/*

  * $Header: /home/projects/jaxen/scm/jaxen/src/java/main/org/jaxen/BaseXPath.java,v 1.50 2007/04/16 15:44:37 elharo Exp $

  * $Revision: 1.50 $

  * $Date: 2007/04/16 15:44:37 $

  *

  * ====================================================================

  *

  * Copyright 2000-2002 bob mcwhirter & James Strachan.

  * All rights reserved.

  *

  * Redistribution and use in source and binary forms, with or without

  * modification, are permitted provided that the following conditions are

  * met:

  * 

  *   * Redistributions of source code must retain the above copyright

  *     notice, this list of conditions and the following disclaimer.

  * 

  *   * Redistributions in binary form must reproduce the above copyright

  *     notice, this list of conditions and the following disclaimer in the

  *     documentation and/or other materials provided with the distribution.

  * 

  *   * Neither the name of the Jaxen Project nor the names of its

  *     contributors may be used to endorse or promote products derived 

  *     from this software without specific prior written permission.

  * 

  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS

  * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED

  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A

  * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER

  * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,

  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,

  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR

  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF

  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING

  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS

  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

  *

  * ====================================================================

  * This software consists of voluntary contributions made by many 

  * individuals on behalf of the Jaxen Project and was originally 

  * created by bob mcwhirter <bob@werken.com> and 

  * James Strachan <jstrachan@apache.org>.  For more information on the 

  * Jaxen Project, please see <http://www.jaxen.org/>.

  * 

  * $Id: BaseXPath.java,v 1.50 2007/04/16 15:44:37 elharo Exp $

  */

 package org.jaxen;

 import java.io.Serializable;

 import java.util.List;

 import org.jaxen.expr.Expr;

 import org.jaxen.expr.XPathExpr;

 import org.jaxen.function.BooleanFunction;

 import org.jaxen.function.NumberFunction;

 import org.jaxen.function.StringFunction;

 import org.jaxen.saxpath.SAXPathException;

 import org.jaxen.saxpath.XPathReader;

 import org.jaxen.saxpath.helpers.XPathReaderFactory;

 import org.jaxen.util.SingletonList;

 /** Base functionality for all concrete, implementation-specific XPaths.

  *

  *  <p>

  *  This class provides generic functionality for further-defined

  *  implementation-specific XPaths.

  *  </p>

  *

  *  <p>

  *  If you want to adapt the Jaxen engine so that it can traverse your own

  *  object model, then this is a good base class to derive from.

  *  Typically you only really need to provide your own 

  *  {@link org.jaxen.Navigator} implementation.

  *  </p>

  *

  *  @see org.jaxen.dom4j.Dom4jXPath XPath for dom4j

  *  @see org.jaxen.jdom.JDOMXPath   XPath for JDOM

  *  @see org.jaxen.dom.DOMXPath     XPath for W3C DOM

  *

  *  @author <a href="mailto:bob@werken.com">bob mcwhirter</a>

  *  @author <a href="mailto:jstrachan@apache.org">James Strachan</a>

  */

 public class BaseXPath implements XPath, Serializable

 {

     /** Original expression text. */

     private final String exprText;

     /** the parsed form of the XPath expression */

     private final XPathExpr xpath;

     /** the support information and function, namespace and variable contexts */

     private ContextSupport support;

     /** the implementation-specific Navigator for retrieving XML nodes **/

     private Navigator navigator;

     /** Construct given an XPath expression string. 

      *

      *  @param xpathExpr the XPath expression

      *

      *  @throws JaxenException if there is a syntax error while

      *          parsing the expression

      */

     protected BaseXPath(String xpathExpr) throws JaxenException

     {

         try

         {

             XPathReader reader = XPathReaderFactory.createReader();

             JaxenHandler handler = new JaxenHandler();

             reader.setXPathHandler( handler );

             reader.parse( xpathExpr );

             this.xpath = handler.getXPathExpr();

         }

         catch (org.jaxen.saxpath.XPathSyntaxException e)

         {

             throw new org.jaxen.XPathSyntaxException( e );

         }

         catch (SAXPathException e)

         {

             throw new JaxenException( e );

         }

         this.exprText = xpathExpr;

     }

     /** Construct given an XPath expression string.

      *

      *  @param xpathExpr the XPath expression

      *

      *  @param navigator the XML navigator to use

      *

      *  @throws JaxenException if there is a syntax error while

      *          parsing the expression

      */

     public BaseXPath(String xpathExpr, Navigator navigator) throws JaxenException

     {

         this( xpathExpr );

         this.navigator = navigator;

     }

     /** Evaluate this XPath against a given context.

      *  The context of evaluation may be any object type

      *  the navigator recognizes as a node.

      *  The return value is either a <code>String</code>,

      *  <code>Double</code>, <code>Boolean</code>, or <code>List</code>

      *  of nodes.

      *

      *  <p>

      *  When using this method, one must be careful to

      *  test the class of the returned object.  If the returned 

      *  object is a list, then the items in this 

      *  list will be the actual <code>Document</code>,

      *  <code>Element</code>, <code>Attribute</code>, etc. objects

      *  as defined by the concrete XML object-model implementation,

      *  directly from the context document.  This method <strong>does

      *  not return <em>copies</em> of anything</strong>, but merely 

      *  returns references to objects within the source document.

      *  </p>

      *  

      * @param context the node, node-set or Context object for evaluation. 

      *      This value can be null.

      *

      * @return the result of evaluating the XPath expression

      *          against the supplied context

      * @throws JaxenException if an XPath error occurs during expression evaluation

      * @throws ClassCastException if the context is not a node

      */

     public Object evaluate(Object context) throws JaxenException

     {

         List answer = selectNodes(context);

         if ( answer != null

              &&

              answer.size() == 1 )

         {

             Object first = answer.get(0);

             if ( first instanceof String

                  ||

                  first instanceof Number

                  ||

                  first instanceof Boolean ) 

             {

                 return first;

             }

         }

         return answer;

     }

     /** Select all nodes that are selected by this XPath

      *  expression. If multiple nodes match, multiple nodes

      *  will be returned. Nodes will be returned

      *  in document-order, as defined by the XPath

      *  specification. If the expression selects a non-node-set

      *  (i.e. a number, boolean, or string) then a List

      *  containing just that one object is returned.

      *  </p>

      *

      * @param node the node, node-set or Context object for evaluation. 

      *     This value can be null.

      *

      * @return the node-set of all items selected

      *          by this XPath expression

      * @throws JaxenException if an XPath error occurs during expression evaluation

      *

      * @see #selectNodesForContext

      */

     public List selectNodes(Object node) throws JaxenException

     {

         Context context = getContext( node );

         return selectNodesForContext( context );

     }

     /** Select only the first node selected by this XPath

      *  expression.  If multiple nodes match, only one node will be

      *  returned. The selected node will be the first

      *  selected node in document-order, as defined by the XPath

      *  specification.

      *  </p>

      *

      * @param node the node, node-set or Context object for evaluation. 

      *     This value can be null.

      *

      * @return the node-set of all items selected

      *          by this XPath expression

      * @throws JaxenException if an XPath error occurs during expression evaluation

      *

      * @see #selectNodes

      */

     public Object selectSingleNode(Object node) throws JaxenException

     {

         List results = selectNodes( node );

         if ( results.isEmpty() )

         {

             return null;

         }

         return results.get( 0 );

     }

     /**

      * Returns the XPath string-value of the argument node.

      * 

      * @param node the node whose value to take

      * @return the XPath string value of this node

      * @throws JaxenException if an XPath error occurs during expression evaluation

      * @deprecated replaced by {@link #stringValueOf}

      */

     public String valueOf(Object node) throws JaxenException

     {

         return stringValueOf( node );

     }

     /** Retrieves the string-value of the result of

      *  evaluating this XPath expression when evaluated 

      *  against the specified context.

      *

      *  <p>

      *  The string-value of the expression is determined per

      *  the <code>string(..)</code> core function defined

      *  in the XPath specification.  This means that an expression

      *  that selects zero nodes will return the empty string,

      *  while an expression that selects one-or-more nodes will

      *  return the string-value of the first node.

      *  </p>

      *

      * @param node the node, node-set or Context object for evaluation. This value can be null.

      *

      * @return the string-value of the result of evaluating this expression with the specified context node

      * @throws JaxenException if an XPath error occurs during expression evaluation

      */

     public String stringValueOf(Object node) throws JaxenException

     {

         Context context = getContext( node );

         Object result = selectSingleNodeForContext( context );

         if ( result == null )

         {

             return "";

         }

         return StringFunction.evaluate( result,

                                         context.getNavigator() );

     }

     /** Retrieve a boolean-value interpretation of this XPath

      *  expression when evaluated against a given context.

      *

      *  <p>

      *  The boolean-value of the expression is determined per

      *  the <code>boolean(..)</code> function defined

      *  in the XPath specification.  This means that an expression

      *  that selects zero nodes will return <code>false</code>,

      *  while an expression that selects one or more nodes will

      *  return <code>true</code>.

      *  </p>

      *

      * @param node the node, node-set or Context object for evaluation. This value can be null.

      *

      * @return the boolean-value of the result of evaluating this expression with the specified context node

      * @throws JaxenException if an XPath error occurs during expression evaluation

      */

     public boolean booleanValueOf(Object node) throws JaxenException

     {

         Context context = getContext( node );

         List result = selectNodesForContext( context );

         if ( result == null ) return false;

         return BooleanFunction.evaluate( result, context.getNavigator() ).booleanValue();

     }

     /** Retrieve a number-value interpretation of this XPath

      *  expression when evaluated against a given context.

      *

      *  <p>

      *  The number-value of the expression is determined per

      *  the <code>number(..)</code> core function as defined

      *  in the XPath specification. This means that if this

      *  expression selects multiple nodes, the number-value

      *  of the first node is returned.

      *  </p>

      *

      * @param node the node, node-set or Context object for evaluation. This value can be null.

      *

      * @return a <code>Double</code> indicating the numeric value of

      *      evaluating this expression against the specified context

      * @throws JaxenException if an XPath error occurs during expression evaluation

      */

     public Number numberValueOf(Object node) throws JaxenException

     {

         Context context = getContext( node );

         Object result = selectSingleNodeForContext( context );

         return NumberFunction.evaluate( result,

                                         context.getNavigator() );

     }

     // Helpers

     /** Add a namespace prefix-to-URI mapping for this XPath

      *  expression.

      *

      *  <p>

      *  Namespace prefix-to-URI mappings in an XPath are independent

      *  of those used within any document.  Only the mapping explicitly

      *  added to this XPath will be available for resolving the

      *  XPath expression.

      *  </p>

      *

      *  <p>

      *  This is a convenience method for adding mappings to the

      *  default {@link NamespaceContext} in place for this XPath.

      *  If you have installed a custom <code>NamespaceContext</code>

      *  that is not a <code>SimpleNamespaceContext</code>,

      *  then this method will throw a <code>JaxenException</code>.

      *  </p>

      *

      *  @param prefix the namespace prefix

      *  @param uri the namespace URI

      *

      *  @throws JaxenException if the <code>NamespaceContext</code>

      *          used by this XPath is not a <code>SimpleNamespaceContext</code>

      */

     public void addNamespace(String prefix,

                              String uri) throws JaxenException

     {

         NamespaceContext nsContext = getNamespaceContext();

         if ( nsContext instanceof SimpleNamespaceContext )

         {

             ((SimpleNamespaceContext)nsContext).addNamespace( prefix,

                                                               uri );

             return;

         }

         throw new JaxenException("Operation not permitted while using a non-simple namespace context.");

     }

     // ------------------------------------------------------------

     // ------------------------------------------------------------

     //     Properties

     // ------------------------------------------------------------

     // ------------------------------------------------------------

     /** Set a <code>NamespaceContext</code> for use with this

      *  XPath expression.

      *

      *  <p>

      *  A <code>NamespaceContext</code> is responsible for translating

      *  namespace prefixes within the expression into namespace URIs.

      *  </p>

      *

      *  @param namespaceContext the <code>NamespaceContext</code> to

      *         install for this expression

      *

      *  @see NamespaceContext

      *  @see NamespaceContext#translateNamespacePrefixToUri

      */

     public void setNamespaceContext(NamespaceContext namespaceContext)

     {

         getContextSupport().setNamespaceContext(namespaceContext);

     }

     /** Set a <code>FunctionContext</code> for use with this XPath

      *  expression.

      *

      *  <p>

      *  A <code>FunctionContext</code> is responsible for resolving

      *  all function calls used within the expression.

      *  </p>

      *

      *  @param functionContext the <code>FunctionContext</code> to

      *         install for this expression

      *

      *  @see FunctionContext

      *  @see FunctionContext#getFunction

      */

     public void setFunctionContext(FunctionContext functionContext)

     {

         getContextSupport().setFunctionContext(functionContext);

     }

     /** Set a <code>VariableContext</code> for use with this XPath

      *  expression.

      *

      *  <p>

      *  A <code>VariableContext</code> is responsible for resolving

      *  all variables referenced within the expression.

      *  </p>

      *

      *  @param variableContext The <code>VariableContext</code> to

      *         install for this expression

      *

      *  @see VariableContext

      *  @see VariableContext#getVariableValue

      */

     public void setVariableContext(VariableContext variableContext)

     {

         getContextSupport().setVariableContext(variableContext);

     }

     /** Retrieve the <code>NamespaceContext</code> used by this XPath

      *  expression.

      *

      *  <p>

      *  A <code>NamespaceContext</code> is responsible for mapping

      *  prefixes used within the expression to namespace URIs.

      *  </p>

      *

      *  <p>

      *  If this XPath expression has not previously had a <code>NamespaceContext</code>

      *  installed, a new default <code>NamespaceContext</code> will be created,

      *  installed and returned.

      *  </p>

      *

      *  @return the <code>NamespaceContext</code> used by this expression

      *

      *  @see NamespaceContext

      */

     public NamespaceContext getNamespaceContext()

     {

         return getContextSupport().getNamespaceContext();

     }

     /** Retrieve the <code>FunctionContext</code> used by this XPath

      *  expression.

      *

      *  <p>

      *  A <code>FunctionContext</code> is responsible for resolving

      *  all function calls used within the expression.

      *  </p>

      *

      *  <p>

      *  If this XPath expression has not previously had a <code>FunctionContext</code>

      *  installed, a new default <code>FunctionContext</code> will be created,

      *  installed and returned.

      *  </p>

      *

      *  @return the <code>FunctionContext</code> used by this expression

      *

      *  @see FunctionContext

      */

     public FunctionContext getFunctionContext()

     {

         return getContextSupport().getFunctionContext();

     }

     /** Retrieve the <code>VariableContext</code> used by this XPath

      *  expression.

      *

      *  <p>

      *  A <code>VariableContext</code> is responsible for resolving

      *  all variables referenced within the expression.

      *  </p>

      *

      *  <p>

      *  If this XPath expression has not previously had a <code>VariableContext</code>

      *  installed, a new default <code>VariableContext</code> will be created,

      *  installed and returned.

      *  </p>

      *  

      *  @return the <code>VariableContext</code> used by this expression

      *

      *  @see VariableContext

      */

     public VariableContext getVariableContext()

     {

         return getContextSupport().getVariableContext();

     }

     /** Retrieve the root expression of the internal

      *  compiled form of this XPath expression.

      *

      *  <p>

      *  Internally, Jaxen maintains a form of Abstract Syntax

      *  Tree (AST) to represent the structure of the XPath expression.

      *  This is normally not required during normal consumer-grade

      *  usage of Jaxen.  This method is provided for hard-core users

      *  who wish to manipulate or inspect a tree-based version of

      *  the expression.

      *  </p>

      *

      *  @return the root of the AST of this expression

      */

     public Expr getRootExpr() 

     {

         return xpath.getRootExpr();

     }

     /** Return the original expression text.

      *

      *  @return the normalized XPath expression string

      */

     public String toString()

     {

         return this.exprText;

     }

     /** Returns a string representation of the parse tree.

      *

      *  @return a string representation of the parse tree.

      */

     public String debug()

     {

         return this.xpath.toString();

     }

     // ------------------------------------------------------------

     // ------------------------------------------------------------

     //     Implementation methods

     // ------------------------------------------------------------

     // ------------------------------------------------------------

     /** Create a {@link Context} wrapper for the provided

      *  implementation-specific object.

      *

      *  @param node the implementation-specific object 

      *         to be used as the context

      *

      *  @return a <code>Context</code> wrapper around the object

      */

     protected Context getContext(Object node)

     {

         if ( node instanceof Context )

         {

             return (Context) node;

         }

         Context fullContext = new Context( getContextSupport() );

         if ( node instanceof List )

         {

             fullContext.setNodeSet( (List) node );

         }

         else

         {

             List list = new SingletonList(node);

             fullContext.setNodeSet( list );

         }

         return fullContext;

     }

     /** Retrieve the {@link ContextSupport} aggregation of

      *  <code>NamespaceContext</code>, <code>FunctionContext</code>,

      *  <code>VariableContext</code>, and {@link Navigator}.

      *

      *  @return aggregate <code>ContextSupport</code> for this

      *          XPath expression

      */

     protected ContextSupport getContextSupport()

     {

         if ( support == null )

         {

             support = new ContextSupport( 

                 createNamespaceContext(),

                 createFunctionContext(),

                 createVariableContext(),

                 getNavigator() 

             );

         }

         return support;

     }

     /** Retrieve the XML object-model-specific {@link Navigator} 

      *  for us in evaluating this XPath expression.

      *

      *  @return the implementation-specific <code>Navigator</code>

      */

     public Navigator getNavigator()

     {

         return navigator;

     }

     // ------------------------------------------------------------

     // ------------------------------------------------------------

     //     Factory methods for default contexts

     // ------------------------------------------------------------

     // ------------------------------------------------------------

     /** Create a default <code>FunctionContext</code>.

      *

      *  @return a default <code>FunctionContext</code>

      */

     protected FunctionContext createFunctionContext()

     {

         return XPathFunctionContext.getInstance();

     }

     /** Create a default <code>NamespaceContext</code>.

      *

      *  @return a default <code>NamespaceContext</code> instance

      */

     protected NamespaceContext createNamespaceContext()

     {

         return new SimpleNamespaceContext();

     }

     /** Create a default <code>VariableContext</code>.

      *

      *  @return a default <code>VariableContext</code> instance

      */

     protected VariableContext createVariableContext()

     {

         return new SimpleVariableContext();

     }

     /** Select all nodes that match this XPath

      *  expression on the given Context object. 

      *  If multiple nodes match, multiple nodes

      *  will be returned in document-order, as defined by the XPath

      *  specification. If the expression selects a non-node-set

      *  (i.e. a number, boolean, or string) then a List

      *  containing just that one object is returned.

      *  </p>

      *

      * @param context the Context which gets evaluated

      *

      * @return the node-set of all items selected

      *          by this XPath expression

      * @throws JaxenException if an XPath error occurs during expression evaluation

      *

      */

     protected List selectNodesForContext(Context context) throws JaxenException

     {

         List list = this.xpath.asList( context );