package com.atlassian.activeobjects.osgi;
   
   import com.google.common.base.Function;
   import com.google.common.base.Predicate;
   import com.google.common.collect.ImmutableList;
   import org.osgi.framework.BundleContext;
   import org.slf4j.Logger;
   import org.slf4j.LoggerFactory;
   
  import java.net.URL;
  import java.util.Enumeration;
  
  import static com.google.common.base.Preconditions.checkNotNull;
  import static com.google.common.collect.Iterables.filter;
  
  final class BundleContextScanner {
      private final Logger log = LoggerFactory.getLogger(this.getClass());
  
      <T> Iterable<T> findClasses(BundleContext bundleContext, String packageName, Function<String, T> f, Predicate<T> p) {
          checkNotNull(bundleContext);
          checkNotNull(packageName);
          checkNotNull(f);
          checkNotNull(p);
  
          return filter(toIterable(getBundleEntries(bundleContext, packageName), f), p);
      }
  
      private Enumeration getBundleEntries(BundleContext bundleContext, String packageName) {
          log.debug("Scanning package '{}' of bundle {}", packageName, bundleContext.getBundle());
          return bundleContext.getBundle().findEntries(toFolder(packageName), "*.class", true);
      }
  
      private <T> Iterable<T> toIterable(Enumeration entries, Function<String, T> f) {
          final ImmutableList.Builder<T> classes = ImmutableList.builder();
          if (entries != null) {
              while (entries.hasMoreElements()) {
                  final String className = getClassName((URL) entries.nextElement());
                  log.debug("Found class '{}'", className);
                  //noinspection ConstantConditions
                  classes.add(f.apply(className));
              }
          }
          return classes.build();
      }
  
      private String getClassName(URL url) {
          return getClassName(url.getFile());
      }
  
      private String getClassName(String file) {
          String className = file.substring(1);  // remove the leading /
          className = className.substring(0, className.lastIndexOf('.')); // remove the .class
          return className.replace('/', '.');
      }
  
      private String toFolder(String packageName) {
          return '/' + packageName.replace('.', '/');
      }
  }