/*
    * 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.builder;
  
  import java.util.Collection;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.Map;
  
  import org.apache.commons.configuration2.ConfigurationUtils;
  import org.apache.commons.configuration2.ImmutableConfiguration;
  import org.apache.commons.configuration2.Initializable;
  import org.apache.commons.configuration2.beanutils.BeanDeclaration;
  import org.apache.commons.configuration2.beanutils.BeanHelper;
  import org.apache.commons.configuration2.beanutils.ConstructorArg;
  import org.apache.commons.configuration2.event.Event;
  import org.apache.commons.configuration2.event.EventListener;
  import org.apache.commons.configuration2.event.EventListenerList;
  import org.apache.commons.configuration2.event.EventListenerRegistrationData;
  import org.apache.commons.configuration2.event.EventSource;
  import org.apache.commons.configuration2.event.EventType;
  import org.apache.commons.configuration2.ex.ConfigurationException;
  import org.apache.commons.configuration2.ex.ConfigurationRuntimeException;
  import org.apache.commons.configuration2.reloading.ReloadingController;
  
  /**
   * <p>
   * An implementation of the {@code ConfigurationBuilder} interface which is able to create different concrete
   * {@code ImmutableConfiguration} implementations based on reflection.
   * </p>
   * <p>
   * When constructing an instance of this class the concrete {@code ImmutableConfiguration} implementation class has to
   * be provided. Then properties for the new {@code ImmutableConfiguration} instance can be set. The first call to
   * {@code getConfiguration()} creates and initializes the new {@code ImmutableConfiguration} object. It is cached and
   * returned by subsequent calls. This cache - and also the initialization properties set so far - can be flushed by
   * calling one of the {@code reset()} methods. That way other {@code ImmutableConfiguration} instances with different
   * properties can be created.
   * </p>
   * <p>
   * If the newly created {@code ImmutableConfiguration} object implements the {@code Initializable} interface, its
   * {@code initialize()} method is called after all initialization properties have been set. This way a concrete
   * implementation class can perform arbitrary initialization steps.
   * </p>
   * <p>
   * There are multiple options for setting up a {@code BasicConfigurationBuilder} instance:
   * </p>
   * <ul>
   * <li>All initialization properties can be set in one or multiple calls of the {@code configure()} method. In each call
   * an arbitrary number of {@link BuilderParameters} objects can be passed. The API allows method chaining and is
   * intended to be used from Java code.</li>
   * <li>If builder instances are created by other means - for example using a dependency injection framework -, the fluent API
   * approach may not be suitable. For those use cases it is also possible to pass in all initialization parameters as a
   * map. The keys of the map have to match initialization properties of the {@code ImmutableConfiguration} object to be
   * created, the values are the corresponding property values. For instance, the key <em>throwExceptionOnMissing</em> in
   * the map will cause the method {@code setThrowExceptionOnMissing()} on the {@code ImmutableConfiguration} object to be
   * called with the corresponding value as parameter.</li>
   * </ul>
   * <p>
   * A builder instance can be constructed with an <em>allowFailOnInit</em> flag. If set to <strong>true</strong>,
   * exceptions during initialization of the configuration are ignored; in such a case an empty configuration object is
   * returned. A use case for this flag is a scenario in which a configuration is optional and created on demand the first
   * time configuration data is to be stored. Consider an application that stores user-specific configuration data in the
   * user's home directory: When started for the first time by a new user there is no configuration file; so it makes
   * sense to start with an empty configuration object. On application exit, settings can be stored in this object and
   * written to the associated file. Then they are available on next application start.
   * </p>
   * <p>
   * This class is thread-safe. Multiple threads can modify initialization properties and call {@code getConfiguration()}.
   * However, the intended use case is that the builder is configured by a single thread first. Then
   * {@code getConfiguration()} can be called concurrently, and it is guaranteed that always the same
   * {@code ImmutableConfiguration} instance is returned until the builder is reset.
   * </p>
   *
   * @param <T> the concrete type of {@code ImmutableConfiguration} objects created by this builder
   * @since 2.0
   */
  public class BasicConfigurationBuilder<T extends ImmutableConfiguration> implements ConfigurationBuilder<T> {
  
      /**
       * Registers an event listener at an event source object.
       *
       * @param evSrc the event source
       * @param regData the registration data object
       * @param <E> the type of the event listener
       */
     private static <E extends Event> void registerListener(final EventSource evSrc, final EventListenerRegistrationData<E> regData) {
         evSrc.addEventListener(regData.getEventType(), regData.getListener());
     }
 
     /**
      * Removes an event listener from an event source object.
      *
      * @param evSrc the event source
      * @param regData the registration data object
      * @param <E> the type of the event listener
      */
     private static <E extends Event> void removeListener(final EventSource evSrc, final EventListenerRegistrationData<E> regData) {
         evSrc.removeEventListener(regData.getEventType(), regData.getListener());
     }
 
     /** The class of the objects produced by this builder instance. */
     private final Class<? extends T> resultClass;
 
     /** An object managing the event listeners registered at this builder. */
     private final EventListenerList eventListeners;
 
     /** A flag whether exceptions on initializing configurations are allowed. */
     private final boolean allowFailOnInit;
 
     /** The map with current initialization parameters. */
     private Map<String, Object> parameters;
 
     /** The current bean declaration. */
     private BeanDeclaration resultDeclaration;
 
     /** The result object of this builder. */
     private volatile T result;
 
     /**
      * Creates a new instance of {@code BasicConfigurationBuilder} and initializes it with the given result class. No
      * initialization properties are set.
      *
      * @param resCls the result class (must not be <strong>null</strong>)
      * @throws IllegalArgumentException if the result class is <strong>null</strong>
      */
     public BasicConfigurationBuilder(final Class<? extends T> resCls) {
         this(resCls, null);
     }
 
     /**
      * Creates a new instance of {@code BasicConfigurationBuilder} and initializes it with the given result class and an
      * initial set of builder parameters. The <em>allowFailOnInit</em> flag is set to <strong>false</strong>.
      *
      * @param resCls the result class (must not be <strong>null</strong>)
      * @param params a map with initialization parameters
      * @throws IllegalArgumentException if the result class is <strong>null</strong>
      */
     public BasicConfigurationBuilder(final Class<? extends T> resCls, final Map<String, Object> params) {
         this(resCls, params, false);
     }
 
     /**
      * Creates a new instance of {@code BasicConfigurationBuilder} and initializes it with the given result class, an
      * initial set of builder parameters, and the <em>allowFailOnInit</em> flag. The map with parameters may be <strong>null</strong>,
      * in this case no initialization parameters are set.
      *
      * @param resCls the result class (must not be <strong>null</strong>)
      * @param params a map with initialization parameters
      * @param allowFailOnInit a flag whether exceptions on initializing a newly created {@code ImmutableConfiguration}
      *        object are allowed
      * @throws IllegalArgumentException if the result class is <strong>null</strong>
      */
     public BasicConfigurationBuilder(final Class<? extends T> resCls, final Map<String, Object> params, final boolean allowFailOnInit) {
         if (resCls == null) {
             throw new IllegalArgumentException("Result class must not be null.");
         }
 
         resultClass = resCls;
         this.allowFailOnInit = allowFailOnInit;
         eventListeners = new EventListenerList();
         updateParameters(params);
     }
 
     /**
      * {@inheritDoc} This implementation also takes care that the event listener is added to the managed configuration
      * object.
      *
      * @throws IllegalArgumentException if the event type or the listener is <strong>null</strong>
      */
     @Override
     public <E extends Event> void addEventListener(final EventType<E> eventType, final EventListener<? super E> listener) {
         installEventListener(eventType, listener);
     }
 
     /**
      * Adds the content of the given map to the already existing initialization parameters.
      *
      * @param params the map with additional initialization parameters; may be <strong>null</strong>, then this call has no effect
      * @return a reference to this builder for method chaining
      */
     public synchronized BasicConfigurationBuilder<T> addParameters(final Map<String, Object> params) {
         final Map<String, Object> newParams = new HashMap<>(getParameters());
         if (params != null) {
             newParams.putAll(params);
         }
         updateParameters(newParams);
         return this;
     }
 
     /**
      * Checks whether the class of the result configuration is compatible with this builder's result class. This is done to
      * ensure that only objects of the expected result class are created.
      *
      * @param inst the result instance to be checked
      * @throws ConfigurationRuntimeException if an invalid result class is detected
      */
     private void checkResultInstance(final Object inst) {
         if (!getResultClass().isInstance(inst)) {
             throw new ConfigurationRuntimeException("Incompatible result object: " + inst);
         }
     }
 
     /**
      * Appends the content of the specified {@code BuilderParameters} objects to the current initialization parameters.
      * Calling this method multiple times will create a union of the parameters provided.
      *
      * @param params an arbitrary number of objects with builder parameters
      * @return a reference to this builder for method chaining
      * @throws NullPointerException if a <strong>null</strong> array is passed
      */
     public BasicConfigurationBuilder<T> configure(final BuilderParameters... params) {
         final Map<String, Object> newParams = new HashMap<>();
         for (final BuilderParameters p : params) {
             newParams.putAll(p.getParameters());
             handleEventListenerProviders(p);
         }
         return setParameters(newParams);
     }
 
     /**
      * Connects this builder with a {@code ReloadingController}. With this method support for reloading can be added to an
      * arbitrary builder object. Event listeners are registered at the reloading controller and this builder with connect
      * both objects:
      * <ul>
      * <li>When the reloading controller detects that a reload is required, the builder's {@link #resetResult()} method is
      * called; so the managed result object is invalidated.</li>
      * <li>When a new result object has been created the controller's reloading state is reset, so that new changes can be
      * detected again.</li>
      * </ul>
      *
      * @param controller the {@code ReloadingController} to connect to (must not be <strong>null</strong>)
      * @throws IllegalArgumentException if the controller is <strong>null</strong>
      */
     public final void connectToReloadingController(final ReloadingController controller) {
         if (controller == null) {
             throw new IllegalArgumentException("ReloadingController must not be null.");
         }
         ReloadingBuilderSupportListener.connect(this, controller);
     }
 
     /**
      * Copies all {@code EventListener} objects registered at this builder to the specified target configuration builder.
      * This method is intended to be used by derived classes which support inheritance of their properties to other builder
      * objects.
      *
      * @param target the target configuration builder (must not be <strong>null</strong>)
      * @throws NullPointerException if the target builder is <strong>null</strong>
      */
     protected synchronized void copyEventListeners(final BasicConfigurationBuilder<?> target) {
         copyEventListeners(target, eventListeners);
     }
 
     /**
      * Copies all event listeners in the specified list to the specified target configuration builder. This method is
      * intended to be used by derived classes which have to deal with managed configuration builders that need to be
      * initialized with event listeners.
      *
      * @param target the target configuration builder (must not be <strong>null</strong>)
      * @param listeners the event listeners to be copied over
      * @throws NullPointerException if the target builder is <strong>null</strong>
      */
     protected void copyEventListeners(final BasicConfigurationBuilder<?> target, final EventListenerList listeners) {
         target.eventListeners.addAll(listeners);
     }
 
     /**
      * Creates a new, initialized result object. This method is called by {@code getConfiguration()} if no valid result
      * object exists. This base implementation performs two steps:
      * <ul>
      * <li>{@code createResultInstance()} is called to create a new, uninitialized result object.</li>
      * <li>{@code initResultInstance()} is called to process all initialization parameters.</li>
      * </ul>
      * It also evaluates the <em>allowFailOnInit</em> flag, i.e. if initialization causes an exception and this flag is set,
      * the exception is ignored, and the newly created, uninitialized configuration is returned. Note that this method is
      * called in a synchronized block.
      *
      * @return the newly created result object
      * @throws ConfigurationException if an error occurs
      */
     protected T createResult() throws ConfigurationException {
         final T resObj = createResultInstance();
 
         try {
             initResultInstance(resObj);
         } catch (final ConfigurationException cex) {
             if (!isAllowFailOnInit()) {
                 throw cex;
             }
         }
 
         return resObj;
     }
 
     /**
      * Creates a new {@code BeanDeclaration} which is used for creating new result objects dynamically. This implementation
      * creates a specialized {@code BeanDeclaration} object that is initialized from the given map of initialization
      * parameters. The {@code BeanDeclaration} must be initialized with the result class of this builder, otherwise
      * exceptions will be thrown when the result object is created. Note: This method is invoked in a synchronized block.
      *
      * @param params a snapshot of the current initialization parameters
      * @return the {@code BeanDeclaration} for creating result objects
      * @throws ConfigurationException if an error occurs
      */
     protected BeanDeclaration createResultDeclaration(final Map<String, Object> params) throws ConfigurationException {
         return new BeanDeclaration() {
             @Override
             public String getBeanClassName() {
                 return getResultClass().getName();
             }
 
             @Override
             public String getBeanFactoryName() {
                 return null;
             }
 
             @Override
             public Object getBeanFactoryParameter() {
                 return null;
             }
 
             @Override
             public Map<String, Object> getBeanProperties() {
                 // the properties are equivalent to the parameters
                 return params;
             }
 
             @Override
             public Collection<ConstructorArg> getConstructorArgs() {
                 // no constructor arguments
                 return Collections.emptySet();
             }
 
             @Override
             public Map<String, Object> getNestedBeanDeclarations() {
                 // no nested beans
                 return Collections.emptyMap();
             }
         };
     }
 
     /**
      * Creates the new, uninitialized result object. This is the first step of the process of producing a result object for
      * this builder. This implementation uses the {@link BeanHelper} class to create a new object based on the
      * {@link BeanDeclaration} returned by {@link #getResultDeclaration()}. Note: This method is invoked in a synchronized
      * block.
      *
      * @return the newly created, yet uninitialized result object
      * @throws ConfigurationException if an exception occurs
      */
     protected T createResultInstance() throws ConfigurationException {
         final Object bean = fetchBeanHelper().createBean(getResultDeclaration());
         checkResultInstance(bean);
         return getResultClass().cast(bean);
     }
 
     /**
      * Obtains the {@code BeanHelper} object to be used when dealing with bean declarations. This method checks whether this
      * builder was configured with a specific {@code BeanHelper} instance. If so, this instance is used. Otherwise, the
      * default {@code BeanHelper} is returned.
      *
      * @return the {@code BeanHelper} to be used
      */
     protected final BeanHelper fetchBeanHelper() {
         final BeanHelper helper = BasicBuilderParameters.fetchBeanHelper(getParameters());
         return helper != null ? helper : BeanHelper.INSTANCE;
     }
 
     /**
      * Returns an {@code EventSource} for the current result object. If there is no current result or if it does not extend
      * {@code EventSource}, a dummy event source is returned.
      *
      * @return the {@code EventSource} for the current result object
      */
     private EventSource fetchEventSource() {
         return ConfigurationUtils.asEventSource(result, true);
     }
 
     /**
      * Sends the specified builder event to all registered listeners.
      *
      * @param event the event to be fired
      */
     protected void fireBuilderEvent(final ConfigurationBuilderEvent event) {
         eventListeners.fire(event);
     }
 
     /**
      * {@inheritDoc} This implementation creates the result configuration on first access. Later invocations return the same
      * object until this builder is reset. The double-check idiom for lazy initialization is used (Bloch, Effective Java,
      * item 71).
      */
     @Override
     public T getConfiguration() throws ConfigurationException {
         fireBuilderEvent(new ConfigurationBuilderEvent(this, ConfigurationBuilderEvent.CONFIGURATION_REQUEST));
 
         T resObj = result;
         boolean created = false;
         if (resObj == null) {
             synchronized (this) {
                 resObj = result;
                 if (resObj == null) {
                     result = resObj = createResult();
                     created = true;
                 }
             }
         }
 
         if (created) {
             fireBuilderEvent(new ConfigurationBuilderResultCreatedEvent(this, ConfigurationBuilderResultCreatedEvent.RESULT_CREATED, resObj));
         }
         return resObj;
     }
 
     /**
      * Gets a map with initialization parameters where all parameters starting with the reserved prefix have been
      * filtered out.
      *
      * @return the filtered parameters map
      */
     private Map<String, Object> getFilteredParameters() {
         final Map<String, Object> filteredMap = new HashMap<>(getParameters());
         filteredMap.keySet().removeIf(key -> key.startsWith(BuilderParameters.RESERVED_PARAMETER_PREFIX));
         return filteredMap;
     }
 
     /**
      * Gets a (unmodifiable) map with the current initialization parameters set for this builder. The map is populated
      * with the parameters set using the various configuration options.
      *
      * @return a map with the current set of initialization parameters
      */
     protected final synchronized Map<String, Object> getParameters() {
         if (parameters != null) {
             return parameters;
         }
         return Collections.emptyMap();
     }
 
     /**
      * Gets the result class of this builder. The objects produced by this builder have the class returned here.
      *
      * @return the result class of this builder
      */
     public Class<? extends T> getResultClass() {
         return resultClass;
     }
 
     /**
      * Gets the {@code BeanDeclaration} that is used to create and initialize result objects. The declaration is created
      * on first access (by invoking {@link #createResultDeclaration(Map)}) based on the current initialization parameters.
      *
      * @return the {@code BeanDeclaration} for dynamically creating a result object
      * @throws ConfigurationException if an error occurs
      */
     protected final synchronized BeanDeclaration getResultDeclaration() throws ConfigurationException {
         if (resultDeclaration == null) {
             resultDeclaration = createResultDeclaration(getFilteredParameters());
         }
         return resultDeclaration;
     }
 
     /**
      * Checks whether the specified parameters object implements the {@code EventListenerProvider} interface. If so, the
      * event listeners it provides are added to this builder.
      *
      * @param params the parameters object
      */
     private void handleEventListenerProviders(final BuilderParameters params) {
         if (params instanceof EventListenerProvider) {
             eventListeners.addAll(((EventListenerProvider) params).getListeners());
         }
     }
 
     /**
      * Performs special initialization of the result object. This method is called after parameters have been set on a newly
      * created result instance. If supported by the result class, the {@code initialize()} method is now called.
      *
      * @param obj the newly created result object
      */
     private void handleInitializable(final T obj) {
         if (obj instanceof Initializable) {
             ((Initializable) obj).initialize();
         }
     }
 
     /**
      * Initializes a newly created result object. This is the second step of the process of producing a result object for
      * this builder. This implementation uses the {@link BeanHelper} class to initialize the object's property based on the
      * {@link BeanDeclaration} returned by {@link #getResultDeclaration()}. Note: This method is invoked in a synchronized
      * block. This is required because internal state is accessed. Sub classes must not call this method without proper
      * synchronization.
      *
      * @param obj the object to be initialized
      * @throws ConfigurationException if an error occurs
      */
     protected void initResultInstance(final T obj) throws ConfigurationException {
         fetchBeanHelper().initBean(obj, getResultDeclaration());
         registerEventListeners(obj);
         handleInitializable(obj);
     }
 
     /**
      * Adds the specified event listener to this object. This method is called by {@code addEventListener()}, it does the
      * actual listener registration. Because it is final it can be called by sub classes in the constructor if there is
      * already the need to register an event listener.
      *
      * @param eventType the event type object
      * @param listener the listener to be registered
      * @param <E> the event type
      */
     protected final <E extends Event> void installEventListener(final EventType<E> eventType, final EventListener<? super E> listener) {
         fetchEventSource().addEventListener(eventType, listener);
         eventListeners.addEventListener(eventType, listener);
     }
 
     /**
      * Returns the <em>allowFailOnInit</em> flag. See the header comment for information about this flag.
      *
      * @return the <em>allowFailOnInit</em> flag
      */
     public boolean isAllowFailOnInit() {
         return allowFailOnInit;
     }
 
     /**
      * Registers the available event listeners at the given object. This method is called for each result object created by
      * the builder.
      *
      * @param obj the object to initialize
      */
     private void registerEventListeners(final T obj) {
         final EventSource evSrc = ConfigurationUtils.asEventSource(obj, true);
         eventListeners.getRegistrations().forEach(regData -> registerListener(evSrc, regData));
     }
 
     /**
      * {@inheritDoc} This implementation also takes care that the event listener is removed from the managed configuration
      * object.
      */
     @Override
     public <E extends Event> boolean removeEventListener(final EventType<E> eventType, final EventListener<? super E> listener) {
         fetchEventSource().removeEventListener(eventType, listener);
         return eventListeners.removeEventListener(eventType, listener);
     }
 
     /**
      * Removes all available event listeners from the given result object. This method is called when the result of this
      * builder is reset. Then the old managed configuration should no longer generate events.
      *
      * @param obj the affected result object
      */
     private void removeEventListeners(final T obj) {
         final EventSource evSrc = ConfigurationUtils.asEventSource(obj, true);
         eventListeners.getRegistrations().forEach(regData -> removeListener(evSrc, regData));
     }
 
     /**
      * Resets this builder. This is a convenience method which combines calls to {@link #resetResult()} and
      * {@link #resetParameters()}.
      */
     public synchronized void reset() {
         resetParameters();
         resetResult();
     }
 
     /**
      * Removes all initialization parameters of this builder. This method can be called if this builder is to be reused for
      * creating result objects with a different configuration.
      */
     public void resetParameters() {
         setParameters(null);
     }
 
     /**
      * Clears an existing result object. An invocation of this method causes a new {@code ImmutableConfiguration} object to
      * be created the next time {@link #getConfiguration()} is called.
      */
     public void resetResult() {
         final T oldResult;
         synchronized (this) {
             oldResult = result;
             result = null;
             resultDeclaration = null;
         }
 
         if (oldResult != null) {
             removeEventListeners(oldResult);
         }
         fireBuilderEvent(new ConfigurationBuilderEvent(this, ConfigurationBuilderEvent.RESET));
     }
 
     /**
      * Sets the initialization parameters of this builder. Already existing parameters are replaced by the content of the
      * given map.
      *
      * @param params the new initialization parameters of this builder; can be <strong>null</strong>, then all initialization
      *        parameters are removed
      * @return a reference to this builder for method chaining
      */
     public synchronized BasicConfigurationBuilder<T> setParameters(final Map<String, Object> params) {
         updateParameters(params);
         return this;
     }
 
     /**
      * Replaces the current map with parameters by a new one.
      *
      * @param newParams the map with new parameters (may be <strong>null</strong>)
      */
     private void updateParameters(final Map<String, Object> newParams) {
         final Map<String, Object> map = new HashMap<>();
         if (newParams != null) {
             map.putAll(newParams);
         }
         parameters = Collections.unmodifiableMap(map);
     }
 }