ForumMigration.java

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/*
 * Turró i Cutiller Foundation. License notice.
 * Copyright (C) 2021 Lluis Turró Cutiller <http://www.turro.org/>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
package org.turro.forum;
 
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantLock;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.stream.Stream;
import org.turro.elephant.context.ElephantContext;
import org.turro.elephant.db.ElephantPU;
import org.turro.elephant.entities.db.Topic;
import org.turro.jpa.Dao;
import org.turro.jpa.DaoUtil;
 
public class ForumMigration implements Runnable {
  
  private final Dao oldForumDao, newForumDao;
  private String currentEntity = null;
  private Topic currentTopic = null;
 
  public static void migrate() {
    ForumMigration migration = new ForumMigration(Dao.getDaoByPU("contactsPU"));
    if(migration.isNecessary()) new Thread(migration, "ElephantForum migration").start();
  }
 
  private boolean isNecessary() {
    return DaoUtil.isEmpty(newForumDao, "Topic");
  }
 
  private void start() {
    try(Stream<CommentItEntry> comments = oldForumDao.stream(CommentItEntry.class, getSelect())) {
      comments.forEach((comment) -> {
        if(comment.getEntityPath().equals(currentEntity)) {
          comment.migratePost(newForumDao, currentTopic);
        } else {
          currentTopic = comment.migrateTopic(newForumDao);
          currentEntity = comment.getEntityPath();
        }
      });
    }
  }
 
  private String getSelect() {
    return "select new org.turro.forum.CommentItEntry(t.path, t.creator.id, t.dateCreation, t.body) " +
           "from CommentIt t where t.creator is not null and t.path like '/dossier/%' " +
           "order by t.path";
  }
  
  private ForumMigration(Dao oldForumDao) {
    this.oldForumDao = oldForumDao;
    this.newForumDao = new ElephantPU();
  }
 
  private static final ReentrantLock LOCK = new ReentrantLock();
 
  @Override
  public void run() {
    if(!LOCK.isLocked()) {
      try {
        if(LOCK.tryLock(0, TimeUnit.SECONDS)) {
          try {
            if(isNecessary()) {
              start();
            }
          } finally {
            LOCK.unlock();
          }
        }
      } catch (InterruptedException ex) {
        Logger.getLogger(ForumMigration.class.getName()).log(Level.SEVERE, ElephantContext.logMsg(null), ex);
      }
    }
  }
  
}