/*
 * 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.
 */

package org.apache.jena.rdf.model;

import java.util.Calendar;

import org.apache.jena.datatypes.RDFDatatype ;
import org.apache.jena.datatypes.xsd.XSDDatatype ;
import org.apache.jena.datatypes.xsd.XSDDateTime ;
import org.apache.jena.graph.Node;
import org.apache.jena.graph.NodeFactory ;
import org.apache.jena.rdf.model.impl.LiteralImpl;
import org.apache.jena.rdf.model.impl.PropertyImpl;
import org.apache.jena.rdf.model.impl.ResourceImpl;
import org.apache.jena.rdf.model.impl.StatementImpl;

/** A Factory class for creating resources.
 *
 * <p> This class creates resources and properties and things of that ilk.
 * These resources are <i>not</i> associated with a user-modifiable
 * model: doing getModel() on them will return null.
 * </p>
 *
 * <p> It is designed as a singleton.  There are static convenience
 * methods on this class itself, so the easy way to create resource
 * is for example to do something like:</p>
 * <pre>
 *   <code>Resource r = ResourceFactory.createResource();</code>
 * </pre>
 *
 * <p> If a factory object is needed, then this can be obtained using
 * the <code>getInstance</code> method on the class.  The factory
 * object used may be changed using the <code>setInstance</code>
 * method.</p>
*/
public class ResourceFactory {
    protected static Interface instance = new Impl();

    private ResourceFactory() {
    }

    /** Get the current factory object.
     *
     *  @return the current factory object
     */
    public static Interface getInstance() {
        return instance;
    }
    /** Set the current factory object.
     *
     * @param newInstance the new factory object
     * @return the previous factory object
     */
    public static Interface setInstance(Interface newInstance) {
        Interface previousInstance = instance;
        instance = newInstance;
        return previousInstance;
    }

    /** Create a new anonymous resource.
     *
     * <p>Uses the current factory object to create a new anonymous resource.</p>
     *
     * @return a new anonymous resource
     */
    public static Resource createResource() {
        return instance.createResource();
    }

    /** Create a new resource.
     *
     * <p>Uses the current factory object to create a new resource.</p>
     *
     * @param uriref URIREF of the resource
     * @return a new resource
     */
    public static Resource createResource(String uriref) {
        return instance.createResource(uriref);
    }

    /**
     * Create a new resource representing an RDF-star triple term.
     * @param statement
     * @return a new resource
     */
    public static Resource createStmtResource(Statement statement) {
        return instance.createStmtResource(statement);
    }

    /**
     * Answer a string (xsd:string) literal.
     * This is the equivalent of a plain literal with no language from RDF 1.0
     * (also called a simple literal in SPARQL)
     *
     * Using {@link #createStringLiteral} is preferred; "plain literal" is RDF 1.0 terminology.
     *
     * @param string
     *            the string which forms the value of the literal
     * @return a Literal node with that string as value
     */
    public static Literal createPlainLiteral( String string ) {
        return instance.createStringLiteral( string );
    }

    /**
     * Answer a string (xsd:string) literal.
     * This is the equivalent of a plain literal with no language from RDF 1.0
     * (also called a simple literal in SPARQL)
     *
     * @param string
     *            the string which forms the value of the literal
     * @return a Literal node with that string as value
     */
    public static Literal createStringLiteral( String string ) {
        return instance.createStringLiteral( string );
    }
    /**
     * Answer a literal with language and the given content. The literal will
     * have datatype rdf:langString.
     *
     * @param string
     *            the string which forms the value of the literal
     * @param lang
     *            The language tag to be used
     * @return a Literal node with that string as value
     */
    public static Literal createLangLiteral( String string , String lang ) {
        return instance.createLangLiteral( string , lang );
    }

    /**
     * Answer a typed literal.
     * @param string the string which forms the value of the literal
     * @param dType RDFDatatype of the type literal
     * @return a Literal node with that string as value
     */
    public static Literal createTypedLiteral( String string , RDFDatatype dType) {
        return instance.createTypedLiteral( string , dType);
    }

    /**
     * Answer a typed literal.
     * @param value a java Object, the default RDFDatatype for that object will be used
     * @return a Literal node with that value
     */
    public static Literal createTypedLiteral( Object value ) {
        return instance.createTypedLiteral(value);
    }

    /** Create a new property.
     *
     * <p>Uses the current factory object to create a new resource.</p>
     *
     * @param uriref URIREF of the property
     * @return a new property
     */
    public static Property createProperty(String uriref) {
        return instance.createProperty(uriref);
    }

    /** Create a new property.
     *
     * <p>Uses the current factory object to create a new property.</p>
     *
     * @param namespace URIREF of the namespace of the property
     * @param localName localname of the property
     * @return a new property
     */
    public static Property createProperty(String namespace, String localName) {
        return instance.createProperty(namespace, localName);
    }

    /**
     * Create a new statement.
     * <p>
     * Uses the current factory object to create a new statement.</p>
     *
     * @param subject the subject of the new statement
     * @param predicate the predicate of the new statement
     * @param object the object of the new statement
     * @return a new resource
     */
    public static Statement createStatement(
        Resource subject,
        Property predicate,
        RDFNode object) {
        return instance.createStatement(subject, predicate, object);
    }

    /** The interface to resource factory objects.
     */
    public interface Interface {

        /** Create a new anonymous resource.
         *
         * @return a new anonymous resource
         */
        public Resource createResource();

        /** Create a new resource.
         *
         * @param uriref URIREF of the resource
         * @return a new resource
         */
        public Resource createResource(String uriref);

        /** Create a new resource representing an RDF-star triple term.
         *
         * @param statement
         * @return a new resource
         */
        public Resource createStmtResource(Statement statement);

        /**
         * Answer a string (xsd:string) literal.
         * This is the equivalent of a plain liteal with no language from RDF 1.0
         * (also called a simple literal in SPARQL)
         *
         * @param string
         *            the string which forms the value of the literal
         * @return a Literal node with that string as value
         */
        public Literal createStringLiteral( String string );

        /**
         * Answer a plain (untyped) literal with no language and the given content.
         *
         * @param string the string which forms the value of the literal
         * @param lang The language tag to be used
         * @return a Literal node with that string as value
         */

        public Literal createLangLiteral( String string , String lang );

        /**
         * Answer a typed literal.
         *
         * @param string the string which forms the value of the literal
         * @param datatype RDFDatatype of the type literal
         * @return a Literal node with that string as value
         */
        public Literal createTypedLiteral( String string , RDFDatatype datatype) ;


        /**
         * Answer a typed literal.
         * @param value a java Object, the default RDFDatatype for that object will be used
         * @return a Literal node with that value
         */
        public Literal createTypedLiteral( Object value ) ;

        /** Create a new property.
         *
         * @param uriref URIREF of the property
         * @return a new property
         */
        public Property createProperty(String uriref);

        /** Create a new property.
         *
         * @param namespace uriref of the namespace
         * @param localName localname of the property
         * @return a new property
         */
        public Property createProperty(String namespace, String localName);

        /** Create a new statement.
         *
         * @param subject subject of the new statement
         * @param predicate predicate of the new statement
         * @param object object of the new statement
         * @return a new statement
         */
        public Statement createStatement(
            Resource subject,
            Property predicate,
            RDFNode object);
    }

    static class Impl implements Interface {

        Impl() {
        }

        @Override
        public Resource createResource() {
            return new ResourceImpl();
        }

        @Override
        public Resource createResource(String uriref) {
            return new ResourceImpl(uriref);
        }

        @Override
        public Resource createStmtResource(Statement statement) {
            return new ResourceImpl(statement, null);
        }

        @Override
        public Literal createStringLiteral( String string ) {
            return new LiteralImpl(  NodeFactory.createLiteralLang( string, "" ), null );
        }

        @Override
        public Literal createLangLiteral( String string , String lang ) {
            return new LiteralImpl(  NodeFactory.createLiteralLang( string, lang ), null );
        }

        @Override
        public Literal createTypedLiteral( String string , RDFDatatype dType)
        {
            return new LiteralImpl(NodeFactory.createLiteralDT(string, dType), null) ;
        }

        @Override
        public Literal createTypedLiteral( Object value ) {
            Node n;
            if (value instanceof Calendar) {
                Object valuec = new XSDDateTime( (Calendar) value);
                n = NodeFactory.createLiteralByValue(valuec, XSDDatatype.XSDdateTime);
            } else {
                n = NodeFactory.createLiteralByValue(value);
            }
            return new LiteralImpl(n, null) ;
        }

        @Override
        public Property createProperty(String uriref) {
            return new PropertyImpl(uriref);
        }

        @Override
        public Property createProperty(String namespace, String localName) {
            return new PropertyImpl(namespace, localName);
        }

        @Override
        public Statement createStatement(
            Resource subject,
            Property predicate,
            RDFNode object) {
            return new StatementImpl(subject, predicate, object);
        }
    }
}
