/**
    * This file Copyright (c) 2015 Magnolia International
    * Ltd.  (http://www.magnolia-cms.com). All rights reserved.
    *
    *
    * This file is dual-licensed under both the Magnolia
    * Network Agreement and the GNU General Public License.
    * You may elect to use one or the other of these licenses.
    *
   * This file is distributed in the hope that it will be
   * useful, but AS-IS and WITHOUT ANY WARRANTY; without even the
   * implied warranty of MERCHANTABILITY or FITNESS FOR A
   * PARTICULAR PURPOSE, TITLE, or NONINFRINGEMENT.
   * Redistribution, except as permitted by whichever of the GPL
   * or MNA you select, is prohibited.
   *
   * 1. For the GPL license (GPL), you can redistribute and/or
   * modify this file under the terms of the GNU General
   * Public License, Version 3, as published by the Free Software
   * Foundation.  You should have received a copy of the GNU
   * General Public License, Version 3 along with this program;
   * if not, write to the Free Software Foundation, Inc., 51
   * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * 2. For the Magnolia Network Agreement (MNA), this file
   * and the accompanying materials are made available under the
   * terms of the MNA which accompanies this distribution, and
   * is available at http://www.magnolia-cms.com/mna.html
   *
   * Any modifications to this file must keep this entire header
   * intact.
   *
   */
  package info.magnolia.classpathwatch;
  
  import java.io.IOException;
  import java.net.URL;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.List;
  import java.util.Set;
  
  import org.reflections.Reflections;
  import org.reflections.scanners.ResourcesScanner;
  import org.reflections.util.ClasspathHelper;
  import org.reflections.util.ConfigurationBuilder;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import com.google.common.base.Function;
  import com.google.common.base.Predicate;
  import com.google.common.base.Predicates;
  import com.google.common.collect.Collections2;
  
  /**
   * Scans the classpath for resources and checks for resource changes through their last-modified date.
   */
  public class ClasspathScanner implements Runnable {
  
      private static final Logger log = LoggerFactory.getLogger(ClasspathScanner.class);
  
      private final Predicate<String> resourcesFilter;
      private final Predicate<? super URL> urlsFilter;
  
      private long lastScan;
  
      private List<Function<String, Void>> callbacks = new ArrayList<>();
  
      /**
       * Constructor is protected, use {@link ClasspathScannerService} to get an instance.
       *
       * @param resourcesFilter used to dramatically decrease the amount of resources to check for changes (checking lastModified of several thousand resources *is* long)
       * @param urlsFilter the URL exclusions filter for Reflections
       */
      ClasspathScanner(Predicate<String> resourcesFilter, Predicate<? super URL> urlsFilter) {
          this.resourcesFilter = resourcesFilter;
          this.urlsFilter = urlsFilter;
          lastScan = System.currentTimeMillis(); // initial value, to avoid considering all resources as new on startup
      }
  
      @Override
      public void run() {
          // 1. Scan classpath for resources
          final long start = System.currentTimeMillis();
  
          final Collection<URL> classpathUrls = classpathUrls();
          // e.g.
          // file:/Users/<user>/.m2/repository/info/magnolia/magnolia-module-sample/1.0/magnolia-module-sample-1.0.jar (served by maven)
          // file:/Users/<user>/<dev-directory>/magnolia-module-sample/target/classes/ (served by IDE)
  
          final Reflections reflections = new Reflections(new ConfigurationBuilder()
                  .setScanners(new ResourcesScanner())
                  .setUrls(classpathUrls)
                  .filterInputsBy(resourcesFilter)
                  );
  
          final Set<String> resources = reflections.getResources(Predicates.<String>alwaysTrue()); // predicate here is used for matching only the "simple name" of the resource; we do the pattern filtering upfront in ConfigurationBuilder anyway
          long scanDone = System.currentTimeMillis();
          log.debug("Took {}ms to find {} resources", scanDone - start, resources.size());
 
         // 2. Check for recent lastModified dates
         for (String resource : resources) {
             URL resourceUrl = getUrl(resource);
             // TODO Only watch changes for resources served by the IDE (assume jars are not hot-swapped)?
             long lastModified = getLastModified(resourceUrl);
 
             if (lastModified > lastScan) {
                 log.debug("Found resource change at {}, triggering callback.", resource);
                 for (Function<String, Void> callback : callbacks) {
                     try {
                         callback.apply(resource);
                     } catch (Throwable t) {
                         log.error("Caught exception while invoking callback:", t);
                     }
                 }
                 // TODO find added/deleted files too?
             }
         }
         log.debug("Took {}ms to check for recent changes", System.currentTimeMillis() - scanDone);
         lastScan = System.currentTimeMillis();
     }
 
     public void watchResourceChanges(Function<String, Void> callbackFunction) {
         callbacks.add(callbackFunction);
     }
 
     protected Collection<URL> classpathUrls() {
         final Collection<URL> allURLs = ClasspathHelper.forClassLoader(ClasspathHelper.contextClassLoader());
         return Collections2.filter(allURLs, urlsFilter);
     }
 
     protected URL getUrl(String resourcePath) {
         final URL url = ClasspathHelper.contextClassLoader().getResource(resourcePath);
         if (url == null) {
             throw new IllegalStateException("Can't find resource at " + resourcePath);
         }
         return url;
     }
 
     protected long getLastModified(URL resourceUrl) {
         try {
             return resourceUrl.openConnection().getLastModified();
         } catch (IOException e) {
             throw new RuntimeException("Last modified time could not be retrieved for path " + resourceUrl.toExternalForm() + " : " + e, e);
         }
     }
 
 }