Plugins.java

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/*
 * Turró i Cutiller Foundation. License notice.
 * Copyright (C) 2017 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.action;
 
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import org.turro.string.Strings;
import org.turro.annotation.ElephantPlugin;
import org.turro.reflection.ClassNames;
import org.turro.reflection.Reflections;
 
public class Plugins {
  
  /* Plugins */
  
  private static List<IElephantPlugin> _plugins;
  private static List<Class> _pluginClass;
  private static final Lock lock = new ReentrantLock();
  
  public static Map<String, Object> execute(String name, Map params) {
    loadPlugins();
    Map<String, Object> results = new HashMap<>();
    for(IElephantPlugin iPlugin : _plugins) {
      if(iPlugin.itsMe(name))  {
        iPlugin.setContext(params, results);
        iPlugin.execute();
        if(iPlugin.stopPropagating()) break;
      }
    }
    return results;
  }
 
  public static <T> T loadImplementation(Class<T> jclass) {
    return loadImplementation(jclass, null);
  }
  
  public static <T> T loadImplementation(Class<T> jclass, String label) {
    loadPlugins();
    for(Class pclass : _pluginClass) {
      if(Reflections.of(pclass).canCast(jclass))  {
        if(Strings.isBlank(label) || 
                ((ElephantPlugin) pclass.getAnnotation(ElephantPlugin.class)).label().equals(label)) {
          return (T) Reflections.of(pclass).instance();
        }
      }
    }
    return null;
  }
 
  private static void loadPlugins() {
    if(_plugins == null) {
      lock.lock();
      try {
        if(_plugins == null) {
          _plugins = new ArrayList<>();
          _pluginClass = new ArrayList<>();
          List<String> plugins = ClassNames.cached().byAnnotation(ElephantPlugin.class.getName());
          if(plugins != null) {
            for(String plugin : plugins) {
              Class iPluginClass = Reflections.check(plugin);
              if(iPluginClass != null) {
                _pluginClass.add(iPluginClass);
                IElephantPlugin iPlugin = (IElephantPlugin) Reflections.of(iPluginClass)
                        .is(IElephantPlugin.class).instance();
                if(iPlugin != null) {
                  _plugins.add(iPlugin);
                }
              }
            }
          }
        }
      } finally {
        lock.unlock();
      }
    }
  }
 
  private Plugins() {
  }
 
}