/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You under the Apache License, Version 2.0
    * (the "License"); you may not use this file except in compliance with
    * the License.  You may obtain a copy of the License at
    *
    *     https://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.commons.configuration2.convert;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Iterator;
  import java.util.List;
  
  import org.apache.commons.lang3.Strings;
  
  /**
   * <p>
   * A specialized implementation of {@code ListDelimiterHandler} which simulates the list delimiter handling as it was
   * used by {@code PropertiesConfiguration} in Commons Configuration 1.x.
   * </p>
   * <p>
   * This class mainly exists for compatibility reasons. It is intended to be used by applications which have to deal with
   * properties files created by an older version of this library.
   * </p>
   * <p>
   * In the 1.x series of Commons Configuration list handling was not fully consistent. The escaping of property values
   * was done in a different way if they contained a list delimiter or not. From version 2.0 on, escaping is more
   * stringent which might cause slightly different results when parsing properties files created by or for Configuration
   * 1.x. If you encounter such problems, you can switch to this {@code ListDelimiterHandler} implementation rather than
   * the default one. In other cases, this class should not be used!
   * </p>
   * <p>
   * Implementation note: An instance of this class can safely be shared between multiple {@code Configuration} instances.
   * </p>
   *
   * @since 2.0
   */
  public class LegacyListDelimiterHandler extends AbstractListDelimiterHandler {
  
      /** Constant for the escaping character. */
      private static final String ESCAPE = "\\";
  
      /** Constant for the escaped escaping character. */
      private static final String DOUBLE_ESC = ESCAPE + ESCAPE;
  
      /** Constant for a duplicated sequence of escaping characters. */
      private static final String QUAD_ESC = DOUBLE_ESC + DOUBLE_ESC;
  
      /**
       * Returns the number of trailing backslashes. This is sometimes needed for the correct handling of escape characters.
       *
       * @param line the string to investigate
       * @return the number of trailing backslashes
       */
      private static int countTrailingBS(final String line) {
          int bsCount = 0;
          for (int idx = line.length() - 1; idx >= 0 && line.charAt(idx) == '\\'; idx--) {
              bsCount++;
          }
  
          return bsCount;
      }
  
      /** The list delimiter character. */
      private final char delimiter;
  
      /**
       * Creates a new instance of {@code LegacyListDelimiterHandler} and sets the list delimiter character.
       *
       * @param listDelimiter the list delimiter character
       */
      public LegacyListDelimiterHandler(final char listDelimiter) {
          delimiter = listDelimiter;
      }
  
      /**
       * {@inheritDoc} This implementation performs delimiter escaping for a single value (which is not part of a list).
       */
      @Override
      public Object escape(final Object value, final ValueTransformer transformer) {
          return escapeValue(value, false, transformer);
      }
  
      /**
       * Performs the escaping of backslashes in the specified properties value. Because a double backslash is used to escape
       * the escape character of a list delimiter, double backslashes also have to be escaped if the property is part of a
       * (single line) list. In addition, because the output is written into a properties file, each occurrence of a backslash
       * again has to be doubled. This method is called by {@code escapeValue()}.
      *
      * @param value the value to be escaped
      * @param inList a flag whether the value is part of a list
      * @return the value with escaped backslashes as string
      */
     protected String escapeBackslashs(final Object value, final boolean inList) {
         String strValue = String.valueOf(value);
 
         if (inList && strValue.contains(DOUBLE_ESC)) {
             strValue = Strings.CS.replace(strValue, DOUBLE_ESC, QUAD_ESC);
         }
 
         return strValue;
     }
 
     /**
      * {@inheritDoc} This implementation performs a special encoding of backslashes at the end of a string so that they are
      * not interpreted as escape character for a following list delimiter.
      */
     @Override
     public Object escapeList(final List<?> values, final ValueTransformer transformer) {
         if (!values.isEmpty()) {
             final Iterator<?> it = values.iterator();
             String lastValue = escapeValue(it.next(), true, transformer);
             final StringBuilder buf = new StringBuilder(lastValue);
             while (it.hasNext()) {
                 // if the last value ended with an escape character, it has
                 // to be escaped itself; otherwise the list delimiter will
                 // be escaped
                 if (lastValue.endsWith(ESCAPE) && countTrailingBS(lastValue) / 2 % 2 != 0) {
                     buf.append(ESCAPE).append(ESCAPE);
                 }
                 buf.append(getDelimiter());
                 lastValue = escapeValue(it.next(), true, transformer);
                 buf.append(lastValue);
             }
             return buf.toString();
         }
         return null;
     }
 
     /**
      * {@inheritDoc} This is just a dummy implementation. It is never called.
      */
     @Override
     protected String escapeString(final String s) {
         return null;
     }
 
     /**
      * Escapes the given property value. This method is called on saving the configuration for each property value. It
      * ensures a correct handling of backslash characters and also takes care that list delimiter characters in the value
      * are escaped.
      *
      * @param value the property value
      * @param inList a flag whether the value is part of a list
      * @param transformer the {@code ValueTransformer}
      * @return the escaped property value
      */
     protected String escapeValue(final Object value, final boolean inList, final ValueTransformer transformer) {
         String escapedValue = String.valueOf(transformer.transformValue(escapeBackslashs(value, inList)));
         if (getDelimiter() != 0) {
             escapedValue = Strings.CS.replace(escapedValue, String.valueOf(getDelimiter()), ESCAPE + getDelimiter());
         }
         return escapedValue;
     }
 
     /**
      * Gets the list delimiter character.
      *
      * @return the list delimiter character
      */
     public char getDelimiter() {
         return delimiter;
     }
 
     /**
      * {@inheritDoc} This implementation simulates the old splitting algorithm. The string is split at the delimiter
      * character if it is not escaped. If the delimiter character is not found, the input is returned unchanged.
      */
     @Override
     protected Collection<String> splitString(final String s, final boolean trim) {
         if (s.indexOf(getDelimiter()) < 0) {
             return Collections.singleton(s);
         }
 
         final List<String> list = new ArrayList<>();
 
         StringBuilder token = new StringBuilder();
         int begin = 0;
         boolean inEscape = false;
         final char esc = ESCAPE.charAt(0);
 
         while (begin < s.length()) {
             final char c = s.charAt(begin);
             if (inEscape) {
                 // last character was the escape marker
                 // can current character be escaped?
                 if (c != getDelimiter() && c != esc) {
                     // no, also add escape character
                     token.append(esc);
                 }
                 token.append(c);
                 inEscape = false;
             } else if (c == getDelimiter()) {
                 // found a list delimiter -> add token and
                 // resetDefaultFileSystem buffer
                 String t = token.toString();
                 if (trim) {
                     t = t.trim();
                 }
                 list.add(t);
                 token = new StringBuilder();
             } else if (c == esc) {
                 // eventually escape next character
                 inEscape = true;
             } else {
                 token.append(c);
             }
 
             begin++;
         }
 
         // Trailing delimiter?
         if (inEscape) {
             token.append(esc);
         }
         // Add last token
         String t = token.toString();
         if (trim) {
             t = t.trim();
         }
         list.add(t);
 
         return list;
     }
 }