importDb feature in wallet core

packages/taler-wallet-core/src/db.ts

@@ -1873,3 +1873,30 @@ export function exportDb(db: IDBDatabase): Promise<any> {
     }
   });
 }
+
+export interface DatabaseDump {
+  name: string,
+  stores: { [s: string]: any },
+  version: string,
+}
+
+export function importDb(db: IDBDatabase, dump: DatabaseDump): Promise<any> {
+  return new Promise((resolve, reject) => {
+    const tx = db.transaction(Array.from(db.objectStoreNames), "readwrite");
+    tx.addEventListener("complete", () => {
+      tx.commit();
+      resolve(db);
+    });
+    for (let i = 0; i < db.objectStoreNames.length; i++) {
+      const name = db.objectStoreNames[i];
+      const storeDump = dump.stores[name];
+      if (!storeDump) continue;
+      Object.keys(storeDump).forEach(async key => {
+        const value = storeDump[key]
+        if (!value) return;
+        tx.objectStore(name).put(value)
+      })
+
+    }
+  });
+}