make basic ui remember one session

ui/app.js

@@ -2,11 +2,36 @@
 
 import Session from "../models/session.js";
 import SessionView from "./session.js";
+import WbDb from "../data/db.js";
+import SessionRepo from "../data/session_repo.js";
 
 export default class App {
-  #session = new Session();
+  #session = null;
+
+  constructor() {
+    let db = WbDb.get();
+    if (db.open)
+      this.#dbReady();
+    else
+      db.addEventListener(WbDb.EVENT_CHANGE, this.#dbReady.bind(this));
+  }
+
+  async #dbReady() {
+    let sessions = await SessionRepo.getAll();
+    if (sessions.length === 0) {
+      this.#session = new Session();
+      SessionRepo.put(this.#session);
+    } else
+      this.#session = sessions[0];
+
+    m.redraw();
+  }
 
   view() {
+    if (this.#session === null) {
+      return m("p", "Warte auf Datenbank.");
+    }
+
     return m(SessionView, { model: this.#session });
   }
 }