/*
 * Copyright 2011 Google Inc.
 * 
 * Licensed 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 com.google.gwt.sample.core.linker;

import com.google.gwt.core.ext.LinkerContext;
import com.google.gwt.core.ext.TreeLogger;
import com.google.gwt.core.ext.UnableToCompleteException;
import com.google.gwt.core.ext.linker.AbstractLinker;
import com.google.gwt.core.ext.linker.Artifact;
import com.google.gwt.core.ext.linker.ArtifactSet;
import com.google.gwt.core.ext.linker.EmittedArtifact;
import com.google.gwt.core.ext.linker.LinkerOrder;
import com.google.gwt.core.ext.linker.LinkerOrder.Order;
import com.google.gwt.core.ext.linker.impl.SelectionInformation;

import java.util.Arrays;
import java.util.Date;

/**
 * Linker for public path resources in the Application Cache.
 * <p>
 * <strong>Warning</strong>This linker sends all permutations to clients, 
 * making it inappropriate for most production use.</strong>
 * <p>
 * To use:
 * <ol>
 * <li>Add {@code manifest="YOURMODULENAME/appcache.nocache.manifest"} to the
 * {@code <html>} tag in your base html file. E.g.,
 * {@code <html manifest="mymodule/appcache.nocache.manifest">}</li>
 * <li>Add a mime-mapping to your web.xml file:
 * <p>
 * <pre>{@code <mime-mapping>
 * <extension>manifest</extension>
 * <mime-type>text/cache-manifest</mime-type>
 * </mime-mapping>
 * }</pre>
 * </li>
 * </ol>
 * <p>
 * On every compile, this linker will regenerate the appcache.nocache.manifest
 * file with files from the public path of your module.
 * <p>
 * To obtain a manifest that contains other files in addition to those
 * generated by this linker, create a class that inherits from this one
 * and overrides {@code otherCachedFiles()}, and use it as a linker instead:
 * <p>
 * <pre><blockquote>
 * {@code @Shardable}
 * public class MyAppCacheLinker extends AbstractAppCacheLinker {
 *   {@code @Override}
 *   protected String[] otherCachedFiles() {
 *     return new String[] {"/MyApp.html","/MyApp.css"};
 *   }
 * }
 * </blockquote></pre>
 */
@LinkerOrder(Order.POST)
public class SimpleAppCacheLinker extends AbstractLinker {

  private static final String MANIFEST = "appcache.nocache.manifest";

  @Override
  public String getDescription() {
    return "AppCacheLinker";
  }

  @Override
  public ArtifactSet link(TreeLogger logger, LinkerContext context, ArtifactSet artifacts,
      boolean onePermutation)
      throws UnableToCompleteException {
    
    ArtifactSet toReturn = new ArtifactSet(artifacts);
    
    if (onePermutation) {
      return toReturn;
    }

    if (toReturn.find(SelectionInformation.class).isEmpty()) {
      logger.log(TreeLogger.INFO, "DevMode warning: Clobbering " + MANIFEST + " to allow debugging. "
          + "Recompile before deploying your app!");
      artifacts = null;
    }
    
    // Create the general cache-manifest resource for the landing page:
    toReturn.add(emitLandingPageCacheManifest(context, logger, artifacts));
    return toReturn;
  }

  /**
   * Override this method to force the linker to also include more files
   * in the manifest. 
   */
  protected String[] otherCachedFiles() {
    return null;
  }

  /**
   * Creates the cache-manifest resource specific for the landing page.
   * 
   * @param context the linker environment
   * @param logger the tree logger to record to 
   * @param artifacts {@code null} to generate an empty cache manifest
   */
  private Artifact<?> emitLandingPageCacheManifest(LinkerContext context, TreeLogger logger,
      ArtifactSet artifacts)
      throws UnableToCompleteException {
    StringBuilder publicSourcesSb = new StringBuilder();
    StringBuilder staticResoucesSb = new StringBuilder();

    if (artifacts != null) {
      // Iterate over all emitted artifacts, and collect all cacheable artifacts
      for (@SuppressWarnings("rawtypes") Artifact artifact : artifacts) {
        if (artifact instanceof EmittedArtifact) {
          EmittedArtifact ea = (EmittedArtifact) artifact;
          String pathName = ea.getPartialPath();
          if (pathName.endsWith("symbolMap") 
              || pathName.endsWith(".xml.gz") 
              || pathName.endsWith("rpc.log")
              || pathName.endsWith("gwt.rpc")
              || pathName.endsWith("manifest.txt")
              || pathName.startsWith("rpcPolicyManifest")) {
            // skip these resources
          } else {
            publicSourcesSb.append(pathName + "\n");
          }
        }
      }

      String[] cacheExtraFiles = getCacheExtraFiles(); 
      for (int i = 0; i < cacheExtraFiles.length; i++) {
        staticResoucesSb.append(cacheExtraFiles[i]);
        staticResoucesSb.append("\n");
      }
    }

    // build cache list
    StringBuilder sb = new StringBuilder();
    sb.append("CACHE MANIFEST\n");
    sb.append("# Unique id #" + (new Date()).getTime() + "." + Math.random() + "\n");
    // we have to generate this unique id because the resources can change but
    // the hashed cache.html files can remain the same.
    sb.append("# Note: must change this every time for cache to invalidate\n");
    sb.append("\n");
    sb.append("CACHE:\n");
    sb.append("# Static app files\n");
    sb.append(staticResoucesSb.toString());
    sb.append("\n# Generated app files\n");
    sb.append(publicSourcesSb.toString());
    sb.append("\n\n");
    sb.append("# All other resources require the user to be online.\n");
    sb.append("NETWORK:\n");
    sb.append("*\n");

    logger.log(TreeLogger.INFO, "Be sure your landing page's <html> tag declares a manifest:"
        + " <html manifest=" + context.getModuleFunctionName() + "/" + MANIFEST + "\">");

    // Create the manifest as a new artifact and return it:
    return emitString(logger, sb.toString(), MANIFEST);
  }

  /**
   * Obtains the extra files to include in the manifest. Ensures the returned
   * array is not null. 
   */
  private String[] getCacheExtraFiles() {
    String[] cacheExtraFiles = otherCachedFiles();
    return cacheExtraFiles == null ? 
        new String[0] : Arrays.copyOf(cacheExtraFiles, cacheExtraFiles.length);
  }
}