Base256Emoji.java

package io.multibase;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

/*
 * Copyright 2025 Michael Vorburger.ch
 *
 * 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.
 */

/**
 * <a
 * href="https://github.com/multiformats/multibase/blob/master/rfcs/Base256Emoji.md">Base256Emoji</a>
 * is an encoding mapping each 0-255 byte value to (or from) a specific single Unicode Emoji
 * character.
 *
 * @author <a href="https://www.vorburger.ch/">Michael Vorburger.ch</a>
 */
public class Base256Emoji {

  // from https://github.com/multiformats/multibase/blob/master/rfcs/Base256Emoji.md
  private static final String[] EMOJIS = {
    "🚀", "🪐", "☄", "🛰", "🌌", "🌑", "🌒", "🌓", "🌔", "🌕",
    "🌖", "🌗", "🌘", "🌍", "🌏", "🌎", "🐉", "☀", "💻", "🖥",
    "💾", "💿", "😂", "❤", "😍", "🤣", "😊", "🙏", "💕", "😭",
    "😘", "👍", "😅", "👏", "😁", "🔥", "🥰", "💔", "💖", "💙",
    "😢", "🤔", "😆", "🙄", "💪", "😉", "☺", "👌", "🤗", "💜",
    "😔", "😎", "😇", "🌹", "🤦", "🎉", "💞", "✌", "✨", "🤷",
    "😱", "😌", "🌸", "🙌", "😋", "💗", "💚", "😏", "💛", "🙂",
    "💓", "🤩", "😄", "😀", "🖤", "😃", "💯", "🙈", "👇", "🎶",
    "😒", "🤭", "❣", "😜", "💋", "👀", "😪", "😑", "💥", "🙋",
    "😞", "😩", "😡", "🤪", "👊", "🥳", "😥", "🤤", "👉", "💃",
    "😳", "✋", "😚", "😝", "😴", "🌟", "😬", "🙃", "🍀", "🌷",
    "😻", "😓", "⭐", "✅", "🥺", "🌈", "😈", "🤘", "💦", "✔",
    "😣", "🏃", "💐", "☹", "🎊", "💘", "😠", "☝", "😕", "🌺",
    "🎂", "🌻", "😐", "🖕", "💝", "🙊", "😹", "🗣", "💫", "💀",
    "👑", "🎵", "🤞", "😛", "🔴", "😤", "🌼", "😫", "⚽", "🤙",
    "☕", "🏆", "🤫", "👈", "😮", "🙆", "🍻", "🍃", "🐶", "💁",
    "😲", "🌿", "🧡", "🎁", "⚡", "🌞", "🎈", "❌", "✊", "👋",
    "😰", "🤨", "😶", "🤝", "🚶", "💰", "🍓", "💢", "🤟", "🙁",
    "🚨", "💨", "🤬", "✈", "🎀", "🍺", "🤓", "😙", "💟", "🌱",
    "😖", "👶", "🥴", "▶", "➡", "❓", "💎", "💸", "⬇", "😨",
    "🌚", "🦋", "😷", "🕺", "⚠", "🙅", "😟", "😵", "👎", "🤲",
    "🤠", "🤧", "📌", "🔵", "💅", "🧐", "🐾", "🍒", "😗", "🤑",
    "🌊", "🤯", "🐷", "☎", "💧", "😯", "💆", "👆", "🎤", "🙇",
    "🍑", "❄", "🌴", "💣", "🐸", "💌", "📍", "🥀", "🤢", "👅",
    "💡", "💩", "👐", "📸", "👻", "🤐", "🤮", "🎼", "🥵", "🚩",
    "🍎", "🍊", "👼", "💍", "📣", "🥂"
  };

  // TODO Propose adding a Guava dependency to use ImmutableMap instead of this

  private static final Map<String, Integer> EMOJI_TO_INDEX;
  private static final int MAP_EXPECTED_SIZE = EMOJIS.length;
  private static final float MAP_LOAD_FACTOR = 1.0f;

  static {
    if (EMOJIS.length != 256) {
      throw new IllegalStateException("EMOJIS.length must be 256, but is " + EMOJIS.length);
    }

    Map<String, Integer> mutableMap = new HashMap<>(MAP_EXPECTED_SIZE, MAP_LOAD_FACTOR);
    for (int i = 0; i < EMOJIS.length; i++) {
      mutableMap.put(EMOJIS[i], i);
    }
    EMOJI_TO_INDEX = Collections.unmodifiableMap(mutableMap);
  }

  public static String encode(byte[] in) {
    StringBuilder sb = new StringBuilder(in.length);
    for (byte b : in) {
      sb.append(EMOJIS[b & 0xFF]);
    }
    return sb.toString();
  }

  public static byte[] decode(String in) {
    int length = in.codePointCount(0, in.length());
    byte[] bytes = new byte[length];

    for (int i = 0; i < in.codePointCount(0, in.length()); i++) {
      int cp = in.codePointAt(in.offsetByCodePoints(0, i));
      String emoji = new String(Character.toChars(cp));
      Integer index = EMOJI_TO_INDEX.get(emoji);
      if (index == null) {
        throw new IllegalArgumentException("Unknown Base256Emoji character: " + emoji);
      }
      bytes[i] = (byte) (index & 0xFF);
    }

    return bytes;
  }
}