/**
    * This file Copyright (c) 2015-2018 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.resourceloader.layered;
  
  import static info.magnolia.resourceloader.ResourceOriginChange.Type.*;
  import static info.magnolia.resourceloader.ResourceOriginChange.resourceChange;
  import static java.util.Comparator.comparing;
  import static java.util.stream.Collectors.toList;
  
  import info.magnolia.resourceloader.AbstractResourceOrigin;
  import info.magnolia.resourceloader.Resource;
  import info.magnolia.resourceloader.ResourceChangeHandler;
  import info.magnolia.resourceloader.ResourceChangeHandlerRegistration;
  import info.magnolia.resourceloader.ResourceOrigin;
  import info.magnolia.resourceloader.ResourceOriginChange;
  import info.magnolia.resourceloader.ResourceOriginFactory;
  import info.magnolia.resourceloader.util.Functions;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.Reader;
  import java.nio.charset.Charset;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.List;
  import java.util.Optional;
  import java.util.function.Predicate;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import com.google.auto.factory.AutoFactory;
  import com.google.common.collect.Lists;
  import com.google.common.collect.Ordering;
  
  /**
   * An implementation of {@link ResourceOrigin} which aggregates
   * other instances of {@link ResourceOrigin}; resources located on the same path will
   * be served from the foremost ResourceOrigin, but resources that exist only on one path will always be served.
   */
  @AutoFactory(implementing = ResourceOriginFactory.class)
  public class LayeredResourceOrigin extends AbstractResourceOrigin<LayeredResource> {
  
      private static final Logger log = LoggerFactory.getLogger(LayeredResourceOrigin.class);
  
      private final List<ResourceOrigin<?>> origins;
  
      // No injected arguments so far, which is fine. Just keeping a factory for consistency.
      LayeredResourceOrigin(String name, ResourceOrigin<?>... origins) {
          super(name);
          this.origins = Arrays.asList(origins);
      }
  
      @Override
      public LayeredResource getRoot() {
          final List<Resource> roots = origins.stream()
                  .map(ResourceOrigin::getRoot)
                  .collect(toList());
          return newLayeredResource(roots);
      }
  
      @Override
      public ResourceChangeHandlerRegistration registerResourceChangeHandler(final ResourceChangeHandler changeHandler) {
          final ResourceChangeHandler relayingChangeHandler = new RelayingChangeHandler(changeHandler);
  
          final List<ResourceChangeHandlerRegistration> registrations = Lists.newArrayListWithCapacity(origins.size() + 1);
          registrations.add(super.registerResourceChangeHandler(relayingChangeHandler));
  
         for (final ResourceOrigin origin : origins) {
             registrations.add(origin.registerResourceChangeHandler(relayingChangeHandler));
         }
 
         return new AggregateChangeHandlerRegistration(registrations);
     }
 
     @Override
     public LayeredResource getByPath(String path) {
         List<Resource> matchingResources = origins.stream()
                 .filter(origin -> origin.hasPath(path))
                 .map(origin -> origin.getByPath(path))
                 .collect(toList());
         if (matchingResources.isEmpty()) {
             throw new ResourceNotFoundException(this, path);
         }
         return newLayeredResource(matchingResources);
     }
 
     @Override
     public boolean hasPath(String path) {
         return origins.stream().anyMatch(origin -> origin.hasPath(path));
     }
 
     @Override
     protected boolean isFile(LayeredResource resource) {
         return resource.getFirst().isFile();
     }
 
     @Override
     protected boolean isDirectory(LayeredResource resource) {
         return resource.getFirst().isDirectory();
     }
 
     @Override
     protected boolean isEditable(LayeredResource resource) {
         return resource.getFirst().isEditable();
     }
 
     @Override
     protected String getPath(LayeredResource resource) {
         return resource.getFirst().getPath();
     }
 
     @Override
     protected String getName(LayeredResource resource) {
         return resource.getFirst().getName();
     }
 
     @Override
     protected long getLastModified(LayeredResource resource) {
         return resource.getFirst().getLastModified();
     }
 
     @Override
     protected List<LayeredResource> listChildren(LayeredResource resource) {
         List<LayeredResource> layeredResources = new ArrayList<>();
 
         // expecting layers to be correctly ordered
         final List<Resource> layers = resource.getLayers();
         for (Resource layer : layers) {
             List<Resource> layerChildren = layer.listChildren();
 
             // optimizing first round, just transform whole first layer into layered resources
             if (layeredResources.isEmpty()) {
                 layerChildren.stream()
                         .map(input -> new LayeredResource(LayeredResourceOrigin.this, input.getPath(), Lists.newArrayList(input)))
                         .forEachOrdered(layeredResources::add);
                 continue;
             }
 
             for (final Resource r : layerChildren) {
                 Optional<LayeredResource> matchingResource = layeredResources.stream()
                         .filter(input -> r.getPath().equals(input.getPath()) && r.isFile() == input.isFile())
                         .findFirst();
                 if (matchingResource.isPresent()) {
                     LayeredResource l = matchingResource.get();
                     l.getLayers().add(r);
                 } else {
                     LayeredResource l = new LayeredResource(this, r.getPath(), Lists.newArrayList(r));
                     layeredResources.add(l);
                 }
             }
         }
         return Ordering.from(comparing(Resource::getPath)).immutableSortedCopy(layeredResources);
     }
 
     @Override
     protected LayeredResource getParent(LayeredResource resource) {
         // This would only get the parents from the layers in the given resource, but that parent might exist in other resources too
         // final List<Resource> parents = Lists.transform(resource.getLayers(), Functions.getParent());
 
         // So instead, we pick the parent of the first layer, and do a getByPath, which feels a bit underwhelming.
         Resource parent = resource.getFirst().getParent();
         return parent != null ? getByPath(parent.getPath()) : null;
     }
 
     @Override
     protected InputStream doOpenStream(LayeredResource resource) throws IOException {
         return resource.getFirst().openStream();
     }
 
     @Override
     protected Reader openReader(LayeredResource resource) throws IOException {
         return resource.getFirst().openReader();
     }
 
     /**
      * Overridden to throw an exception; since we override {@link #openReader(LayeredResource)},
      * this method used in {@link AbstractResourceOrigin#openReader(info.magnolia.resourceloader.AbstractResource)}
      * should never be called.
      */
     @Override
     protected Charset getCharsetFor(LayeredResource resource) {
         throw new IllegalStateException("This method should not be called");
     }
 
     protected LayeredResource newLayeredResource(List<Resource> resources) {
         // Sanity checks -- are all the resources on the same path and are they all dir/files ?
         final String path = resources.get(0).getPath();
         final boolean isDirectory = resources.get(0).isDirectory();
         if (!resources.stream().allMatch(Functions.pathEquals(path))) {
             throw new IllegalStateException("Given resources don't match path [" + path + "]: " + resources);
         }
         Predicate<Resource> dirOrFilePredicate = isDirectory ? Resource::isDirectory : Resource::isFile;
         if (!resources.stream().allMatch(dirOrFilePredicate)) {
             log.warn("Resources at {} are not all directory/file: {}", path, resources);
             resources = resources.stream()
                     .filter(dirOrFilePredicate)
                     .collect(toList());
         }
         return new LayeredResource(this, path, resources);
     }
 
     /**
      * Gathers all the {@link ResourceChangeHandlerRegistration handler registrations} from all the layers related to the same
      * {@link RelayingChangeHandler}.
      */
     private static class AggregateChangeHandlerRegistration implements ResourceChangeHandlerRegistration {
 
         private final List<ResourceChangeHandlerRegistration> registrations;
 
         public AggregateChangeHandlerRegistration(List<ResourceChangeHandlerRegistration> registrations) {
             this.registrations = registrations;
         }
 
         @Override
         public void unRegister() {
             for (final ResourceChangeHandlerRegistration registration : registrations) {
                 registration.unRegister();
             }
 
         }
     }
 
     /**
      * Wraps another {@link ResourceChangeHandler resource change handler}, gets the changes from the 'layer' {@link ResourceOrigin resource origins} and
      * relays those to the wrapped handler in a modified form:
      * <ul>
      * <li>Original change's {@link ResourceOrigin origin} is replaced with the current {@link LayeredResourceOrigin};</li>
      * <li>{@link ResourceOriginChange Resource changes} not related to the currently used 'layer' are not communicated at all (ignored);</li>
      * <li>If a currently utilised 'layer' is deleted revealing some other layer under it - then the deletion is treated as a modification.</li>
      * </ul>
      */
     private class RelayingChangeHandler implements ResourceChangeHandler {
 
         private final ResourceChangeHandler delegate;
 
         RelayingChangeHandler(ResourceChangeHandler delegate) {
             this.delegate = delegate;
         }
 
         @Override
         public void onResourceChanged(ResourceOriginChange change) {
             final Optional<LayeredResource> resource = hasPath(change.getRelatedResourcePath()) ? Optional.of(getByPath(change.getRelatedResourcePath())) : Optional.empty();
             final ResourceOriginChange.Builder relayedChange =
                     resourceChange().
                         inOrigin(LayeredResourceOrigin.this).
                         at(change.getRelatedResourcePath());
 
             switch (change.getType()) {
             case MODIFIED:
                 // Dispatch resource modification iff it is actively used at the moment - otherwise ignore the change
                 if (resource.isPresent() && resource.get().getFirst().getOrigin().equals(change.getRelatedOrigin())) {
                     delegate.onResourceChanged(relayedChange.ofType(MODIFIED).build());
                 }
                 break;
             case ADDED:
                 // Dispatch resource addition iff it is actively used at the moment - otherwise ignore the change
                 if (resource.isPresent() && resource.get().getFirst().getOrigin().equals(change.getRelatedOrigin())) {
                     delegate.onResourceChanged(relayedChange.ofType(ADDED).build());
                 }
                 break;
             case REMOVED:
                 // if resource isn't present in any layer anymore - report it as deleted
                 if (!resource.isPresent()) {
                     delegate.onResourceChanged(relayedChange.ofType(REMOVED).build());
                 } else {
                     // resource is still present in one of the layers (e.g. hotfix on a file system resource was deleted) - treat that as modification
                     delegate.onResourceChanged(relayedChange.ofType(MODIFIED).build());
                 }
                 break;
             }
         }
     }
 }