Basic bot

.gitignore

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+obj
+.idea
+.vs
+bin

Handler/GoodByeCommand/GoodbyeHandler.cs

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+using Discord.WebSocket;
+using MediatR;
+
+namespace Lunaris2.Handler.GoodByeCommand
+{
+    public record GoodbyeCommand(SocketSlashCommand Message) : IRequest;
+
+    public class GoodbyeHandler : IRequestHandler<GoodbyeCommand>
+    {
+        public async Task Handle(GoodbyeCommand message, CancellationToken cancellationToken)
+        {
+            await message.Message.RespondAsync($"Goodbye, {message.Message.User.Username}! :c");
+        }
+    }
+}

Handler/HelloCommand/HelloHandler.cs

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+using Discord.WebSocket;
+using Lunaris2.SlashCommand;
+using MediatR;
+using Newtonsoft.Json;
+
+namespace Lunaris2.Handler.HelloCommand
+{
+    public record HelloCommand(SocketSlashCommand Message) : IRequest;
+
+    public class HelloHandler : IRequestHandler<HelloCommand>
+    {
+        public async Task Handle(HelloCommand message, CancellationToken cancellationToken)
+        {
+            Console.WriteLine(JsonConvert.SerializeObject(Command.GetAllCommands()));
+            
+            await message.Message.RespondAsync($"Hello, {message.Message.User.Username}!");
+        }
+    }
+}

Handler/MessageReceivedHandler.cs

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+using Lunaris2.Handler.GoodByeCommand;
+using Lunaris2.Notification;
+using Lunaris2.SlashCommand;
+using MediatR;
+
+namespace Lunaris2.Handler;
+
+public class MessageReceivedHandler(ISender mediator) : INotificationHandler<MessageReceivedNotification>
+{
+    public async Task Handle(MessageReceivedNotification notification, CancellationToken cancellationToken)
+    {
+        switch (notification.Message.CommandName)
+        {
+            case Command.Hello.Name:
+                await mediator.Send(new HelloCommand.HelloCommand(notification.Message), cancellationToken);
+                break;
+            case Command.Goodbye.Name:
+                await mediator.Send(new GoodbyeCommand(notification.Message), cancellationToken);
+                break;
+            default:
+                break;
+        }
+    }
+}

Lunaris2.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Discord.Net" Version="3.14.1" />
+    <PackageReference Include="Discord.Net.Commands" Version="3.14.1" />
+    <PackageReference Include="Discord.Net.Core" Version="3.14.1" />
+    <PackageReference Include="Discord.Net.Interactions" Version="3.14.1" />
+    <PackageReference Include="Discord.Net.Rest" Version="3.14.1" />
+    <PackageReference Include="MediatR" Version="12.2.0" />
+    <PackageReference Include="Microsoft.Extensions.Configuration" Version="8.0.0" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="8.0.0" />
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="8.0.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <None Update="appsettings.json">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
+
+</Project>

Lunaris2.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.9.34701.34
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Lunaris2", "Lunaris2.csproj", "{3A16FD4C-EE50-4B05-9A75-0DDCD93AA615}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{3A16FD4C-EE50-4B05-9A75-0DDCD93AA615}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{3A16FD4C-EE50-4B05-9A75-0DDCD93AA615}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{3A16FD4C-EE50-4B05-9A75-0DDCD93AA615}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{3A16FD4C-EE50-4B05-9A75-0DDCD93AA615}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {4E738D71-9DB0-456E-9BF2-0CE3FED1DE44}
+	EndGlobalSection
+EndGlobal

Notification/DiscordEventListener.cs

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+using Discord.WebSocket;
+using MediatR;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Lunaris2.Notification;
+
+public class DiscordEventListener(DiscordSocketClient client, IServiceScopeFactory serviceScope)
+{
+    private readonly CancellationToken _cancellationToken = new CancellationTokenSource().Token;
+
+    private IMediator Mediator
+    {
+        get
+        {
+            var scope = serviceScope.CreateScope();
+            return scope.ServiceProvider.GetRequiredService<IMediator>();
+        }
+    }
+
+    public async Task StartAsync()
+    {
+        client.SlashCommandExecuted += OnMessageReceivedAsync;
+
+        await Task.CompletedTask;
+    }
+
+    private Task OnMessageReceivedAsync(SocketSlashCommand  arg)
+    {
+        return Mediator.Publish(new MessageReceivedNotification(arg), _cancellationToken);
+    }
+}

Notification/MessageReceivedNotification.cs

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+using Discord.WebSocket;
+using MediatR;
+
+namespace Lunaris2.Notification;
+
+public class MessageReceivedNotification(SocketSlashCommand message) : INotification
+{
+    public SocketSlashCommand  Message { get; } = message ?? throw new ArgumentNullException(nameof(message));
+}

Program.cs

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+using System.Reflection;
+using Discord;
+using Discord.Commands;
+using Discord.Interactions;
+using Discord.WebSocket;
+using Lunaris2.Notification;
+using Lunaris2.SlashCommand;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Lunaris2;
+
+public class Program
+{
+    private DiscordSocketClient? _client;
+    private CommandService? _commands;
+    private IServiceProvider? _services;
+    private IConfiguration? _config;
+
+    private static void Main(string[] args) => new Program()
+        .RunBotAsync()
+        .GetAwaiter()
+        .GetResult();
+
+    private async Task RunBotAsync()
+    {
+        var config = new DiscordSocketConfig
+        {
+            GatewayIntents = GatewayIntents.All
+        };
+        
+        _client = new DiscordSocketClient(config);
+        _client.Ready += Client_Ready;
+        _commands = new CommandService();
+        _services = new ServiceCollection()
+            .AddSingleton(_client)
+            .AddSingleton(_commands)
+            .AddMediatR(cfg => cfg.RegisterServicesFromAssembly(Assembly.GetExecutingAssembly()))
+            .AddSingleton<DiscordEventListener>()
+            .AddSingleton(x => new InteractionService(x.GetRequiredService<DiscordSocketClient>()))
+            .BuildServiceProvider();
+        
+        _client.Log += Log;
+        _config = new ConfigurationBuilder()
+            .SetBasePath(AppContext.BaseDirectory)
+            .AddJsonFile("appsettings.json")
+            .Build();
+        
+        await _client.LoginAsync(TokenType.Bot, _config["Token"]);
+        await _client.StartAsync();
+
+        var listener = _services.GetRequiredService<DiscordEventListener>();
+        await listener.StartAsync();
+        
+        await Task.Delay(Timeout.Infinite);
+    }
+
+    private async Task Client_Ready()
+    {
+        _client.RegisterCommands();
+    }
+    
+    private Task Log(LogMessage arg)
+    {
+        Console.WriteLine(arg);
+        return Task.CompletedTask;
+    }
+}

SlashCommand/Command.cs

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+namespace Lunaris2.SlashCommand;
+
+public static class Command
+{
+    public static class Hello
+    {
+        public const string Name = "hello";
+        public const string Description = "Say hello to the bot!";
+    }
+
+    public static class Goodbye
+    {
+        public const string Name = "goodbye";
+        public const string Description = "Say goodbye to the bot!";
+    }
+    
+    public static string[] GetAllCommands()
+    {
+        return typeof(Command)
+            .GetNestedTypes()
+            .Select(command => command.GetField("Name")?.GetValue(null)?.ToString())
+            .ToArray()!;
+    }
+}

SlashCommand/SlashCommandBuilder.cs

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+using Discord.Net;
+using Discord.WebSocket;
+using Newtonsoft.Json;
+
+namespace Lunaris2.SlashCommand;
+
+public class SlashCommandBuilder(string commandName, string commandDescription)
+{
+    private string CommandName { get; set; } = commandName;
+    private string CommandDescription { get; set; } = commandDescription;
+
+    public async Task CreateSlashCommand(DiscordSocketClient client)
+    {
+        var registeredCommands = await client.GetGlobalApplicationCommandsAsync();
+        await RemoveUnusedCommands(Command.GetAllCommands(), registeredCommands);
+        
+        if (await CommandExists(registeredCommands))
+            return;
+
+        var globalCommand = new Discord.SlashCommandBuilder();
+        globalCommand.WithName(CommandName);
+        globalCommand.WithDescription(CommandDescription);
+
+        try
+        {
+            await client.CreateGlobalApplicationCommandAsync(globalCommand.Build());
+            Console.WriteLine($"Command {CommandName} has been registered.");
+        }
+        catch(HttpException exception)
+        {
+            var json = JsonConvert.SerializeObject(exception.Errors, Formatting.Indented);
+            Console.WriteLine(json);
+        }
+    }
+
+    private static async Task RemoveUnusedCommands(string[] commands, IEnumerable<SocketApplicationCommand> registeredCommands)
+    {
+        // Remove commands from Discord(registeredCommands) that are not in the list of commands
+        foreach(var command in registeredCommands)
+        {
+            if (commands.Contains(command.Name)) 
+                continue;
+            
+            await command.DeleteAsync();
+            Console.WriteLine($"Command {command.Name} has been removed.");
+        }
+    }
+    
+    private async Task<bool> CommandExists(IEnumerable<SocketApplicationCommand> registeredCommands)
+    {
+        if (!registeredCommands.Any(command => command.Name == CommandName && command.Description == CommandDescription))
+            return false;
+        
+        Console.WriteLine($"Command {CommandName} already exists.");
+        return true;
+    }
+}

SlashCommand/SlashCommandRegistration.cs

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+using Discord.WebSocket;
+
+namespace Lunaris2.SlashCommand;
+
+public static class SlashCommandRegistration
+{
+    public static void RegisterCommands(this DiscordSocketClient client)
+    {
+        RegisterCommand(client, Command.Hello.Name, Command.Hello.Description);
+        RegisterCommand(client, Command.Goodbye.Name, Command.Goodbye.Description);
+    }
+
+    private static void RegisterCommand(DiscordSocketClient client, string commandName, string commandDescription)
+    {
+        var command = new SlashCommandBuilder(commandName, commandDescription);
+        _ = command.CreateSlashCommand(client);
+    }
+}

appsettings.json

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+{
+    "Logging": {
+        "LogLevel": {
+            "Default": "Debug",
+            "System": "Information",
+            "Microsoft": "Information"
+        }
+    },
+    "Token": "YOUR_BOT_TOKEN"
+}