fileStorage/sagas: remove editor init from fileStorage

This is still a bit of a hack but is one step towards being able to
remove the 'editor' context.

src/editor/sagas.ts

@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2022 The Pybricks Authors
+
+import { monaco } from 'react-monaco-editor';
+import { eventChannel } from 'redux-saga';
+import { fork, put, race, select, take, takeEvery } from 'typed-redux-saga/macro';
+import {
+    fileStorageDidFailToReadFile,
+    fileStorageDidInitialize,
+    fileStorageDidReadFile,
+    fileStorageReadFile,
+} from '../fileStorage/actions';
+import { RootState } from '../reducers';
+
+function* handleDidCreateEditor(editor: monaco.editor.ICodeEditor): Generator {
+    // first, we need to be sure that file storage is ready
+
+    const isFileStorageInitialized = yield* select(
+        (s: RootState) => s.fileStorage.isInitialized,
+    );
+
+    if (!isFileStorageInitialized) {
+        yield* take(fileStorageDidInitialize);
+    }
+
+    // then we can load the most recently used file
+    // REVISIT: should this be here or elsewhere?
+
+    yield* put(fileStorageReadFile('main.py'));
+
+    const { succeeded } = yield* race({
+        succeeded: take(fileStorageDidReadFile.when((a) => a.fileName === 'main.py')),
+        failed: take(
+            fileStorageDidFailToReadFile.when((a) => a.fileName === 'main.py'),
+        ),
+    });
+
+    // TODO: what to do in case of failure?
+
+    if (succeeded) {
+        editor.setValue(succeeded.fileContents);
+    }
+
+    // TODO: subscribe to actions that act on the editor
+}
+
+function* monitorEditors(): Generator {
+    const ch = eventChannel<monaco.editor.ICodeEditor>((emit) => {
+        const subscription = monaco.editor.onDidCreateEditor(emit);
+        return () => subscription.dispose();
+    });
+
+    yield* takeEvery(ch, handleDidCreateEditor);
+}
+
+export default function* (): Generator {
+    yield* fork(monitorEditors);
+}