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// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
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package org.apache.juneau.utils;

import static org.apache.juneau.internal.FileUtils.*;

import java.io.*;
import java.util.*;
import java.util.ResourceBundle.*;

/**
 * Utility class for finding resources for a class.
 *
 * <p>
 * Same as {@link Class#getResourceAsStream(String)} except looks for resources with localized file names.
 *
 * <p>
 * If the <c>locale</c> is specified, then we look for resources whose name matches that locale.
 * For example, if looking for the resource <js>"MyResource.txt"</js> for the Japanese locale, we will look for
 * files in the following order:
 * <ol>
 *    <li><js>"MyResource_ja_JP.txt"</js>
 *    <li><js>"MyResource_ja.txt"</js>
 *    <li><js>"MyResource.txt"</js>
 * </ol>
 */
public class ClasspathResourceFinderSimple implements ClasspathResourceFinder {

   /**
    * Reusable instance.
    */
   public static final ClasspathResourceFinderSimple INSTANCE = new ClasspathResourceFinderSimple();

   private static final ResourceBundle.Control RB_CONTROL = ResourceBundle.Control.getControl(Control.FORMAT_DEFAULT);
   private static final List<Locale> ROOT_LOCALE = Arrays.asList(Locale.ROOT);


   @Override /* ClasspathResourceFinder */
   public InputStream findResource(Class<?> baseClass, String name, Locale locale) throws IOException {
      return findClasspathResource(baseClass, name, locale);
   }

   /**
    * Workhorse method for retrieving a resource from the classpath.
    *
    * <p>
    * This method can be overridden by subclasses to provide customized handling of resource retrieval from the classpath.
    *
    * @param baseClass The base class providing the classloader.
    * @param name The resource name.
    * @param locale
    *    The resource locale.
    *    <br>If <jk>null</jk>, won't look for localized file names.
    * @return The resource stream, or <jk>null</jk> if it couldn't be found.
    * @throws IOException Thrown by underlying stream.
    */
   protected InputStream findClasspathResource(Class<?> baseClass, String name, Locale locale) throws IOException {

      if (locale == null)
         return getResourceAsStream(baseClass, name);

      for (String n : getCandidateFileNames(name, locale)) {
         InputStream is = getResourceAsStream(baseClass, n);
         if (is != null)
            return is;
      }
      return null;
   }

   private InputStream getResourceAsStream(Class<?> baseClass, String name) {
      return baseClass.getResourceAsStream(name);
   }

   /**
    * Returns the candidate file names for the specified file name in the specified locale.
    *
    * <p>
    * For example, if looking for the <js>"MyResource.txt"</js> file in the Japanese locale, the iterator will return
    * names in the following order:
    * <ol>
    *    <li><js>"MyResource_ja_JP.txt"</js>
    *    <li><js>"MyResource_ja.txt"</js>
    *    <li><js>"MyResource.txt"</js>
    * </ol>
    *
    * <p>
    * If the locale is <jk>null</jk>, then it will only return <js>"MyResource.txt"</js>.
    *
    * @param fileName The name of the file to get candidate file names on.
    * @param l
    *    The locale.
    *    <br>If <jk>null</jk>, won't look for localized file names.
    * @return An iterator of file names to look at.
    */
   protected static Iterable<String> getCandidateFileNames(final String fileName, final Locale l) {
      return new Iterable<String>() {
         @Override
         public Iterator<String> iterator() {
            return new Iterator<String>() {
               final Iterator<Locale> locales = getCandidateLocales(l).iterator();
               String baseName, ext;

               @Override
               public boolean hasNext() {
                  return locales.hasNext();
               }

               @Override
               public String next() {
                  Locale l2 = locales.next();
                  if (l2.toString().isEmpty())
                     return fileName;
                  if (baseName == null)
                     baseName = getBaseName(fileName);
                  if (ext == null)
                     ext = getExtension(fileName);
                  return baseName + "_" + l2.toString() + (ext.isEmpty() ? "" : ('.' + ext));
               }
               @Override
               public void remove() {
                  throw new UnsupportedOperationException();
               }
            };
         }
      };
   }

   /**
    * Returns the candidate locales for the specified locale.
    *
    * <p>
    * For example, if <c>locale</c> is <js>"ja_JP"</js>, then this method will return:
    * <ol>
    *    <li><js>"ja_JP"</js>
    *    <li><js>"ja"</js>
    *    <li><js>""</js>
    * </ol>
    *
    * @param locale The locale to get the list of candidate locales for.
    * @return The list of candidate locales.
    */
   static final List<Locale> getCandidateLocales(Locale locale) {
      if (locale == null)
         return ROOT_LOCALE;
      return RB_CONTROL.getCandidateLocales("", locale);
   }
}