/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements. See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You 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 org.apache.logging.log4j.util;
  
  import org.apache.logging.log4j.Logger;
  import org.apache.logging.log4j.spi.Provider;
  import org.apache.logging.log4j.status.StatusLogger;
  
  import java.io.IOException;
  import java.net.URL;
  import java.util.ArrayList;
  import java.util.Enumeration;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Properties;
  
  /**
   *
   */
  public final class ProviderUtil {
  
      private static final String PROVIDER_RESOURCE = "META-INF/log4j-provider.properties";
      private static final String API_VERSION = "Log4jAPIVersion";
  
      private static final String[] COMPATIBLE_API_VERSIONS = {
          "2.0.0"
      };
  
      private static final Logger LOGGER = StatusLogger.getLogger();
  
      private static final List<Provider> PROVIDERS = new ArrayList<Provider>();
  
      private ProviderUtil() {
      }
  
      static {
          final ClassLoader cl = findClassLoader();
          Enumeration<URL> enumResources = null;
          try {
              enumResources = cl.getResources(PROVIDER_RESOURCE);
          } catch (final IOException e) {
              LOGGER.fatal("Unable to locate " + PROVIDER_RESOURCE, e);
          }
  
          if (enumResources != null) {
              while (enumResources.hasMoreElements()) {
                  final Properties props = new Properties();
                  final URL url = enumResources.nextElement();
                  try {
                      props.load(url.openStream());
                  } catch (final IOException ioe) {
                      LOGGER.error("Unable to read " + url.toString(), ioe);
                  }
                  if (!validVersion(props.getProperty(API_VERSION))) {
                      continue;
                  }
                  PROVIDERS.add(new Provider(props, url));
              }
          }
      }
  
      public static Iterator<Provider> getProviders() {
          return PROVIDERS.iterator();
      }
  
      public static boolean hasProviders() {
          return PROVIDERS.size() > 0;
      }
  
      public static ClassLoader findClassLoader() {
          ClassLoader cl;
          if (System.getSecurityManager() == null) {
              cl = Thread.currentThread().getContextClassLoader();
          } else {
              cl = java.security.AccessController.doPrivileged(
                  new java.security.PrivilegedAction<ClassLoader>() {
                      public ClassLoader run() {
                          return Thread.currentThread().getContextClassLoader();
                      }
                  }
              );
          }
          if (cl == null) {
              cl = ProviderUtil.class.getClassLoader();
          }
 
         return cl;
     }
 
     private static boolean validVersion(final String version) {
         for (final String v : COMPATIBLE_API_VERSIONS) {
             if (version.startsWith(v)) {
                 return true;
             }
         }
         return false;
     }
 }