KasinoBot/CommandHandler.cs

using Discord;
using Discord.Commands;
using Discord.WebSocket;
using Microsoft.Extensions.DependencyInjection;
using System;
using System.Reflection;
using System.Threading.Tasks;

namespace KasinoBot
{
    public class CommandHandler
    {
        private readonly CommandService _commands;
        private readonly DiscordSocketClient _discord;
        private readonly IServiceProvider _services;

        public CommandHandler(IServiceProvider services)
        {
            _commands = services.GetRequiredService<CommandService>();
            _discord = services.GetRequiredService<DiscordSocketClient>();
            _services = services;

            _commands.CommandExecuted += CommandExecutedAsync;
            _discord.MessageReceived += MessageReceivedAsync;
        }

        public async Task InitializeAsync()
        {
            await _commands.AddModulesAsync(Assembly.GetEntryAssembly(), _services);
        }

        public async Task MessageReceivedAsync(SocketMessage rawMessage)
        {
            if (!(rawMessage is SocketUserMessage message))
                return;
            if (message.Source != MessageSource.User)
                return;

            var argPos = 0;
            if (!message.HasCharPrefix('~', ref argPos))
                return;

            var context = new SocketCommandContext(_discord, message);
            await _commands.ExecuteAsync(context, argPos, _services);
        }

        public async Task CommandExecutedAsync(Optional<CommandInfo> command, ICommandContext context, IResult result)
        {
            if (!command.IsSpecified)
                return;

            if (result.IsSuccess)
                return;

            Console.WriteLine($"[{context.User.Username} | {context.Guild.Name}] Command error: {result}");
            await context.Channel.SendMessageAsync($"Command error: {result}");
        }
    }
}