Restructured the project structure back to the way it was, there's no reasonable way to split the modules

src/NadekoBot/_common/ModuleBehaviors/IBehavior.cs

@@ -0,0 +1,6 @@
+namespace NadekoBot.Common.ModuleBehaviors;
+
+public interface IBehavior
+{
+    public virtual string Name => this.GetType().Name;
+}

src/NadekoBot/_common/ModuleBehaviors/IExecNoCommand.cs

@@ -0,0 +1,19 @@
+namespace NadekoBot.Common.ModuleBehaviors;
+
+/// <summary>
+///     Executed if no command was found for this message
+/// </summary>
+public interface IExecNoCommand : IBehavior
+{
+    /// <summary>
+    /// Executed at the end of the lifecycle if no command was found
+    /// <see cref="IExecOnMessage"/> →
+    /// <see cref="IInputTransformer"/> →
+    /// <see cref="IExecPreCommand"/> →
+    /// [<see cref="IExecPostCommand"/> | *<see cref="IExecNoCommand"/>*]
+    /// </summary>
+    /// <param name="guild"></param>
+    /// <param name="msg"></param>
+    /// <returns>A task representing completion</returns>
+    Task ExecOnNoCommandAsync(IGuild guild, IUserMessage msg);
+}

src/NadekoBot/_common/ModuleBehaviors/IExecOnMessage.cs

@@ -0,0 +1,21 @@
+namespace NadekoBot.Common.ModuleBehaviors;
+
+/// <summary>
+///     Implemented by modules to handle non-bot messages received
+/// </summary>
+public interface IExecOnMessage : IBehavior
+{
+    int Priority { get; }
+
+    /// <summary>
+    /// Ran after a non-bot message was received
+    /// *<see cref="IExecOnMessage"/>* →
+    /// <see cref="IInputTransformer"/> →
+    /// <see cref="IExecPreCommand"/> →
+    /// [<see cref="IExecPostCommand"/> | <see cref="IExecNoCommand"/>]
+    /// </summary>
+    /// <param name="guild">Guild where the message was sent</param>
+    /// <param name="msg">The message that was received</param>
+    /// <returns>Whether further processing of this message should be blocked</returns>
+    Task<bool> ExecOnMessageAsync(IGuild guild, IUserMessage msg);
+}

src/NadekoBot/_common/ModuleBehaviors/IExecPostCommand.cs

@@ -0,0 +1,22 @@
+namespace NadekoBot.Common.ModuleBehaviors;
+
+/// <summary>
+/// This interface's method is executed after the command successfully finished execution.
+/// ***There is no support for this method in NadekoBot services.***
+/// It is only meant to be used in medusa system
+/// </summary>
+public interface IExecPostCommand : IBehavior
+{
+    /// <summary>
+    /// Executed after a command was successfully executed
+    /// <see cref="IExecOnMessage"/> →
+    /// <see cref="IInputTransformer"/> →
+    /// <see cref="IExecPreCommand"/> →
+    /// [*<see cref="IExecPostCommand"/>* | <see cref="IExecNoCommand"/>]
+    /// </summary>
+    /// <param name="ctx">Command context</param>
+    /// <param name="moduleName">Module name</param>
+    /// <param name="commandName">Command name</param>
+    /// <returns>A task representing completion</returns>
+    ValueTask ExecPostCommandAsync(ICommandContext ctx, string moduleName, string commandName);
+}

src/NadekoBot/_common/ModuleBehaviors/IExecPreCommand.cs

@@ -0,0 +1,25 @@
+namespace NadekoBot.Common.ModuleBehaviors;
+
+/// <summary>
+/// This interface's method is executed after a command was found but before it was executed.
+/// Able to block further processing of a command
+/// </summary>
+public interface IExecPreCommand : IBehavior
+{
+    public int Priority { get; }
+
+    /// <summary>
+    /// <para>
+    /// Ran after a command was found but before execution.
+    /// </para>
+    /// <see cref="IExecOnMessage"/> →
+    /// <see cref="IInputTransformer"/> →
+    /// *<see cref="IExecPreCommand"/>* →
+    /// [<see cref="IExecPostCommand"/> | <see cref="IExecNoCommand"/>]
+    /// </summary>
+    /// <param name="context">Command context</param>
+    /// <param name="moduleName">Name of the module</param>
+    /// <param name="command">Command info</param>
+    /// <returns>Whether further processing of the command is blocked</returns>
+    Task<bool> ExecPreCommandAsync(ICommandContext context, string moduleName, CommandInfo command);
+}

src/NadekoBot/_common/ModuleBehaviors/IInputTransformer.cs

@@ -0,0 +1,25 @@
+namespace NadekoBot.Common.ModuleBehaviors;
+
+/// <summary>
+/// Implemented by services which may transform input before a command is searched for
+/// </summary>
+public interface IInputTransformer : IBehavior
+{
+    /// <summary>
+    /// Ran after a non-bot message was received
+    /// <see cref="IExecOnMessage"/> ->
+    /// *<see cref="IInputTransformer"/>* ->
+    /// <see cref="IExecPreCommand"/> ->
+    /// [<see cref="IExecPostCommand"/> OR <see cref="IExecNoCommand"/>]
+    /// </summary>
+    /// <param name="guild">Guild</param>
+    /// <param name="channel">Channel in which the message was sent</param>
+    /// <param name="user">User who sent the message</param>
+    /// <param name="input">Content of the message</param>
+    /// <returns>New input, if any, otherwise null</returns>
+    Task<string?> TransformInput(
+        IGuild guild,
+        IMessageChannel channel,
+        IUser user,
+        string input);
+}

src/NadekoBot/_common/ModuleBehaviors/IReadyExecutor.cs

@@ -0,0 +1,13 @@
+namespace NadekoBot.Common.ModuleBehaviors;
+
+/// <summary>
+///     All services which need to execute something after
+///     the bot is ready should implement this interface
+/// </summary>
+public interface IReadyExecutor : IBehavior
+{
+    /// <summary>
+    ///     Executed when bot is ready
+    /// </summary>
+    public Task OnReadyAsync();
+}