docs: beginnings of SOPClassHandlerModule docs

docs/latest/extensions/modules/sop-class-handler.md

@@ -1,6 +1,37 @@
 # Module: SOP Class Handler
 
-...
+An extension can register a SOP Class Handler Module by defining a
+`getSopClassHandlerModule` method. The SOP Class Handler is a bit different from
+the other modules, as it doesn't provide a `1:1` schema for UI or provide it's
+own components. It instead defines:
+
+- `sopClassUids`: an array of string SOP Class UIDs that the
+  `getDisplaySetFromSeries` method should be applied to.
+- `getDisplaySetFromSeries`: a method that maps series and study metadata to a
+  display set
+
+A `displaySet` has the following shape:
+
+```js
+return {
+  plugin: 'html',
+  modality: 'SR',
+  displaySetInstanceUid: 0,
+  wadoRoot: study.getData().wadoRoot,
+  wadoUri: instance.getData().wadouri,
+  sopInstanceUid: instance.getSOPInstanceUID(),
+  seriesInstanceUid: series.getSeriesInstanceUID(),
+  studyInstanceUid: study.getStudyInstanceUID(),
+  authorizationHeaders,
+};
+```
+
+Where the `plugin` key is used to influence the default `ViewportComponent` for
+rendering the `displaySet`. Additional properties are passed to the
+`ViewportComponent` and used by the default `StudyBrowser` to render
+"thumbnails" for each `displaySet`
+
+## Example SOP Class Handler Module
 
 ```js
 const SOP_CLASS_UIDS = {
@@ -8,7 +39,16 @@ const SOP_CLASS_UIDS = {
   ENHANCED_SR: '1.2.840.10008.5.1.4.1.1.88.22',
 };
 
-const sopClassHandlerModule = {
+export default {
+  id: 'example-sop-class-handler-module',
+
+/**
+ * @param {object} params
+ * @param {ServicesManager} params.servicesManager
+ * @param {CommandsManager} params.commandsManager
+ */
+getSopClassHandlerModule({ servicesManager, commandsManager }) {
+  return {
     id: 'OHIFDicomHtmlSopClassHandler',
     sopClassUids: Object.values(SOP_CLASS_UIDS),
 
@@ -32,5 +72,19 @@ const sopClassHandlerModule = {
         authorizationHeaders,
       };
     },
+  }
 };
 ```
+
+## `@ohif/viewer` usage
+
+We use the `sopClassHandlerModule`s in three different places:
+
+- `ViewerLocalFileData.js`
+- `ViewerRetrieveStudyData.js`
+- `StandaloneRouting.js`
+
+Each time, it is used to map study and series data to `displaySets`. It does
+this by working alongside the `StudyMetadataManager` in `@ohif/core`. That
+manager has the method `createDisplaySets` that takes an array of
+`sopClassHandlerModules`.