docs: commands module docs

docs/latest/extensions/modules/commands.md

@@ -1,34 +1,136 @@
 # Module: Commands
 
-The Commands Module allows us to register one or more commands scoped to
-specific contexts. Commands can be run by [hotkeys][#], [toolbar buttons][#],
-and any registered custom react component (like a [viewport][#] or [panel][#]).
+- [Overview](#overview)
+- [Command Definitions](#command-definitions)
+- [Commands Manager](#commands-manager)
+  - [Instantiating](#instatiating)
+  - [Public API](#public-api)
+  - [Contexts](#contexts)
+
+## Overview
+
+An extension can register a Commands Module by defining a `getCommandsModule`
+method. The Commands Module allows us to register one or more commands scoped to
+specific [contexts](./../index.md#contexts). Commands have several unique
+characteristics that make them tremendously powerful:
+
+- Multiple implementations for the same command can be defined
+- Only the correct command's implementation will be run, dependent on the
+  application's "context"
+- Commands can be called from extensions, modules, and the consuming application
+
 Here is a simple example commands module:
 
 ```js
-{
-    getCommandsModule() {
-        return {
-            actions: {
-                speak: ({ viewports, words }) => {
-                    console.log(viewports, words);
-                },
-            },
-            definitions: {
-                rotateViewportCW: {
-                    commandFn: actions.rotateViewport,
-                    storeContexts: ['viewports'],
-                    options: { rotation: 90 }
-                },
-                rotateViewportCCW: {
-                    commandFn: actions.rotateViewport,
-                    storeContexts: ['viewports'],
-                    options: { rotation: -90 },
-                    context: 'ACTIVE_VIEWER::CORNERSTONE'
-                },
-            },
-            defaultContext: 'VIEWER'
-        }
-    }
+export default {
+  id: 'example-commands-module',
+
+  /**
+   * @param {object} params
+   * @param {ServicesManager} params.servicesManager
+   * @param {CommandsManager} params.commandsManager
+   */
+  getCommandsModule({ servicesManager, commandsManager }) {
+    return {
+      definitions: {
+        sayHello: {
+          commandFn: ({ words }) => {
+            console.log(words);
+          },
+          options: { words: 'Hello!' },
+        },
+      },
+      defaultContext: 'VIEWER',
+    };
+  },
+};
+```
+
+Each definition returned by the Commands Module is registered to the
+`ExtensionManager`'s `CommandsManager`.
+
+## Command Definitions
+
+The command definition consists of a named command (`myCommandName` below) and a
+`commandFn`. The command name is used to call the command, and the `commandFn`
+is the "command" that is actioned.
+
+```js
+myCommandName: {
+	commandFn: ({ viewports, other, options }) => { },
+	storeContexts: ['viewports'],
+	options: { words: 'Just kidding! Goodbye!' },
+	context: 'ACTIVE_VIEWPORT::CORNERSTONE',
 }
 ```
+
+| Property        | Type               | Description                                                                                                                             |
+| --------------- | ------------------ | --------------------------------------------------------------------------------------------------------------------------------------- |
+| `commandFn`     | func               | The function to call when command is run. Receives `options` and `storeContexts`.                                                       |
+| `storeContexts` | string[]           | (optional) Expected state objects to be passed in as props. Located using `getAppState` fn defined at `CommandsManager`'s instatiation. |
+| `options`       | object             | (optional) Arguments to pass at the time of calling to the `commandFn`                                                                  |
+| `context`       | string[] \| string | (optional) Overrides the `defaultContext`. Let's us know if command is currently "available" to be run.                                 |
+
+## `CommandsManager`
+
+The `CommandsManager` is a class defined in the `@ohif/core` project. A single
+instance of it should be defined in the consuming application, and it should be
+used when constructing the `ExtensionManager`.
+
+### Instantiating
+
+When we instantiate the `CommandsManager`, we need to pass it two methods:
+
+- `getAppState` - Should return the application's state when called
+- `getActiveContexts` - Should return the application's active contexts when
+  called
+
+These methods are used internally to help determine which commands are currently
+valid, and how to provide them with any state they may need at the time they are
+called.
+
+```js
+const commandsManager = new CommandsManager({
+  getAppState,
+  getActiveContexts,
+});
+```
+
+### Public API
+
+If you would like to run a command in the consuming app or an extension, you can
+use one of the following methods:
+
+```js
+// Returns all commands for a given context
+commandsManager.getContext('string');
+
+// Attempts to run a command
+commandsManager.runCommand('speak', { command: 'hello' });
+
+// Run command, but override the active contexts
+commandsManager.runCommand('speak', { command: 'hello' }, ['VIEWER']);
+```
+
+The `ExtensionManager` handles registering commands and creating contexts, so
+most consumer's won't need these methods. If you find yourself using these, ask
+yourself "why can't I register these commands via an extension?"
+
+```js
+// Used by the `ExtensionManager` to register new commands
+commandsManager.registerCommand('context', 'name', commandDefinition);
+
+// Creates a new context; clears the context if it already exists
+commandsManager.createContext('string');
+```
+
+### Contexts
+
+It is up to the consuming application to define what contexts are possible, and
+which ones are currently active. As extensions depend heavily on these, we will
+likely publish guidance around creating contexts, and ways to override extension
+defined contexts in the near future. If you would like to discuss potential
+changes to how contexts work, please don't hesistate to createa new GitHub
+issue.
+
+[Some additional information on Contexts can be found here.](./../index.md#contexts)