using System;
using System.Collections.Generic;
using System.Linq;

namespace SharpChat {
    public class ChannelsUsersContext {
        private readonly Dictionary<string, HashSet<long>> ChannelUsers = new();
        private readonly Dictionary<long, HashSet<string>> UserChannels = new();
        private readonly Dictionary<long, string> UserLastChannel = new();

        public string GetUserLastChannel(long userId) {
            return UserLastChannel.ContainsKey(userId)
                ? UserLastChannel[userId]
                : string.Empty;
        }

        public string GetUserLastChannel(UserInfo userInfo) {
            return GetUserLastChannel(userInfo.UserId);
        }

        public void SetUserLastChannel(long userId, string channelName) {
            channelName = channelName.ToLowerInvariant();
            if(UserLastChannel.ContainsKey(userId))
                UserLastChannel[userId] = channelName;
            else
                UserLastChannel.Add(userId, channelName);
        }

        public void SetUserLastChannel(UserInfo userInfo, ChannelInfo channelInfo) {
            SetUserLastChannel(userInfo.UserId, channelInfo.Name);
        }

        public void DeleteUserLastChannel(long userId) {
            if(UserLastChannel.ContainsKey(userId))
                UserLastChannel.Remove(userId);
        }

        public void DeleteUserLastChannel(UserInfo userInfo) {
            DeleteUserLastChannel(userInfo.UserId);
        }

        public bool IsUserLastChannel(long userId, string channelName) {
            return !string.IsNullOrWhiteSpace(channelName)
                && GetUserLastChannel(userId).Equals(channelName, StringComparison.InvariantCultureIgnoreCase);
        }

        public bool IsUserLastChannel(UserInfo userInfo, ChannelInfo channelInfo) {
            return IsUserLastChannel(userInfo.UserId, channelInfo.Name);
        }

        public string[] GetUserChannelNames(long userId) {
            if(!UserChannels.ContainsKey(userId))
                return Array.Empty<string>();

            return UserChannels[userId].ToArray();
        }

        public string[] GetUserChannelNames(UserInfo userInfo) {
            return GetUserChannelNames(userInfo.UserId);
        }

        public long[] GetChannelUserIds(string channelName) {
            channelName = channelName.ToLowerInvariant();
            if(!ChannelUsers.ContainsKey(channelName))
                return Array.Empty<long>();

            return ChannelUsers[channelName].ToArray();
        }

        public long[] GetChannelUserIds(string channelName, Func<string, string> sanitise) {
            foreach(KeyValuePair<string, HashSet<long>> kvp in ChannelUsers)
                if(sanitise(kvp.Key).Equals(channelName, StringComparison.InvariantCultureIgnoreCase))
                    return kvp.Value.ToArray();

            return Array.Empty<long>();
        }

        public long[] GetChannelUserIds(ChannelInfo channelInfo) {
            return GetChannelUserIds(channelInfo.Name);
        }

        public void Join(string channelName, long userId) {
            channelName = channelName.ToLowerInvariant();
            if(ChannelUsers.ContainsKey(channelName))
                ChannelUsers[channelName].Add(userId);
            else
                ChannelUsers.Add(channelName, new HashSet<long> { userId });

            if(UserChannels.ContainsKey(userId))
                UserChannels[userId].Add(channelName);
            else
                UserChannels.Add(userId, new HashSet<string> { channelName });

            SetUserLastChannel(userId, channelName);
        }

        public void Join(ChannelInfo channelInfo, UserInfo userInfo) {
            Join(channelInfo.Name, userInfo.UserId);
        }

        public void Leave(string channelName, long userId) {
            channelName = channelName.ToLowerInvariant();
            if(ChannelUsers.ContainsKey(channelName)) {
                if(ChannelUsers[channelName].Count < 2)
                    ChannelUsers.Remove(channelName);
                else
                    ChannelUsers[channelName].Remove(userId);
            }

            if(UserChannels.ContainsKey(userId)) {
                if(UserChannels[userId].Count < 2)
                    UserChannels.Remove(userId);
                else
                    UserChannels[userId].Remove(channelName);
            }

            if(IsUserLastChannel(userId, channelName))
                DeleteUserLastChannel(userId);
        }

        public void Leave(ChannelInfo channelInfo, UserInfo userInfo) {
            Leave(channelInfo.Name, userInfo.UserId);
        }

        public bool Has(string channelName, long userId) {
            channelName = channelName.ToLowerInvariant();
            return ChannelUsers.ContainsKey(channelName)
                && ChannelUsers[channelName].Contains(userId);
        }

        public bool Has(ChannelInfo channelInfo, UserInfo userInfo) {
            return Has(channelInfo.Name, userInfo.UserId);
        }

        public long[] FilterUsers(string channelName, long[] userIds) {
            if(userIds.Length < 1)
                return userIds;

            channelName = channelName.ToLowerInvariant();
            if(!ChannelUsers.ContainsKey(channelName))
                return Array.Empty<long>();

            List<long> filtered = new();
            HashSet<long> channelUserIds = ChannelUsers[channelName];
            foreach(long userId in userIds)
                if(channelUserIds.Contains(userId))
                    filtered.Add(userId);

            return filtered.ToArray();
        }

        public UserInfo[] FilterUsers(ChannelInfo channelInfo, UserInfo[] userInfos) {
            if(userInfos.Length < 1)
                return userInfos;

            long[] filteredIds = FilterUsers(channelInfo.Name, userInfos.Select(u => u.UserId).ToArray());
            if(filteredIds.Length < 1)
                return Array.Empty<UserInfo>();

            return userInfos.Where(u => filteredIds.Contains(u.UserId)).ToArray();
        }

        public bool HasUsers(string channelName, long[] userIds) {
            return FilterUsers(channelName, userIds).SequenceEqual(userIds);
        }

        public bool HasUsers(ChannelInfo channelInfo, UserInfo[] userInfos) {
            return HasUsers(channelInfo.Name, userInfos.Select(u => u.UserId).ToArray());
        }

        public string[] FilterChannels(long userId, string[] channelNames) {
            if(channelNames.Length < 1)
                return channelNames;

            if(!UserChannels.ContainsKey(userId))
                return Array.Empty<string>();

            List<string> filtered = new();
            HashSet<string> userChannelNames = UserChannels[userId];
            foreach(string channelName in userChannelNames)
                if(userChannelNames.Contains(channelName))
                    filtered.Add(channelName);

            return filtered.ToArray();
        }

        public ChannelInfo[] FilterChannels(UserInfo userInfo, ChannelInfo[] channelInfos) {
            if(channelInfos.Length < 1)
                return channelInfos;

            string[] filteredNames = FilterChannels(userInfo.UserId, channelInfos.Select(c => c.Name).ToArray());
            if(filteredNames.Length < 1)
                return Array.Empty<ChannelInfo>();

            return channelInfos.Where(c => filteredNames.Contains(c.Name.ToLowerInvariant())).ToArray();
        }

        public bool HasChannels(long userId, string[] channelNames) {
            if(!UserChannels.ContainsKey(userId))
                return false;

            HashSet<string> userChannelNames = UserChannels[userId];
            foreach(string channelName in channelNames)
                if(!userChannelNames.Contains(channelName.ToLowerInvariant()))
                    return false;

            return true;
        }

        public bool HasChannels(UserInfo userInfo, ChannelInfo[] channelInfos) {
            return HasChannels(userInfo.UserId, channelInfos.Select(c => c.Name).ToArray());
        }

        public void DeleteUser(long userId) {
            if(!UserChannels.ContainsKey(userId))
                return;

            HashSet<string> channelNames = UserChannels[userId];
            UserChannels.Remove(userId);
            DeleteUserLastChannel(userId);

            foreach(string channelName in channelNames) {
                if(!ChannelUsers.ContainsKey(channelName))
                    continue;

                ChannelUsers[channelName].Remove(userId);
            }
        }

        public void DeleteUser(UserInfo userInfo) {
            DeleteUser(userInfo.UserId);
        }

        public void DeleteChannel(string channelName) {
            channelName = channelName.ToLowerInvariant();
            if(!ChannelUsers.ContainsKey(channelName))
                return;

            HashSet<long> userIds = ChannelUsers[channelName];
            ChannelUsers.Remove(channelName);

            foreach(long userId in userIds) {
                if(!UserChannels.ContainsKey(userId))
                    continue;

                UserChannels[userId].Remove(channelName);

                if(IsUserLastChannel(userId, channelName))
                    DeleteUserLastChannel(userId);
            }
        }

        public void DeleteChannel(ChannelInfo channelInfo) {
            DeleteChannel(channelInfo.Name);
        }
    }
}