Rough notes, extensions

docs/latest/architecture/extensions.md

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+# Extensions
+
+Extensions are a way to add powerful They do this through An extension can be added through the `ExtensionManager` exposed by `ohif-core`. Common
+
+## Custom Extensions
+
+At a glance, an extension is a class or object that has a `getExtensionId()` method, and one or more "module" methods that are used to register a specific kind of functionality. You can read more about each kind of "module" below.
+
+```js
+class myCustomExtension {
+
+    /** Required */
+    getExtensionId: () => 'my-extension-id';
+
+    /** React component that receives props from ConnectLayoutManager
+     *  If more than one viewport module is registered, SopClassHandler
+     *  is used to help determine which component is used */
+    getViewportModule: () => reactViewportComponent;
+
+    /** React component that adds buttons/behavior to the viewer Toolbar */ 
+    getToolbarModule: () => reactToolbarComponent;
+
+    /** Provides a whitelist of SOPClassUIDs the viewport is capable of rendering.
+     *  Can modify default behavior for methods like `getDisplaySetFromSeries` */
+    getSopClassHandler: () => {
+        id: 'some-other-unique-id',
+        type: PLUGIN_TYPES.SOP_CLASS_HANDLER,
+        sopClassUids: ['string'],
+        getDisplaySetFromSeries: (series, study, dicomWebClient, authorizationHeaders) => ...
+    };
+
+    // Not yet used
+    getPanelModule: () => null;
+}
+```
+
+### Modules
+
+#### Viewport
+
+...
+
+#### Toolbar
+
+...
+
+#### SopClassHandler
+
+...
+
+#### Panel
+
+...
+
+
+## OHIF Maintained Extensions
+
+A small number of powerful extensions for popular use cases are maintained by OHIF. They're co-located in the [`OHIF/Viewers`](https://github.com/OHIF/Viewers/tree/react/) repository, in the top level [`extensions/`](https://github.com/OHIF/Viewers/tree/react/extensions) directory. 
+
+
+{% include "./_maintained-extensions-table.md" %}
+
+[extension types](https://github.com/OHIF/ohif-core/blob/master/src/plugins.js#L1-L6)
+
+Interface:
+- getExtensionId()
+- "types" (modules on extension)
+    - getViewport()
+    - getToolbar()
+    - getPanel()
+    - getSop_Class_Handler()
+
+calls: (for each module on extension)
+```
+store.dispatch(addPlugin({
+    id: extensionId,
+    type: PLUGIN_TYPE,
+    component: getViewport() --> Viewport Component
+}))
+```
+
+({
+    type: 'ADD_PLUGIN',
+    plugin
+})
+
+https://github.com/OHIF/ohif-core/blob/43c08a29eff3fb646a0e83a03a236ddd84f4a6e8/src/redux/reducers/plugins.js#L7-L30
+
+- Connected Layout Manager
+    - AvailablePlugins that match Viewport type
+
+ToolbarRow
+    - AvailablePlugins that match Toolbar type
+