New time_until command

src/Commands/Common/TimeUntilCommand.cs

@@ -0,0 +1,62 @@
+using System;
+using System.Threading.Tasks;
+using DSharpPlus;
+using DSharpPlus.Commands;
+using DSharpPlus.Commands.ArgumentModifiers;
+using DSharpPlus.Commands.Converters;
+using DSharpPlus.Commands.Processors.TextCommands;
+using Humanizer;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace OoLunar.Tomoe.Commands.Common
+{
+    /// <summary>
+    /// "Time until in 4 hours: 4 hours, 43 minutes, 33 seconds"
+    /// </summary>
+    /// <remarks>
+    /// I'm only getting 4 and a half hours of sleep tonight.
+    /// </remarks>
+    public static class TimeUntilCommand
+    {
+        private static readonly DateTimeOffsetConverter _dateTimeArgumentConverter = new();
+
+        /// <summary>
+        /// Calculates how long you have to wait until a specific time.
+        /// </summary>
+        /// <param name="when">When you want to know how long you have to wait.</param>
+        [Command("time_until")]
+        public static async ValueTask ExecuteAsync(CommandContext context, [RemainingText] string? when = null)
+        {
+            if (string.IsNullOrWhiteSpace(when))
+            {
+                await context.RespondAsync("Invalid timestamp: `null`");
+                return;
+            }
+
+            when = when.Trim();
+            TextConverterContext converterContext = new()
+            {
+                Channel = context.Channel,
+                Command = context.Command,
+                Extension = context.Extension,
+                RawArguments = when,
+                Message = null!,
+                ServiceScope = context.ServiceProvider.CreateAsyncScope(),
+                Splicer = context.Extension.GetProcessor<TextCommandProcessor>().Configuration.TextArgumentSplicer,
+                User = context.User
+            };
+
+            converterContext.NextArgument();
+            if (!(await _dateTimeArgumentConverter.ConvertAsync(converterContext)).IsDefined(out DateTimeOffset dateTimeOffset) || dateTimeOffset == default)
+            {
+                await context.RespondAsync($"Invalid timestamp: `{when}`");
+                return;
+            }
+
+            TimeSpan offset = (await context.GetTimeZoneAsync()).BaseUtcOffset;
+            DateTimeOffset untilDate = dateTimeOffset.ToOffset(offset).Subtract(offset);
+            TimeSpan untilTime = untilDate - DateTimeOffset.UtcNow;
+            await context.RespondAsync($"Time until {Formatter.Timestamp(untilDate)}: {untilTime.Humanize(3)}");
+        }
+    }
+}