Add job scheduler for DeleteTempReply (#212)

src/DiscordTranslationBot/Commands/TempReplies/DeleteTempReply.cs

@@ -0,0 +1,101 @@
+using System.ComponentModel.DataAnnotations;
+using Discord;
+using Discord.Net;
+using DiscordTranslationBot.Discord.Models;
+
+namespace DiscordTranslationBot.Commands.TempReplies;
+
+/// <summary>
+/// Deletes a temp reply.
+/// If there is a reaction associated with the source message, it will be cleared, too.
+/// </summary>
+public sealed class DeleteTempReply : ICommand
+{
+    /// <summary>
+    /// The temp reply to delete.
+    /// </summary>
+    [Required]
+    public required IUserMessage Reply { get; init; }
+
+    /// <summary>
+    /// The source message ID that the temp reply is associated with.
+    /// </summary>
+    public required ulong SourceMessageId { get; init; }
+
+    /// <summary>
+    /// The reaction associated with the source message, if any.
+    /// </summary>
+    public ReactionInfo? ReactionInfo { get; init; }
+}
+
+public sealed partial class DeleteTempReplyHandler : ICommandHandler<DeleteTempReply>
+{
+    private readonly Log _log;
+
+    public DeleteTempReplyHandler(ILogger<DeleteTempReplyHandler> logger)
+    {
+        _log = new Log(logger);
+    }
+
+    public async ValueTask<Unit> Handle(DeleteTempReply command, CancellationToken cancellationToken)
+    {
+        try
+        {
+            // If there is also a reaction and the source message still exists, remove the reaction from it.
+            if (command.ReactionInfo is not null)
+            {
+                var sourceMessage = await command.Reply.Channel.GetMessageAsync(
+                    command.SourceMessageId,
+                    options: new RequestOptions { CancelToken = cancellationToken });
+
+                if (sourceMessage is not null)
+                {
+                    await sourceMessage.RemoveReactionAsync(
+                        command.ReactionInfo.Emote,
+                        command.ReactionInfo.UserId,
+                        new RequestOptions { CancelToken = cancellationToken });
+                }
+            }
+
+            // Delete the reply message.
+            try
+            {
+                await command.Reply.DeleteAsync(new RequestOptions { CancelToken = cancellationToken });
+                _log.DeletedTempMessage(command.Reply.Id);
+            }
+            catch (HttpException ex) when (ex.DiscordCode == DiscordErrorCode.UnknownMessage)
+            {
+                // The message was likely already deleted.
+                _log.TempMessageNotFound(command.Reply.Id);
+            }
+        }
+        catch (Exception ex)
+        {
+            _log.FailedToDeleteTempMessage(ex, command.Reply.Id);
+            throw;
+        }
+
+        return Unit.Value;
+    }
+
+    private sealed partial class Log
+    {
+        private readonly ILogger _logger;
+
+        public Log(ILogger logger)
+        {
+            _logger = logger;
+        }
+
+        [LoggerMessage(Level = LogLevel.Information, Message = "Deleted temp message ID {replyId}.")]
+        public partial void DeletedTempMessage(ulong replyId);
+
+        [LoggerMessage(
+            Level = LogLevel.Information,
+            Message = "Temp message ID {replyId} was not found and likely manually deleted.")]
+        public partial void TempMessageNotFound(ulong replyId);
+
+        [LoggerMessage(Level = LogLevel.Error, Message = "Failed to delete temp message ID {replyId}.")]
+        public partial void FailedToDeleteTempMessage(Exception ex, ulong replyId);
+    }
+}

src/DiscordTranslationBot/Commands/TempReplies/SendTempReply.cs

@@ -1,8 +1,7 @@
 using System.ComponentModel.DataAnnotations;
 using Discord;
-using Discord.Net;
 using DiscordTranslationBot.Discord.Models;
-using IMessage = Discord.IMessage;
+using DiscordTranslationBot.Jobs;
 
 namespace DiscordTranslationBot.Commands.TempReplies;
 
@@ -45,13 +44,16 @@ public sealed class SendTempReply : ICommand
 public sealed partial class SendTempReplyHandler : ICommandHandler<SendTempReply>
 {
     private readonly Log _log;
+    private readonly IScheduler _scheduler;
 
     /// <summary>
     /// Initializes a new instance of the <see cref="SendTempReplyHandler" /> class.
     /// </summary>
+    /// <param name="scheduler">Scheduler to use.</param>
     /// <param name="logger">Logger to use.</param>
-    public SendTempReplyHandler(ILogger<SendTempReplyHandler> logger)
+    public SendTempReplyHandler(IScheduler scheduler, ILogger<SendTempReplyHandler> logger)
     {
+        _scheduler = scheduler;
         _log = new Log(logger);
     }
 
@@ -84,55 +86,18 @@ public async ValueTask<Unit> Handle(SendTempReply command, CancellationToken can
             typingState.Dispose();
         }
 
-        _log.WaitingToDeleteTempMessage(reply.Id, command.DeletionDelay.TotalSeconds);
-        await Task.Delay(command.DeletionDelay, cancellationToken);
-        await DeleteTempReplyAsync(reply, command, cancellationToken);
+        _scheduler.Schedule(
+            new DeleteTempReply
+            {
+                Reply = reply,
+                SourceMessageId = command.SourceMessage.Id,
+                ReactionInfo = command.ReactionInfo
+            },
+            command.DeletionDelay);
 
-        return Unit.Value;
-    }
+        _log.DeleteTempMessageScheduled(reply.Id, command.DeletionDelay.TotalSeconds);
 
-    /// <summary>
-    /// Deletes a temp reply. If there is a reaction associated with the source message, it will be cleared, too.
-    /// </summary>
-    /// <param name="reply">The reply to delete.</param>
-    /// <param name="command">The command.</param>
-    /// <param name="cancellationToken">The cancellation token.</param>
-    private async Task DeleteTempReplyAsync(IMessage reply, SendTempReply command, CancellationToken cancellationToken)
-    {
-        try
-        {
-            // If there is also a reaction and the source message still exists, remove the reaction from it.
-            if (command.ReactionInfo is not null)
-            {
-                var sourceMessage = await reply.Channel.GetMessageAsync(
-                    command.SourceMessage.Id,
-                    options: new RequestOptions { CancelToken = cancellationToken });
-
-                if (sourceMessage is not null)
-                {
-                    await sourceMessage.RemoveReactionAsync(
-                        command.ReactionInfo.Emote,
-                        command.ReactionInfo.UserId,
-                        new RequestOptions { CancelToken = cancellationToken });
-                }
-            }
-
-            // Delete the reply message.
-            try
-            {
-                await reply.DeleteAsync(new RequestOptions { CancelToken = cancellationToken });
-                _log.DeletedTempMessage(reply.Id);
-            }
-            catch (HttpException ex) when (ex.DiscordCode == DiscordErrorCode.UnknownMessage)
-            {
-                // The message was already deleted.
-            }
-        }
-        catch (Exception ex)
-        {
-            _log.FailedToDeleteTempMessage(ex, reply.Id);
-            throw;
-        }
+        return Unit.Value;
     }
 
     private sealed partial class Log
@@ -146,18 +111,12 @@ public Log(ILogger logger)
 
         [LoggerMessage(
             Level = LogLevel.Error,
-            Message = "Failed to send temp message for reaction to message ID {referencedMessageId} with text: {text}")]
-        public partial void FailedToSendTempMessage(Exception ex, ulong referencedMessageId, string text);
+            Message = "Failed to send temp message for reaction to message ID {sourceMessageId} with text: {text}")]
+        public partial void FailedToSendTempMessage(Exception ex, ulong sourceMessageId, string text);
 
         [LoggerMessage(
             Level = LogLevel.Information,
             Message = "Temp message ID {replyId} will be deleted in {totalSeconds}s.")]
-        public partial void WaitingToDeleteTempMessage(ulong replyId, double totalSeconds);
-
-        [LoggerMessage(Level = LogLevel.Information, Message = "Deleted temp message ID {replyId}.")]
-        public partial void DeletedTempMessage(ulong replyId);
-
-        [LoggerMessage(Level = LogLevel.Error, Message = "Failed to delete temp message ID {replyId}.")]
-        public partial void FailedToDeleteTempMessage(Exception ex, ulong replyId);
+        public partial void DeleteTempMessageScheduled(ulong replyId, double totalSeconds);
     }
 }

src/DiscordTranslationBot/Jobs/JobExtensions.cs

@@ -0,0 +1,9 @@
+namespace DiscordTranslationBot.Jobs;
+
+internal static class JobExtensions
+{
+    public static IServiceCollection AddJobs(this IServiceCollection services)
+    {
+        return services.AddSingleton<IScheduler, Scheduler>().AddHostedService<SchedulerBackgroundService>();
+    }
+}

src/DiscordTranslationBot/Jobs/Scheduler.cs

@@ -0,0 +1,101 @@
+using System.Diagnostics.CodeAnalysis;
+
+namespace DiscordTranslationBot.Jobs;
+
+public sealed partial class Scheduler : IScheduler
+{
+    private readonly Log _log;
+    private readonly IMediator _mediator;
+    private readonly PriorityQueue<Func<CancellationToken, Task>, DateTimeOffset> _queue = new();
+    private readonly TimeProvider _timeProvider;
+
+    public Scheduler(IMediator mediator, TimeProvider timeProvider, ILogger<Scheduler> logger)
+    {
+        _mediator = mediator;
+        _timeProvider = timeProvider;
+        _log = new Log(logger);
+    }
+
+    public int Count => _queue.Count;
+
+    public void Schedule(ICommand command, DateTimeOffset executeAt)
+    {
+        if (executeAt <= _timeProvider.GetUtcNow())
+        {
+            throw new InvalidOperationException("Tasks can only be scheduled to execute in the future.");
+        }
+
+        _queue.Enqueue(async ct => await _mediator.Send(command, ct), executeAt);
+        _log.ScheduledCommand(command.GetType().Name, executeAt.ToLocalTime(), _queue.Count);
+    }
+
+    public void Schedule(ICommand command, TimeSpan executionDelay)
+    {
+        Schedule(command, _timeProvider.GetUtcNow() + executionDelay);
+    }
+
+    public bool TryGetNextTask([NotNullWhen(true)] out Func<CancellationToken, Task>? task)
+    {
+        if (_queue.TryPeek(out _, out var executeAt) && executeAt <= _timeProvider.GetUtcNow())
+        {
+            task = _queue.Dequeue();
+            _log.DequeuedTask(executeAt.ToLocalTime(), _queue.Count);
+            return true;
+        }
+
+        task = null;
+        return false;
+    }
+
+    private sealed partial class Log
+    {
+        private readonly ILogger _logger;
+
+        public Log(ILogger logger)
+        {
+            _logger = logger;
+        }
+
+        [LoggerMessage(
+            Level = LogLevel.Information,
+            Message =
+                "Scheduled command '{commandName}' to be executed at {executeAt}. Total tasks in queue: {totalTasks}.")]
+        public partial void ScheduledCommand(string commandName, DateTimeOffset executeAt, int totalTasks);
+
+        [LoggerMessage(
+            Level = LogLevel.Information,
+            Message =
+                "Dequeued a task scheduled to be executed at {executeAt}. Remaining tasks in queue: {remainingTasks}.")]
+        public partial void DequeuedTask(DateTimeOffset executeAt, int remainingTasks);
+    }
+}
+
+public interface IScheduler
+{
+    /// <summary>
+    /// The count tasks in the queue.
+    /// </summary>
+    public int Count { get; }
+
+    /// <summary>
+    /// Queues a Mediator command to run at a specific time.
+    /// </summary>
+    /// <param name="command">Mediator command to schedule.</param>
+    /// <param name="executeAt">Time to execute the task at.</param>
+    public void Schedule(ICommand command, DateTimeOffset executeAt);
+
+    /// <summary>
+    /// Queues a Mediator command to run at a specific time.
+    /// </summary>
+    /// <param name="command">Mediator command to schedule.</param>
+    /// <param name="executionDelay">Delay for executing the task from now.</param>
+    public void Schedule(ICommand command, TimeSpan executionDelay);
+
+    /// <summary>
+    /// Try to get the next scheduled task to be executed.
+    /// If a task exists, it is dequeued.
+    /// </summary>
+    /// <param name="task">Scheduled task.</param>
+    /// <returns>Scheduled task to be executed or null.</returns>
+    public bool TryGetNextTask([NotNullWhen(true)] out Func<CancellationToken, Task>? task);
+}

src/DiscordTranslationBot/Jobs/SchedulerBackgroundService.cs

@@ -0,0 +1,65 @@
+namespace DiscordTranslationBot.Jobs;
+
+public sealed partial class SchedulerBackgroundService : BackgroundService
+{
+    private readonly Log _log;
+    private readonly IScheduler _scheduler;
+
+    public SchedulerBackgroundService(IScheduler scheduler, ILogger<SchedulerBackgroundService> logger)
+    {
+        _scheduler = scheduler;
+        _log = new Log(logger);
+    }
+
+    public override Task StartAsync(CancellationToken cancellationToken)
+    {
+        _log.Starting();
+        return base.StartAsync(cancellationToken);
+    }
+
+    public override Task StopAsync(CancellationToken cancellationToken)
+    {
+        _log.Stopping(_scheduler.Count);
+        return base.StopAsync(cancellationToken);
+    }
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            if (_scheduler.TryGetNextTask(out var task))
+            {
+                _log.TaskExecuting();
+                await task(stoppingToken);
+                _log.TaskExecuted();
+            }
+
+            // Wait some time before checking the queue again to reduce overloading CPU resources.
+            await Task.Delay(TimeSpan.FromSeconds(1), stoppingToken);
+        }
+    }
+
+    private sealed partial class Log
+    {
+        private readonly ILogger _logger;
+
+        public Log(ILogger logger)
+        {
+            _logger = logger;
+        }
+
+        [LoggerMessage(Level = LogLevel.Information, Message = "Starting scheduler background service...")]
+        public partial void Starting();
+
+        [LoggerMessage(
+            Level = LogLevel.Information,
+            Message = "Stopping scheduler background service with {remainingTasks} remaining tasks in the queue...")]
+        public partial void Stopping(int remainingTasks);
+
+        [LoggerMessage(Level = LogLevel.Information, Message = "Executing scheduled task...")]
+        public partial void TaskExecuting();
+
+        [LoggerMessage(Level = LogLevel.Information, Message = "Executed scheduled task.")]
+        public partial void TaskExecuted();
+    }
+}