/*

 * Copyright (c) 2015, Oracle and/or its affiliates. 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 Oracle 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.

 */

import java.lang.invoke.MethodHandle;

import java.lang.invoke.MethodHandles;

import java.lang.invoke.MethodType;

import java.util.ArrayList;

import java.util.List;

import jdk.dynalink.CallSiteDescriptor;

import jdk.dynalink.NamedOperation;

import jdk.dynalink.NamespaceOperation;

import jdk.dynalink.Operation;

import jdk.dynalink.StandardNamespace;

import jdk.dynalink.StandardOperation;

import jdk.dynalink.linker.GuardedInvocation;

import jdk.dynalink.linker.GuardingDynamicLinker;

import jdk.dynalink.linker.GuardingDynamicLinkerExporter;

import jdk.dynalink.linker.LinkRequest;

import jdk.dynalink.linker.LinkerServices;

import jdk.dynalink.linker.TypeBasedGuardingDynamicLinker;

import jdk.dynalink.linker.support.Guards;

import jdk.dynalink.linker.support.Lookup;

import org.w3c.dom.Element;

import org.w3c.dom.Node;

import org.w3c.dom.NodeList;

/**

 * This is a dynalink pluggable linker (see http://openjdk.java.net/jeps/276).

 * This linker handles XML DOM Element objects specially. This linker links

 * special properties starting with "_" and treats those as child element names

 * to access. This kind of child element access makes it easy to write XML DOM

 * accessing scripts. See for example ./dom_linker_gutenberg.js.

 */

public final class DOMLinkerExporter extends GuardingDynamicLinkerExporter {

    static {

        System.out.println("pluggable dynalink DOM linker loaded");

    }

    // return List of child Elements of the given Element matching the given name.

    private static List<Element> getChildElements(final Element elem, final String name) {

        final NodeList nodeList = elem.getChildNodes();

        final List<Element> childElems = new ArrayList<>();

        final int len = nodeList.getLength();

        for (int i = 0; i < len; i++) {

            final Node node = nodeList.item(i);

            if (node.getNodeType() == Node.ELEMENT_NODE &&

                ((Element)node).getTagName().equals(name)) {

                childElems.add((Element)node);

            }

        }

        return childElems;

    }

    // method that returns either unique child element matching given name

    // or a list of child elements of that name (if there are more than one matches).

    public static Object getElementsByName(final Object elem, final String name) {

        final List<Element> elems = getChildElements((Element)elem, name);

        return elems.size() == 1? elems.get(0) : elems;

    }

    // method to extract text context under a given DOM Element

    public static Object getElementText(final Object elem) {

        final NodeList nodeList = ((Element)elem).getChildNodes();

        final int len = nodeList.getLength();

        final StringBuilder text = new StringBuilder();

        for (int i = 0; i < len; i++) {

            final Node node = nodeList.item(i);

            if (node.getNodeType() == Node.TEXT_NODE) {

                text.append(node.getNodeValue());

            }

        }

        return text.toString();

    }

    private static final MethodHandle ELEMENTS_BY_NAME;

    private static final MethodHandle ELEMENT_TEXT;

    private static final MethodHandle IS_ELEMENT;

    static {

        ELEMENTS_BY_NAME = Lookup.PUBLIC.findStatic(DOMLinkerExporter.class,

            "getElementsByName",

            MethodType.methodType(Object.class, Object.class, String.class));

        ELEMENT_TEXT = Lookup.PUBLIC.findStatic(DOMLinkerExporter.class,

            "getElementText",

            MethodType.methodType(Object.class, Object.class));

        IS_ELEMENT = Guards.isInstance(Element.class, MethodType.methodType(Boolean.TYPE, Object.class));

    }

    @Override

    public List<GuardingDynamicLinker> get() {

        final ArrayList<GuardingDynamicLinker> linkers = new ArrayList<>();

        linkers.add(new TypeBasedGuardingDynamicLinker() {

            @Override

            public boolean canLinkType(final Class<?> type) {

                return Element.class.isAssignableFrom(type);

            }

            @Override

            public GuardedInvocation getGuardedInvocation(final LinkRequest request,

                final LinkerServices linkerServices) throws Exception {

                final Object self = request.getReceiver();

                if (! (self instanceof Element)) {

                    return null;

                }

                final CallSiteDescriptor desc = request.getCallSiteDescriptor();

                final Operation op = desc.getOperation();

                final Object name = NamedOperation.getName(op);

                final boolean getProp = NamespaceOperation.contains(

                        NamedOperation.getBaseOperation(op),

                        StandardOperation.GET, StandardNamespace.PROPERTY);

                if (getProp && name instanceof String) {

                    final String nameStr = (String)name;

                    // Treat names starting with "_" as special names.

                    // Everything else is linked other dynalink bean linker!

                    // This avoids collision with Java methods of org.w3c.dom.Element class

                    // Assumption is that Java APIs won't start with "_" character!!

                    if (nameStr.equals("_")) {

                        // short-hand to get text content under a given DOM Element

                        return new GuardedInvocation(ELEMENT_TEXT, IS_ELEMENT);

                    } else if (nameStr.startsWith("_")) {

                        return new GuardedInvocation(

                            MethodHandles.insertArguments(ELEMENTS_BY_NAME, 1, nameStr.substring(1)),

                            IS_ELEMENT);

                    }

                }

                return null;

            }

        });

        return linkers;

    }

}