using BirthdayBot.BackgroundServices;
using BirthdayBot.Data;
using Discord.Interactions;
using Discord.Net;
using Microsoft.Extensions.DependencyInjection;
using System.Reflection;
using static BirthdayBot.TextCommands.CommandsCommon;

namespace BirthdayBot;

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

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

    public const string InternalError = ":x: An unknown error occurred. If it persists, please notify the bot owner.";

    /// <summary>
    /// Prepares and configures the shard instances, but does not yet start its connection.
    /// </summary>
    internal ShardInstance(ShardManager manager, IServiceProvider services, Dictionary<string, CommandHandler> textCmds) {
        _manager = manager;
        _services = services;
        _textDispatch = textCmds;

        DiscordClient = _services.GetRequiredService<DiscordSocketClient>();
        DiscordClient.Log += Client_Log;
        DiscordClient.Ready += Client_Ready;
        DiscordClient.MessageReceived += Client_MessageReceived;

        _interactionService = _services.GetRequiredService<InteractionService>();
        DiscordClient.InteractionCreated += DiscordClient_InteractionCreated;
        _interactionService.SlashCommandExecuted += InteractionService_SlashCommandExecuted;

        // 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 _interactionService.AddModulesAsync(Assembly.GetExecutingAssembly(), _services).ConfigureAwait(false);
        await DiscordClient.LoginAsync(TokenType.Bot, Config.BotToken).ConfigureAwait(false);
        await DiscordClient.StartAsync().ConfigureAwait(false);
    }

    /// <summary>
    /// Does all necessary steps to stop this shard, including canceling background tasks and disconnecting.
    /// </summary>
    public void Dispose() {
        // TODO are these necessary?
        _interactionService.SlashCommandExecuted -= InteractionService_SlashCommandExecuted;
        DiscordClient.InteractionCreated -= DiscordClient_InteractionCreated;
        DiscordClient.Log -= Client_Log;
        DiscordClient.Ready -= Client_Ready;
        DiscordClient.MessageReceived -= Client_MessageReceived;

        _interactionService.Dispose();
        _background.Dispose();
        DiscordClient.LogoutAsync().Wait(5000);
        DiscordClient.StopAsync().Wait(5000);
        DiscordClient.Dispose();
        Log(nameof(ShardInstance), "Shard instance disposed.");
    }

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

    private Task Client_Log(LogMessage arg) {
        // Suppress certain messages
        if (arg.Message != null) {
            // These warnings appear often as of Discord.Net v3...
            if (arg.Message.StartsWith("Unknown Dispatch ") || arg.Message.StartsWith("Unknown Channel")) return Task.CompletedTask;
            switch (arg.Message) // Connection status messages replaced by ShardManager's output
            {
                case "Connecting":
                case "Connected":
                case "Ready":
                case "Disconnecting":
                case "Disconnected":
                case "Resumed previous session":
                case "Failed to resume previous session":
                case "Discord.WebSocket.GatewayReconnectException: Server requested a reconnect":
                    return Task.CompletedTask;
            }

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

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

        return Task.CompletedTask;
    }

    /// <summary>
    /// Registers all available slash commands.
    /// Additionally, sets the shard's status to display the help command.
    /// </summary>
    private async Task Client_Ready() {
        await DiscordClient.SetGameAsync(CommandPrefix + "help");

#if !DEBUG
        // Update slash/interaction commands
        if (ShardId == 0) await _interactionService.RegisterCommandsGloballyAsync(true).ConfigureAwait(false);
#else
        // Debug: Register our commands locally instead, in each guild we're in
        foreach (var g in DiscordClient.Guilds) {
            await _interactionService.RegisterCommandsToGuildAsync(g.Id, true).ConfigureAwait(false);
            // TODO log?
        }
#endif
    }

    /// <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 (!_textDispatch.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(InternalError).Wait();
                } catch (HttpException) { } // Fail silently
            }
        }
    }

    private Task InteractionService_SlashCommandExecuted(SlashCommandInfo arg1, IInteractionContext arg2, IResult arg3) {
        // TODO extract command and subcommands to log here
        Log("Interaction", $"/{arg1.Name} executed by {arg2.Guild.Name}!{arg2.User}.");
        if (!arg3.IsSuccess) {
            Log("Interaction", Enum.GetName(typeof(InteractionCommandError), arg3.Error) + ": " + arg3.ErrorReason);
        }

        // TODO finish this up
        return Task.CompletedTask;
    }
    
    private async Task DiscordClient_InteractionCreated(SocketInteraction arg) {
        // TODO verify this whole thing - it's a hastily done mash-up of example code and my old code
        var context = new SocketInteractionContext(DiscordClient, arg);

        // Specific reply for DM messages
        if (context.Channel is not SocketGuildChannel) {
            Log("Interaction", $"DM interaction. User ID {context.User.Id}, {context.User}");
            await arg.RespondAsync("DMs are not supported by this bot.").ConfigureAwait(false);
            return;
        }

        // Blocklist/moderated check
        var gconf = await GuildConfiguration.LoadAsync(context.Guild.Id, false);
        if (!gconf!.IsBotModerator((SocketGuildUser)arg.User)) // Except if moderator
        {
            if (await gconf.IsUserBlockedAsync(arg.User.Id)) {
                Log("Interaction", $"Blocking interaction per guild policy. User ID {context.User.Id}, {context.User}");
                await arg.RespondAsync(ApplicationCommands.BotModuleBase.AccessDeniedError, ephemeral: true).ConfigureAwait(false);
                return;
            }
        }

        try {
            await _interactionService.ExecuteCommandAsync(context, _services);
        } catch (Exception ex) {
            Console.WriteLine(ex);

            // If a Slash Command execution fails it is most likely that the original interaction acknowledgement will persist. It is a good idea to delete the original
            // response, or at least let the user know that something went wrong during the command execution.
            if (arg.Type == InteractionType.ApplicationCommand)
                await arg.GetOriginalResponseAsync().ContinueWith(async (msg) => await msg.Result.DeleteAsync());
        }
    }
}