package com.atlassian.sal.core.pluginsettings;
   
   import java.io.IOException;
   import java.io.StringWriter;
   import java.io.Writer;
   
   /**
    * Escape utility methods which only escapes VERTICAL_TAB and NEW_LINE.
    *
   * The escape logic is custom made here instead of using StringEscapeUtils in apache common since
   * we don't want to interfere with other special characters that we don't use in {@link AbstractStringPluginSettings}.
   *
   * For example, in that case if the data read from the backing store is "this is \\me", we're not sure whether
   * it's escaped or non-escaped.
   *
   * @since 2.2.0
   */
  class EscapeUtils {
      // Not for instantiation.
      private EscapeUtils() {
      }
  
      protected static final char VERTICAL_TAB = '\f';
      protected static final char NEW_LINE = '\n';
  
      /**
       * This only escapes VERTICAL_TAB and NEW_LINE.
       */
      protected static String escape(String str) {
          if (str == null) {
              return null;
          }
  
          StringWriter writer = new StringWriter(str.length() * 2);
          try {
              escape(writer, str);
          } catch (IOException e) {
              throw new RuntimeException("exception while writing to StringWriter (should be impossible in this context)", e);
          }
  
          return writer.toString();
      }
  
      private static void escape(Writer out, String str) throws IOException {
          int len = str.length();
          for (int i = 0; i < len; i++) {
              char ch = str.charAt(i);
  
              if (ch == VERTICAL_TAB) {
                  out.write('\\');
                  out.write('f');
              } else if (ch == NEW_LINE) {
                  out.write('\\');
                  out.write('n');
              } else if (ch == '\\') {
                  out.write('\\');
                  out.write('\\');
              } else {
                  out.write(ch);
              }
          }
      }
  
      public static String unescape(String str) {
          if (str == null) {
              return null;
          }
          try {
              StringWriter writer = new StringWriter(str.length());
              unescape(writer, str);
              return writer.toString();
          } catch (IOException e) {
              throw new RuntimeException("exception while writing to StringWriter (should be impossible in this context)", e);
          }
      }
  
      private static void unescape(Writer out, String str) throws IOException {
          int len = str.length();
          boolean hadSlash = false;
  
          for (int i = 0; i < len; i++) {
              char ch = str.charAt(i);
              if (hadSlash) {
                  switch (ch) {
                      case 'f':
                          out.write('\f');
                          break;
                      case 'n':
                          out.write('\n');
                          break;
                      default:
                          out.write(ch);
                          break;
                  }
                  // the slash is taken care of.
                  hadSlash = false;
                  continue;
              } else if (ch == '\\') {
                  hadSlash = true;
                 continue;
             }
             out.write(ch);
         }
         // the the slash is the last character, then just give it out.
         if (hadSlash) {
             out.write('\\');
         }
     }
 }