayerRoomUser(api.LocalUser.Value.Id)
            {
                User = api.LocalUser.Value
            };

            var room = new MultiplayerRoom(roomId)
            {
                Settings =
                {
                    Name = apiRoom.Name.Value,
                    MatchType = apiRoom.Type.Value,
                    Password = password,
                    QueueMode = apiRoom.QueueMode.Value
                },
                Playlist = serverSidePlaylist.ToList(),
                Users = { localUser },
                Host = localUser
            };

            await updatePlaylistOrder(room).ConfigureAwait(false);
            await updateCurrentItem(room, false).ConfigureAwait(false);

            RoomSetupAction?.Invoke(room);
            RoomSetupAction = null;

            return room;
        }

        protected override void OnRoomJoined()
        {
            Debug.Assert(APIRoom != null);
            Debug.Assert(Room != null);

            // emulate the server sending this after the join room. scheduler required to make sure the join room event is fired first (in Join).
            changeMatchType(Room.Settings.MatchType).Wait();
        }

        protected override Task LeaveRoomInternal() => Task.CompletedTask;

        public override Task TransferHost(int userId) => ((IMultiplayerClient)this).HostChanged(userId);

        public override Task KickUser(int userId)
        {
            Debug.Assert(Room != null);

            return ((IMultiplayerClient)this).UserKicked(Room.Users.Single(u => u.UserID == userId));
        }

        public override async Task ChangeSettings(MultiplayerRoomSettings settings)
        {
            Debug.Assert(Room != null);
            Debug.Assert(APIRoom != null);
            Debug.Assert(currentItem != null);

            // Server is authoritative for the time being.
            settings.PlaylistItemId = Room.Settings.PlaylistItemId;

            await changeQueueMode(settings.QueueMode).ConfigureAwait(false);

            await ((IMultiplayerClient)this).SettingsChanged(settings).ConfigureAwait(false);

            foreach (var user in Room.Users.Where(u => u.State == MultiplayerUserState.Ready))
                ChangeUserState(user.UserID, MultiplayerUserState.Idle);

            await changeMatchType(settings.MatchType).ConfigureAwait(false);
        }

        public override Task ChangeState(MultiplayerUserState newState)
        {
            ChangeUserState(api.LocalUser.Value.Id, newState);
            return Task.CompletedTask;
        }

        public override Task ChangeBeatmapAvailability(BeatmapAvailability newBeatmapAvailability)
        {
            ChangeUserBeatmapAvailability(api.LocalUser.Value.Id, newBeatmapAvailability);
            return Task.CompletedTask;
        }

        public void ChangeUserMods(int userId, IEnumerable<Mod> newMods)
            => ChangeUserMods(userId, newMods.Select(m => new APIMod(m)).ToList());

        public void ChangeUserMods(int userId, IEnumerable<APIMod> newMods)
        {
            Debug.Assert(Room != null);
            ((IMultiplayerClient)this).UserModsChanged(userId, newMods.ToList());
        }

        public override Task ChangeUserMods(IEnumerable<APIMod> newMods)
        {
            ChangeUserMods(api.LocalUser.Value.Id, newMods);
            return Task.CompletedTask;
        }

        public override async Task SendMatchRequest(MatchUserRequest request)
        {
            Debug.Assert(Room != null);
            Debug.Assert(LocalUser != null);

            switch (request)
            {
                case ChangeTeamRequest changeTeam:

                    TeamVersusRoomState roomState = (TeamVersusRoomState)Room.MatchState!;
                    TeamVersusUserState userState = (TeamVersusUserState)LocalUser.MatchState!;

                    var targetTeam = roomState.Teams.FirstOrDefault(t => t.ID == changeTeam.TeamID);

                    if (targetTeam != null)
                    {
                        userState.TeamID = targetTeam.ID;

                        await ((IMultiplayerClient)this).MatchUserStateChanged(LocalUser.UserID, userState).ConfigureAwait(false);
                    }

                    break;
            }
        }

        public override Task StartMatch()
        {
            Debug.Assert(Room != null);

            ChangeRoomState(MultiplayerRoomState.WaitingForLoad);
            foreach (var user in Room.Users.Where(u => u.State == MultiplayerUserState.Ready))
                ChangeUserState(user.UserID, MultiplayerUserState.WaitingForLoad);

            return ((IMultiplayerClient)this).LoadRequested();
        }

        public async Task AddUserPlaylistItem(int userId, MultiplayerPlaylistItem item)
        {
            Debug.Assert(Room != null);
            Debug.Assert(APIRoom != null);
            Debug.Assert(currentItem != null);

            if (Room.Settings.QueueMode == QueueMode.HostOnly && Room.Host?.UserID != LocalUser?.UserID)
                throw new InvalidOperationException("Local user is not the room host.");

            item.OwnerID = userId;

            switch (Room.Settings.QueueMode)
            {
                case QueueMode.HostOnly:
                    // In host-only mode, the current item is re-used.
                    item.ID = currentItem.ID;
                    item.GameplayOrder = currentItem.GameplayOrder;

                    serverSidePlaylist[currentIndex] = item;
                    await ((IMultiplayerClient)this).PlaylistItemChanged(item).ConfigureAwait(false);

                    // Note: Unlike the server, this is the easiest way to update the current item at this point.
                    await updateCurrentItem(Room, false).ConfigureAwait(false);
                    break;

                default:
                    await addItem(item).ConfigureAwait(false);

                    // The current item can change as a result of an item being added. For example, if all items earlier in the queue were expired.
                    await updateCurrentItem(Room).ConfigureAwait(false);
                    break;
            }
        }

        public override Task AddPlaylistItem(MultiplayerPlaylistItem item) => AddUserPlaylistItem(api.LocalUser.Value.OnlineID, item);

        protected override Task<APIBeatmap> GetAPIBeatmap(int beatmapId, CancellationToken cancellationToken = default)
        {
            IBeatmapSetInfo? set = roomManager.ServerSideRooms.SelectMany(r => r.Playlist)
                                              .FirstOrDefault(p => p.BeatmapID == beatmapId)?.Beatmap.Value.BeatmapSet
                                   ?? beatmaps.QueryBeatmap(b => b.OnlineID == beatmapId)?.BeatmapSet;

            if (set == null)
                throw new InvalidOperationException("Beatmap not found.");

            return Task.FromResult(new APIBeatmap
            {
                BeatmapSet = new APIBeatmapSet { OnlineID = set.OnlineID },
                OnlineID = beatmapId,
                Checksum = set.Beatmaps.First(b => b.OnlineID == beatmapId).MD5Hash
            });
        }

        private async Task changeMatchType(MatchType type)
        {
            Debug.Assert(Room != null);

            switch (type)
            {
                case MatchType.HeadToHead:
                    await ((IMultiplayerClient)this).MatchRoomStateChanged(null).ConfigureAwait(false);

                    foreach (var user in Room.Users)
                        await ((IMultiplayerClient)this).MatchUserStateChanged(user.UserID, null).ConfigureAwait(false);
                    break;

                case MatchType.TeamVersus:
                    await ((IMultiplayerClient)this).MatchRoomStateChanged(TeamVersusRoomState.CreateDefault()).ConfigureAwait(false);

                    foreach (var user in Room.Users)
                        await ((IMultiplayerClient)this).MatchUserStateChanged(user.UserID, new TeamVersusUserState()).ConfigureAwait(false);
                    break;
            }
        }

        private async Task changeQueueMode(QueueMode newMode)
        {
            Debug.Assert(Room != null);
            Debug.Assert(APIRoom != null);
            Debug.Assert(currentItem != null);

            // When changing to host-only mode, ensure that at least one non-expired playlist item exists by duplicating the current item.
            if (newMode == QueueMode.HostOnly && serverSidePlaylist.All(item => item.Expired))
                await duplicateCurrentItem().ConfigureAwait(false);

            await updatePlaylistOrder(Room).ConfigureAwait(false);
            await updateCurrentItem(Room).ConfigureAwait(false);
        }

        public async Task FinishCurrentItem()
        {
            Debug.Assert(Room != null);
            Debug.Assert(APIRoom != null);
            Debug.Assert(currentItem != null);

            // Expire the current playlist item.
            currentItem.Expired = true;
            await ((IMultiplayerClient)this).PlaylistItemChanged(currentItem).ConfigureAwait(false);

            // In host-only mode, a duplicate playlist item will be used for the next round.
            if (Room.Settings.QueueMode == QueueMode.HostOnly)
                await duplicateCurrentItem().ConfigureAwait(false);

            await updateCurrentItem(Room).ConfigureAwait(false);
        }

        private async Task duplicateCurrentItem()
        {
            Debug.Assert(currentItem != null);

            await addItem(new MultiplayerPlaylistItem
            {
                BeatmapID = currentItem.BeatmapID,
                BeatmapChecksum = currentItem.BeatmapChecksum,
                RulesetID = currentItem.RulesetID,
                RequiredMods = currentItem.RequiredMods,
                AllowedMods = currentItem.AllowedMods
            }).ConfigureAwait(false);
        }

        private async Task addItem(MultiplayerPlaylistItem item)
        {
            Debug.Assert(Room != null);

            // Add the item to the list first in order to compute gameplay order.
            serverSidePlaylist.Add(item);
            await updatePlaylistOrder(Room).ConfigureAwait(false);

            item.ID = serverSidePlaylist[^2].ID + 1;
            await ((IMultiplayerClient)this).PlaylistItemAdded(item).ConfigureAwait(false);
        }

        private async Task updateCurrentItem(MultiplayerRoom room, bool notify = true)
        {
            // The playlist is already in correct gameplay order, so pick the next non-expired item or default to the last item.
            MultiplayerPlaylistItem nextItem = serverSidePlaylist.FirstOrDefault(i => !i.Expired) ?? room.Playlist.Last();
            currentIndex = serverSidePlaylist.IndexOf(nextItem);

            long lastItem = room.Settings.PlaylistItemId;
            room.Settings.PlaylistItemId = nextItem.ID;

            if (notify && nextItem.ID != lastItem)
                await ((IMultiplayerClient)this).SettingsChanged(room.Settings).ConfigureAwait(false);
        }

        private async Task updatePlaylistOrder(MultiplayerRoom room)
        {
            List<MultiplayerPlaylistItem> orderedItems;

            switch (room.Settings.QueueMode)
            {
                default:
                    orderedItems = serverSidePlaylist.OrderBy(item => item.ID == 0 ? int.MaxValue : item.ID).ToList();
                    break;

                case QueueMode.AllPlayersRoundRobin:
                    // Todo: This could probably be more efficient, likely at the cost of increased complexity.
                    // Number of "expired" or "used" items per player.
                    Dictionary<int, int> perUserCounts = serverSidePlaylist
                                                         .GroupBy(item => item.OwnerID)
                                                         .ToDictionary(group => group.Key, group => group.Count(item => item.Expired));

                    // We'll run a simulation over all items which are not expired ("unprocessed"). Expired items will not have their ordering updated.
                    List<MultiplayerPlaylistItem> processedItems = serverSidePlaylist.Where(item => item.Expired).ToList();
                    List<MultiplayerPlaylistItem> unprocessedItems = serverSidePlaylist.Where(item => !item.Expired).ToList();

                    // In every iteration of the simulation, pick the first available item from the user with the lowest number of items in the queue to add to the result set.
                    // If multiple users have the same number of items in the queue, then the item with the lowest ID is chosen.
                    while (unprocessedItems.Count > 0)
                    {
                        MultiplayerPlaylistItem candidateItem = unprocessedItems
                                                                .OrderBy(item => perUserCounts[item.OwnerID])
                                                                .ThenBy(item => item.ID == 0 ? int.MaxValue : item.ID)
                                                                .First();

                        unprocessedItems.Remove(candidateItem);
                        processedItems.Add(candidateItem);

                        perUserCounts[candidateItem.OwnerID]++;
                    }

                    orderedItems = processedItems;
                    break;
            }

            for (int i = 0; i < orderedItems.Count; i++)
            {
                // Items which are already ordered correct don't need to be updated.
                if (orderedItems[i].GameplayOrder == i)
                    continue;

                orderedItems[i].GameplayOrder = i;

                // Items which have an ID of 0 are not in the database, so avoid propagating database/hub events for them.
                if (orderedItems[i].ID <= 0)
                    continue;

                await ((IMultiplayerClient)this).PlaylistItemChanged(orderedItems[i]).ConfigureAwait(false);
            }

            serverSidePlaylist = orderedItems;
        }
    }
}