using BirthdayBot.BackgroundServices;
using BirthdayBot.Data;
using Discord;
using Discord.Net;
using Discord.WebSocket;
using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using static BirthdayBot.UserInterface.CommandsCommon;

namespace BirthdayBot
{
    /// <summary>
    /// Single shard instance for Birthday Bot. This shard independently handles all input and output to Discord.
    /// </summary>
    class ShardInstance : IDisposable
    {
        private readonly ShardManager _manager;
        private readonly ShardBackgroundWorker _background;
        private readonly Dictionary<string, CommandHandler> _dispatchCommands;

        public DiscordSocketClient DiscordClient { get; }
        public int ShardId => DiscordClient.ShardId;
        /// <summary>
        /// Returns a value showing the time in which the last background run successfully completed.
        /// </summary>
        public DateTimeOffset LastBackgroundRun => _background.LastBackgroundRun;
        /// <summary>
        /// Returns the name of the background service currently in execution.
        /// </summary>
        public string CurrentExecutingService => _background.CurrentExecutingService;
        public Configuration Config => _manager.Config;

        /// <summary>
        /// Prepares and configures the shard instances, but does not yet start its connection.
        /// </summary>
        public ShardInstance(ShardManager manager, DiscordSocketClient client, Dictionary<string, CommandHandler> commands)
        {
            _manager = manager;
            _dispatchCommands = commands;

            DiscordClient = client;
            DiscordClient.Log += Client_Log;
            DiscordClient.Ready += Client_Ready;
            DiscordClient.MessageReceived += Client_MessageReceived;

            // Background task constructor begins background processing immediately.
            _background = new ShardBackgroundWorker(this);
        }
        
        /// <summary>
        /// Starts up this shard's connection to Discord and background task handling associated with it.
        /// </summary>
        public async Task StartAsync()
        {
            await DiscordClient.LoginAsync(TokenType.Bot, Config.BotToken).ConfigureAwait(false);
            await DiscordClient.StartAsync().ConfigureAwait(false);
        }

        /// <summary>
        /// Does all necessary steps to stop this shard. This method may block for a few seconds as it waits
        /// for the process to finish, but will force its disposal after at most 30 seconds.
        /// </summary>
        public void Dispose()
        {
            // Unsubscribe from own events
            DiscordClient.Log -= Client_Log;
            DiscordClient.Ready -= Client_Ready;
            DiscordClient.MessageReceived -= Client_MessageReceived;

            _background.Dispose();
            try
            {
                if (!DiscordClient.LogoutAsync().Wait(15000))
                    Log("Instance", "Warning: Client has not yet logged out. Continuing cleanup.");
            }
            catch (Exception ex)
            {
                Log("Instance", "Warning: Client threw an exception when logging out: " + ex.Message);
            }
            try
            {
                if (!DiscordClient.StopAsync().Wait(5000))
                    Log("Instance", "Warning: Client has not yet stopped. Continuing cleanup.");
            }
            catch (Exception ex)
            {
                Log("Instance", "Warning: Client threw an exception when stopping: " + ex.Message);
            }

            var clientDispose = Task.Run(DiscordClient.Dispose);
            if (!clientDispose.Wait(10000)) Log("Instance", "Warning: Client is hanging on dispose. Will continue.");
            else Log("Instance", "Shard instance disposed.");
        }

        public void Log(string source, string message) => Program.Log($"Shard {ShardId:00}] [{source}", message);

        /// <summary>
        /// Direct access to invoke the background task of updating birthdays in a guild, for use by the testing command.
        /// </summary>
        public static Task<string> ForceBirthdayUpdateAsync(SocketGuild guild)
            => BirthdayRoleUpdate.SingleProcessGuildAsync(guild);

        public void RequestDownloadUsers(ulong guildId) => _background.UserDownloader.RequestDownload(guildId);

        #region Event handling
        private Task Client_Log(LogMessage arg)
        {
            // Suppress certain messages
            if (arg.Message != null)
            {
                if (arg.Message.StartsWith("Unknown Dispatch ")) return Task.CompletedTask;
                switch (arg.Message) // Connection status messages replaced by ShardManager's output
                {
                    case "Connecting":
                    case "Connected":
                    case "Ready":
                    case "Failed to resume previous session":
                    case "Resumed previous session":
                    case "Disconnecting":
                    case "Disconnected":
                    case "WebSocket connection was closed":
                    case "Server requested a reconnect":
                        return Task.CompletedTask;
                }
                if (arg.Message == "Heartbeat Errored")
                {
                    // Replace this with a custom message; do not show stack trace
                    Log("Discord.Net", $"{arg.Severity}: {arg.Message} - {arg.Exception.Message}");
                    return Task.CompletedTask;
                }

                Log("Discord.Net", $"{arg.Severity}: {arg.Message}");
            }

            if (arg.Exception != null) Log("Discord.Net", arg.Exception.ToString());

            return Task.CompletedTask;
        }

        /// <summary>
        /// Sets the shard's status to display the help command.
        /// </summary>
        private async Task Client_Ready() => await DiscordClient.SetGameAsync(CommandPrefix + "help");

        /// <summary>
        /// Determines if the incoming message is an incoming command, and dispatches to the appropriate handler if necessary.
        /// </summary>
        private async Task Client_MessageReceived(SocketMessage msg)
        {
            if (msg.Channel is not SocketTextChannel channel) return;
            if (msg.Author.IsBot || msg.Author.IsWebhook) return;
            if (((IMessage)msg).Type != MessageType.Default) return;
            var author = (SocketGuildUser)msg.Author;

            // Limit 3:
            // For all cases: base command, 2 parameters.
            // Except this case: "bb.config", subcommand name, subcommand parameters in a single string
            var csplit = msg.Content.Split(" ", 3, StringSplitOptions.RemoveEmptyEntries);
            if (csplit.Length > 0 && csplit[0].StartsWith(CommandPrefix, StringComparison.OrdinalIgnoreCase))
            {
                // Determine if it's something we're listening for.
                if (!_dispatchCommands.TryGetValue(csplit[0][CommandPrefix.Length..], out CommandHandler command)) return;

                // Load guild information here
                var gconf = await GuildConfiguration.LoadAsync(channel.Guild.Id, false);

                // Ban check
                if (!gconf.IsBotModerator(author)) // skip check if user is a moderator
                {
                    if (await gconf.IsUserBlockedAsync(author.Id)) return; // silently ignore
                }

                // Execute the command
                try
                {
                    Log("Command", $"{channel.Guild.Name}/{author.Username}#{author.Discriminator}: {msg.Content}");
                    await command(this, gconf, csplit, channel, author);
                }
                catch (Exception ex)
                {
                    if (ex is HttpException) return;
                    Log("Command", ex.ToString());
                    try
                    {
                        channel.SendMessageAsync(":x: An unknown error occurred. It has been reported to the bot owner.").Wait();
                        // TODO webhook report
                    }
                    catch (HttpException) { } // Fail silently
                }
            }
        }
        #endregion
    }
}