# Modular Commands

## Overview

Cmd2 also enables developers to modularize their command definitions into
[CommandSet][cmd2.CommandSet] objects. CommandSets represent a logical grouping of commands within a
`cmd2` application. By default, `CommandSet` objects need to be manually registered. However, it is
possible for all `CommandSet` objects to be discovered and loaded automatically when the
[cmd2.Cmd][] class is instantiated with this mixin by setting `auto_load_commands=True`. This also
enables the developer to dynamically add/remove commands from the `cmd2` application. This could be
useful for loadable plugins that add additional capabilities. Additionally, it allows for
object-oriented encapsulation and garbage collection of state that is specific to a CommandSet.

### Features

- Modular Command Sets - Commands can be broken into separate modules rather than in one god class
  holding all commands.
- Automatic Command Discovery - In your application, merely defining and importing a CommandSet is
  sufficient for `cmd2` to discover and load your command if you set `auto_load_commands=True`. No
  manual registration is necessary.
- Dynamically Loadable/Unloadable Commands - Command functions and CommandSets can both be loaded
  and unloaded dynamically during application execution. This can enable features such as
  dynamically loaded modules that add additional commands.
- Events handlers - Four event handlers are provided in `CommandSet` class for custom initialization
  and cleanup steps. See [Event Handlers](#event-handlers).
- Subcommand Injection - Subcommands can be defined separately from the base command. This allows
  for a more action-centric instead of object-centric command system while still organizing your
  code and handlers around the objects being managed.

See API documentation for [cmd2.CommandSet][].

See [the examples](https://github.com/python-cmd2/cmd2/tree/main/examples/modular_commands) for more
details.

## Defining Commands

### Command Sets

CommandSets group multiple commands together. The plugin will inspect functions within a
`CommandSet` using the same rules as when they're defined in `cmd2.Cmd`. Commands must be prefixed
with `do_`, help functions with `help_`, and completer functions with `complete_`.

The [@with_default_category][cmd2.with_default_category] decorator is provided to categorize all
commands within a CommandSet class in the same command category. Individual commands in a CommandSet
class may override the default category by using the [@with_category][cmd2.with_category] decorator
on that method.

CommandSet command methods will always expect the same parameters as when defined in a `cmd2.Cmd`
sub-class, except that `self` will now refer to the `CommandSet` instead of the cmd2 instance. The
cmd2 instance can be accessed through `self._cmd` that is populated when the `CommandSet` is
registered.

CommandSets will only be auto-loaded if the initializer takes no arguments. If you need to provide
initializer arguments, see [Manual CommandSet Construction](#manual-commandset-construction).

```py
import cmd2
from cmd2 import CommandSet, with_default_category

@with_default_category('My Category')
class AutoLoadCommandSet(CommandSet):
    def __init__(self):
        super().__init__()

    def do_hello(self, _: cmd2.Statement):
        self._cmd.poutput('Hello')

    def do_world(self, _: cmd2.Statement):
        self._cmd.poutput('World')

class ExampleApp(cmd2.Cmd):
    """
    CommandSets are automatically loaded. Nothing needs to be done.
    """
    def __init__(self, *args, **kwargs):
        super().__init__(*args, auto_load_commands=True, **kwargs)

    def do_something(self, arg):
        self.poutput('this is the something command')
```

### Manual CommandSet Construction

If a CommandSet class requires parameters to be provided to the initializer, you may manually
construct CommandSets and pass in the initializer to Cmd2.

```py
import cmd2
from cmd2 import CommandSet, with_default_category

@with_default_category('My Category')
class CustomInitCommandSet(CommandSet):
    def __init__(self, arg1, arg2):
        super().__init__()

        self._arg1 = arg1
        self._arg2 = arg2

    def do_show_arg1(self, _: cmd2.Statement):
        self._cmd.poutput(f'Arg1: {self._arg1}')

    def do_show_arg2(self, _: cmd2.Statement):
        self._cmd.poutput(f'Arg2: {self._arg2}')

class ExampleApp(cmd2.Cmd):
    """
    CommandSets with initializer parameters are provided in the initializer
    """
    def __init__(self, *args, **kwargs):
        # gotta have this or neither the plugin or cmd2 will initialize
        super().__init__(*args, auto_load_commands=True, **kwargs)

    def do_something(self, arg):
        self.last_result = 5
        self.poutput('this is the something command')


def main():
    my_commands = CustomInitCommandSet(1, 2)
    app = ExampleApp(command_sets=[my_commands])
    app.cmdloop()
```

### Dynamic Commands

You can also dynamically load and unload commands by installing and removing CommandSets at runtime.
For example, you can support runtime loadable plugins or add/remove commands based on your state.

You may need to disable command auto-loading if you need to dynamically load commands at runtime.

```py
import argparse
import cmd2
from cmd2 import CommandSet, with_argparser, with_category, with_default_category


@with_default_category('Fruits')
class LoadableFruits(CommandSet):
    def __init__(self):
        super().__init__()

    def do_apple(self, _: cmd2.Statement):
        self._cmd.poutput('Apple')

    def do_banana(self, _: cmd2.Statement):
        self._cmd.poutput('Banana')


@with_default_category('Vegetables')
class LoadableVegetables(CommandSet):
    def __init__(self):
        super().__init__()

    def do_arugula(self, _: cmd2.Statement):
        self._cmd.poutput('Arugula')

    def do_bokchoy(self, _: cmd2.Statement):
        self._cmd.poutput('Bok Choy')


class ExampleApp(cmd2.Cmd):
    """
    CommandSets are loaded via the `load` and `unload` commands
    """

    def __init__(self, *args, **kwargs):
        # gotta have this or neither the plugin or cmd2 will initialize
        super().__init__(*args, auto_load_commands=False, **kwargs)

        self._fruits = LoadableFruits()
        self._vegetables = LoadableVegetables()

    load_parser = cmd2.Cmd2ArgumentParser()
    load_parser.add_argument('cmds', choices=['fruits', 'vegetables'])

    @with_argparser(load_parser)
    @with_category('Command Loading')
    def do_load(self, ns: argparse.Namespace):
        if ns.cmds == 'fruits':
            try:
                self.register_command_set(self._fruits)
                self.poutput('Fruits loaded')
            except ValueError:
                self.poutput('Fruits already loaded')

        if ns.cmds == 'vegetables':
            try:
                self.register_command_set(self._vegetables)
                self.poutput('Vegetables loaded')
            except ValueError:
                self.poutput('Vegetables already loaded')

    @with_argparser(load_parser)
    def do_unload(self, ns: argparse.Namespace):
        if ns.cmds == 'fruits':
            self.unregister_command_set(self._fruits)
            self.poutput('Fruits unloaded')

        if ns.cmds == 'vegetables':
            self.unregister_command_set(self._vegetables)
            self.poutput('Vegetables unloaded')


if __name__ == '__main__':
    app = ExampleApp()
    app.cmdloop()
```

## Event Handlers

The following functions are called at different points in the [CommandSet][cmd2.CommandSet] life
cycle.

[on_register][cmd2.command_definition.CommandSet.on_register] - Called by `cmd2.Cmd` as the first
step to registering a `CommandSet`. The commands defined in this class have not be added to the CLI
object at this point. Subclasses can override this to perform any initialization requiring access to
the Cmd object (e.g. configure commands and their parsers based on CLI state data).

[on_registered][cmd2.command_definition.CommandSet.on_registered] - Called by `cmd2.Cmd` after a
`CommandSet` is registered and all its commands have been added to the CLI. Subclasses can override
this to perform custom steps related to the newly added commands (e.g. setting them to a disabled
state).

[on_unregister][cmd2.command_definition.CommandSet.on_unregister] - Called by `cmd2.Cmd` as the
first step to unregistering a `CommandSet`. Subclasses can override this to perform any cleanup
steps which require their commands being registered in the CLI.

[on_unregistered][cmd2.command_definition.CommandSet.on_unregistered] - Called by `cmd2.Cmd` after a
`CommandSet` has been unregistered and all its commands removed from the CLI. Subclasses can
override this to perform remaining cleanup steps.

## Injecting Subcommands

### Description

Using the [@with_argparser][cmd2.with_argparser] and [@as_subcommand_to][cmd2.as_subcommand_to]
decorators, it is possible to easily define subcommands for your command. This has a tendency to
drive your interface into an object-centric interface. For example, imagine you have a tool that
manages your media collection and you want to manage movies or shows. An object-centric approach
would push you to have base commands such as `movies` and `shows` which each have subcommands `add`,
`edit`, `list`, `delete`. If you wanted to present an action-centric command set, so that `add`,
`edit`, `list`, and `delete` are the base commands, you'd have to organize your code around these
similar actions rather than organizing your code around similar objects being managed.

Subcommand injection allows you to inject subcommands into a base command to present an interface
that is sensible to a user while still organizing your code in whatever structure makes more logical
sense to the developer.

### Example

This example is a variation on the Dynamic Commands example above. A `cut` command is introduced as
a base command and each CommandSet adds a subcommand to it.

```py
import argparse
import cmd2
from cmd2 import CommandSet, with_argparser, with_category, with_default_category


@with_default_category('Fruits')
class LoadableFruits(CommandSet):
    def __init__(self):
        super().__init__()

    def do_apple(self, _: cmd2.Statement):
        self._cmd.poutput('Apple')

    banana_parser = cmd2.Cmd2ArgumentParser()
    banana_parser.add_argument('direction', choices=['discs', 'lengthwise'])

    @cmd2.as_subcommand_to('cut', 'banana', banana_parser)
    def cut_banana(self, ns: argparse.Namespace):
        """Cut banana"""
        self._cmd.poutput('cutting banana: ' + ns.direction)


@with_default_category('Vegetables')
class LoadableVegetables(CommandSet):
    def __init__(self):
        super().__init__()

    def do_arugula(self, _: cmd2.Statement):
        self._cmd.poutput('Arugula')

    bokchoy_parser = cmd2.Cmd2ArgumentParser()
    bokchoy_parser.add_argument('style', choices=['quartered', 'diced'])

    @cmd2.as_subcommand_to('cut', 'bokchoy', bokchoy_parser)
    def cut_bokchoy(self, _: argparse.Namespace):
        self._cmd.poutput('Bok Choy')


class ExampleApp(cmd2.Cmd):
    """
    CommandSets are loaded dynamically at runtime via other commands.
    """

    def __init__(self, *args, **kwargs):
        # gotta have this or neither the plugin or cmd2 will initialize
        super().__init__(*args, auto_load_commands=False, **kwargs)

        self._fruits = LoadableFruits()
        self._vegetables = LoadableVegetables()

    load_parser = cmd2.Cmd2ArgumentParser()
    load_parser.add_argument('cmds', choices=['fruits', 'vegetables'])

    @with_argparser(load_parser)
    @with_category('Command Loading')
    def do_load(self, ns: argparse.Namespace):
        if ns.cmds == 'fruits':
            try:
                self.register_command_set(self._fruits)
                self.poutput('Fruits loaded')
            except ValueError:
                self.poutput('Fruits already loaded')

        if ns.cmds == 'vegetables':
            try:
                self.register_command_set(self._vegetables)
                self.poutput('Vegetables loaded')
            except ValueError:
                self.poutput('Vegetables already loaded')

    @with_argparser(load_parser)
    def do_unload(self, ns: argparse.Namespace):
        if ns.cmds == 'fruits':
            self.unregister_command_set(self._fruits)
            self.poutput('Fruits unloaded')

        if ns.cmds == 'vegetables':
            self.unregister_command_set(self._vegetables)
            self.poutput('Vegetables unloaded')

    cut_parser = cmd2.Cmd2ArgumentParser()
    cut_subparsers = cut_parser.add_subparsers(title='item', help='item to cut')

    @with_argparser(cut_parser)
    def do_cut(self, ns: argparse.Namespace):
        handler = ns.cmd2_handler.get()
        if handler is not None:
            # Call whatever subcommand function was selected
            handler(ns)
        else:
            # No subcommand was provided, so call help
            self.poutput('This command does nothing without sub-parsers registered')
            self.do_help('cut')


if __name__ == '__main__':
    app = ExampleApp()
    app.cmdloop()
```