feat: implement sending welcome message

src/StevesBot.Worker/Discord/DiscordGatewayClient.cs

@@ -25,7 +25,7 @@ internal sealed class DiscordGatewayClient : IDiscordGatewayClient
     },
   };
   private readonly AsyncLock _lock = new();
-  private readonly Dictionary<string, Func<DiscordEvent, IServiceProvider, Task>> _eventHandlers = [];
+  private readonly Dictionary<string, Func<DiscordEvent, IServiceProvider, CancellationToken, Task>> _eventHandlers = [];
 
   private string _gatewayUrl = string.Empty;
   private IWebSocket? _webSocket;
@@ -85,7 +85,7 @@ internal sealed class DiscordGatewayClient : IDiscordGatewayClient
     await CloseIfOpenAsync(WebSocketCloseStatus.NormalClosure, "Disconnecting", cancellationToken);
   }
 
-  public void On(string eventName, Func<DiscordEvent, IServiceProvider, Task> handler)
+  public void On(string eventName, Func<DiscordEvent, IServiceProvider, CancellationToken, Task> handler)
   {
     if (DiscordEventTypes.IsValidEvent(eventName) is false)
     {
@@ -103,7 +103,7 @@ internal sealed class DiscordGatewayClient : IDiscordGatewayClient
     _eventHandlers[eventName] += handler;
   }
 
-  public void Off(string eventName, Func<DiscordEvent, IServiceProvider, Task> handler)
+  public void Off(string eventName, Func<DiscordEvent, IServiceProvider, CancellationToken, Task> handler)
   {
     if (DiscordEventTypes.IsValidEvent(eventName) is false)
     {
@@ -271,7 +271,7 @@ internal sealed class DiscordGatewayClient : IDiscordGatewayClient
           {
             await using var scope = _serviceScopeFactory.CreateAsyncScope();
             // TODO: Pass cancellation token to handler
-            await handler(de, scope.ServiceProvider);
+            await handler(de, scope.ServiceProvider, cancellationToken);
           }
 # pragma warning disable CA1031 // Do not catch general exception types
           catch (Exception ex)

src/StevesBot.Worker/Discord/DiscordRestClient.cs

@@ -17,10 +17,10 @@ internal sealed class DiscordRestClient : IDiscordRestClient
 
   public async Task<string> GetGatewayUrlAsync(CancellationToken cancellationToken)
   {
-    var uri = new Uri("gateway", UriKind.Relative);
-    var response = await _httpClient.GetAsync(uri, cancellationToken);
+    var gatewayEndpoint = new Uri("gateway", UriKind.Relative);
+    var response = await _httpClient.GetAsync(gatewayEndpoint, cancellationToken);
 
-    if (!response.IsSuccessStatusCode)
+    if (response.IsSuccessStatusCode is false)
     {
       _logger.LogError("Failed to get gateway URL: {StatusCode}", response.StatusCode);
       throw new DiscordRestClientException("Failed to get gateway URL.");
@@ -36,8 +36,49 @@ internal sealed class DiscordRestClient : IDiscordRestClient
 
     return gatewayResponse.Url;
   }
+
+  public async Task<MessageCreateData> CreateMessageAsync(string channelId, CreateMessageRequest request, CancellationToken cancellationToken)
+  {
+    var channelEndpoint = new Uri($"channels/{channelId}/messages", UriKind.Relative);
+    var response = await _httpClient.PostAsJsonAsync(channelEndpoint, request, cancellationToken);
+
+    if (response.IsSuccessStatusCode is false)
+    {
+      _logger.LogError("Failed to create message: {StatusCode}", response.StatusCode);
+      throw new DiscordRestClientException("Failed to create message.");
+    }
+
+    var messageCreateData = await response.Content.ReadFromJsonAsync<MessageCreateData>(cancellationToken);
+
+    if (messageCreateData is null)
+    {
+      _logger.LogError("Failed to deserialize message create response.");
+      throw new DiscordRestClientException("Failed to deserialize message create response.");
+    }
+
+    return messageCreateData;
+  }
 }
 
-internal record GatewayResponse(
+internal sealed record GatewayResponse(
   [property: JsonPropertyName("url")] string Url
 );
+
+internal sealed record CreateMessageRequest(
+  [property: JsonPropertyName("content")] string Content,
+  [property: JsonPropertyName("message_reference")] MessageReference? MessageReference
+);
+
+internal sealed record MessageReference(
+  [property: JsonPropertyName("type")] int Type,
+  [property: JsonPropertyName("message_id")] string MessageId,
+  [property: JsonPropertyName("channel_id")] string ChannelId,
+  [property: JsonPropertyName("guild_id")] string GuildId,
+  [property: JsonPropertyName("fail_if_not_exists")] bool FailIfNotExists
+);
+
+internal static class MessageReferenceTypes
+{
+  public const int Default = 0;
+  public const int Forward = 1;
+}

src/StevesBot.Worker/Discord/IDiscordGatewayClient.cs

@@ -4,6 +4,6 @@ internal interface IDiscordGatewayClient : IDisposable
 {
   Task ConnectAsync(CancellationToken cancellationToken);
   Task DisconnectAsync(CancellationToken cancellationToken);
-  void On(string eventName, Func<DiscordEvent, IServiceProvider, Task> handler);
-  void Off(string eventName, Func<DiscordEvent, IServiceProvider, Task> handler);
+  void On(string eventName, Func<DiscordEvent, IServiceProvider, CancellationToken, Task> handler);
+  void Off(string eventName, Func<DiscordEvent, IServiceProvider, CancellationToken, Task> handler);
 }

src/StevesBot.Worker/Discord/IDiscordRestClient.cs

@@ -3,4 +3,5 @@ namespace StevesBot.Worker.Discord;
 internal interface IDiscordRestClient
 {
   Task<string> GetGatewayUrlAsync(CancellationToken cancellationToken);
+  Task<MessageCreateData> CreateMessageAsync(string channelId, CreateMessageRequest request, CancellationToken cancellationToken);
 }

src/StevesBot.Worker/Program.cs

@@ -1,3 +1,5 @@
+using System.Net.Http.Headers;
+
 using Microsoft.Extensions.Options;
 
 var builder = Host.CreateApplicationBuilder(args);
@@ -22,6 +24,7 @@ builder.Services
     var discordOptions = sp.GetRequiredService<DiscordClientOptions>();
     c.BaseAddress = new Uri(discordOptions.ApiUrl);
     c.DefaultRequestHeaders.Authorization = new("Bot", discordOptions.AppToken);
+    c.DefaultRequestHeaders.Add("User-Agent", $"DiscordBot (https://github.com/StevanFreeborn/steves-bot, 0.0.0)");
   })
   .AddStandardResilienceHandler();
 

src/StevesBot.Worker/Worker.cs

@@ -16,34 +16,32 @@ internal class Worker : IHostedService
   {
     _logger.LogInformation("Connecting Discord Gateway Client");
 
-    // TODO: Provide access to the gateway client
-    // in delegate...don't try to resolve it from the service provider
-    // TODO: Provide .On and .Off method overloads to allow
-    // caller to not need to use discard for unused parameters
-    _discordGatewayClient.On(DiscordEventTypes.MessageCreate, static (discordEvent, sp) =>
+    _discordGatewayClient.On(DiscordEventTypes.MessageCreate, static async (discordEvent, sp, cancellationToken) =>
     {
       var discordRestClient = sp.GetRequiredService<IDiscordRestClient>();
       var logger = sp.GetRequiredService<ILogger<DiscordGatewayClient>>();
 
-      // TODO: When a user join message is received,
-      // we are going to reply to the message with
-      // a welcome greeting
-      // A user join message is type 8
-      // Will need to use REST API to reply to the message
-
-      if (
-        discordEvent is MessageCreateDiscordEvent mcde &&
-        mcde.IsMessageType(DiscordMessageTypes.UserJoin)
-      )
+      if (discordEvent is not MessageCreateDiscordEvent mcde || mcde.IsMessageType(DiscordMessageTypes.UserJoin) == false)
       {
-        logger.LogInformation("Guild Id: {GuildId}", mcde.Data.GuildId);
-        logger.LogInformation("Channel Id: {ChannelId}", mcde.Data.ChannelId);
-        logger.LogInformation("Message Id: {MessageId}", mcde.Data.Id);
-        logger.LogInformation("User Id: {UserId}", mcde.Data.Author.Id);
-        return Task.CompletedTask;
+        return;
       }
 
-      return Task.CompletedTask;
+      logger.LogInformation("Received user join message for user: {UserId}", mcde.Data.Author.Id);
+
+      var request = new CreateMessageRequest(
+        Content: $"Welcome to the server <@{mcde.Data.Author.Id}>! We're glad to have you here.",
+        MessageReference: new(
+          Type: MessageReferenceTypes.Default,
+          MessageId: mcde.Data.Id,
+          ChannelId: mcde.Data.ChannelId,
+          GuildId: mcde.Data.GuildId,
+          FailIfNotExists: false
+        )
+      );
+
+      var message = await discordRestClient.CreateMessageAsync(mcde.Data.ChannelId, request, cancellationToken);
+
+      logger.LogInformation("Created welcome message with Id: {MessageId} for user: {UserId}", message.Id, mcde.Data.Author.Id);
     });
 
     return _discordGatewayClient.ConnectAsync(cancellationToken);