Read change ID sequence from notedb

Change-Id: Ib500a93d6368c7ef134422102afd8b561addd52f

gerrit-server/src/main/java/com/google/gerrit/server/Sequences.java

@@ -0,0 +1,56 @@
+// Copyright (C) 2016 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;
+
+import com.google.gerrit.reviewdb.server.ReviewDb;
+import com.google.gerrit.server.config.AllProjectsName;
+import com.google.gerrit.server.git.GitRepositoryManager;
+import com.google.gerrit.server.notedb.NotesMigration;
+import com.google.gerrit.server.notedb.RepoSequence;
+import com.google.gwtorm.server.OrmException;
+import com.google.inject.Inject;
+import com.google.inject.Provider;
+import com.google.inject.Singleton;
+
+@Singleton
+public class Sequences {
+  private final Provider<ReviewDb> db;
+  private final NotesMigration migration;
+  private final RepoSequence changeSeq;
+
+  @Inject
+  Sequences(Provider<ReviewDb> db,
+      NotesMigration migration,
+      GitRepositoryManager repoManager,
+      AllProjectsName allProjects) {
+    this.db = db;
+    this.migration = migration;
+    if (migration.readChanges()) {
+      changeSeq = new RepoSequence(
+          repoManager, allProjects, "changes", ReviewDb.FIRST_CHANGE_ID, 100);
+    } else {
+      changeSeq = null;
+    }
+  }
+
+  @SuppressWarnings("deprecation")
+  public int nextChangeId() throws OrmException {
+    if (migration.readChanges()) {
+      return changeSeq.next();
+    } else {
+      return db.get().nextChangeId();
+    }
+  }
+}