Switch to Interaction Framework for slash commands

ApplicationCommands.cs

@@ -0,0 +1,292 @@
+using Discord.Interactions;
+using NodaTime;
+using System.Collections.ObjectModel;
+using System.Globalization;
+using System.Text;
+
+namespace WorldTime;
+
+public class ApplicationCommands : InteractionModuleBase<ShardedInteractionContext> {
+    const string ErrNotAllowed = ":x: Only server moderators may use this command.";
+
+    const string EmbedHelpField1 = $"`/help` - {HelpHelp}\n"
+        + $"`/list` - {HelpList}\n"
+        + $"`/set` - {HelpSet}\n"
+        + $"`/remove` - {HelpRemove}";
+    const string EmbedHelpField2 = $"`/set-for` - {HelpSetFor}\n`/remove-for` - {HelpRemoveFor}";
+
+    #region Help strings
+    const string HelpHelp = "Displays a list of available bot commands.";
+    const string HelpList = "Shows the current time for all recently active known users.";
+    const string HelpSet = "Adds or updates your time zone to the bot.";
+    const string HelpSetFor = "Sets/updates time zone for a given user.";
+    const string HelpRemove = "Removes your time zone information from this bot.";
+    const string HelpRemoveFor = "Removes time zone for a given user.";
+    #endregion
+    private const string ErrInvalidZone = ":x: Not a valid zone name."
+        + " To find your time zone, refer to: <https://kevinnovak.github.io/Time-Zone-Picker/>.";
+    private const string ErrNoUserCache = ":warning: Please try the command again.";
+
+    private static readonly ReadOnlyDictionary<string, string> _tzNameMap;
+
+    public DiscordShardedClient ShardedClient { get; set; } = null!;
+    public Database Database { get; set; } = null!;
+
+    static ApplicationCommands() {
+        Dictionary<string, string> tzNameMap = new(StringComparer.OrdinalIgnoreCase);
+        foreach (var name in DateTimeZoneProviders.Tzdb.Ids) tzNameMap.Add(name, name);
+        _tzNameMap = new(tzNameMap);
+    }
+
+    [SlashCommand("help", HelpHelp)]
+    public async Task CmdHelp() {
+        var version = System.Reflection.Assembly.GetExecutingAssembly().GetName().Version!.ToString(3);
+        var guildct = ShardedClient.Guilds.Count;
+        var uniquetz = await Database.GetDistinctZoneCountAsync();
+        await RespondAsync(embed: new EmbedBuilder() {
+            Title = "Help & About",
+            Description = $"World Time v{version} - Serving {guildct} communities across {uniquetz} time zones.\n\n"
+                + "This bot is provided for free, without any paywalled 'premium' features. "
+                + "If you've found this bot useful, please consider contributing via the "
+                + "bot author's page on Ko-fi: https://ko-fi.com/noithecat.",
+            Footer = new EmbedFooterBuilder() {
+                IconUrl = Context.Client.CurrentUser.GetAvatarUrl(),
+                Text = "World Time"
+            }
+        }.AddField(inline: false, name: "Commands", value: EmbedHelpField1
+        ).AddField(inline: false, name: "Admin commands", value: EmbedHelpField2
+        ).AddField(inline: false, name: "Zones", value:
+            "This bot accepts zone names from the IANA Time Zone Database (a.k.a. Olson Database). " +
+            "A useful tool to determine yours can be found at: https://kevinnovak.github.io/Time-Zone-Picker/"
+        ).Build());
+    }
+
+    [RequireGuildContext]
+    [SlashCommand("list", HelpList)]
+    public async Task CmdList([Summary(description: "A specific user whose time to look up.")]SocketGuildUser? user = null) {
+        if (!await AreUsersDownloadedAsync(Context.Guild)) {
+            await RespondAsync(ErrNoUserCache, ephemeral: true);
+            return;
+        }
+
+        if (user != null) {
+            await CmdListUserAsync(user);
+            return;
+        }
+
+        var userlist = await Database.GetGuildZonesAsync(Context.Guild.Id);
+        if (userlist.Count == 0) {
+            await RespondAsync(":x: Nothing to show. Register your time zones with the bot using the `/set` command.");
+            return;
+        }
+        // Order times by popularity to limit how many are shown, group by printed name
+        var sortedlist = new SortedDictionary<string, List<ulong>>();
+        foreach ((string area, List<ulong> users) in userlist.OrderByDescending(o => o.Value.Count).Take(20)) {
+            // Filter further to top 20 distinct timezones, even if they are not displayed in the final result
+            var areaprint = TzPrint(area);
+            if (!sortedlist.ContainsKey(areaprint)) sortedlist.Add(areaprint, new List<ulong>());
+            sortedlist[areaprint].AddRange(users);
+        }
+
+        const int MaxSingleLineLength = 750;
+        const int MaxSingleOutputLength = 900;
+
+        // Build zone listings with users
+        var outputlines = new List<string>();
+        foreach ((string area, List<ulong> users) in sortedlist) {
+            var buffer = new StringBuilder();
+            buffer.Append(area[4..] + ": ");
+            bool empty = true;
+            foreach (var userid in users) {
+                var userinstance = Context.Guild.GetUser(userid);
+                if (userinstance == null) continue;
+                if (empty) empty = !empty;
+                else buffer.Append(", ");
+                var useradd = FormatName(userinstance);
+                if (buffer.Length + useradd.Length > MaxSingleLineLength) {
+                    buffer.Append("others...");
+                    break;
+                } else buffer.Append(useradd);
+            }
+            if (!empty) outputlines.Add(buffer.ToString());
+        }
+
+        // Prepare for output - send buffers out if they become too large
+        outputlines.Sort();
+        bool hasOutputOneLine = false;
+        // First output is shown as an interaction response, followed then as regular channel messages
+        async Task doOutput(Embed msg) {
+            if (!hasOutputOneLine) {
+                await RespondAsync(embed: msg);
+                hasOutputOneLine = true;
+            } else {
+                await ReplyAsync(embed: msg);
+            }
+        }
+
+        var resultout = new StringBuilder();
+        foreach (var line in outputlines) {
+            if (resultout.Length + line.Length > MaxSingleOutputLength) {
+                await doOutput(new EmbedBuilder().WithDescription(resultout.ToString()).Build());
+                resultout.Clear();
+            }
+            if (resultout.Length > 0) resultout.AppendLine(); // avoids trailing newline by adding to the previous line
+            resultout.Append(line);
+        }
+        if (resultout.Length > 0) {
+            await doOutput(new EmbedBuilder().WithDescription(resultout.ToString()).Build());
+        }
+    }
+
+    private async Task CmdListUserAsync(SocketGuildUser parameter) {
+        // Not meant as a command handler - called by CmdList
+        var result = await Database.GetUserZoneAsync(parameter);
+        if (result == null) {
+            bool isself = Context.User.Id == parameter.Id;
+            if (isself) await RespondAsync(":x: You do not have a time zone. Set it with `tz.set`.", ephemeral: true);
+            else await RespondAsync(":x: The given user does not have a time zone set.", ephemeral: true);
+            return;
+        }
+
+        var resulttext = TzPrint(result)[4..] + ": " + FormatName(parameter);
+        await RespondAsync(embed: new EmbedBuilder().WithDescription(resulttext).Build());
+    }
+
+    [SlashCommand("set", HelpSet)]
+    public async Task CmdSet([Summary(description: "The new time zone to set.")]string zone) {
+        var parsedzone = ParseTimeZone(zone);
+        if (parsedzone == null) {
+            await RespondAsync(ErrInvalidZone, ephemeral: true);
+            return;
+        }
+        await Database.UpdateUserAsync((SocketGuildUser)Context.User, parsedzone);
+        await RespondAsync($":white_check_mark: Your time zone has been set to **{parsedzone}**.");
+    }
+
+    [RequireGuildContext]
+    [SlashCommand("set-for", HelpSetFor)]
+    public async Task CmdSetFor([Summary(description: "The user whose time zone to modify.")] SocketGuildUser user,
+                                 [Summary(description: "The new time zone to set.")] string zone) {
+        if (!IsUserAdmin(user)) {
+            await RespondAsync(ErrNotAllowed, ephemeral: true).ConfigureAwait(false);
+            return;
+        }
+
+        // Extract parameters
+        var newtz = ParseTimeZone(zone);
+        if (newtz == null) {
+            await RespondAsync(ErrInvalidZone);
+            return;
+        }
+
+        await Database.UpdateUserAsync(user, newtz).ConfigureAwait(false);
+        await RespondAsync($":white_check_mark: Time zone for **{user}** set to **{newtz}**.");
+    }
+
+    [RequireGuildContext]
+    [SlashCommand("remove", HelpRemove)]
+    public async Task CmdRemove() {
+        var success = await Database.DeleteUserAsync((SocketGuildUser)Context.User);
+        if (success) await RespondAsync(":white_check_mark: Your zone has been removed.");
+        else await RespondAsync(":x: You don't have a time zone set.");
+    }
+
+    [RequireGuildContext]
+    [SlashCommand("remove-for", HelpRemoveFor)]
+    public async Task CmdRemoveFor([Summary(description: "The user whose time zone to remove.")] SocketGuildUser user) {
+        if (!IsUserAdmin(user)) {
+            await RespondAsync(ErrNotAllowed, ephemeral: true).ConfigureAwait(false);
+            return;
+        }
+
+        if (await Database.DeleteUserAsync(user))
+            await RespondAsync($":white_check_mark: Removed zone information for {user}.");
+        else
+            await RespondAsync($":white_check_mark: No time zone is set for {user}.");
+    }
+
+    #region Helper methods
+    /// <summary>
+    /// Returns a string displaying the current time in the given time zone.
+    /// The result begins with four numbers for sorting purposes. Must be trimmed before output.
+    /// </summary>
+    private static string TzPrint(string zone) {
+        var tzdb = DateTimeZoneProviders.Tzdb;
+        DateTimeZone tz = tzdb.GetZoneOrNull(zone)!;
+        if (tz == null) throw new Exception("Encountered unknown time zone: " + zone);
+
+        var now = SystemClock.Instance.GetCurrentInstant().InZone(tz);
+        var sortpfx = now.ToString("MMdd", DateTimeFormatInfo.InvariantInfo);
+        var fullstr = now.ToString("dd'-'MMM' 'HH':'mm' 'x' (UTC'o<g>')'", DateTimeFormatInfo.InvariantInfo);
+        return $"{sortpfx}● `{fullstr}`";
+    }
+
+    /// <summary>
+    /// Checks given time zone input. Returns a valid string for use with NodaTime, or null.
+    /// </summary>
+    private static string? ParseTimeZone(string tzinput) {
+        if (tzinput.Equals("Asia/Calcutta", StringComparison.OrdinalIgnoreCase)) tzinput = "Asia/Kolkata";
+        if (_tzNameMap.TryGetValue(tzinput, out var name)) return name;
+        return null;
+    }
+
+    /// <summary>
+    /// Formats a user's name to a consistent, readable format which makes use of their nickname.
+    /// </summary>
+    private static string FormatName(SocketGuildUser user) {
+        static string escapeFormattingCharacters(string input) {
+            var result = new StringBuilder();
+            foreach (var c in input) {
+                if (c is '\\' or '_' or '~' or '*' or '@') {
+                    result.Append('\\');
+                }
+                result.Append(c);
+            }
+            return result.ToString();
+        }
+
+        var username = escapeFormattingCharacters(user.Username);
+        if (user.Nickname != null) {
+            return $"**{escapeFormattingCharacters(user.Nickname)}** ({username}#{user.Discriminator})";
+        }
+        return $"**{username}**#{user.Discriminator}";
+    }
+
+    /// <summary>
+    /// Checks if the given user can be considered a guild admin ('Manage Server' is set).
+    /// </summary>
+    // TODO replace this with a precondition, or there's also a new permission scheme going around?
+    private static bool IsUserAdmin(SocketGuildUser user)
+        => user.GuildPermissions.Administrator || user.GuildPermissions.ManageGuild;
+
+    /// <summary>
+    /// Checks if the member cache for the specified guild needs to be filled, and sends a request if needed.
+    /// </summary>
+    /// <remarks>
+    /// Due to a quirk in Discord.Net, the user cache cannot be filled until the command handler is no longer executing
+    /// regardless of if the request runs on its own thread, thus requiring the user to run the command again.
+    /// </remarks>
+    /// <returns>
+    /// True if the guild's members are already downloaded. If false, the command handler must notify the user.
+    /// </returns>
+    private static async Task<bool> AreUsersDownloadedAsync(SocketGuild guild) {
+        static bool HasMostMembersDownloaded(SocketGuild guild) {
+            if (guild.HasAllMembers) return true;
+            if (guild.MemberCount > 30) {
+                // For guilds of size over 30, require 85% or more of the members to be known
+                // (26/30, 42/50, 255/300, etc)
+                return guild.DownloadedMemberCount >= (int)(guild.MemberCount * 0.85);
+            } else {
+                // For smaller guilds, fail if two or more members are missing
+                return guild.MemberCount - guild.DownloadedMemberCount <= 2;
+            }
+        }
+        if (HasMostMembersDownloaded(guild)) return true;
+        else {
+            // Event handler hangs if awaited normally or used with Task.Run
+            await Task.Factory.StartNew(guild.DownloadUsersAsync).ConfigureAwait(false);
+            return false;
+        }
+    }
+    #endregion
+}

CommandsSlash.cs

@@ -1,297 +0,0 @@
-using System.Text;
-
-namespace WorldTime;
-
-internal class CommandsSlash : CommandsCommon {
-    delegate Task CommandResponder(SocketSlashCommand arg);
-
-    const string ErrGuildOnly = ":x: This command can only be run within a server.";
-    const string ErrNotAllowed = ":x: Only server moderators may use this command.";
-
-    const string EmbedHelpField1 = $"`/help` - {HelpHelp}\n"
-        + $"`/list` - {HelpList}\n"
-        + $"`/set` - {HelpSet}\n"
-        + $"`/remove` - {HelpRemove}";
-    const string EmbedHelpField2 = $"`/set-for` - {HelpSetFor}\n`/remove-for` - {HelpRemoveFor}";
-
-    #region Help strings
-    const string HelpHelp = "Displays a list of available bot commands.";
-    const string HelpList = "Shows the current time for all recently active known users.";
-    const string HelpSet = "Adds or updates your time zone to the bot.";
-    const string HelpSetFor = "Sets/updates time zone for a given user.";
-    const string HelpRemove = "Removes your time zone information from this bot.";
-    const string HelpRemoveFor = "Removes time zone for a given user.";
-    #endregion
-
-    public CommandsSlash(WorldTime inst, Database db) : base(db, inst) {
-        inst.DiscordClient.SlashCommandExecuted += DiscordClient_SlashCommandExecuted;
-        inst.DiscordClient.ShardReady += DiscordClient_ShardReady;
-    }
-
-    private async Task DiscordClient_ShardReady(DiscordSocketClient arg) {
-#if !DEBUG
-        // Update our commands here, only when the first shard connects
-        if (arg.ShardId != 0) return;
-#endif
-        var cmds = new ApplicationCommandProperties[] {
-            new SlashCommandBuilder()
-                .WithName("help").WithDescription(HelpHelp).Build(),
-            new SlashCommandBuilder()
-                .WithName("list")
-                .WithDescription(HelpList)
-                .AddOption("user", ApplicationCommandOptionType.User, "A specific user whose time to look up.", isRequired: false)
-                .Build(),
-            new SlashCommandBuilder()
-                .WithName("set")
-                .WithDescription(HelpSet)
-                .AddOption("zone", ApplicationCommandOptionType.String, "The new time zone to set.", isRequired: true)
-                .Build(),
-            new SlashCommandBuilder()
-                .WithName("set-for")
-                .WithDescription(HelpSetFor)
-                .AddOption("user", ApplicationCommandOptionType.User, "The user whose time zone to modify.", isRequired: true)
-                .AddOption("zone", ApplicationCommandOptionType.String, "The new time zone to set.", isRequired: true)
-                .Build(),
-            new SlashCommandBuilder()
-                .WithName("remove").WithDescription(HelpRemove).Build(),
-            new SlashCommandBuilder()
-                .WithName("remove-for")
-                .WithDescription(HelpRemoveFor)
-                .AddOption("user", ApplicationCommandOptionType.User, "The user whose time zone to remove.", isRequired: true)
-                .Build()
-        };
-#if !DEBUG
-        // Remove any unneeded/unused commands
-        var existingcmdnames = cmds.Select(c => c.Name.Value).ToHashSet();
-        foreach (var gcmd in await arg.GetGlobalApplicationCommandsAsync()) {
-            if (!existingcmdnames.Contains(gcmd.Name)) {
-                Program.Log("Command registration", $"Found registered unused command /{gcmd.Name} - sending removal request");
-                await gcmd.DeleteAsync();
-            }
-        }
-        // And update what we have
-        Program.Log("Command registration", $"Bulk updating {cmds.Length} global command(s)");
-        await arg.BulkOverwriteGlobalApplicationCommandsAsync(cmds).ConfigureAwait(false);
-#else
-        // Debug: Register our commands locally instead, in each guild we're in
-        foreach (var g in arg.Guilds) {
-            await g.DeleteApplicationCommandsAsync().ConfigureAwait(false);
-            await g.BulkOverwriteApplicationCommandAsync(cmds).ConfigureAwait(false);
-        }
-
-        foreach (var gcmd in await arg.GetGlobalApplicationCommandsAsync()) {
-            Program.Log("Command registration", $"Found global command /{gcmd.Name} and we're DEBUG - sending removal request");
-            await gcmd.DeleteAsync();
-        }
-#endif
-    }
-
-    private async Task DiscordClient_SlashCommandExecuted(SocketSlashCommand arg) {
-        SocketGuildChannel? rptChannel = arg.Channel as SocketGuildChannel;
-        var rptId = rptChannel?.Guild.Id ?? arg.User.Id;
-        Program.Log("Command executed", $"/{arg.CommandName} by {arg.User} in { (rptChannel != null ? "guild" : "DM. User") } ID {rptId}");
-
-        CommandResponder responder = arg.Data.Name switch {
-            "help" => CmdHelp,
-            "list" => CmdList,
-            "set" => CmdSet,
-            "set-for" => CmdSetFor,
-            "remove" => CmdRemove,
-            "remove-for" => CmdRemoveFor,
-            _ => UnknownCommandHandler
-        };
-        try {
-            await responder(arg).ConfigureAwait(false);
-        } catch (Exception e) {
-            Program.Log("Command exception", e.ToString());
-            // TODO respond with error message?
-        }
-    }
-
-    private async Task UnknownCommandHandler(SocketSlashCommand arg) {
-        Program.Log("Command invoked", $"/{arg.Data.Name} is an unknown command!");
-        await arg.RespondAsync("Oops, that command isn't supposed to be there... Please try something else.",
-            ephemeral: true).ConfigureAwait(false);
-    }
-
-    private async Task CmdHelp(SocketSlashCommand arg) {
-        var version = System.Reflection.Assembly.GetExecutingAssembly().GetName().Version!.ToString(3);
-        var guildct = _instance.DiscordClient.Guilds.Count;
-        var uniquetz = await _database.GetDistinctZoneCountAsync();
-        await arg.RespondAsync(embed: new EmbedBuilder() {
-            Title = "Help & About",
-            Description = $"World Time v{version} - Serving {guildct} communities across {uniquetz} time zones.\n\n"
-                + "This bot is provided for free, without any paywalled 'premium' features. "
-                + "If you've found this bot useful, please consider contributing via the "
-                + "bot author's page on Ko-fi: https://ko-fi.com/noithecat.",
-            Footer = new EmbedFooterBuilder() {
-                IconUrl = _instance.DiscordClient.CurrentUser.GetAvatarUrl(),
-                Text = "World Time"
-            }
-        }.AddField(inline: false, name: "Commands", value: EmbedHelpField1
-        ).AddField(inline: false, name: "Admin commands", value: EmbedHelpField2
-        ).AddField(inline: false, name: "Zones", value:
-            "This bot accepts zone names from the IANA Time Zone Database (a.k.a. Olson Database). " +
-            "A useful tool to determine yours can be found at: https://kevinnovak.github.io/Time-Zone-Picker/"
-        ).Build());
-    }
-
-    private async Task CmdList(SocketSlashCommand arg) {
-        if (arg.Channel is not SocketGuildChannel gc) {
-            await arg.RespondAsync(ErrGuildOnly).ConfigureAwait(false);
-            return;
-        }
-
-        if (arg.Data.Options.FirstOrDefault()?.Value is SocketGuildUser parameter) {
-            await CmdListUser(arg, parameter);
-            return;
-        }
-
-        var guild = gc.Guild;
-        if (!await AreUsersDownloadedAsync(guild).ConfigureAwait(false)) {
-            await arg.RespondAsync(ErrNoUserCache, ephemeral: true).ConfigureAwait(false);
-            return;
-        }
-
-        var userlist = await _database.GetGuildZonesAsync(guild.Id).ConfigureAwait(false);
-        if (userlist.Count == 0) {
-            await arg.RespondAsync(":x: Nothing to show. " +
-                $"To register your time zone with the bot, use the `/set` command.").ConfigureAwait(false);
-            return;
-        }
-        // Order times by popularity to limit how many are shown, group by printed name
-        var sortedlist = new SortedDictionary<string, List<ulong>>();
-        foreach ((string area, List<ulong> users) in userlist.OrderByDescending(o => o.Value.Count).Take(20)) {
-            // Filter further to top 20 distinct timezones, even if they are not displayed in the final result
-            var areaprint = TzPrint(area);
-            if (!sortedlist.ContainsKey(areaprint)) sortedlist.Add(areaprint, new List<ulong>());
-            sortedlist[areaprint].AddRange(users);
-        }
-
-        // Build zone listings with users
-        var outputlines = new List<string>();
-        foreach ((string area, List<ulong> users) in sortedlist) {
-            var buffer = new StringBuilder();
-            buffer.Append(area[4..] + ": ");
-            bool empty = true;
-            foreach (var userid in users) {
-                var userinstance = guild.GetUser(userid);
-                if (userinstance == null) continue;
-                if (empty) empty = !empty;
-                else buffer.Append(", ");
-                var useradd = FormatName(userinstance);
-                if (buffer.Length + useradd.Length > MaxSingleLineLength) {
-                    buffer.Append("others...");
-                    break;
-                } else buffer.Append(useradd);
-            }
-            if (!empty) outputlines.Add(buffer.ToString());
-        }
-
-        // Prepare for output - send buffers out if they become too large
-        outputlines.Sort();
-        bool hasOutputOneLine = false;
-        // First output is shown as an interaction response, followed then as regular channel messages
-        async Task doOutput(Embed msg) {
-            if (!hasOutputOneLine) {
-                await arg.RespondAsync(embed: msg).ConfigureAwait(false);
-                hasOutputOneLine = true;
-            } else {
-                await arg.Channel.SendMessageAsync(embed: msg).ConfigureAwait(false);
-            }
-        }
-
-        var resultout = new StringBuilder();
-        foreach (var line in outputlines) {
-            if (resultout.Length + line.Length > MaxSingleOutputLength) {
-                await doOutput(new EmbedBuilder().WithDescription(resultout.ToString()).Build()).ConfigureAwait(false);
-                resultout.Clear();
-            }
-            if (resultout.Length > 0) resultout.AppendLine(); // avoids trailing newline by adding to the previous line
-            resultout.Append(line);
-        }
-        if (resultout.Length > 0) {
-            await doOutput(new EmbedBuilder().WithDescription(resultout.ToString()).Build()).ConfigureAwait(false);
-        }
-    }
-
-    private async Task CmdListUser(SocketSlashCommand arg, SocketGuildUser parameter) {
-        // Not meant as a command handler - called by CmdList
-        var result = await _database.GetUserZoneAsync(parameter).ConfigureAwait(false);
-        if (result == null) {
-            bool isself = arg.User.Id == parameter.Id;
-            if (isself) await arg.RespondAsync(":x: You do not have a time zone. Set it with `tz.set`.", ephemeral: true)
-                    .ConfigureAwait(false);
-            else await arg.RespondAsync(":x: The given user does not have a time zone set.", ephemeral: true).ConfigureAwait(false);
-            return;
-        }
-
-        var resulttext = TzPrint(result)[4..] + ": " + FormatName(parameter);
-        await arg.RespondAsync(embed: new EmbedBuilder().WithDescription(resulttext).Build()).ConfigureAwait(false);
-    }
-
-    private async Task CmdSet(SocketSlashCommand arg) {
-        if (arg.Channel is not SocketGuildChannel) {
-            await arg.RespondAsync(ErrGuildOnly).ConfigureAwait(false);
-            return;
-        }
-
-        var input = (string)arg.Data.Options.First().Value;
-        input = ParseTimeZone(input);
-        if (input == null) {
-            await arg.RespondAsync(ErrInvalidZone, ephemeral: true).ConfigureAwait(false);
-            return;
-        }
-        await _database.UpdateUserAsync((SocketGuildUser)arg.User, input).ConfigureAwait(false);
-        await arg.RespondAsync($":white_check_mark: Your time zone has been set to **{input}**.").ConfigureAwait(false);
-    }
-
-    private async Task CmdSetFor(SocketSlashCommand arg) {
-        if (arg.Channel is not SocketGuildChannel) {
-            await arg.RespondAsync(ErrGuildOnly).ConfigureAwait(false);
-            return;
-        }
-
-        if (!IsUserAdmin((SocketGuildUser)arg.User)) {
-            await arg.RespondAsync(ErrNotAllowed, ephemeral: true).ConfigureAwait(false);
-            return;
-        }
-
-        // Extract parameters
-        var opts = arg.Data.Options.ToDictionary(o => o.Name, o => o);
-        var user = (SocketGuildUser)opts["user"].Value;
-        var zone = (string)opts["zone"].Value;
-
-        var newtz = ParseTimeZone(zone);
-        if (newtz == null) {
-            await arg.RespondAsync(ErrInvalidZone).ConfigureAwait(false);
-            return;
-        }
-
-        await _database.UpdateUserAsync(user, newtz).ConfigureAwait(false);
-        await arg.RespondAsync($":white_check_mark: Time zone for **{user}** set to **{newtz}**.").ConfigureAwait(false);
-    }
-
-    private async Task CmdRemove(SocketSlashCommand arg) {
-        if (arg.Channel is not SocketGuildChannel) {
-            await arg.RespondAsync(ErrGuildOnly).ConfigureAwait(false);
-            return;
-        }
-
-        var success = await _database.DeleteUserAsync((SocketGuildUser)arg.User).ConfigureAwait(false);
-        if (success) await arg.RespondAsync(":white_check_mark: Your zone has been removed.").ConfigureAwait(false);
-        else await arg.RespondAsync(":x: You don't have a time zone set.").ConfigureAwait(false);
-    }
-
-    private async Task CmdRemoveFor(SocketSlashCommand arg) {
-        if (arg.Channel is not SocketGuildChannel) {
-            await arg.RespondAsync(ErrGuildOnly).ConfigureAwait(false);
-            return;
-        }
-
-        if (!IsUserAdmin((SocketGuildUser)arg.User)) {
-            await arg.RespondAsync(ErrNotAllowed, ephemeral: true).ConfigureAwait(false);
-            return;
-        }
-    }
-}

Database.cs

@@ -6,13 +6,13 @@ namespace WorldTime;
 /// <summary>
 /// Database abstractions
 /// </summary>
-internal class Database {
+public class Database {
     private const string UserDatabase = "userdata";
     private const string CutoffInterval = "INTERVAL '30 days'"; // TODO make configurable?
 
     private readonly string _connectionString;
 
-    public Database(string connectionString) {
+    internal Database(string connectionString) {
         _connectionString = connectionString;
         DoInitialDatabaseSetupAsync().ConfigureAwait(false).GetAwaiter().GetResult();
     }
@@ -42,7 +42,7 @@ internal class Database {
     /// <summary>
     /// Checks if a given guild contains at least one user data entry with recent enough activity.
     /// </summary>
-    public async Task<bool> HasAnyAsync(SocketGuild guild) {
+    internal async Task<bool> HasAnyAsync(SocketGuild guild) {
         using var db = await OpenConnectionAsync().ConfigureAwait(false);
         using var c = db.CreateCommand();
         c.CommandText = $@"
@@ -61,7 +61,7 @@ LIMIT 1
     /// <summary>
     /// Gets the number of unique time zones in the database.
     /// </summary>
-    public async Task<int> GetDistinctZoneCountAsync() {
+    internal async Task<int> GetDistinctZoneCountAsync() {
         using var db = await OpenConnectionAsync().ConfigureAwait(false);
         using var c = db.CreateCommand();
         c.CommandText = $"SELECT COUNT(DISTINCT zone) FROM {UserDatabase}";
@@ -72,7 +72,7 @@ LIMIT 1
     /// Updates the last activity field for the specified guild user, if existing in the database.
     /// </summary>
     /// <returns>True if a value was updated, implying that the specified user exists in the database.</returns>
-    public async Task<bool> UpdateLastActivityAsync(SocketGuildUser user) {
+    internal async Task<bool> UpdateLastActivityAsync(SocketGuildUser user) {
         using var db = await OpenConnectionAsync().ConfigureAwait(false);
         using var c = db.CreateCommand();
         c.CommandText = $"UPDATE {UserDatabase} SET last_active = now() " +
@@ -89,7 +89,7 @@ LIMIT 1
     /// Removes the specified user from the database.
     /// </summary>
     /// <returns>True if the removal was successful. False typically if the user did not exist.</returns>
-    public async Task<bool> DeleteUserAsync(SocketGuildUser user) {
+    internal async Task<bool> DeleteUserAsync(SocketGuildUser user) {
         using var db = await OpenConnectionAsync().ConfigureAwait(false);
         using var c = db.CreateCommand();
         c.CommandText = $"DELETE FROM {UserDatabase} " +
@@ -103,7 +103,7 @@ LIMIT 1
     /// <summary>
     /// Inserts/updates the specified user in the database.
     /// </summary>
-    public async Task UpdateUserAsync(SocketGuildUser user, string timezone) {
+    internal async Task UpdateUserAsync(SocketGuildUser user, string timezone) {
         using var db = await OpenConnectionAsync().ConfigureAwait(false);
         using var c = db.CreateCommand();
         c.CommandText = $"INSERT INTO {UserDatabase} (guild_id, user_id, zone) " +
@@ -120,7 +120,7 @@ LIMIT 1
     /// <summary>
     /// Retrieves the time zone name of a single user.
     /// </summary>
-    public async Task<string?> GetUserZoneAsync(SocketGuildUser user) {
+    internal async Task<string?> GetUserZoneAsync(SocketGuildUser user) {
         using var db = await OpenConnectionAsync().ConfigureAwait(false);
         using var c = db.CreateCommand();
         c.CommandText = $"SELECT zone FROM {UserDatabase} " +
@@ -138,7 +138,7 @@ LIMIT 1
     /// <returns>
     /// An unsorted dictionary. Keys are time zones, values are user IDs representative of those zones.
     /// </returns>
-    public async Task<Dictionary<string, List<ulong>>> GetGuildZonesAsync(ulong guildId) {
+    internal async Task<Dictionary<string, List<ulong>>> GetGuildZonesAsync(ulong guildId) {
         using var db = await OpenConnectionAsync().ConfigureAwait(false);
         using var c = db.CreateCommand();
         c.CommandText = $@" -- Simpler query than 1.x; most filtering is now done by caller

RequireGuildContextAttribute.cs

@@ -0,0 +1,15 @@
+using Discord.Interactions;
+
+namespace WorldTime;
+/// <summary>
+/// Implements the included precondition from Discord.Net, requiring a guild context while using our custom error message.<br/><br/>
+/// Combining this with <see cref="RequireBotModeratorAttribute"/> is redundant. If possible, only use the latter instead.
+/// </summary>
+class RequireGuildContextAttribute : RequireContextAttribute {
+    public const string Error = "Command not received within a guild context.";
+    public const string Reply = ":x: This command is only available within a server.";
+
+    public override string ErrorMessage => Error;
+
+    public RequireGuildContextAttribute() : base(ContextType.Guild) { }
+}

WorldTime.cs

@@ -1,5 +1,8 @@
 global using Discord;
 global using Discord.WebSocket;
+using Discord.Interactions;
+using Microsoft.Extensions.DependencyInjection;
+using System.Reflection;
 using System.Text;
 
 namespace WorldTime;
@@ -25,31 +28,38 @@ internal class WorldTime : IDisposable {
 
     private readonly Task _statusTask;
     private readonly CancellationTokenSource _mainCancel;
-    private readonly CommandsSlash _commands;
     private readonly CommandsText _commandsTxt;
+    private readonly IServiceProvider _services;
 
     internal Configuration Config { get; }
-    internal DiscordShardedClient DiscordClient { get; }
+    internal DiscordShardedClient DiscordClient => _services.GetRequiredService<DiscordShardedClient>();
-    internal Database Database { get; }
+    internal Database Database => _services.GetRequiredService<Database>();
 
     public WorldTime(Configuration cfg, Database d) {
         var ver = System.Reflection.Assembly.GetExecutingAssembly().GetName().Version;
         Program.Log(nameof(WorldTime), $"Version {ver!.ToString(3)} is starting...");
 
         Config = cfg;
-        Database = d;
 
-        // Configure client
+        // Configure client, set up command handling
-        DiscordClient = new DiscordShardedClient(new DiscordSocketConfig() {
+        var clientConf = new DiscordSocketConfig() {
             LogLevel = LogSeverity.Info,
             DefaultRetryMode = RetryMode.RetryRatelimit,
             MessageCacheSize = 0, // disable message cache
             GatewayIntents = GatewayIntents.Guilds | GatewayIntents.GuildMembers | GatewayIntents.GuildMessages
-        });
+        };
+        _services = new ServiceCollection()
+            .AddSingleton(new DiscordShardedClient(clientConf))
+            .AddSingleton(s => new InteractionService(s.GetRequiredService<DiscordShardedClient>()))
+            .AddSingleton(d)
+            .BuildServiceProvider();
         DiscordClient.Log += DiscordClient_Log;
         DiscordClient.ShardReady += DiscordClient_ShardReady;
         DiscordClient.MessageReceived += DiscordClient_MessageReceived;
-        _commands = new CommandsSlash(this, Database);
+        var iasrv = _services.GetRequiredService<InteractionService>();
+        DiscordClient.InteractionCreated += DiscordClient_InteractionCreated;
+        iasrv.SlashCommandExecuted += InteractionService_SlashCommandExecuted;
+
         _commandsTxt = new CommandsText(this, Database);
 
         // Start status reporting thread
@@ -59,6 +69,7 @@ internal class WorldTime : IDisposable {
     }
 
     public async Task StartAsync() {
+        await _services.GetRequiredService<InteractionService>().AddModulesAsync(Assembly.GetExecutingAssembly(), _services);
         await DiscordClient.LoginAsync(TokenType.Bot, Config.BotToken).ConfigureAwait(false);
         await DiscordClient.StartAsync().ConfigureAwait(false);
     }
@@ -148,7 +159,25 @@ internal class WorldTime : IDisposable {
         return Task.CompletedTask;
     }
 
-    private Task DiscordClient_ShardReady(DiscordSocketClient arg) => arg.SetGameAsync("/help");
+    private async Task DiscordClient_ShardReady(DiscordSocketClient arg) {
+        // TODO get rid of this eventually? or change it to something fun...
+        await arg.SetGameAsync("/help");
+
+#if !DEBUG
+        // Update slash/interaction commands
+        if (arg.ShardId == 0) {
+            await _services.GetRequiredService<InteractionService>().RegisterCommandsGloballyAsync();
+            Program.Log("Command registration", "Updated global command registration.");
+        }
+#else
+        // Debug: Register our commands locally instead, in each guild we're in
+        var iasrv = _services.GetRequiredService<InteractionService>();
+        foreach (var g in arg.Guilds) {
+            await iasrv.RegisterCommandsToGuildAsync(g.Id, true).ConfigureAwait(false);
+            Program.Log("Command registration", $"Updated DEBUG command registration in guild {g.Id}.");
+        }
+#endif
+    }
 
     /// <summary>
     /// Non-specific handler for incoming events.
@@ -178,5 +207,55 @@ internal class WorldTime : IDisposable {
             await Task.Factory.StartNew(guild.DownloadUsersAsync).ConfigureAwait(false);
         }
     }
+
+    const string InternalError = ":x: An unknown error occurred. If it persists, please notify the bot owner.";
+
+    // Slash command preparation and invocation
+    private async Task DiscordClient_InteractionCreated(SocketInteraction arg) {
+        var context = new ShardedInteractionContext(DiscordClient, arg);
+
+        try {
+            await _services.GetRequiredService<InteractionService>().ExecuteCommandAsync(context, _services);
+        } catch (Exception ex) {
+            Program.Log(nameof(DiscordClient_InteractionCreated), $"Unhandled exception. {ex}");
+            if (arg.Type == InteractionType.ApplicationCommand) {
+                if (arg.HasResponded) await arg.ModifyOriginalResponseAsync(prop => prop.Content = InternalError);
+                else await arg.RespondAsync(InternalError);
+            }
+        }
+    }
+
+    // Slash command logging and failed execution handling
+    private static async Task InteractionService_SlashCommandExecuted(SlashCommandInfo info, IInteractionContext context, IResult result) {
+        string sender;
+        if (context.Guild != null) {
+            sender = $"{context.Guild}!{context.User}";
+        } else {
+            sender = $"{context.User} in non-guild context";
+        }
+        var logresult = $"{(result.IsSuccess ? "Success" : "Fail")}: `/{info}` by {sender}.";
+
+        if (result.Error != null) {
+            // Additional log information with error detail
+            logresult += " " + Enum.GetName(typeof(InteractionCommandError), result.Error) + ": " + result.ErrorReason;
+
+            // Specific responses to errors, if necessary
+            if (result.Error == InteractionCommandError.UnmetPrecondition) {
+                string errReply = result.ErrorReason switch {
+                    RequireGuildContextAttribute.Error => RequireGuildContextAttribute.Reply,
+                    _ => result.ErrorReason
+                };
+                await context.Interaction.RespondAsync(errReply, ephemeral: true);
+            } else {
+                // Generic error response
+                // TODO when implementing proper application error logging, see here
+                var ia = context.Interaction;
+                if (ia.HasResponded) await ia.ModifyOriginalResponseAsync(p => p.Content = InternalError);
+                else await ia.RespondAsync(InternalError);
+            }
+        }
+
+        Program.Log("Command", logresult);
+    }
     #endregion
 }

WorldTime.csproj

@@ -11,10 +11,11 @@
 
   <ItemGroup>
     <PackageReference Include="CommandLineParser" Version="2.8.0" />
-    <PackageReference Include="Discord.Net" Version="3.4.1" />
+    <PackageReference Include="Discord.Net" Version="3.6.1" />
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="6.0.0" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
-    <PackageReference Include="NodaTime" Version="3.0.10" />
+    <PackageReference Include="NodaTime" Version="3.1.0" />
-    <PackageReference Include="Npgsql" Version="6.0.3" />
+    <PackageReference Include="Npgsql" Version="6.0.4" />
   </ItemGroup>
 
 </Project>