/*
 * 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.
 */
// $Id: ValidatorHandler.java 446598 2006-09-15 12:55:40Z jeremias $

package javax.xml.validation;

import org.w3c.dom.ls.LSResourceResolver;
import org.xml.sax.ContentHandler;
import org.xml.sax.ErrorHandler;
import org.xml.sax.SAXNotRecognizedException;
import org.xml.sax.SAXNotSupportedException;

/**
 * Streaming validator that works on SAX stream.
 * 
 * <p>
 * A {@link ValidatorHandler} object is a thread-unsafe, non-reentrant object.
 * In other words, it is the application's responsibility to make
 * sure that one {@link ValidatorHandler} object is not used from
 * more than one thread at any given time.
 * 
 * <p>
 * {@link ValidatorHandler} checks if the SAX events follow 
 * the set of constraints described in the associated {@link Schema},
 * and additionally it may modify the SAX events (for example
 * by adding default values, etc.)
 * 
 * <p>
 * {@link ValidatorHandler} extends from {@link ContentHandler},
 * but it refines the underlying {@link ContentHandler} in
 * the following way:
 * <ol>
 *  <li>startElement/endElement events must receive non-null String
 *      for <code>uri</code>, <code>localName</code>, and <code>qname</code>,
 *      even though SAX allows some of them to be null.
 *      Similarly, the user-specified {@link ContentHandler} will receive non-null
 *      Strings for all three parameters.
 * 
 *  <li>Applications must ensure that {@link ValidatorHandler}'s
 *      {@link ContentHandler#startPrefixMapping(String,String)} and
 *      {@link ContentHandler#endPrefixMapping(String)} are invoked
 *      properly. Similarly, the user-specified {@link ContentHandler}
 *      will receive startPrefixMapping/endPrefixMapping events.
 *      If the {@link ValidatorHandler} introduces additional namespace
 *      bindings, the user-specified {@link ContentHandler} will receive
 *      additional startPrefixMapping/endPrefixMapping events.
 * 
 *  <li>{@link org.xml.sax.Attributes} for the
 *      {@link ContentHandler#startElement(String,String,String,Attributes)} method
 *      may or may not include xmlns* attributes.
 * </ol>
 * 
 * <p>
 * A {@link ValidatorHandler} is automatically reset every time
 * the startDocument method is invoked.
 * 
 * <h2>Recognized Properties and Features</h2>
 * <p>
 * This spec defines the following feature that must be recognized
 * by all {@link ValidatorHandler} implementations.
 * 
 * <h3><code>http://xml.org/sax/features/namespace-prefixes</code></h3>
 * <p>
 * This feature controls how a {@link ValidatorHandler} introduces
 * namespace bindings that were not present in the original SAX event
 * stream.
 * When this feature is set to true, it must make
 * sure that the user's {@link ContentHandler} will see 
 * the corresponding <code>xmlns*</code> attribute in
 * the {@link org.xml.sax.Attributes} object of the
 * {@link ContentHandler#startElement(String,String,String,Attributes)}
 * callback. Otherwise, <code>xmlns*</code> attributes must not be
 * added to {@link org.xml.sax.Attributes} that's passed to the
 * user-specified {@link ContentHandler}.
 * <p> 
 * (Note that regardless of this switch, namespace bindings are
 * always notified to applications through 
 * {@link ContentHandler#startPrefixMapping(String,String)} and
 * {@link ContentHandler#endPrefixMapping(String)} methods of the
 * {@link ContentHandler} specified by the user.)
 * 
 * <p>
 * Note that this feature does <em>NOT</em> affect the way
 * a {@link ValidatorHandler} receives SAX events. It merely
 * changes the way it augments SAX events.
 * 
 * <p>This feature is set to <code>false</code> by default.</p>
 * 
 * @author  <a href="mailto:Kohsuke.Kawaguchi@Sun.com">Kohsuke Kawaguchi</a>
 * @version $Revision: 446598 $, $Date: 2006-09-15 15:55:40 +0300 (Fri, 15 Sep 2006) $
 * @since 1.5
 */
public abstract class ValidatorHandler implements ContentHandler {
    
    /**
     * Constructor for derived classes.
     * 
     * <p>
     * The constructor does nothing.
     * 
     * <p>
     * Derived classes must create {@link ValidatorHandler} objects that have
     * <tt>null</tt> {@link ErrorHandler} and
     * <tt>null</tt> {@link LSResourceResolver}.
     */
    protected ValidatorHandler() {
    }
    
    /**
     * Sets the {@link ContentHandler} which receives
     * the augmented validation result.
     *
     * <p>
     * When a {@link ContentHandler} is specified, a
     * {@link ValidatorHandler} will work as a filter
     * and basically copy the incoming events to the
     * specified {@link ContentHandler}.
     * 
     * <p>
     * In doing so, a {@link ValidatorHandler} may modify
     * the events, for example by adding defaulted attributes.
     * 
     * <p>
     * A {@link ValidatorHandler} may buffer events to certain
     * extent, but to allow {@link ValidatorHandler} to be used
     * by a parser, the following requirement has to be met.
     * 
     * <ol>
     *  <li>When
     *      {@link ContentHandler#startElement(String, String, String, Attributes)},
     *      {@link ContentHandler#endElement(String, String, String)},
     *      {@link ContentHandler#startDocument()}, or
     *      {@link ContentHandler#endDocument()}
     *      are invoked on a {@link ValidatorHandler},
     *      the same method on the user-specified {@link ContentHandler}
     *      must be invoked for the same event before the callback
     *      returns.
     *  <li>{@link ValidatorHandler} may not introduce new elements that
     *      were not present in the input.
     * 
     *  <li>{@link ValidatorHandler} may not remove attributes that were
     *      present in the input.
     * </ol> 
     * 
     * <p>
     * When a callback method on the specified {@link ContentHandler}
     * throws an exception, the same exception object must be thrown
     * from the {@link ValidatorHandler}. The {@link ErrorHandler}
     * should not be notified of such an exception.
     * 
     * <p>
     * This method can be called even during a middle of a validation.
     *
     * @param receiver
     *      A {@link ContentHandler} or a null value. 
     */
    public abstract void setContentHandler(ContentHandler receiver);
    
    /**
     * Gets the {@link ContentHandler} which receives the
     * augmented validation result.
     * 
     * @return
     *      This method returns the object that was last set through
     *      the {@link #getContentHandler()} method, or null
     *      if that method has never been called since this {@link ValidatorHandler}
     *      has created.
     * 
     * @see #setContentHandler(ContentHandler)
     */
    public abstract ContentHandler getContentHandler();
    
    /**
     * Sets the {@link ErrorHandler} to receive errors encountered
     * during the validation.
     * 
     * <p>
     * Error handler can be used to customize the error handling process
     * during a validation. When an {@link ErrorHandler} is set,
     * errors found during the validation will be first sent
     * to the {@link ErrorHandler}.
     * 
     * <p>
     * The error handler can abort further validation immediately
     * by throwing {@link org.xml.sax.SAXException} from the handler. Or for example
     * it can print an error to the screen and try to continue the
     * validation by returning normally from the {@link ErrorHandler} 
     * 
     * <p>
     * If any {@link Throwable} is thrown from an {@link ErrorHandler},
     * the same {@link Throwable} object will be thrown toward the
     * root of the call stack.
     * 
     * <p>
     * {@link ValidatorHandler} is not allowed to
     * throw {@link org.xml.sax.SAXException} without first reporting it to
     * {@link ErrorHandler}.
     * 
     * <p>
     * When the {@link ErrorHandler} is null, the implementation will
     * behave as if the following {@link ErrorHandler} is set:
     * <pre>
     * class DraconianErrorHandler implements {@link ErrorHandler} {
     *     public void fatalError( {@link org.xml.sax.SAXParseException} e ) throws {@link org.xml.sax.SAXException} {
     *         throw e;
     *     }
     *     public void error( {@link org.xml.sax.SAXParseException} e ) throws {@link org.xml.sax.SAXException} {
     *         throw e;
     *     }
     *     public void warning( {@link org.xml.sax.SAXParseException} e ) throws {@link org.xml.sax.SAXException} {
     *         // noop
     *     }
     * }
     * </pre>
     * 
     * <p>
     * When a new {@link ValidatorHandler} object is created, initially
     * this field is set to null.
     * 
     * @param   errorHandler
     *      A new error handler to be set. This parameter can be null.
     */
    public abstract void setErrorHandler(ErrorHandler errorHandler);
    
    /**
     * Gets the current {@link ErrorHandler} set to this {@link ValidatorHandler}.
     * 
     * @return
     *      This method returns the object that was last set through
     *      the {@link #setErrorHandler(ErrorHandler)} method, or null
     *      if that method has never been called since this {@link ValidatorHandler}
     *      has created.
     * 
     * @see #setErrorHandler(ErrorHandler)
     */
    public abstract ErrorHandler getErrorHandler();
    
    /**
     * Sets the {@link LSResourceResolver} to customize
     * resource resolution while in a validation episode.
     * 
     * <p>
     * {@link ValidatorHandler} uses a {@link LSResourceResolver}
     * when it needs to locate external resources while a validation,
     * although exactly what constitutes "locating external resources" is
     * up to each schema language.
     * 
     * <p>
     * When the {@link LSResourceResolver} is null, the implementation will
     * behave as if the following {@link LSResourceResolver} is set:
     * <pre>
     * class DumbLSResourceResolver implements {@link LSResourceResolver} {
     *     public {@link org.w3c.dom.ls.LSInput} resolveResource(
     *         String publicId, String systemId, String baseURI) {
     *         
     *         return null; // always return null
     *     }
     * }
     * </pre>
     * 
     * <p>
     * If a {@link LSResourceResolver} throws a {@link RuntimeException}
     *  (or instances of its derived classes),
     * then the {@link ValidatorHandler} will abort the parsing and  
     * the caller of the <code>validate</code> method will receive
     * the same {@link RuntimeException}. 
     * 
     * <p>
     * When a new {@link ValidatorHandler} object is created, initially
     * this field is set to null.
     * 
     * @param   resourceResolver
     *      A new resource resolver to be set. This parameter can be null.
     */
    public abstract void setResourceResolver(LSResourceResolver resourceResolver);
    
    /**
     * Gets the current {@link LSResourceResolver} set to this {@link ValidatorHandler}.
     * 
     * @return
     *      This method returns the object that was last set through
     *      the {@link #setResourceResolver(LSResourceResolver)} method, or null
     *      if that method has never been called since this {@link ValidatorHandler}
     *      has created.
     * 
     * @see #setErrorHandler(ErrorHandler)
     */
    public abstract LSResourceResolver getResourceResolver();
    
    /**
     * Obtains the {@link TypeInfoProvider} implementation of this
     * {@link ValidatorHandler}.
     * 
     * <p>
     * The obtained {@link TypeInfoProvider} can be queried during a parse
     * to access the type information determined by the validator.
     * 
     * <p>
     * Some schema languages do not define the notion of type,
     * for those languages, this method may not be supported.
     * However, to be compliant with this specification, implementations
     * for W3C XML Schema 1.0 must support this operation. 
     * 
     * @return
     *      null if the validator / schema language does not support
     *      the notion of {@link org.w3c.dom.TypeInfo}.
     *      Otherwise a non-null valid {@link TypeInfoProvider}.
     */
    public abstract TypeInfoProvider getTypeInfoProvider();
    
    
    /**
     * Look up the value of a feature flag.
     *
     * <p>The feature name is any fully-qualified URI.  It is
     * possible for a {@link ValidatorHandler} to recognize a feature name but
     * temporarily be unable to return its value.
     * Some feature values may be available only in specific
     * contexts, such as before, during, or after a validation.
     *
     * <p>Implementors are free (and encouraged) to invent their own features,
     * using names built on their own URIs.</p>
     *
     * @param name The feature name, which is a non-null fully-qualified URI.
     * @return The current value of the feature (true or false).
     * @exception org.xml.sax.SAXNotRecognizedException If the feature
     *            value can't be assigned or retrieved.
     * @exception org.xml.sax.SAXNotSupportedException When the
     *            {@link ValidatorHandler} recognizes the feature name but 
     *            cannot determine its value at this time.
     * @throws NullPointerException
     *          When the name parameter is null.
     * @see #setFeature(String, boolean)
     */
    public boolean getFeature(String name) throws SAXNotRecognizedException, SAXNotSupportedException {
        if(name==null)
            throw new NullPointerException();
        throw new SAXNotRecognizedException(name);
    }
    
    /**
     * Set the value of a feature flag.
     *
     * <p>
     * Feature can be used to control the way a {@link ValidatorHandler}
     * parses schemas, although {@link ValidatorHandler}s are not required
     * to recognize any specific property names.</p>
     *
     * <p>The feature name is any fully-qualified URI.  It is
     * possible for a {@link ValidatorHandler} to expose a feature value but
     * to be unable to change the current value.
     * Some feature values may be immutable or mutable only 
     * in specific contexts, such as before, during, or after 
     * a validation.</p>
     *
     * @param name The feature name, which is a non-null fully-qualified URI.
     * @param value The requested value of the feature (true or false).
     * 
     * @exception org.xml.sax.SAXNotRecognizedException If the feature
     *            value can't be assigned or retrieved.
     * @exception org.xml.sax.SAXNotSupportedException When the
     *            {@link ValidatorHandler} recognizes the feature name but 
     *            cannot set the requested value.
     * @throws NullPointerException
     *          When the name parameter is null.
     * 
     * @see #getFeature(String)
     */
    public void setFeature(String name, boolean value) throws SAXNotRecognizedException, SAXNotSupportedException {
        if(name==null)
            throw new NullPointerException();
        throw new SAXNotRecognizedException(name);
    }
    
    /**
     * Set the value of a property.
     *
     * <p>The property name is any fully-qualified URI.  It is
     * possible for a {@link ValidatorHandler} to recognize a property name but
     * to be unable to change the current value.
     * Some property values may be immutable or mutable only 
     * in specific contexts, such as before, during, or after 
     * a validation.</p>
     *
     * <p>{@link ValidatorHandler}s are not required to recognize setting
     * any specific property names.</p>
     *
     * @param name The property name, which is a non-null fully-qualified URI.
     * @param object The requested value for the property.
     * 
     * @exception org.xml.sax.SAXNotRecognizedException If the property
     *            value can't be assigned or retrieved.
     * @exception org.xml.sax.SAXNotSupportedException When the
     *            {@link ValidatorHandler} recognizes the property name but 
     *            cannot set the requested value.
     * @throws NullPointerException
     *          When the name parameter is null.
     */
    public void setProperty(String name, Object object) throws SAXNotRecognizedException, SAXNotSupportedException {
        if(name==null)
            throw new NullPointerException();
        throw new SAXNotRecognizedException(name);
    }
    
    /**
     * Look up the value of a property.
     *
     * <p>The property name is any fully-qualified URI.  It is
     * possible for a {@link ValidatorHandler} to recognize a property name but
     * temporarily be unable to return its value.
     * Some property values may be available only in specific
     * contexts, such as before, during, or after a validation.</p>
     *
     * <p>{@link ValidatorHandler}s are not required to recognize any specific
     * property names.</p>
     *
     * <p>Implementors are free (and encouraged) to invent their own properties,
     * using names built on their own URIs.</p>
     *
     * @param name The property name, which is a non-null fully-qualified URI.
     * @return The current value of the property.
     * @exception org.xml.sax.SAXNotRecognizedException If the property
     *            value can't be assigned or retrieved.
     * @exception org.xml.sax.SAXNotSupportedException When the
     *            XMLReader recognizes the property name but 
     *            cannot determine its value at this time.
     * @throws NullPointerException
     *          When the name parameter is null.
     * @see #setProperty(String, Object)
     */
    public Object getProperty(String name) throws SAXNotRecognizedException, SAXNotSupportedException {
        if(name==null)
            throw new NullPointerException();
        throw new SAXNotRecognizedException(name);
    }
}
