EmojiTrie.java

package com.vdurmont.emoji;

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

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

  public EmojiTrie(Collection<Emoji> emojis) {
    for (Emoji emoji : emojis) {
      Node tree = root;
      for (char c: emoji.getUnicode().toCharArray()) {
        if (!tree.hasChild(c)) {
          tree.addChild(c);
        }
        tree = tree.getChild(c);
      }
      tree.setEmoji(emoji);
    }
  }


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

    Node tree = root;
    for (char c : sequence) {
      if (!tree.hasChild(c)) {
        return Matches.IMPOSSIBLE;
      }
      tree = tree.getChild(c);
    }

    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) {
    Node tree = root;
    for (char c : unicode.toCharArray()) {
      if (!tree.hasChild(c)) {
        return null;
      }
      tree = tree.getChild(c);
    }
    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<Character, Node> children = new HashMap<Character, Node>();
    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;
    }
  }
}