Extract a method from ChangeNoteUtil for parsing a NoteDb ident

Change-Id: Ie422f5d081976d2a003003cde0986c6465972f8c

java/com/google/gerrit/server/notedb/NoteDbUtil.java

@@ -0,0 +1,39 @@
+// Copyright (C) 2017 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.notedb;
+
+import com.google.common.primitives.Ints;
+import com.google.gerrit.reviewdb.client.Account;
+import java.util.Optional;
+import org.eclipse.jgit.lib.PersonIdent;
+
+public class NoteDbUtil {
+  public static Optional<Account.Id> parseIdent(PersonIdent ident, String serverId) {
+    String email = ident.getEmailAddress();
+    int at = email.indexOf('@');
+    if (at >= 0) {
+      String host = email.substring(at + 1, email.length());
+      if (host.equals(serverId)) {
+        Integer id = Ints.tryParse(email.substring(0, at));
+        if (id != null) {
+          return Optional.of(new Account.Id(id));
+        }
+      }
+    }
+    return Optional.empty();
+  }
+
+  private NoteDbUtil() {}
+}