Discord.Net/docs/guides/commands/commands.md

# The Command Service 

>[!WARNING]
>This article is out of date and has not been rewritten yet. 
Information is not guaranteed to be accurate. 

[Discord.Commands](xref:Discord.Commands) provides an Attribute-based 
command parser. 

## Setup 

To use Commands, you must create a [Commands Service] and a Command 
Handler. 

Included below is a very barebone Command Handler. You can extend your 
Command Handler as much as you like; however, the below is the bare 
minimum. 

The `CommandService` will optionally accept a [CommandServiceConfig], 
which _does_ set a few default values for you. It is recommended to 
look over the properties in [CommandServiceConfig] and their default 
values. 

[!code-csharp[Command Handler](samples/command_handler.cs)] 

[Command Service]: xref:Discord.Commands.CommandService 
[CommandServiceConfig]: xref:Discord.Commands.CommandServiceConfig 

## With Attributes 

In 1.0, Commands can be defined ahead of time with attributes, or at 
runtime with builders. 

For most bots, ahead-of-time Commands should be all you need, and this 
is the recommended method of defining Commands. 

### Modules 

The first step to creating Commands is to create a _module_. 

A Module is an organizational pattern that allows you to write your 
Commands in different classes and have them automatically loaded. 

Discord.NET's implementation of Modules is influenced heavily from 
ASP.NET Core's Controller pattern. This means that the lifetime of a 
module instance is only as long as the Command is being invoked. 

**Avoid using long-running code** in your modules wherever possible. 
You should **not** be implementing very much logic into your modules, 
instead, outsource to a service for that.

If you are unfamiliar with Inversion of Control, it is recommended to 
read the MSDN article on [IoC] and [Dependency Injection]. 

To begin, create a new class somewhere in your project and inherit the 
class from [ModuleBase]. This class **must** be `public`. 

>[!NOTE] 
>[ModuleBase] is an _abstract_ class, meaning that you may extend it 
>or override it as you see fit. Your module may inherit from any 
>extension of ModuleBase. 

By now, your module should look like this: 
[!code-csharp[Empty Module](samples/empty-module.cs)] 

[IoC]: https://msdn.microsoft.com/en-us/library/ff921087.aspx 
[Dependency Injection]: https://msdn.microsoft.com/en-us/library/ff921152.aspx 
[ModuleBase]: xref:Discord.Commands.ModuleBase`1 

### Adding Commands 

The next step to creating Commands is actually creating the Commands. 

To create a Command, add a method to your module of type `Task`. 
Typically, you will want to mark this method as `async`, although it 
is not required. 

Adding parameters to a Command is done by adding parameters to the 
parent Task. 

For example, to take an integer as an argument from the user, add `int 
arg`; to take a user as an argument from the user, add `IUser user`. 
In 1.0, a Command can accept nearly any type of argument; a full list 
of types that are parsed by default can be found in the below section 
on _Type Readers_. 

Parameters, by default, are always required. To make a parameter 
optional, give it a default value. To accept a comma-separated list, 
set the parameter to `params Type[]`. 

Should a parameter include spaces, it **must** be wrapped in quotes. 
For example, for a Command with a parameter `string food`, you would 
execute it with `!favoritefood "Key Lime Pie"`. 

If you would like a parameter to parse until the end of a Command, 
flag the parameter with the [RemainderAttribute]. This will allow a 
user to invoke a Command without wrapping a parameter in quotes. 

Finally, flag your Command with the [CommandAttribute] (you must 
specify a name for this Command, except for when it is part of a 
Module Group - see below). 

[RemainderAttribute]: xref:Discord.Commands.RemainderAttribute 
[CommandAttribute]: xref:Discord.Commands.CommandAttribute 

### Command Overloads 

You may add overloads to your Commands, and the Command parser will 
automatically pick up on it. 

If for whatever reason, you have two Commands which are ambiguous to 
each other, you may use the @Discord.Commands.PriorityAttribute to 
specify which should be tested before the other. 

The `Priority` attributes are sorted in ascending order; the higher 
priority will be called first. 

### Command Context 

Every Command can access the execution context through the [Context] 
property on [ModuleBase]. `ICommandContext` allows you to access the 
message, channel, guild, and user that the Command was invoked from, 
as well as the underlying Discord client that the Command was invoked 
from. 

Different types of Contexts may be specified using the generic variant 
of [ModuleBase]. When using a [SocketCommandContext], for example, the 
properties on this context will already be Socket entities, so you 
will not need to cast them. 

To reply to messages, you may also invoke [ReplyAsync], instead of 
accessing the channel through the [Context] and sending a message. 

[Context]: xref:Discord.Commands.ModuleBase`1#Discord_Commands_ModuleBase_1_Context
[SocketCommandContext]: xref:Discord.Commands.SocketCommandContext 

>![WARNING] 
>Contexts should **NOT** be mixed! You cannot have one module that 
>uses CommandContext and another that uses SocketCommandContext. 

### Example Module 

At this point, your module should look comparable to this example: 
[!code-csharp[Example Module](samples/module.cs)] 

#### Loading Modules Automatically 

The Command Service can automatically discover all classes in an 
Assembly that inherits [ModuleBase] and load them. 

To opt a module out of auto-loading, flag it with 
[DontAutoLoadAttribute]. 

Invoke [CommandService.AddModulesAsync] to discover modules and 
install them. 

[DontAutoLoadAttribute]: xref:Discord.Commands.DontAutoLoadAttribute 
[CommandService.AddModulesAsync]: xref:Discord_Commands_CommandService#Discord_Commands_CommandService_AddModulesAsync_Assembly_ 

#### Loading Modules Manually 

To manually load a module, invoke [CommandService.AddModuleAsync], by 
passing in the generic type of your module and optionally, a 
dependency map. 

[CommandService.AddModuleAsync]: xref:Discord.Commands.CommandService#Discord_Commands_CommandService_AddModuleAsync__1

### Module Constructors 

Modules are constructed using Dependency Injection. Any parameters 
that are placed in the Module's constructor must be injected into an 
@System.IServiceProvider first. Alternatively, you may accept an 
`IServiceProvider` as an argument and extract services yourself. 

### Module Properties 

Modules with `public` settable properties will have the dependencies 
injected after the construction of the Module. 

### Module Groups 

Module Groups allow you to create a module where Commands are 
prefixed. To create a group, flag a module with the 
@Discord.Commands.GroupAttribute. 

Module groups also allow you to create **nameless Commands**, where 
the [CommandAttribute] is configured with no name. In this case, the 
Command will inherit the name of the group it belongs to. 

### Submodules 

Submodules are Modules that reside within another one. Typically, 
submodules are used to create nested groups (although not required to 
create nested groups). 

[!code-csharp[Groups and Submodules](samples/groups.cs)] 

## With Builders 

**TODO** 

## Dependency Injection 

The Command Service is bundled with a very barebone Dependency 
Injection service for your convenience. It is recommended that you use 
DI when writing your modules. 

### Setup 

First, you need to create an @System.IServiceProvider; you may create 
your own one if you wish. 

Next, add the dependencies that your modules will use to the map. 

Finally, pass the map into the `LoadAssembly` method. Your modules 
will be automatically loaded with this dependency map. 

[!code-csharp[IServiceProvider Setup](samples/dependency_map_setup.cs)]

### Usage in Modules 

In the constructor of your Module, any parameters will be filled in by 
the @System.IServiceProvider that you've passed into `LoadAssembly`. 

Any publicly settable properties will also be filled in the same 
manner. 

>[!NOTE] 
> Annotating a property with the [DontInject] attribute will 
prevent it from being injected. 

>[!NOTE] 
>If you accept `CommandService` or `IServiceProvider` as a parameter 
in your constructor, or as an injectable property, these entries will 
be filled by the `CommandService` that the Module is loaded from, and 
the `ServiceProvider` that is passed into it respectively. 

[!code-csharp[ServiceProvider in Modules](samples/dependency_module.cs)] 

# Preconditions 

Precondition serve as a permissions system for your Commands. Keep in 
mind, however, that they are not limited to _just_ permissions and can 
be as complex as you want them to be. 

>[!NOTE] 
>Preconditions can be applied to Modules, Groups, or Commands. 

## Bundled Preconditions 

Commands ship with four bundled preconditions; you may view their 
usages on their respective API pages. 

- @Discord.Commands.RequireContextAttribute
- @Discord.Commands.RequireOwnerAttribute
- @Discord.Commands.RequireBotPermissionAttribute
- @Discord.Commands.RequireUserPermissionAttribute

## Custom Preconditions 

To write your own precondition, create a new class that inherits from 
@Discord.Commands.PreconditionAttribute. 

In order for your precondition to function, you will need to override 
the [CheckPermissions] method. 

Your IDE should provide an option to fill this in for you. 

Return [PreconditionResult.FromSuccess] if the context meets the 
required parameters, otherwise return [PreconditionResult.FromError] 
and optionally include an error message. 

[!code-csharp[Custom Precondition](samples/require_owner.cs)] 

[CheckPermissions]: xref:Discord.Commands.PreconditionAttribute#Discord_Commands_PreconditionAttribute_CheckPermissions_Discord_Commands_CommandContext_Discord_Commands_CommandInfo_Discord_Commands_IDependencyMap_
[PreconditionResult.FromSuccess]: xref:Discord.Commands.PreconditionResult#Discord_Commands_PreconditionResult_FromSuccess
[PreconditionResult.FromError]: xref:Discord.Commands.PreconditionResult#Discord_Commands_PreconditionResult_FromError_System_String_

# Type Readers 

Type Readers allow you to parse different types of arguments in
your commands.

By default, the following Types are supported arguments:

- bool
- char
- sbyte/byte
- ushort/short
- uint/int
- ulong/long
- float, double, decimal
- string
- DateTime/DateTimeOffset/TimeSpan
- IMessage/IUserMessage
- IChannel/IGuildChannel/ITextChannel/IVoiceChannel/IGroupChannel
- IUser/IGuildUser/IGroupUser
- IRole

### Creating a Type Readers 

To create a `TypeReader`, create a new class that imports @Discord and 
@Discord.Commands and ensure the class inherits from 
@Discord.Commands.TypeReader. 

Next, satisfy the `TypeReader` class by overriding the [Read] method. 

>[!NOTE]
>In many cases, Visual Studio can fill this in for you, using the
>"Implement Abstract Class" IntelliSense hint.

Inside this task, add whatever logic you need to parse the input 
string. 

Finally, return a `TypeReaderResult`. If you were able to successfully 
parse the input, return `TypeReaderResult.FromSuccess(parsedInput)`, 
otherwise, return `TypeReaderResult.FromError` and optionally include 
an error message. 

[Read]: xref:Discord.Commands.TypeReader#Discord_Commands_TypeReader_Read_Discord_Commands_CommandContext_System_String_

#### Sample 

[!code-csharp[TypeReaders](samples/typereader.cs)] 

### Installing TypeReaders 

TypeReaders are not automatically discovered by the Command Service 
and must be explicitly added. 

To install a TypeReader, invoke [CommandService.AddTypeReader](xref:Discord.Commands.CommandService#Discord_Commands_CommandService_AddTypeReader__1_Discord_Commands_TypeReader_).