/*
 * Copyright 2015-2020 The OpenZipkin Authors
 *
 * 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 zipkin2.internal;

// code originally imported from zipkin.Util
public final class HexCodec {
  public static final char[] HEX_DIGITS = {
    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'
  };

  /**
   * Parses a 1 to 32 character lower-hex string with no prefix into an unsigned long, tossing any
   * bits higher than 64.
   */
  public static long lowerHexToUnsignedLong(String lowerHex) {
    int length = lowerHex.length();
    if (length < 1 || length > 32) throw isntLowerHexLong(lowerHex);

    // trim off any high bits
    int beginIndex = length > 16 ? length - 16 : 0;

    return lowerHexToUnsignedLong(lowerHex, beginIndex);
  }

  /**
   * Parses a 16 character lower-hex string with no prefix into an unsigned long, starting at the
   * specified index.
   */
  public static long lowerHexToUnsignedLong(String lowerHex, int index) {
    long result = 0;
    for (int endIndex = Math.min(index + 16, lowerHex.length()); index < endIndex; index++) {
      char c = lowerHex.charAt(index);
      result <<= 4;
      if (c >= '0' && c <= '9') {
        result |= c - '0';
      } else if (c >= 'a' && c <= 'f') {
        result |= c - 'a' + 10;
      } else {
        throw isntLowerHexLong(lowerHex);
      }
    }
    return result;
  }

  static NumberFormatException isntLowerHexLong(String lowerHex) {
    throw new NumberFormatException(
        lowerHex + " should be a 1 to 32 character lower-hex string with no prefix");
  }

  HexCodec() {}
}