Unload guild datas when they become unavailable (#146)

Closes #120

---------

Signed-off-by: Macintosh II <mctaylxrs@outlook.com>
Signed-off-by: Macintosh II <95250141+mctaylors@users.noreply.github.com>

src/Responders/GuildUnloadedResponder.cs

@@ -0,0 +1,38 @@
+using JetBrains.Annotations;
+using Microsoft.Extensions.Logging;
+using Octobot.Data;
+using Octobot.Services;
+using Remora.Discord.API.Abstractions.Gateway.Events;
+using Remora.Discord.Gateway.Responders;
+using Remora.Results;
+
+namespace Octobot.Responders;
+
+/// <summary>
+///     Handles removing guild ID from <see cref="GuildData" /> if the guild becomes unavailable.
+/// </summary>
+[UsedImplicitly]
+public class GuildUnloadedResponder : IResponder<IGuildDelete>
+{
+    private readonly GuildDataService _guildData;
+    private readonly ILogger<GuildUnloadedResponder> _logger;
+
+    public GuildUnloadedResponder(
+        GuildDataService guildData, ILogger<GuildUnloadedResponder> logger)
+    {
+        _guildData = guildData;
+        _logger = logger;
+    }
+
+    public Task<Result> RespondAsync(IGuildDelete gatewayEvent, CancellationToken ct = default)
+    {
+        var guildId = gatewayEvent.ID;
+        var isDataRemoved = _guildData.UnloadGuildData(guildId);
+        if (isDataRemoved)
+        {
+            _logger.LogInformation("Left guild {GuildId}", guildId);
+        }
+
+        return Task.FromResult(Result.FromSuccess());
+    }
+}

src/Services/GuildDataService.cs

@@ -142,4 +142,9 @@ public sealed class GuildDataService : IHostedService
     {
         return _datas.Keys;
     }
+
+    public bool UnloadGuildData(Snowflake id)
+    {
+        return _datas.TryRemove(id, out _);
+    }
 }