/*
    * 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.lang.reflect.Array;
  import java.nio.file.Path;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.LinkedList;
  import java.util.Set;
  
  /**
   * <p>
   * An abstract base class for concrete {@code ListDelimiterHandler} implementations.
   * </p>
   * <p>
   * This base class provides a fully functional implementation for parsing a value object which can deal with different
   * cases like collections, arrays, iterators, etc. This logic is typically needed by every concrete subclass. Other
   * methods are partly implemented handling special corner cases like <strong>null</strong> values; concrete subclasses do not have
   * do implement the corresponding checks.
   * </p>
   *
   * @since 2.0
   */
  public abstract class AbstractListDelimiterHandler implements ListDelimiterHandler {
  
      static Collection<?> flatten(final ListDelimiterHandler handler, final Object value, final int limit, final Set<Object> dejaVu) {
          if (value instanceof String) {
              return handler.split((String) value, true);
          }
          dejaVu.add(value);
          final Collection<Object> result = new LinkedList<>();
          if (value instanceof Path) {
              // Don't handle as an Iterable.
              result.add(value);
          } else if (value instanceof Iterable) {
              flattenIterator(handler, result, ((Iterable<?>) value).iterator(), limit, dejaVu);
          } else if (value instanceof Iterator) {
              flattenIterator(handler, result, (Iterator<?>) value, limit, dejaVu);
          } else if (value != null) {
              if (value.getClass().isArray()) {
                  for (int len = Array.getLength(value), idx = 0, size = 0; idx < len && size < limit; idx++, size = result.size()) {
                      result.addAll(handler.flatten(Array.get(value, idx), limit - size));
                  }
              } else {
                  result.add(value);
              }
          }
          return result;
      }
  
      /**
       * Flattens the given iterator. For each element in the iteration {@code flatten()} is called recursively.
       *
       * @param handler the working handler
       * @param target the target collection
       * @param iterator the iterator to process
       * @param limit a limit for the number of elements to extract
       * @param dejaVue Previously visited objects.
       */
      static void flattenIterator(final ListDelimiterHandler handler, final Collection<Object> target, final Iterator<?> iterator, final int limit,
              final Set<Object> dejaVue) {
          int size = target.size();
          while (size < limit && iterator.hasNext()) {
              final Object next = iterator.next();
              if (!dejaVue.contains(next)) {
                  target.addAll(flatten(handler, next, limit - size, dejaVue));
                  size = target.size();
              }
          }
      }
  
      /**
       * Constructs a new instance.
       */
      public AbstractListDelimiterHandler() {
          // empty
      }
  
      /**
       * {@inheritDoc} This implementation checks whether the object to be escaped is a string. If yes, it delegates to
       * {@link #escapeString(String)}, otherwise no escaping is performed. Eventually, the passed in transformer is invoked
       * so that additional encoding can be performed.
       */
     @Override
     public Object escape(final Object value, final ValueTransformer transformer) {
         return transformer.transformValue(value instanceof String ? escapeString((String) value) : value);
     }
 
     /**
      * Escapes the specified string. This method is called by {@code escape()} if the passed in object is a string. Concrete
      * subclasses have to implement their specific escaping logic here, so that the list delimiters they support are
      * properly escaped.
      *
      * @param s the string to be escaped (not <strong>null</strong>)
      * @return the escaped string
      */
     protected abstract String escapeString(String s);
 
     /**
      * Performs the actual work as advertised by the {@code parse()} method. This method delegates to
      * {@link #flatten(Object, int)} without specifying a limit.
      *
      * @param value the value to be processed
      * @return a &quot;flat&quot; collection containing all primitive values of the passed in object
      */
     private Collection<?> flatten(final Object value) {
         return flatten(value, Integer.MAX_VALUE);
     }
 
     /**
      * {@inheritDoc} Depending on the type of the passed in object the following things happen:
      * <ul>
      * <li>Strings are checked for delimiter characters and split if necessary. This is done by calling the {@code split()}
      * method.</li>
      * <li>For objects implementing the {@code Iterable} interface, the corresponding {@code Iterator} is obtained, and
      * contained elements are added to the resulting iteration.</li>
      * <li>Arrays are treated as {@code Iterable} objects.</li>
      * <li>All other types are directly inserted.</li>
      * <li>Recursive combinations are supported, for example a collection containing an array that contains strings: The resulting
      * collection will only contain primitive objects.</li>
      * </ul>
      */
     @Override
     public Iterable<?> parse(final Object value) {
         return flatten(value);
     }
 
     /**
      * {@inheritDoc} This implementation handles the case that the passed in string is <strong>null</strong>. In this case, an empty
      * collection is returned. Otherwise, this method delegates to {@link #splitString(String, boolean)}.
      */
     @Override
     public Collection<String> split(final String s, final boolean trim) {
         return s == null ? new ArrayList<>(0) : splitString(s, trim);
     }
 
     /**
      * Actually splits the passed in string which is guaranteed to be not <strong>null</strong>. This method is called by the base
      * implementation of the {@code split()} method. Here the actual splitting logic has to be implemented.
      *
      * @param s the string to be split (not <strong>null</strong>)
      * @param trim a flag whether the single components have to be trimmed
      * @return a collection with the extracted components of the passed in string
      */
     protected abstract Collection<String> splitString(String s, boolean trim);
 }