/*
    * ====================================================================
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you 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.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   *
   */
  package org.apache.http.client.utils;
  
  import java.util.StringTokenizer;
  
  import org.apache.http.annotation.Immutable;
  
  /**
   * Implementation from pseudo code in RFC 3492.
   *
   * @since 4.0
   */
  @Immutable
  public class Rfc3492Idn implements Idn {
      private static final int base = 36;
      private static final int tmin = 1;
      private static final int tmax = 26;
      private static final int skew = 38;
      private static final int damp = 700;
      private static final int initial_bias = 72;
      private static final int initial_n = 128;
      private static final char delimiter = '-';
      private static final String ACE_PREFIX = "xn--";
  
      private int adapt(int delta, final int numpoints, final boolean firsttime) {
          if (firsttime) {
              delta = delta / damp;
          } else {
              delta = delta / 2;
          }
          delta = delta + (delta / numpoints);
          int k = 0;
          while (delta > ((base - tmin) * tmax) / 2) {
            delta = delta / (base - tmin);
            k = k + base;
          }
          return k + (((base - tmin + 1) * delta) / (delta + skew));
      }
  
      private int digit(final char c) {
          if ((c >= 'A') && (c <= 'Z')) {
              return (c - 'A');
          }
          if ((c >= 'a') && (c <= 'z')) {
              return (c - 'a');
          }
          if ((c >= '0') && (c <= '9')) {
              return (c - '0') + 26;
          }
          throw new IllegalArgumentException("illegal digit: "+ c);
      }
  
      public String toUnicode(final String punycode) {
          final StringBuilder unicode = new StringBuilder(punycode.length());
          final StringTokenizer tok = new StringTokenizer(punycode, ".");
          while (tok.hasMoreTokens()) {
              String t = tok.nextToken();
              if (unicode.length() > 0) {
                  unicode.append('.');
              }
              if (t.startsWith(ACE_PREFIX)) {
                  t = decode(t.substring(4));
              }
              unicode.append(t);
          }
          return unicode.toString();
      }
  
      protected String decode(String input) {
          int n = initial_n;
          int i = 0;
          int bias = initial_bias;
          final StringBuilder output = new StringBuilder(input.length());
          final int lastdelim = input.lastIndexOf(delimiter);
         if (lastdelim != -1) {
             output.append(input.subSequence(0, lastdelim));
             input = input.substring(lastdelim + 1);
         }
 
         while (input.length() > 0) {
             final int oldi = i;
             int w = 1;
             for (int k = base;; k += base) {
                 if (input.length() == 0) {
                     break;
                 }
                 final char c = input.charAt(0);
                 input = input.substring(1);
                 final int digit = digit(c);
                 i = i + digit * w; // FIXME fail on overflow
                 int t;
                 if (k <= bias + tmin) {
                     t = tmin;
                 } else if (k >= bias + tmax) {
                     t = tmax;
                 } else {
                     t = k - bias;
                 }
                 if (digit < t) {
                     break;
                 }
                 w = w * (base - t); // FIXME fail on overflow
             }
             bias = adapt(i - oldi, output.length() + 1, (oldi == 0));
             n = n + i / (output.length() + 1); // FIXME fail on overflow
             i = i % (output.length() + 1);
             // {if n is a basic code point then fail}
             output.insert(i, (char) n);
             i++;
         }
         return output.toString();
     }
 
 }