fix: do not allow multiple concurrent syncs

packages/core/api/sync/index.js

@@ -42,6 +42,7 @@ export default class Sync {
     this._collector = new Collector(this._db);
     this._merger = new Merger(this._db);
     this._tokenManager = new TokenManager(this._db);
+    this._isSyncing = false;
   }
 
   async _fetch(lastSynced, token) {
@@ -52,6 +53,7 @@ export default class Sync {
   }
 
   async _performChecks() {
+    if (this._isSyncing) throw new Error("Sync already running.");
     let lastSynced = (await this._db.context.read("lastSynced")) || 0;
     let token = await this._tokenManager.getAccessToken();
     if (!token) throw new Error("You need to login to sync.");
@@ -65,9 +67,11 @@ export default class Sync {
 
   async start(full, force) {
     if (force) await this._db.context.write("lastSynced", 0);
-
     let { lastSynced, token } = await this._performChecks();
 
+    try {
+      this._isSyncing = true;
+
       if (full) var serverResponse = await this._fetch(lastSynced, token);
 
       // we prepare local data before merging so we always have correct data
@@ -88,6 +92,11 @@ export default class Sync {
       if (lastSynced) {
         await this._db.context.write("lastSynced", lastSynced);
       }
+    } catch (e) {
+      throw e;
+    } finally {
+      this._isSyncing = false;
+    }
   }
 
   async eventMerge(serverResponse) {