/*
    * 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
    *
    *     http://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;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.LinkedHashSet;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.ListIterator;
  import java.util.Set;
  
  import org.apache.commons.configuration2.convert.ListDelimiterHandler;
  import org.apache.commons.configuration2.ex.ConfigurationRuntimeException;
  
  /**
   * <p>
   * {@code CompositeConfiguration} allows you to add multiple {@code Configuration} objects to an aggregated
   * configuration. If you add Configuration1, and then Configuration2, any properties shared will mean that the value
   * defined by Configuration1 will be returned. If Configuration1 doesn't have the property, then Configuration2 will be
   * checked. You can add multiple different types or the same type of properties file.
   * </p>
   * <p>
   * When querying properties the order in which child configurations have been added is relevant. To deal with property
   * updates, a so-called <em>in-memory configuration</em> is used. Per default, such a configuration is created
   * automatically. All property writes target this special configuration. There are constructors which allow you to
   * provide a specific in-memory configuration. If used that way, the in-memory configuration is always the last one in
   * the list of child configurations. This means that for query operations all other configurations take precedence.
   * </p>
   * <p>
   * Alternatively it is possible to mark a child configuration as in-memory configuration when it is added. In this case
   * the treatment of the in-memory configuration is slightly different: it remains in the list of child configurations at
   * the position it was added, i.e. its priority for property queries can be defined by adding the child configurations
   * in the correct order.
   * </p>
   * <p>
   * This configuration class uses a {@code Synchronizer} to control concurrent access. While all methods for reading and
   * writing configuration properties make use of this {@code Synchronizer} per default, the methods for managing the list
   * of child configurations and the in-memory configuration
   * ({@code addConfiguration(), getNumberOfConfigurations(), removeConfiguration(),
   * getConfiguration(), getInMemoryConfiguration()}) are guarded, too. Because most methods for accessing configuration
   * data delegate to the list of child configurations, the thread-safety of a {@code CompositeConfiguration} object also
   * depends on the {@code Synchronizer} objects used by these children.
   * </p>
   */
  public class CompositeConfiguration extends AbstractConfiguration implements Cloneable {
  
      /** List holding all the configuration */
      private List<Configuration> configList = new LinkedList<>();
  
      /**
       * Configuration that holds in memory stuff. Inserted as first so any setProperty() override anything else added.
       */
      private Configuration inMemoryConfiguration;
  
      /**
       * Stores a flag whether the current in-memory configuration is also a child configuration.
       */
      private boolean inMemoryConfigIsChild;
  
      /**
       * Creates an empty CompositeConfiguration object which can then be added some other Configuration files
       */
      public CompositeConfiguration() {
          clear();
      }
  
      /**
       * Create a CompositeConfiguration with an empty in memory configuration and adds the collection of configurations
       * specified.
       *
       * @param configurations the collection of configurations to add
       */
      public CompositeConfiguration(final Collection<? extends Configuration> configurations) {
          this(new BaseConfiguration(), configurations);
      }
  
      /**
       * Creates a CompositeConfiguration object with a specified <em>in-memory configuration</em>. This configuration will
       * store any changes made to the {@code CompositeConfiguration}. Note: Use this constructor if you want to set a special
       * type of in-memory configuration. If you have a configuration which should act as both a child configuration and as
       * in-memory configuration, use {@link #addConfiguration(Configuration, boolean)} with a value of <strong>true</strong> instead.
       *
      * @param inMemoryConfiguration the in memory configuration to use
      */
     public CompositeConfiguration(final Configuration inMemoryConfiguration) {
         this.configList.clear();
         this.inMemoryConfiguration = inMemoryConfiguration;
         this.configList.add(inMemoryConfiguration);
     }
 
     /**
      * Creates a CompositeConfiguration with a specified <em>in-memory configuration</em>, and then adds the given
      * collection of configurations.
      *
      * @param inMemoryConfiguration the in memory configuration to use
      * @param configurations the collection of configurations to add
      * @see #CompositeConfiguration(Configuration)
      */
     public CompositeConfiguration(final Configuration inMemoryConfiguration, final Collection<? extends Configuration> configurations) {
         this(inMemoryConfiguration);
         if (configurations != null) {
             configurations.forEach(this::addConfiguration);
         }
     }
 
     /**
      * Add a configuration.
      *
      * @param config the configuration to add
      */
     public void addConfiguration(final Configuration config) {
         addConfiguration(config, false);
     }
 
     /**
      * Adds a child configuration and optionally makes it the <em>in-memory configuration</em>. This means that all future
      * property write operations are executed on this configuration. Note that the current in-memory configuration is
      * replaced by the new one. If it was created automatically or passed to the constructor, it is removed from the list of
      * child configurations! Otherwise, it stays in the list of child configurations at its current position, but it passes
      * its role as in-memory configuration to the new one.
      *
      * @param config the configuration to be added
      * @param asInMemory <strong>true</strong> if this configuration becomes the new <em>in-memory</em> configuration, <strong>false</strong>
      *        otherwise
      * @since 1.8
      */
     public void addConfiguration(final Configuration config, final boolean asInMemory) {
         syncWrite(() -> {
             if (!configList.contains(config)) {
                 if (asInMemory) {
                     replaceInMemoryConfiguration(config);
                     inMemoryConfigIsChild = true;
                 }
                 if (!inMemoryConfigIsChild) {
                     // As the inMemoryConfiguration contains all manually added
                     // keys, we must make sure that it is always last. "Normal", non
                     // composed configurations add their keys at the end of the
                     // configuration and we want to mimic this behavior.
                     configList.add(configList.indexOf(inMemoryConfiguration), config);
                 } else {
                     // However, if the in-memory configuration is a regular child,
                     // only the order in which child configurations are added is relevant
                     configList.add(config);
                 }
                 if (config instanceof AbstractConfiguration) {
                     ((AbstractConfiguration) config).setThrowExceptionOnMissing(isThrowExceptionOnMissing());
                 }
             }
         }, false);
     }
 
     /**
      * Add a configuration to the start of the list of child configurations.
      *
      * @param config the configuration to add
      * @since 2.3
      */
     public void addConfigurationFirst(final Configuration config) {
         addConfigurationFirst(config, false);
     }
 
     /**
      * Adds a child configuration to the start of the collection and optionally makes it the <em>in-memory
      * configuration</em>. This means that all future property write operations are executed on this configuration. Note
      * that the current in-memory configuration is replaced by the new one. If it was created automatically or passed to the
      * constructor, it is removed from the list of child configurations! Otherwise, it stays in the list of child
      * configurations at its current position, but it passes its role as in-memory configuration to the new one.
      *
      * @param config the configuration to be added
      * @param asInMemory <strong>true</strong> if this configuration becomes the new <em>in-memory</em> configuration, <strong>false</strong>
      *        otherwise
      * @since 2.3
      */
     public void addConfigurationFirst(final Configuration config, final boolean asInMemory) {
         syncWrite(() -> {
             if (!configList.contains(config)) {
                 if (asInMemory) {
                     replaceInMemoryConfiguration(config);
                     inMemoryConfigIsChild = true;
                 }
                 configList.add(0, config);
                 if (config instanceof AbstractConfiguration) {
                     ((AbstractConfiguration) config).setThrowExceptionOnMissing(isThrowExceptionOnMissing());
                 }
             }
         }, false);
     }
 
     /**
      * Add this property to the in-memory Configuration.
      *
      * @param key The Key to add the property to.
      * @param token The Value to add.
      */
     @Override
     protected void addPropertyDirect(final String key, final Object token) {
         inMemoryConfiguration.addProperty(key, token);
     }
 
     /**
      * Adds the value of a property to the given list. This method is used by {@code getList()} for gathering property
      * values from the child configurations.
      *
      * @param dest the list for collecting the data
      * @param config the configuration to query
      * @param key the key of the property
      */
     private void appendListProperty(final List<Object> dest, final Configuration config, final String key) {
         final Object value = interpolate(config.getProperty(key));
         if (value != null) {
             if (value instanceof Collection) {
                 final Collection<?> col = (Collection<?>) value;
                 dest.addAll(col);
             } else {
                 dest.add(value);
             }
         }
     }
 
     /**
      * Removes all child configurations and reinitializes the <em>in-memory configuration</em>. <strong>Attention:</strong>
      * A new in-memory configuration is created; the old one is lost.
      */
     @Override
     protected void clearInternal() {
         configList.clear();
         // recreate the in memory configuration
         inMemoryConfiguration = new BaseConfiguration();
         ((BaseConfiguration) inMemoryConfiguration).setThrowExceptionOnMissing(isThrowExceptionOnMissing());
         ((BaseConfiguration) inMemoryConfiguration).setListDelimiterHandler(getListDelimiterHandler());
         configList.add(inMemoryConfiguration);
         inMemoryConfigIsChild = false;
     }
 
     @Override
     protected void clearPropertyDirect(final String key) {
         configList.forEach(config -> config.clearProperty(key));
     }
 
     /**
      * Returns a copy of this object. This implementation will create a deep clone, i.e. all configurations contained in
      * this composite will also be cloned. This only works if all contained configurations support cloning; otherwise a
      * runtime exception will be thrown. Registered event handlers won't get cloned.
      *
      * @return the copy
      * @since 1.3
      */
     @Override
     public Object clone() {
         try {
             final CompositeConfiguration copy = (CompositeConfiguration) super.clone();
             copy.configList = new LinkedList<>();
             copy.inMemoryConfiguration = ConfigurationUtils.cloneConfiguration(getInMemoryConfiguration());
             copy.configList.add(copy.inMemoryConfiguration);
 
             configList.forEach(config -> {
                 if (config != getInMemoryConfiguration()) {
                     copy.addConfiguration(ConfigurationUtils.cloneConfiguration(config));
                 }
             });
 
             copy.cloneInterpolator(this);
             return copy;
         } catch (final CloneNotSupportedException cnex) {
             // cannot happen
             throw new ConfigurationRuntimeException(cnex);
         }
     }
 
     @Override
     protected boolean containsKeyInternal(final String key) {
         return configList.stream().anyMatch(config -> config.containsKey(key));
     }
 
     /**
      * Tests whether this configuration contains one or more matches to this value. This operation stops at first
      * match but may be more expensive than the containsKey method.
      * @since 2.11.0
      */
     @Override
     protected boolean containsValueInternal(final Object value) {
         return configList.stream().anyMatch(config -> config.containsValue(value));
     }
 
     /**
      * Gets the configuration at the specified index.
      *
      * @param index The index of the configuration to retrieve
      * @return the configuration at this index
      */
     public Configuration getConfiguration(final int index) {
         return syncRead(() -> configList.get(index), false);
     }
 
     /**
      * Gets the &quot;in memory configuration&quot;. In this configuration changes are stored.
      *
      * @return the in memory configuration
      */
     public Configuration getInMemoryConfiguration() {
         return syncReadValue(inMemoryConfiguration, false);
     }
 
     @Override
     protected Iterator<String> getKeysInternal() {
         final Set<String> keys = new LinkedHashSet<>();
         configList.forEach(config -> config.getKeys().forEachRemaining(keys::add));
         return keys.iterator();
     }
 
     @Override
     protected Iterator<String> getKeysInternal(final String key) {
         final Set<String> keys = new LinkedHashSet<>();
         configList.forEach(config -> config.getKeys(key).forEachRemaining(keys::add));
         return keys.iterator();
     }
 
     @Override
     protected Iterator<String> getKeysInternal(final String key, final String delimiter) {
         final Set<String> keys = new LinkedHashSet<>();
         configList.forEach(config -> config.getKeys(key, delimiter).forEachRemaining(keys::add));
         return keys.iterator();
     }
 
     @Override
     public List<Object> getList(final String key, final List<?> defaultValue) {
         final List<Object> list = new ArrayList<>();
 
         // add all elements from the first configuration containing the requested key
         final Iterator<Configuration> it = configList.iterator();
         while (it.hasNext() && list.isEmpty()) {
             final Configuration config = it.next();
             if (config != inMemoryConfiguration && config.containsKey(key)) {
                 appendListProperty(list, config, key);
             }
         }
 
         // add all elements from the in memory configuration
         appendListProperty(list, inMemoryConfiguration, key);
 
         if (list.isEmpty()) {
             // This is okay because we just return this list to the caller
             @SuppressWarnings("unchecked")
             final List<Object> resultList = (List<Object>) defaultValue;
             return resultList;
         }
 
         final ListIterator<Object> lit = list.listIterator();
         while (lit.hasNext()) {
             lit.set(interpolate(lit.next()));
         }
 
         return list;
     }
 
     /**
      * Gets the number of configurations.
      *
      * @return the number of configuration
      */
     public int getNumberOfConfigurations() {
         return syncRead(configList::size, false);
     }
 
     /**
      * Reads property from underlying composite
      *
      * @param key key to use for mapping
      * @return object associated with the given configuration key.
      */
     @Override
     protected Object getPropertyInternal(final String key) {
         return configList.stream().filter(config -> config.containsKey(key)).findFirst().map(config -> config.getProperty(key)).orElse(null);
     }
 
     /**
      * Gets the configuration source, in which the specified key is defined. This method will iterate over all existing
      * child configurations and check whether they contain the specified key. The following constellations are possible:
      * <ul>
      * <li>If exactly one child configuration contains the key, this configuration is returned as the source configuration.
      * This may be the <em>in memory configuration</em> (this has to be explicitly checked by the calling application).</li>
      * <li>If none of the child configurations contain the key, <strong>null</strong> is returned.</li>
      * <li>If the key is contained in multiple child configurations or if the key is <strong>null</strong>, a
      * {@code IllegalArgumentException} is thrown. In this case the source configuration cannot be determined.</li>
      * </ul>
      *
      * @param key the key to be checked
      * @return the source configuration of this key
      * @throws IllegalArgumentException if the source configuration cannot be determined
      * @since 1.5
      */
     public Configuration getSource(final String key) {
         if (key == null) {
             throw new IllegalArgumentException("Key must not be null!");
         }
 
         Configuration source = null;
         for (final Configuration conf : configList) {
             if (conf.containsKey(key)) {
                 if (source != null) {
                     throw new IllegalArgumentException("The key " + key + " is defined by multiple sources!");
                 }
                 source = conf;
             }
         }
 
         return source;
     }
 
     @Override
     public String[] getStringArray(final String key) {
         final List<Object> list = getList(key);
 
         // transform property values into strings
         final String[] tokens = new String[list.size()];
 
         for (int i = 0; i < tokens.length; i++) {
             tokens[i] = String.valueOf(list.get(i));
         }
 
         return tokens;
     }
 
     @Override
     protected boolean isEmptyInternal() {
         return configList.stream().allMatch(Configuration::isEmpty);
     }
 
     /**
      * Remove a configuration. The in memory configuration cannot be removed.
      *
      * @param config The configuration to remove
      */
     public void removeConfiguration(final Configuration config) {
         syncWrite(() -> {
             // Make sure that you can't remove the inMemoryConfiguration from
             // the CompositeConfiguration object
             if (!config.equals(inMemoryConfiguration)) {
                 configList.remove(config);
             }
         }, false);
     }
 
     /**
      * Replaces the current in-memory configuration by the given one.
      *
      * @param config the new in-memory configuration
      */
     private void replaceInMemoryConfiguration(final Configuration config) {
         if (!inMemoryConfigIsChild) {
             // remove current in-memory configuration
             configList.remove(inMemoryConfiguration);
         }
         inMemoryConfiguration = config;
     }
 
     /**
      * {@inheritDoc} This implementation ensures that the in memory configuration is correctly initialized.
      */
     @Override
     public void setListDelimiterHandler(final ListDelimiterHandler listDelimiterHandler) {
         if (inMemoryConfiguration instanceof AbstractConfiguration) {
             ((AbstractConfiguration) inMemoryConfiguration).setListDelimiterHandler(listDelimiterHandler);
         }
         super.setListDelimiterHandler(listDelimiterHandler);
     }
 }