BitcoinCashBase32.java

package main;
 
import java.util.HashMap;
import java.util.Map;

/**
 * Copyright (c) 2018 Tobias Brandt
 * 
 * Distributed under the MIT software license, see the accompanying file LICENSE
 * or http://www.opensource.org/licenses/mit-license.php.
 */
public class BitcoinCashBase32 {

	public static final String CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l";

	private static final char[] CHARS = CHARSET.toCharArray();

	private static Map<Character, Integer> charPositionMap;
	static {
		charPositionMap = new HashMap<>();
		for (int i = 0; i < CHARS.length; i++) {
			charPositionMap.put(CHARS[i], i);
		}
		if (charPositionMap.size() != 32) {
			throw new RuntimeException("The charset must contain 32 unique characters.");
		}
	}

	/**
	 * Encode a byte array as base32 string. This method assumes that all bytes
	 * are only from 0-31
	 * 
	 * @param byteArray
	 * @return
	 */
	public static String encode(byte[] byteArray) {
		StringBuffer sb = new StringBuffer();

		for (int i = 0; i < byteArray.length; i++) {
			int val = (int) byteArray[i];

			if (val < 0 || val > 31) {
				throw new RuntimeException("This method assumes that all bytes are only from 0-31. Was: " + val);
			}

			sb.append(CHARS[val]);
		}

		return sb.toString();
	}

	/**
	 * Decode a base32 string back to the byte array representation
	 * 
	 * @param base32String
	 * @return
	 */
	public static byte[] decode(String base32String) {
		byte[] bytes = new byte[base32String.length()];

		char[] charArray = base32String.toCharArray();
		for (int i = 0; i < charArray.length; i++) {
			Integer position = charPositionMap.get(charArray[i]);
			if (position == null) {
				throw new RuntimeException("There seems to be an invalid char: " + charArray[i]);
			}
			bytes[i] = (byte) ((int) position);
		}

		return bytes;
	}
}