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/*
 * This file is part of the DiffX library.
 *
 * For licensing information please see the file license.txt included in the release.
 * A copy of this licence can also be found at
 *   http://www.opensource.org/licenses/artistic-license-2.0.php
 */
package com.topologi.diffx.xml;

import com.topologi.diffx.xml.esc.XMLEscapeUTF8;

/**
 * A utility class for XML data.
 *
 * @version 2.0, 24 March 2004
 * @author  Christophe Lauret
 */
public final class XMLUtils {

  /**
   * Prevents creation of instances.
   */
  private XMLUtils() {
  }

  /**
   * Replaces characters which are invalid in element values, by the corresponding entity
   * in a given String.
   *
   * these characters are:

   * 
   *  '&' by the ampersand entity "&amp"
   *  '<' by the entity "&lt;"
   * 
   *
   * Empty strings or null return respectively "" and null.
   *
   * 
Note: this function assumes that there are no entities in the given String. If there
   * are existing entities, then the ampersand character will be escaped by the ampersand
   * entity.
   *
   * 
This method does not replaces " (by &quot;) which is an invalid character in
   * attribute values.
   *
   * @see #escapeAttr
   *
   * @param  s The String to be parsed
   *
   * @return a valid string or empty if s is null or empty.
   */
  public static String escape(String s) {
    return XMLEscapeUTF8.UTF8_ESCAPE.toElementText(s);
  }

  /**
   * Replace characters which are invalid in attribute values,
   * by the corresponding entity in a given String.
   *
   * 
these characters are:

   * 
   *  '&' by the ampersand entity "&amp"
   *  '<' by the entity "&lt;"
   *  ''' by the entity "&apos;"
   *  '"' by the entity "&quot;"
   * 
   *
   * Empty strings or null return respectively
   * "" and null.
   *
   * 
Note: this function assumes that there are no entities in
   * the given String. If there are existing entities, then the
   * ampersand character will be escaped by the ampersand entity.
   *
   *
   * @param  s The String to be parsed
   *
   * @return a valid string or empty if s is null or empty.
   */
  public static String escapeAttr(String s) {
    return XMLEscapeUTF8.UTF8_ESCAPE.toAttributeValue(s);
  }

  /**
   * Return a valid element name from the given string.
   *
   * Letters are put to lower case and other characters are replaced by hyphens.
   * If the first character is not a letter it is replaced by 'x'.
   *
   * @param name The candidate element name
   *
   * @return A valid element name
   */
  public static String toElementName(String name) {
    if (name == null) return null;
    char[] elementAsChars = name.toCharArray();
    if (!Character.isLetter(elementAsChars[0])) {
      elementAsChars[0] = 'x';
    } else {
      elementAsChars[0] = Character.toLowerCase(elementAsChars[0]);
    }
    for (int i = 1; i < elementAsChars.length; i++) {
      if (!Character.isLetter(elementAsChars[i])) {
        elementAsChars[i] = '-';
      } else {
        elementAsChars[i] = Character.toLowerCase(elementAsChars[i]);
      }
    }
    return new String(elementAsChars);
  }

}