StringSpan - String.format that works with Android Spannables

StringSpan.java

// based on: https://github.com/george-steel/android-utils/blob/master/src/org/oshkimaadziig/george/androidutils/SpanFormatter.java

public class StringSpan {
  private static final Pattern PATTERN = Pattern.compile("%([^a-zA-z%]*)([[a-zA-Z%]&&[^tT]]|[tT][a-zA-Z])");

  private StringSpan() {
  }

  public static CharSequence format(@NonNull CharSequence format, Object... args) {
    return format(Locale.getDefault(), format, args);
  }

  @SuppressWarnings("ConstantConditions")
  public static CharSequence format(@NonNull Locale locale, @NonNull CharSequence format, Object... args) {
    if (locale == null || format == null) {
      return format;
    }

    SpannableStringBuilder result = new SpannableStringBuilder(format);
    int startPosition = 0;
    int argPosition = -1;
    while (startPosition < result.length()) {
      Matcher matcher = PATTERN.matcher(result);
      if (!matcher.find(startPosition)) {
        break;
      }

      startPosition = matcher.start();
      int endPosition = matcher.end();
      String modifier = matcher.group(1);
      String type = matcher.group(2);

      argPosition++;
      CharSequence charSequence;
      if (type.equals("%")) {
        charSequence = "%";
      } else if (type.equals("n")) {
        charSequence = "\n";
      } else {
        Object arg = args[argPosition];
        charSequence = arg instanceof Spanned && type.equals("s") ? (Spanned) arg : String.format(locale, "%" + modifier + type, arg);
      }
      result.replace(startPosition, endPosition, charSequence);
      startPosition += charSequence.length();
    }
    return result;
  }
}