MnemonicInputNormalizer.java

package com.example.bip39.normalize;

import java.text.Normalizer;
import java.text.Normalizer.Form;
import java.util.Locale;
import java.util.Objects;

public final class MnemonicInputNormalizer {

  private MnemonicInputNormalizer() {}

  public static String normalizeMnemonicInput(String text) {
    Objects.requireNonNull(text, "text must not be null");

    String trimmed = text.strip();
    String whitespaceNormalized = replaceAsciiWhitespaceWithSpace(trimmed);
    String singleSpaced = collapseSpaces(whitespaceNormalized);
    String nfkdNormalized = Normalizer.normalize(singleSpaced, Form.NFKD);
    return nfkdNormalized.toLowerCase(Locale.ROOT);
  }

  private static String replaceAsciiWhitespaceWithSpace(String text) {
    StringBuilder normalized = new StringBuilder(text.length());
    for (int index = 0; index < text.length(); index++) {
      char character = text.charAt(index);
      if (character == '\t' || character == '\n' || character == '\r') {
        normalized.append(' ');
      } else {
        normalized.append(character);
      }
    }
    return normalized.toString();
  }

  private static String collapseSpaces(String text) {
    StringBuilder collapsed = new StringBuilder(text.length());
    boolean previousWasSpace = false;
    for (int index = 0; index < text.length(); index++) {
      char character = text.charAt(index);
      if (character == ' ') {
        if (!previousWasSpace) {
          collapsed.append(character);
        }
        previousWasSpace = true;
      } else {
        collapsed.append(character);
        previousWasSpace = false;
      }
    }
    return collapsed.toString();
  }
}