content: /*
   * Copyright 1999-2022 Alibaba Group Holding Ltd.
   *
   * Licensed 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.
   */
  
  package com.alibaba.nacos.plugin.auth.impl.utils;
  
  import java.util.Arrays;
  
  /**
   * Base64Decoder.
   *
   * @author xYohn
   * @date 2023/8/7
   */
  public class Base64Decode {
      private static final char[] BASE64_ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();
  
      private static final int[] BASE64_IALPHABET = new int[256];
  
      private static final int IALPHABET_MAX_INDEX = BASE64_IALPHABET.length - 1;
  
      private static final int[] IALPHABET = BASE64_IALPHABET;
  
      static {
          Arrays.fill(BASE64_IALPHABET, -1);
          for (int i = 0, iS = BASE64_ALPHABET.length; i < iS; i++) {
              BASE64_IALPHABET[BASE64_ALPHABET[i]] = i;
          }
          BASE64_IALPHABET['='] = 0;
      }
  
      /**
       * Decodes a Base64 encoded String into a newly-allocated byte array using the Base64 encoding scheme.
       *
       * @param input the string to decode
       * @return a byte array containing binary data
       */
      public static byte[] decode(String input) {
  
          // Check special case
          if (input == null || input.equals("")) {
              return new byte[0];
          }
          char[] sArr = input.toCharArray();
          int sLen = sArr.length;
          if (sLen == 0) {
              return new byte[0];
          }
  
          int sIx = 0;
          // Start and end index after trimming.
          int eIx = sLen - 1;
  
          // Trim illegal chars from start
          while (sIx < eIx && IALPHABET[sArr[sIx]] < 0) {
              sIx++;
          }
  
          // Trim illegal chars from end
          while (eIx > 0 && IALPHABET[sArr[eIx]] < 0) {
              eIx--;
          }
  
          // get the padding count (=) (0, 1 or 2)
          // Count '=' at end.
          int pad = sArr[eIx] == '=' ? (sArr[eIx - 1] == '=' ? 2 : 1) : 0;
          // Content count including possible separators
          int cCnt = eIx - sIx + 1;
          int sepCnt = sLen > 76 ? (sArr[76] == '\r' ? cCnt / 78 : 0) << 1 : 0;
          // The number of decoded bytes
          int len = ((cCnt - sepCnt) * 6 >> 3) - pad;
          // Preallocate byte[] of exact length
          byte[] dArr = new byte[len];
  
          // Decode all but the last 0 - 2 bytes.
          int d = 0;
          int three = 3;
          int eight = 8;
          for (int cc = 0, eLen = (len / three) * three; d < eLen; ) {
  
              // Assemble three bytes into an int from four "valid" characters.
              int i = ctoi(sArr[sIx++]) << 18 | ctoi(sArr[sIx++]) << 12 | ctoi(sArr[sIx++]) << 6 | ctoi(sArr[sIx++]);
  
              // Add the bytes
              dArr[d++] = (byte) (i >> 16);
              dArr[d++] = (byte) (i >> 8);
              dArr[d++] = (byte) i;
  
              // If line separator, jump over it.
              if (sepCnt > 0 && ++cc == 19) {
                  sIx += 2;
                  cc = 0;
              }
          }
  
          if (d < len) {
              // Decode last 1-3 bytes (incl '=') into 1-3 bytes
              int i = 0;
              for (int j = 0; sIx <= eIx - pad; j++) {
                  i |= ctoi(sArr[sIx++]) << (18 - j * 6);
              }
  
              for (int r = 16; d < len; r -= eight) {
                  dArr[d++] = (byte) (i >> r);
              }
          }
  
          return dArr;
      }
  
      private static int ctoi(char c) {
          int i = c > IALPHABET_MAX_INDEX ? -1 : IALPHABET[c];
          if (i < 0) {
              String msg = "Illegal base64 character: '" + c + "'";
              throw new IllegalArgumentException(msg);
          }
          return i;
      }
  
  }
  