/**

 * Copyright 2005-2010 Noelios Technologies.

 * 

 * The contents of this file are subject to the terms of one of the following

 * open source licenses: LGPL 3.0 or LGPL 2.1 or CDDL 1.0 or EPL 1.0 (the

 * "Licenses"). You can select the license that you prefer but you may not use

 * this file except in compliance with one of these Licenses.

 * 

 * You can obtain a copy of the LGPL 3.0 license at

 * http://www.opensource.org/licenses/lgpl-3.0.html

 * 

 * You can obtain a copy of the LGPL 2.1 license at

 * http://www.opensource.org/licenses/lgpl-2.1.php

 * 

 * You can obtain a copy of the CDDL 1.0 license at

 * http://www.opensource.org/licenses/cddl1.php

 * 

 * You can obtain a copy of the EPL 1.0 license at

 * http://www.opensource.org/licenses/eclipse-1.0.php

 * 

 * See the Licenses for the specific language governing permissions and

 * limitations under the Licenses.

 * 

 * Alternatively, you can obtain a royalty free commercial license with less

 * limitations, transferable or non-transferable, directly at

 * http://www.noelios.com/products/restlet-engine

 * 

 * Restlet is a registered trademark of Noelios Technologies.

 */



package org.restlet.ext.rdf;



import org.restlet.data.Reference;

import org.restlet.util.Triple;



/**

 * Link between a source resource and a target resource or literal. This exactly

 * maps with the concepts of statement, triple or relationship defined by RDF,

 * the core specification of the Semantic Web. A link is composed of a source

 * node (or subject in RDF terminology), a type URI reference (or predicate in

 * RDF terminology) and a target node (or object in RDF terminology).

 * 

 * We use this class in Restlet to enhance resources and make them part of the

 * Web of data (also know as Linked Data and Hyperdata).

 * 

 * @author Jerome Louvel

 * @see <a href="http://www.w3.org/TR/rdf-concepts/">RDF concepts</a>

 */

public class Link extends Triple<Object, Reference, Object> {



    /**

     * Creates a reference to a blank node. In this API, we support RDF blank

     * nodes using the "_" namespace and local identifiers, in a way similar to

     * the RDF n3 serialization format.

     * 

     * @param identifier

     *            The blank node identifier.

     * @return A reference to a blank node.

     */

    public static Reference createBlankRef(String identifier) {

        return new Reference("_:" + identifier);

    }



    /**

     * Indicates if a reference is identifying a blank node.

     * 

     * @param reference

     *            The reference to test.

     * @return True if a reference is identifying a blank node.

     * @see #createBlankRef(String)

     */

    public static boolean isBlankRef(Reference reference) {

        return ((reference != null) && ("_".equals(reference.getScheme())));

    }



    /**

     * Constructor. Leverages n3 reification feature where a graph itself can be

     * the source node of a link.

     * 

     * @param sourceGraph

     *            The source graph or subject in RDF terminology.

     * @param typeRef

     *            The type reference or predicate in RDF terminology.

     * @param targetLit

     *            The target literal or object in RDF terminology.

     */

    public Link(Graph sourceGraph, Reference typeRef, Literal targetLit) {

        this((Object) sourceGraph, typeRef, (Object) targetLit);

    }



    /**

     * Constructor. Leverages n3 reification feature where a graph itself can be

     * the source node of a link.

     * 

     * @param sourceGraph

     *            The source graph or subject in RDF terminology.

     * @param typeRef

     *            The type reference or predicate in RDF terminology.

     * @param target

     *            The target node or object in RDF terminology.

     */

    public Link(Graph sourceGraph, Reference typeRef, Object target) {

        this((Object) sourceGraph, typeRef, target);

    }



    /**

     * Constructor. Leverages n3 reification feature where a graph itself can be

     * the source node of a link.

     * 

     * @param sourceGraph

     *            The source graph or subject in RDF terminology.

     * @param typeRef

     *            The type reference or predicate in RDF terminology.

     * @param targetRef

     *            The target reference or object in RDF terminology.

     */

    public Link(Graph sourceGraph, Reference typeRef, Reference targetRef) {

        this(sourceGraph, typeRef, (Object) targetRef);

    }



    /**

     * Constructor by copy.

     * 

     * @param from

     *            The link to copy from.

     */

    public Link(Link from) {

        this(from.getSource(), from.getTypeRef(), from.getTarget());

    }



    /**

     * Constructor.

     * 

     * @param source

     *            The source node or subject in RDF terminology.

     * @param typeRef

     *            The type reference or predicate in RDF terminology.

     * @param target

     *            The target node or object in RDF terminology.

     */

    private Link(Object source, Reference typeRef, Object target) {

        super(source, typeRef, target);

    }



    /**

     * Constructor.

     * 

     * @param sourceRef

     *            The source resource reference or subject in RDF terminology.

     * @param typeRef

     *            The type reference or predicate in RDF terminology.

     * @param targetLit

     *            The target literal node or object in RDF terminology.

     */

    public Link(Reference sourceRef, Reference typeRef, Literal targetLit) {

        this(sourceRef, typeRef, (Object) targetLit);

    }



    /**

     * Constructor.

     * 

     * @param sourceRef

     *            The source resource reference or subject in RDF terminology.

     * @param typeRef

     *            The type reference or predicate in RDF terminology.

     * @param targetRef

     *            The target resource reference or object in RDF terminology.

     */

    public Link(Reference sourceRef, Reference typeRef, Reference targetRef) {

        this(sourceRef, typeRef, (Object) targetRef);

    }



    /**

     * Returns the source which can be either a reference or a link or a graph

     * or null. This maps with the concept of subject in RDF terminology.

     * 

     * @return The source.

     */

    public Object getSource() {

        return getFirst();

    }



    /**

     * Returns the source graph. Supports RDF reification or N3 formulae.

     * 

     * @return The source graph.

     * @see #getSource()

     */

    public Graph getSourceAsGraph() {

        return hasGraphSource() ? (Graph) getSource() : null;

    }



    /**

     * Returns the source link. Supports RDF reification.

     * 

     * @return The source link.

     * @see #getSource()

     */

    public Link getSourceAsLink() {

        return hasLinkSource() ? (Link) getSource() : null;

    }



    /**

     * Returns the source resource reference.

     * 

     * @return The source resource reference.

     * @see #getSource()

     */

    public Reference getSourceAsReference() {

        return hasReferenceSource() ? (Reference) getSource() : null;

    }



    /**

     * Returns the target which can be either a literal or a reference or is

     * null. This maps with the concept of object in RDF terminology.

     * 

     * @return The target.

     */

    public Object getTarget() {

        return getThird();

    }



    /**

     * Returns the target graph.

     * 

     * @return The target graph.

     * @see #getTarget()

     */

    public Graph getTargetAsGraph() {

        return hasGraphTarget() ? (Graph) getTarget() : null;

    }



    /**

     * Returns the target link.

     * 

     * @return The target link.

     * @see #getTarget()

     */

    public Link getTargetAsLink() {

        return hasLinkTarget() ? (Link) getTarget() : null;

    }



    /**

     * Returns the target literal.

     * 

     * @return The target literal.

     * @see #getTarget()

     */

    public Literal getTargetAsLiteral() {

        return hasLiteralTarget() ? (Literal) getTarget() : null;

    }



    /**

     * Returns the target resource reference.

     * 

     * @return The target resource reference.

     * @see #getTarget()

     */

    public Reference getTargetAsReference() {

        return hasReferenceTarget() ? (Reference) getTarget() : null;

    }



    /**

     * Returns the type reference. This maps with the concept of predicate in

     * RDF terminology.

     * 

     * @return The type reference.

     */

    public Reference getTypeRef() {

        return getSecond();

    }



    /**

     * Indicates if the source is a graph.

     * 

     * @return True if the source is a graph.

     */

    public boolean hasGraphSource() {

        return getSource() instanceof Graph;

    }



    /**

     * Indicates if the target is a graph.

     * 

     * @return True if the target is a graph.

     */

    public boolean hasGraphTarget() {

        return getTarget() instanceof Graph;

    }



    /**

     * Indicates if the source is a link.

     * 

     * @return True if the source is a link.

     */

    public boolean hasLinkSource() {

        return getSource() instanceof Link;

    }



    /**

     * Indicates if the target is a link.

     * 

     * @return True if the target is a link.

     */

    public boolean hasLinkTarget() {

        return getTarget() instanceof Link;

    }



    /**

     * Indicates if the target is a literal.

     * 

     * @return True if the target is a literal.

     */

    public boolean hasLiteralTarget() {

        return getTarget() instanceof Literal;

    }



    /**

     * Indicates if the source is a reference.

     * 

     * @return True if the source is a reference.

     */

    public boolean hasReferenceSource() {

        return getSource() instanceof Reference;

    }



    /**

     * Indicates if the target is a reference.

     * 

     * @return True if the target is a reference.

     */

    public boolean hasReferenceTarget() {

        return getTarget() instanceof Reference;

    }



    /**

     * Sets the source as a graph. This maps with the concept of subject in RDF

     * terminology.

     * 

     * @param sourceGraph

     *            The source graph.

     */

    public void setSource(Graph sourceGraph) {

        setFirst(sourceGraph);

    }



    /**

     * Sets the source as a link. This maps with the concept of subject in RDF

     * terminology.

     * 

     * @param sourceLink

     *            The source link.

     */

    public void setSource(Link sourceLink) {

        setFirst(sourceLink);

    }



    /**

     * Sets the source resource reference. This maps with the concept of subject

     * in RDF terminology.

     * 

     * @param sourceRef

     *            The source resource reference.

     */

    public void setSource(Reference sourceRef) {

        setFirst(sourceRef);

    }



    /**

     * Sets the target as a graph. This maps with the concept of object in RDF

     * terminology.

     * 

     * @param targetGraph

     *            The target graph.

     */

    public void setTarget(Graph targetGraph) {

        setThird(targetGraph);

    }



    /**

     * Sets the target as a link. This maps with the concept of object in RDF

     * terminology.

     * 

     * @param targetLink

     *            The target link.

     */

    public void setTarget(Link targetLink) {

        setThird(targetLink);

    }



    /**

     * Sets the target literal. This maps with the concept of object in RDF

     * terminology.

     * 

     * @param targetLit

     *            The target literal.

     */

    public void setTarget(Literal targetLit) {

        setThird(targetLit);

    }



    /**

     * Sets the target as a resource reference. This maps with the concept of

     * object in RDF terminology.

     * 

     * @param targetRef

     *            The target resource reference.

     */

    public void setTarget(Reference targetRef) {

        setThird(targetRef);

    }



    /**

     * Sets the type reference. This maps with the concept of predicate in RDF

     * terminology.

     * 

     * @param typeRef

     *            The type reference.

     */

    public void setTypeRef(Reference typeRef) {

        setSecond(typeRef);

    }



}