/*
 * Copyright 2001-2004 The Apache Software Foundation.
 *
 * Licensed 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 javax.xml.transform;

import java.util.Properties;


/**
 * An instance of this abstract class can transform a
 * source tree into a result tree.
 *
 * <p>An instance of this class can be obtained with the <code>
 * {@link TransformerFactory#newTransformer TransformerFactory.newTransformer}
 * method. This instance may then be used to process XML from a
 * variety of sources and write the transformation output to a
 * variety of sinks.</p>
 *
 * <p>An object of this class may not be used in multiple threads
 * running concurrently.  Different Transformers may be used
 * concurrently by different threads.</p>
 *
 * <p>A <code>Transformer</code> may be used multiple times.  Parameters and
 * output properties are preserved across transformations.</p>
 */
public abstract class Transformer {

    /**
     * Default constructor is protected on purpose.
     */
    protected Transformer() {}

    /**
     * Process the source tree to the output result.
     * @param xmlSource  The input for the source tree.
     * @param outputTarget The output target.
     *
     * @throws TransformerException If an unrecoverable error occurs
     * during the course of the transformation.
     */
    public abstract void transform(Source xmlSource, Result outputTarget)
        throws TransformerException;

    /**
     * Add a parameter for the transformation.
     *
     * <p>Pass a qualified name as a two-part string, the namespace URI
     * enclosed in curly braces ({}), followed by the local name. If the
     * name has a null URL, the String only contain the local name. An
     * application can safely check for a non-null URI by testing to see if the first
     * character of the name is a '{' character.</p>
     * <p>For example, if a URI and local name were obtained from an element
     * defined with &lt;xyz:foo xmlns:xyz="http://xyz.foo.com/yada/baz.html"/&gt;,
     * then the qualified name would be "{http://xyz.foo.com/yada/baz.html}foo". Note that
     * no prefix is used.</p>
     *
     * @param name The name of the parameter, which may begin with a namespace URI
     * in curly braces ({}).
     * @param value The value object.  This can be any valid Java object. It is
     * up to the processor to provide the proper object coersion or to simply
     * pass the object on for use in an extension.
     */
    public abstract void setParameter(String name, Object value);

    /**
     * Get a parameter that was explicitly set with setParameter
     * or setParameters.
     *
     * <p>This method does not return a default parameter value, which
     * cannot be determined until the node context is evaluated during
     * the transformation process.
     *
     * @return A parameter that has been set with setParameter.
     */
    public abstract Object getParameter(String name);

    /**
     * Clear all parameters set with setParameter.
     */
    public abstract void clearParameters();

    /**
     * Set an object that will be used to resolve URIs used in
     * document().
     *
     * <p>If the resolver argument is null, the URIResolver value will
     * be cleared, and the default behavior will be used.</p>
     *
     * @param resolver An object that implements the URIResolver interface,
     * or null.
     */
    public abstract void setURIResolver(URIResolver resolver);

    /**
     * Get an object that will be used to resolve URIs used in
     * document(), etc.
     *
     * @return An object that implements the URIResolver interface,
     * or null.
     */
    public abstract URIResolver getURIResolver();

    /**
     * Set the output properties for the transformation.  These
     * properties will override properties set in the Templates
     * with xsl:output.
     *
     * <p>If argument to this function is null, any properties
     * previously set are removed, and the value will revert to the value
     * defined in the templates object.</p>
     *
     * <p>Pass a qualified property key name as a two-part string, the namespace URI
     * enclosed in curly braces ({}), followed by the local name. If the
     * name has a null URL, the String only contain the local name. An
     * application can safely check for a non-null URI by testing to see if the first
     * character of the name is a '{' character.</p>
     * <p>For example, if a URI and local name were obtained from an element
     * defined with &lt;xyz:foo xmlns:xyz="http://xyz.foo.com/yada/baz.html"/&gt;,
     * then the qualified name would be "{http://xyz.foo.com/yada/baz.html}foo". Note that
     * no prefix is used.</p>
     *
     * @param oformat A set of output properties that will be
     * used to override any of the same properties in affect
     * for the transformation.
     *
     * @see javax.xml.transform.OutputKeys
     * @see java.util.Properties
     *
     * @throws IllegalArgumentException if any of the argument keys are not
     * recognized and are not namespace qualified.
     */
    public abstract void setOutputProperties(Properties oformat)
        throws IllegalArgumentException;

    /**
     * Get a copy of the output properties for the transformation.
     *
     * <p>The properties returned should contain properties set by the user,
     * and properties set by the stylesheet, and these properties
     * are "defaulted" by default properties specified by <a href="http://www.w3.org/TR/xslt#output">section 16 of the
     * XSL Transformations (XSLT) W3C Recommendation</a>.  The properties that
     * were specifically set by the user or the stylesheet should be in the base
     * Properties list, while the XSLT default properties that were not
     * specifically set should be the default Properties list.  Thus,
     * getOutputProperties().getProperty(String key) will obtain any
     * property in that was set by {@link #setOutputProperty},
     * {@link #setOutputProperties}, in the stylesheet, <em>or</em> the default
     * properties, while
     * getOutputProperties().get(String key) will only retrieve properties
     * that were explicitly set by {@link #setOutputProperty},
     * {@link #setOutputProperties}, or in the stylesheet.</p>
     *
     * <p>Note that mutation of the Properties object returned will not
     * effect the properties that the transformation contains.</p>
     *
     * <p>If any of the argument keys are not recognized and are not
     * namespace qualified, the property will be ignored.  In other words the
     * behaviour is not orthogonal with setOutputProperties.</p>
     *
     * @returns A copy of the set of output properties in effect
     * for the next transformation.
     *
     * @see javax.xml.transform.OutputKeys
     * @see java.util.Properties
     */
    public abstract Properties getOutputProperties();

    /**
     * Set an output property that will be in effect for the
     * transformation.
     *
     * <p>Pass a qualified property name as a two-part string, the namespace URI
     * enclosed in curly braces ({}), followed by the local name. If the
     * name has a null URL, the String only contain the local name. An
     * application can safely check for a non-null URI by testing to see if the first
     * character of the name is a '{' character.</p>
     * <p>For example, if a URI and local name were obtained from an element
     * defined with &lt;xyz:foo xmlns:xyz="http://xyz.foo.com/yada/baz.html"/&gt;,
     * then the qualified name would be "{http://xyz.foo.com/yada/baz.html}foo". Note that
     * no prefix is used.</p>
     *
     * <p>The Properties object that was passed to {@link #setOutputProperties} won't
     * be effected by calling this method.</p>
     *
     * @param name A non-null String that specifies an output
     * property name, which may be namespace qualified.
     * @param value The non-null string value of the output property.
     *
     * @throws IllegalArgumentException If the property is not supported, and is
     * not qualified with a namespace.
     *
     * @see javax.xml.transform.OutputKeys
     */
    public abstract void setOutputProperty(String name, String value)
        throws IllegalArgumentException;

    /**
     * Get an output property that is in effect for the
     * transformation.  The property specified may be a property
     * that was set with setOutputProperty, or it may be a
     * property specified in the stylesheet.
     *
     * @param name A non-null String that specifies an output
     * property name, which may be namespace qualified.
     *
     * @return The string value of the output property, or null
     * if no property was found.
     *
     * @throws IllegalArgumentException If the property is not supported.
     *
     * @see javax.xml.transform.OutputKeys
     */
    public abstract String getOutputProperty(String name)
        throws IllegalArgumentException;

    /**
     * Set the error event listener in effect for the transformation.
     *
     * @param listener The new error listener.
     * @throws IllegalArgumentException if listener is null.
     */
    public abstract void setErrorListener(ErrorListener listener)
        throws IllegalArgumentException;

    /**
     * Get the error event handler in effect for the transformation.
     *
     * @return The current error handler, which should never be null.
     */
    public abstract ErrorListener getErrorListener();
}
