/*
    * 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.builder.combined;
  
  import java.lang.reflect.Constructor;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Map;
  
  import org.apache.commons.configuration2.Configuration;
  import org.apache.commons.configuration2.ConfigurationUtils;
  import org.apache.commons.configuration2.builder.BasicConfigurationBuilder;
  import org.apache.commons.configuration2.builder.BuilderParameters;
  import org.apache.commons.configuration2.builder.ConfigurationBuilder;
  import org.apache.commons.configuration2.ex.ConfigurationException;
  
  /**
   * <p>
   * A fully-functional, reflection-based implementation of the {@code ConfigurationBuilderProvider} interface which can
   * deal with the default tags defining configuration sources.
   * </p>
   * <p>
   * An instance of this class is initialized with the names of the {@code ConfigurationBuilder} class used by this
   * provider and the concrete {@code Configuration} class. The {@code ConfigurationBuilder} class must be derived from
   * {@link BasicConfigurationBuilder}. When asked for the builder object, an instance of the builder class is created and
   * initialized from the bean declaration associated with the current configuration source.
   * </p>
   * <p>
   * {@code ConfigurationBuilder} objects are configured using parameter objects. When declaring configuration sources in
   * XML it should not be necessary to define the single parameter objects. Rather, simple and complex properties are set
   * in the typical way of a bean declaration (i.e. as attributes of the current XML element or as child elements). This
   * class creates all supported parameter objects (whose names also must be provided at construction time) and takes care
   * that their properties are initialized according to the current bean declaration.
   * </p>
   * <p>
   * The use of reflection to create builder instances allows a generic implementation supporting many concrete builder
   * classes. Another reason for this approach is that builder classes are only loaded if actually needed. Some
   * specialized {@code Configuration} implementations require specific external dependencies which should not be
   * mandatory for the use of {@code CombinedConfigurationBuilder}. Because such classes are lazily loaded, an application
   * only has to include the dependencies it actually uses.
   * </p>
   *
   * @since 2.0
   */
  public class BaseConfigurationBuilderProvider implements ConfigurationBuilderProvider {
      /** The types of the constructor parameters for a basic builder. */
      private static final Class<?>[] CTOR_PARAM_TYPES = {Class.class, Map.class, Boolean.TYPE};
  
      /** The name of the builder class. */
      private final String builderClass;
  
      /** The name of a builder class with reloading support. */
      private final String reloadingBuilderClass;
  
      /** Stores the name of the configuration class to be created. */
      private final String configurationClass;
  
      /** A collection with the names of parameter classes. */
      private final Collection<String> parameterClasses;
  
      /**
       * Creates a new instance of {@code BaseConfigurationBuilderProvider} and initializes all its properties.
       *
       * @param bldrCls the name of the builder class (must not be <b>null</b>)
       * @param reloadBldrCls the name of a builder class to be used if reloading support is required (<b>null</b> if
       *        reloading is not supported)
       * @param configCls the name of the configuration class (must not be <b>null</b>)
       * @param paramCls a collection with the names of parameters classes
       * @throws IllegalArgumentException if a required parameter is missing
       */
      public BaseConfigurationBuilderProvider(final String bldrCls, final String reloadBldrCls, final String configCls, final Collection<String> paramCls) {
          if (bldrCls == null) {
              throw new IllegalArgumentException("Builder class must not be null!");
          }
          if (configCls == null) {
              throw new IllegalArgumentException("Configuration class must not be null!");
          }
  
          builderClass = bldrCls;
          reloadingBuilderClass = reloadBldrCls;
          configurationClass = configCls;
          parameterClasses = initParameterClasses(paramCls);
      }
  
     /**
      * Gets the name of the class of the builder created by this provider.
      *
      * @return the builder class
      */
     public String getBuilderClass() {
         return builderClass;
     }
 
     /**
      * Gets the name of the class of the builder created by this provider if the reload flag is set. If this method
      * returns <b>null</b>, reloading builders are not supported by this provider.
      *
      * @return the reloading builder class
      */
     public String getReloadingBuilderClass() {
         return reloadingBuilderClass;
     }
 
     /**
      * Gets the name of the configuration class created by the builder produced by this provider.
      *
      * @return the configuration class
      */
     public String getConfigurationClass() {
         return configurationClass;
     }
 
     /**
      * Gets an unmodifiable collection with the names of parameter classes supported by this provider.
      *
      * @return the parameter classes
      */
     public Collection<String> getParameterClasses() {
         return parameterClasses;
     }
 
     /**
      * {@inheritDoc} This implementation delegates to some protected methods to create a new builder instance using
      * reflection and to configure it with parameter values defined by the passed in {@code BeanDeclaration}.
      */
     @Override
     public ConfigurationBuilder<? extends Configuration> getConfigurationBuilder(final ConfigurationDeclaration decl) throws ConfigurationException {
         try {
             final Collection<BuilderParameters> params = createParameterObjects();
             initializeParameterObjects(decl, params);
             final BasicConfigurationBuilder<? extends Configuration> builder = createBuilder(decl, params);
             configureBuilder(builder, decl, params);
             return builder;
         } catch (final ConfigurationException cex) {
             throw cex;
         } catch (final Exception ex) {
             throw new ConfigurationException(ex);
         }
     }
 
     /**
      * Determines the <em>allowFailOnInit</em> flag for the newly created builder based on the given
      * {@code ConfigurationDeclaration}. Some combinations of flags in the declaration say that a configuration source is
      * optional, but an empty instance should be created if its creation fail.
      *
      * @param decl the current {@code ConfigurationDeclaration}
      * @return the value of the <em>allowFailOnInit</em> flag
      */
     protected boolean isAllowFailOnInit(final ConfigurationDeclaration decl) {
         return decl.isOptional() && decl.isForceCreate();
     }
 
     /**
      * Creates a collection of parameter objects to be used for configuring the builder. This method creates instances of
      * the parameter classes passed to the constructor.
      *
      * @return a collection with parameter objects for the builder
      * @throws Exception if an error occurs while creating parameter objects via reflection
      */
     protected Collection<BuilderParameters> createParameterObjects() throws Exception {
         final Collection<BuilderParameters> params = new ArrayList<>(getParameterClasses().size());
         for (final String paramcls : getParameterClasses()) {
             params.add(createParameterObject(paramcls));
         }
         return params;
     }
 
     /**
      * Initializes the parameter objects with data stored in the current bean declaration. This method is called before the
      * newly created builder instance is configured with the parameter objects. It maps attributes of the bean declaration
      * to properties of parameter objects. In addition, it invokes the parent {@code CombinedConfigurationBuilder} so that
      * the parameters object can inherit properties already defined for this builder.
      *
      * @param decl the current {@code ConfigurationDeclaration}
      * @param params the collection with (uninitialized) parameter objects
      * @throws Exception if an error occurs
      */
     protected void initializeParameterObjects(final ConfigurationDeclaration decl, final Collection<BuilderParameters> params) throws Exception {
         inheritParentBuilderProperties(decl, params);
         final MultiWrapDynaBean wrapBean = new MultiWrapDynaBean(params);
         decl.getConfigurationBuilder().initBean(wrapBean, decl);
     }
 
     /**
      * Passes all parameter objects to the parent {@code CombinedConfigurationBuilder} so that properties already defined
      * for the parent builder can be added. This method is called before the parameter objects are initialized from the
      * definition configuration. This way properties from the parent builder are inherited, but can be overridden for child
      * configurations.
      *
      * @param decl the current {@code ConfigurationDeclaration}
      * @param params the collection with (uninitialized) parameter objects
      */
     protected void inheritParentBuilderProperties(final ConfigurationDeclaration decl, final Collection<BuilderParameters> params) {
         params.forEach(p -> decl.getConfigurationBuilder().initChildBuilderParameters(p));
     }
 
     /**
      * Creates a new, uninitialized instance of the builder class managed by this provider. This implementation determines
      * the builder class to be used by delegating to {@code determineBuilderClass()}. It then calls the constructor
      * expecting the configuration class, the map with properties, and the<em>allowFailOnInit</em> flag.
      *
      * @param decl the current {@code ConfigurationDeclaration}
      * @param params initialization parameters for the new builder object
      * @return the newly created builder instance
      * @throws Exception if an error occurs
      */
     protected BasicConfigurationBuilder<? extends Configuration> createBuilder(final ConfigurationDeclaration decl, final Collection<BuilderParameters> params)
         throws Exception {
         final Class<?> bldCls = ConfigurationUtils.loadClass(determineBuilderClass(decl));
         final Class<?> configCls = ConfigurationUtils.loadClass(determineConfigurationClass(decl, params));
         final Constructor<?> ctor = bldCls.getConstructor(CTOR_PARAM_TYPES);
         // ? extends Configuration is the minimum constraint
         @SuppressWarnings("unchecked")
         final BasicConfigurationBuilder<? extends Configuration> builder = (BasicConfigurationBuilder<? extends Configuration>) ctor.newInstance(configCls,
             null, isAllowFailOnInit(decl));
         return builder;
     }
 
     /**
      * Configures a newly created builder instance with its initialization parameters. This method is called after a new
      * instance was created using reflection. This implementation passes the parameter objects to the builder's
      * {@code configure()} method.
      *
      * @param builder the builder to be initialized
      * @param decl the current {@code ConfigurationDeclaration}
      * @param params the collection with initialization parameter objects
      * @throws Exception if an error occurs
      */
     protected void configureBuilder(final BasicConfigurationBuilder<? extends Configuration> builder, final ConfigurationDeclaration decl,
         final Collection<BuilderParameters> params) throws Exception {
         builder.configure(params.toArray(new BuilderParameters[params.size()]));
     }
 
     /**
      * Determines the name of the class to be used for a new builder instance. This implementation selects between the
      * normal and the reloading builder class, based on the passed in {@code ConfigurationDeclaration}. If a reloading
      * builder is desired, but this provider has no reloading support, an exception is thrown.
      *
      * @param decl the current {@code ConfigurationDeclaration}
      * @return the name of the builder class
      * @throws ConfigurationException if the builder class cannot be determined
      */
     protected String determineBuilderClass(final ConfigurationDeclaration decl) throws ConfigurationException {
         if (decl.isReload()) {
             if (getReloadingBuilderClass() == null) {
                 throw new ConfigurationException("No support for reloading for builder class " + getBuilderClass());
             }
             return getReloadingBuilderClass();
         }
         return getBuilderClass();
     }
 
     /**
      * Determines the name of the configuration class produced by the builder. This method is called when obtaining the
      * arguments for invoking the constructor of the builder class. This implementation just returns the pre-configured
      * configuration class name. Derived classes may determine this class name dynamically based on the passed in
      * parameters.
      *
      * @param decl the current {@code ConfigurationDeclaration}
      * @param params the collection with parameter objects
      * @return the name of the builder's result configuration class
      * @throws ConfigurationException if an error occurs
      */
     protected String determineConfigurationClass(final ConfigurationDeclaration decl, final Collection<BuilderParameters> params)
         throws ConfigurationException {
         return getConfigurationClass();
     }
 
     /**
      * Creates an instance of a parameter class using reflection.
      *
      * @param paramcls the parameter class
      * @return the newly created instance
      * @throws Exception if an error occurs
      */
     private static BuilderParameters createParameterObject(final String paramcls) throws ReflectiveOperationException {
         return (BuilderParameters) ConfigurationUtils.loadClass(paramcls).getConstructor().newInstance();
     }
 
     /**
      * Creates a new, unmodifiable collection for the parameter classes.
      *
      * @param paramCls the collection with parameter classes passed to the constructor
      * @return the collection to be stored
      */
     private static Collection<String> initParameterClasses(final Collection<String> paramCls) {
         if (paramCls == null) {
             return Collections.emptySet();
         }
         return Collections.unmodifiableCollection(new ArrayList<>(paramCls));
     }
 }