/*
    * $Id: DefinitionManager.java 616890 2008-01-30 20:16:51Z apetrelli $
    *
    * 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.tiles.impl.mgmt;
  
  import org.apache.tiles.Attribute;
  import org.apache.tiles.Definition;
  import org.apache.tiles.context.TilesRequestContext;
  import org.apache.tiles.definition.DefinitionsFactory;
  import org.apache.tiles.definition.DefinitionsFactoryException;
  import org.apache.tiles.definition.NoSuchDefinitionException;
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  
  import java.util.HashMap;
  import java.util.Map;
  
  /***
   * Manages custom and configured definitions, so they can be used by the
   * container, instead of using a simple {@link DefinitionsFactory}.
   *
   * @version $Rev: 616890 $ $Date: 2008-01-30 21:16:51 +0100 (Wed, 30 Jan 2008) $
   */
  public class DefinitionManager {
  
      /***
       * The logging object.
       */
      private static final Log LOG =
          LogFactory.getLog(DefinitionManager.class);
  
      /***
       * The default name of the attribute in which storing custom definitions.
       */
      private static final String DEFAULT_DEFINITIONS_ATTRIBUTE_NAME =
          "org.apache.tiles.impl.mgmt.DefinitionManager.DEFINITIONS";
  
      /***
       * The definitions factory to use to get main definitions.
       */
      private DefinitionsFactory factory;
  
      /***
       * The name of the attribute in which storing custom definitions.
       */
      private String definitionsAttributeName;
  
      /***
       * Constructor.
       */
      public DefinitionManager() {
          definitionsAttributeName = DEFAULT_DEFINITIONS_ATTRIBUTE_NAME;
      }
  
      /***
       * Constructor.
       *
       * @param definitionsAttributeName The name of the attribute in which
       * storing custom definitions.
       */
      public DefinitionManager(String definitionsAttributeName) {
          this.definitionsAttributeName = definitionsAttributeName;
          if (this.definitionsAttributeName == null) {
              this.definitionsAttributeName = DEFAULT_DEFINITIONS_ATTRIBUTE_NAME;
          }
      }
  
      /***
       * Returns the used definitions factory.
       *
       * @return The used definitions factory.
       */
      public DefinitionsFactory getFactory() {
          return factory;
      }
  
      /***
       * Sets the definitions factory to use.
       *
       * @param factory The definitions factory.
       */
      public void setFactory(DefinitionsFactory factory) {
         this.factory = factory;
     }
 
     /***
      * Returns a definition by name.
      *
      * @param definition The name of the definition.
      * @param request The current request.
      * @return The requested definition, either main or custom.
      * @throws DefinitionsFactoryException If something goes wrong when
      * obtaining a main definition.
      */
     public Definition getDefinition(String definition, TilesRequestContext request)
         throws DefinitionsFactoryException {
         Map<String, Definition> definitions =
             getDefinitions(request);
         if (definitions != null && definitions.containsKey(definition)) {
             return definitions.get(definition);
         }
         return getFactory().getDefinition(definition, request);
     }
 
     /***
      * Adds a definition to the set of custom ones.
      *
      * @param definition The definition to add.
      * @param request The current request.
      * @throws DefinitionsFactoryException If something goes wrong during the
      * addition.
      */
     public void addDefinition(Definition definition,
             TilesRequestContext request)
         throws DefinitionsFactoryException {
         validate(definition);
 
         if (definition.isExtending()) {
             this.resolveInheritance(definition, request);
         }
 
         getOrCreateDefinitions(request).put(definition.getName(), definition);
     }
 
     /***
      * Validates a custom definition.
      *
      * @param definition The definition to validate.
      */
     private void validate(Definition definition) {
         Map<String, Attribute> attrs = definition.getAttributes();
         for (Attribute attribute : attrs.values()) {
             if (attribute.getValue() == null) {
                 throw new IllegalArgumentException("Attribute value not defined");
             }
         }
     }
 
     /***
      * Resolve inheritance.
      * First, resolve parent's inheritance, then set template to the parent's
      * template.
      * Also copy attributes setted in parent, and not set in child
      * If instance doesn't extend anything, do nothing.
      *
      * @param definition The definition that needs to have its inheritances
      * resolved.
      * @param request The current request.
      * @throws DefinitionsFactoryException If an inheritance can not be solved.
      */
     protected void resolveInheritance(Definition definition,
             TilesRequestContext request)
         throws DefinitionsFactoryException  {
         // Already done, or not needed ?
         if (!definition.isExtending()) {
             return;
         }
 
         if (LOG.isDebugEnabled()) {
             LOG.debug("Resolve definition for child name='"
                 + definition.getName()
                 + "' extends='" + definition.getExtends() + "'.");
         }
 
         // TODO Factories our factory implementations will be context agnostic,
         //  however, this may cause errors for other implementations.
         //  we should probably make all factories agnostic and allow the manager to
         //  utilize the correct factory based on the context.
         Definition parent = getDefinition(definition.getExtends(), request);
 
         if (parent == null) { // error
             String msg = "Error while resolving definition inheritance: child '"
                 + definition.getName()
                 + "' can't find its ancestor '"
                 + definition.getExtends()
                 + "'. Please check your description file.";
             LOG.error(msg);
             // to do : find better exception
             throw new NoSuchDefinitionException(msg);
         }
 
         // Resolve parent before itself.
         resolveInheritance(parent, request);
         overload(parent, definition);
     }
 
     /***
      * Overloads a child definition with a given parent.
      * All attributes present in child are kept. All missing attributes are
      * copied from the parent.
      * Special attribute 'template','role' and 'extends' are overloaded in child
      * if not defined
      *
      * @param parent The parent definition.
      * @param child  The child that will be overloaded.
      */
     // FIXME This is the same as DefinitionsImpl.overload.
     protected void overload(Definition parent, Definition child) {
         // Iterate on each parent's attribute and add it if not defined in child.
         for (Map.Entry<String, Attribute> entry : parent.getAttributes().entrySet()) {
             if (!child.hasAttributeValue(entry.getKey())) {
                 child.putAttribute(entry.getKey(), new Attribute(entry.getValue()));
             }
         }
 
         if (child.getTemplate() == null) {
             child.setTemplate(parent.getTemplate());
         }
 
         if (child.getRoles() == null) {
             child.setRoles(parent.getRoles());
         }
 
         if (child.getPreparer() == null) {
             child.setPreparer(parent.getPreparer());
         }
     }
 
     /***
      * Returns the map with custom definitions for the current request.
      *
      * @param request The current request.
      * @return A map that connects a definition name to a definition.
      */
     @SuppressWarnings("unchecked")
     protected Map<String, Definition> getDefinitions(
             TilesRequestContext request) {
         return (Map<String, Definition>) request.getRequestScope()
                 .get(definitionsAttributeName);
     }
 
     /***
      * Returns a map of type "definition name -> definition" and, if it has not
      * been defined before, creates one.
      *
      * @param request The current request.
      * @return A map that connects a definition name to a definition.
      */
     @SuppressWarnings("unchecked")
     protected Map<String, Definition> getOrCreateDefinitions(
             TilesRequestContext request) {
         Map<String, Definition> definitions =
             (Map<String, Definition>) request
                 .getRequestScope().get(definitionsAttributeName);
         if (definitions == null) {
             definitions = new HashMap<String, Definition>();
             request.getRequestScope()
                     .put(definitionsAttributeName, definitions);
         }
 
         return definitions;
     }
 }