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The missing emoji library for Java.
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package com.vdurmont.emoji;

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;

public class EmojiTrie {
  private final Node root = new Node();
  final int maxDepth;

  public EmojiTrie(Collection emojis) {
    int maxDepth = 0;
    for (Emoji emoji : emojis) {
      Node tree = root;
      char[] chars = emoji.getUnicode().toCharArray();
      maxDepth = Math.max(maxDepth, chars.length);
      for (char c: chars) {
        if (!tree.hasChild(c)) {
          tree.addChild(c);
        }
        tree = tree.getChild(c);
      }
      tree.setEmoji(emoji);
    }
    this.maxDepth = maxDepth;
  }


  /**
   * Checks if sequence of chars contain an emoji.
   *
   * @param sequence Sequence of char that may contain emoji in full or
   * partially.
   *
   * @return
   * <li>
   *   Matches.EXACTLY if char sequence in its entirety is an emoji
   * </li>
   * <li>
   *   Matches.POSSIBLY if char sequence matches prefix of an emoji
   * </li>
   * <li>
   *   Matches.IMPOSSIBLE if char sequence matches no emoji or prefix of an
   *   emoji
   * </li>
   */
  public Matches isEmoji(char[] sequence) {
    return isEmoji(sequence, 0, sequence.length);
  }

  /**
   * Checks if the sequence of chars within the given bound indices contain an emoji.
   * @see #isEmoji(char[])
   */
  public Matches isEmoji(char[] sequence, int start, int end) {
    if (start < 0 || start > end || end > sequence.length) {
      throw new ArrayIndexOutOfBoundsException(
              "start " + start + ", end " + end + ", length " + sequence.length);
    }

    if (sequence == null) {
      return Matches.POSSIBLY;
    }

    Node tree = root;
    for (int i = start; i < end; i++) {
      if (!tree.hasChild(sequence[i])) {
        return Matches.IMPOSSIBLE;
      }
      tree = tree.getChild(sequence[i]);
    }

    return tree.isEndOfEmoji() ? Matches.EXACTLY : Matches.POSSIBLY;
  }


  /**
   * Finds Emoji instance from emoji unicode
   * @param unicode unicode of emoji to get
   * @return Emoji instance if unicode matches and emoji, null otherwise.
   */
  public Emoji getEmoji(String unicode) {
    return getEmoji(unicode.toCharArray(), 0, unicode.length());
  }

  Emoji getEmoji(char[] sequence, int start, int end) {
    if (start < 0 || start > end || end > sequence.length) {
      throw new ArrayIndexOutOfBoundsException(
              "start " + start + ", end " + end + ", length " + sequence.length);
    }

    Node tree = root;
    for (int i = 0; i < end; i++) {
      if (!tree.hasChild(sequence[i])) {
        return null;
      }
      tree = tree.getChild(sequence[i]);
    }
    return tree.getEmoji();
  }

  public enum Matches {
    EXACTLY, POSSIBLY, IMPOSSIBLE;

    public boolean exactMatch() {
      return this == EXACTLY;
    }

    public boolean impossibleMatch() {
      return this == IMPOSSIBLE;
    }
  }

  private class Node {
    private Map children = new HashMap();
    private Emoji emoji;

    private void setEmoji(Emoji emoji) {
      this.emoji = emoji;
    }

    private Emoji getEmoji() {
      return emoji;
    }

    private boolean hasChild(char child) {
      return children.containsKey(child);
    }

    private void addChild(char child) {
      children.put(child, new Node());
    }

    private Node getChild(char child) {
      return children.get(child);
    }

    private boolean isEndOfEmoji() {
      return emoji != null;
    }
  }
}