Reduce method complexity in /ban, /unban and some other commands (#50)

This PR does numerous things to reduce method complexity:
- Created an extension method
`FeedbackService#SendContextualEmbedResultAsync`, which directly takes a
`Result<Embed>` and checks it once in the extension method instead of
multiple times in all commands;
- Split the command methods for `/ban` and `/unban` into 2 parts:
`Execute(Un)Ban` and `(Un)BanUserAsync`. The former will check all the
needed results and will pass the outputs into the latter;
- Extracted the method for logging an action into Private- and
PublicFeedbackChannels. It now resides in UtilityService. Right now,
only `/ban` and `/unban` make use of that method;
- Created an extension method `Snowflake#EmptyOrEqualTo`, that combines
the task of checking if a Snowflake is empty and checking if that
Snowflake is equal to another Snowflake.

Similar changes will be made to other command groups in future PRs. This
is not done here to make the reviewing process easier.

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

src/Services/UtilityService.cs

@@ -4,6 +4,7 @@ using Boyfriend.Data;
 using Microsoft.Extensions.Hosting;
 using Remora.Discord.API.Abstractions.Objects;
 using Remora.Discord.API.Abstractions.Rest;
+using Remora.Discord.Extensions.Embeds;
 using Remora.Discord.Extensions.Formatting;
 using Remora.Rest.Core;
 using Remora.Results;
@@ -15,15 +16,18 @@ namespace Boyfriend.Services;
 ///     of some Discord APIs.
 /// </summary>
 public class UtilityService : IHostedService {
+    private readonly IDiscordRestChannelAPI             _channelApi;
     private readonly IDiscordRestGuildScheduledEventAPI _eventApi;
     private readonly IDiscordRestGuildAPI               _guildApi;
     private readonly IDiscordRestUserAPI                _userApi;
 
     public UtilityService(
-        IDiscordRestGuildAPI guildApi, IDiscordRestUserAPI userApi, IDiscordRestGuildScheduledEventAPI eventApi) {
+        IDiscordRestChannelAPI channelApi, IDiscordRestGuildScheduledEventAPI eventApi, IDiscordRestGuildAPI guildApi,
+        IDiscordRestUserAPI    userApi) {
+        _channelApi = channelApi;
+        _eventApi = eventApi;
         _guildApi = guildApi;
         _userApi = userApi;
-        _eventApi = eventApi;
     }
 
     public Task StartAsync(CancellationToken ct) {
@@ -132,4 +136,51 @@ public class UtilityService : IHostedService {
             .Aggregate(builder, (current, user) => current.Append($"{Mention.User(user.User)} "));
         return builder.ToString();
     }
+
+    /// <summary>
+    ///     Logs an action in the <see cref="GuildSettings.PublicFeedbackChannel" /> and
+    ///     <see cref="GuildSettings.PrivateFeedbackChannel" />.
+    /// </summary>
+    /// <param name="cfg">The guild configuration.</param>
+    /// <param name="channelId">The ID of the channel where the action was executed.</param>
+    /// <param name="title">The title for the embed.</param>
+    /// <param name="avatar">The user whose avatar will be displayed next to the <paramref name="title" /> of the embed.</param>
+    /// <param name="description">The description of the embed.</param>
+    /// <param name="user">The user who performed the action.</param>
+    /// <param name="ct">The cancellation token for this operation.</param>
+    /// <returns></returns>
+    public Result LogActionAsync(
+        JsonNode cfg,  Snowflake         channelId, string title, IUser avatar, string description,
+        IUser    user, CancellationToken ct = default) {
+        var publicChannel = GuildSettings.PublicFeedbackChannel.Get(cfg);
+        var privateChannel = GuildSettings.PrivateFeedbackChannel.Get(cfg);
+        if (GuildSettings.PublicFeedbackChannel.Get(cfg).EmptyOrEqualTo(channelId)
+            && GuildSettings.PrivateFeedbackChannel.Get(cfg).EmptyOrEqualTo(channelId))
+            return Result.FromSuccess();
+
+        var logEmbed = new EmbedBuilder().WithSmallTitle(title, avatar)
+            .WithDescription(description)
+            .WithActionFooter(user)
+            .WithCurrentTimestamp()
+            .WithColour(ColorsList.Green)
+            .Build();
+
+        if (!logEmbed.IsDefined(out var logBuilt))
+            return Result.FromError(logEmbed);
+
+        var builtArray = new[] { logBuilt };
+
+        // Not awaiting to reduce response time
+        if (publicChannel != channelId.Value)
+            _ = _channelApi.CreateMessageAsync(
+                publicChannel, embeds: builtArray,
+                ct: ct);
+        if (privateChannel != publicChannel
+            && privateChannel != channelId.Value)
+            _ = _channelApi.CreateMessageAsync(
+                privateChannel, embeds: builtArray,
+                ct: ct);
+
+        return Result.FromSuccess();
+    }
 }