package com.atlassian.plugin.osgi.factory.transform;
   
   import static com.google.common.collect.Iterators.forEnumeration;
   
   import com.atlassian.plugin.util.collect.Function;
   
   import com.google.common.collect.ImmutableList;
   
   import java.io.File;
  import java.io.IOException;
  import java.util.jar.JarEntry;
  import java.util.jar.JarFile;
  import java.util.jar.Manifest;
  import java.util.zip.ZipEntry;
  
  /**
   * Utility methods for getting stuff out of a jar.
   * 
   * @since 2.6
   */
  public final class JarUtils
  {
      /**
       * Not for instantiation.
       */
      private JarUtils()
      {}
  
      /**
       * Get the {@link Manifest} from a Jar file, or create a new one if there isn't one already.
       * 
       * @param file the file that is the jar contents
       * @return the manifest or an empty new one if one can't be found.
       */
      static Manifest getManifest(final File file)
      {
          final Manifest result = withJar(file, ManifestExtractor.INSTANCE);
          return (result == null) ? new Manifest() : result;
      }
  
      /**
       * Get the {@link JarEntry entries} from a Jar file.
       * 
       * @param file the file that is the jar contents
       * @return the entries the jar contains.
       */
      static Iterable<JarEntry> getEntries(final File file)
      {
          return withJar(file, JarEntryExtractor.INSTANCE);
      }
  
      /**
       * Get a specific {@link ZipEntry entry} from a Jar file.
       * 
       * @param file the file that is the jar contents
       * @return the specified entry in the jar if it exists or null if it can't be found.
       */
      static JarEntry getEntry(final File file, final String path)
      {
          return withJar(file, new Extractor<JarEntry>()
          {
              public JarEntry get(final JarFile jarFile)
              {
                  return jarFile.getJarEntry(path);
              }
          });
      }
  
      /**
       * Extract something from a jar file.
       * <p>
       * Correctly opens and closes the Jar file. Must not lazily access the Jar as it has an open/closed state.
       * 
       * @param <T> the type of the thing to extract
       * @param file the file that is the jar contents
       * @param extractor 
       * @return the result of the extractor
       * @throws RuntimeException if there are problems accessing the jar contents.
       */
      public static <T> T withJar(final File file, final Extractor<T> extractor)
      {
          JarFile jarFile = null;
          try
          {
              jarFile = new JarFile(file);
              return extractor.get(jarFile);
          }
          catch (final IOException e)
          {
              throw new IllegalArgumentException("File must be a jar: " + file, e);
          }
          finally
          {
              closeQuietly(jarFile);
          }
      }
  
      /**
       * Quietly close jar file.
      *
      * @param jarFile the file to close.
      */
     public static void closeQuietly(final JarFile jarFile)
     {
         if (jarFile != null)
         {
             try
             {
                 jarFile.close();
             }
             catch (final IOException ignore)
             {}
         }
     }
 
     public interface Extractor<T> extends Function<JarFile, T>
     {}
 
     enum ManifestExtractor implements Extractor<Manifest>
     {
         INSTANCE;
 
         public Manifest get(final JarFile input)
         {
             try
             {
                 return input.getManifest();
             }
             catch (final IOException e)
             {
                 throw new RuntimeException(e);
             }
         }
     }
 
     enum JarEntryExtractor implements Extractor<Iterable<JarEntry>>
     {
         INSTANCE;
 
         public Iterable<JarEntry> get(final JarFile jarFile)
         {
             return ImmutableList.copyOf(forEnumeration(jarFile.entries()));
         }
     }
 }