package com.atlassian.plugin.util.resource;
   
   import com.google.common.base.Splitter;
   import org.slf4j.Logger;
   import org.slf4j.LoggerFactory;
   
   import java.io.File;
   import java.io.IOException;
   import java.io.InputStream;
  import java.net.MalformedURLException;
  import java.net.URL;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  
  /**
   * Loads resources from directories configured via the system property {@code plugin.resource.directories}, which should
   * be a comma-delimited list of file paths that contain resources to load.
   *
   * @since 2.2.0
   */
  public class AlternativeDirectoryResourceLoader implements AlternativeResourceLoader {
      private static final Logger log = LoggerFactory.getLogger(AlternativeDirectoryResourceLoader.class);
      private static final Splitter splitter = Splitter.on(',').trimResults().omitEmptyStrings();
  
      public static final String PLUGIN_RESOURCE_DIRECTORIES = "plugin.resource.directories";
  
      private volatile String pluginResourceSystemProperty = "";
      private volatile List<File> resourceDirectories = Collections.emptyList();
  
      public AlternativeDirectoryResourceLoader() {
          getPluginResourceDirs();
      }
  
      private List<File> getPluginResourceDirs() {
          String dirs = System.getProperty(PLUGIN_RESOURCE_DIRECTORIES, "");
          //
          // has the system property changed since we last read it
          if (!dirs.equals(pluginResourceSystemProperty)) {
              List<File> tmp = new ArrayList<>();
              for (String dir : splitter.split(dirs)) {
                  File file = new File(dir);
                  if (file.exists()) {
                      log.debug("Found alternative resource directory " + dir);
                      tmp.add(file);
                  } else {
                      log.warn("Resource directory " + dir + ", which resolves to " + file.getAbsolutePath() + " does not exist");
                  }
              }
              // caching the system property means we don't do the file lookup every time
              // but we can tell then it changes on next read
              pluginResourceSystemProperty = dirs;
              resourceDirectories = tmp;
          }
          return resourceDirectories;
      }
  
  
      /**
       * Retrieve the URL of the resource from the directories.
       *
       * @param path the name of the resource to be loaded
       *
       * @return The URL to the resource, or null if the resource is not found
       */
      public URL getResource(String path) {
          for (File dir : getPluginResourceDirs()) {
              File file = new File(dir, path);
              if (file.exists()) {
                  try {
                      return file.toURI().toURL();
                  } catch (MalformedURLException e) {
                      log.error("Malformed URL: " + file.toString(), e);
                  }
              } else {
                  log.debug("File " + file + " not found, ignoring");
              }
          }
          return null;
      }
  
      /**
       * Load a given resource from the directories.
       *
       * @param name The name of the resource to be loaded.
       *
       * @return An InputStream for the resource, or null if the resource is not found.
       */
      public InputStream getResourceAsStream(String name) {
          URL url = getResource(name);
          if (url != null) {
              try {
                  return url.openStream();
              } catch (IOException e) {
                  log.error("Unable to open URL " + url, e);
              }
          }
          return null;
      }
 
     /**
      * @return the current list of alternate resource directories
      */
     public List<File> getResourceDirectories() {
         return getPluginResourceDirs();
     }
 
 
 }