public abstract class Escaper {
  // TODO(dbeaumont): evaluate custom implementations, considering package private constructor.
  /** Constructor for use by subclasses. */
  protected Escaper() {}

  /**
   * Returns the escaped form of a given literal string.
   *
   * <p>Note that this method may treat input characters differently depending on the specific
   * escaper implementation.
   *
   * <ul>

   *
   */
  public static Escaper urlFormParameterEscaper() {
    return URL_FORM_PARAMETER_ESCAPER;
  }

  private static final Escaper URL_FORM_PARAMETER_ESCAPER =
      new PercentEscaper(URL_FORM_PARAMETER_OTHER_SAFE_CHARS, true);

  /**
   * Returns an {@link Escaper} instance that escapes strings so they can be safely included in <a

   *
   */
  public static Escaper urlFormParameterEscaper() {
    return URL_FORM_PARAMETER_ESCAPER;
  }

  private static final Escaper URL_FORM_PARAMETER_ESCAPER =
      new PercentEscaper(URL_FORM_PARAMETER_OTHER_SAFE_CHARS, true);

  /**
   * Returns an {@link Escaper} instance that escapes strings so they can be safely included in <a

   *
   * @param scale the scale for the quantiles to be calculated, i.e. the q of the q-quantiles, which
   *     must be positive
   */
  public static Scale scale(int scale) {
    return new Scale(scale);
  }

  /**
   * Describes the point in a fluent API chain where only the scale (i.e. the q in q-quantiles) has
   * been specified.
   *
   * @since 20.0
   */
  public static final class Scale {

    assertThrows(IllegalArgumentException.class, () -> intermediate.indexes(1, 11, 3));
  }

  public void testScale_indexes_collection_negative() {
    Quantiles.Scale intermediate = Quantiles.scale(10);
    assertThrows(
        IllegalArgumentException.class, () -> intermediate.indexes(ImmutableList.of(1, -1, 3)));
  }

  public void testScale_indexes_collection_tooHigh() {

    assertThrows(IllegalArgumentException.class, () -> intermediate.indexes(1, 11, 3));
  }

  public void testScale_indexes_collection_negative() {
    Quantiles.Scale intermediate = Quantiles.scale(10);
    assertThrows(
        IllegalArgumentException.class, () -> intermediate.indexes(ImmutableList.of(1, -1, 3)));
  }

  public void testScale_indexes_collection_tooHigh() {

    // Add small multiples of MIN_VALUE and MIN_NORMAL
    for (int scale = 1; scale <= 4; scale++) {
      for (double d : Doubles.asList(Double.MIN_VALUE, Double.MIN_NORMAL)) {
        fractionalBuilder.add(d * scale).add(-d * scale);
      }
    }
    for (int i = Double.MIN_EXPONENT; i <= Double.MAX_EXPONENT; i++) {
      for (int direction : new int[] {1, -1}) {

/**
 * Static utility methods pertaining to {@link Escaper} instances.
 *
 * @author Sven Mawson
 * @author David Beaumont
 * @since 15.0
 */
@GwtCompatible
public final class Escapers {
  private Escapers() {}

  /**
   * Returns an {@link Escaper} that does no escaping, passing all character data through unchanged.
   */
  public static Escaper nullEscaper() {
    return NULL_ESCAPER;
  }

   * output.
   *
   * <p>This escaper does not treat surrogate pairs specially and does not perform Unicode
   * validation on its input.
   */
  @SuppressWarnings("EscapedEntity") // We do mean for the user to see &#x9;" etc.
  public static Escaper xmlAttributeEscaper() {
    return XML_ATTRIBUTE_ESCAPER;
  }

  private static final Escaper XML_ESCAPER;
  private static final Escaper XML_CONTENT_ESCAPER;

    Escaper escaper = Escapers.builder().setSafeRange('a', 'z').build();
    assertThat(escaper.escape("The Quick Brown Fox")).isEqualTo("The Quick Brown Fox");
  }

  public void testBuilderInitialStateNoneUnsafe() {
    // No characters are unsafe by default (safeMin == 0, safeMax == 0xFFFF).
    Escaper escaper = Escapers.builder().setUnsafeReplacement("X").build();