sync: prepare -> collector, other optimizations

packages/core/api/sync/conflicts.js

@@ -0,0 +1,27 @@
+class Conflicts {
+  /**
+   *
+   * @param {import('../index').default} db
+   */
+  constructor(db) {
+    this._db = db;
+  }
+
+  async recalculate() {
+    if (this._db.notes.conflicted.length <= 0) {
+      await this._db.context.write("hasConflicts", false);
+    }
+  }
+
+  async check() {
+    let hasConflicts = await this._db.context.read("hasConflicts");
+    if (hasConflicts) {
+      const mergeConflictError = new Error(
+        "Merge conflicts detected. Please resolve all conflicts to continue syncing."
+      );
+      mergeConflictError.code = "MERGE_CONFLICT";
+      throw mergeConflictError;
+    }
+  }
+}
+export default Conflicts;