/*
 * 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
 *
 *   https://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.
 *
 *   SPDX-License-Identifier: Apache-2.0
 */

package org.apache.jena.graph;

import java.util.Objects;

/** Extension to the RDF Data model.
 *  This class and any subclasses exist for experimentation and custom extensions.
 *  There is no support for them within Apache Jena.
 *  <p>
 *  Extension nodes exist so that the machinery of datastructures (graphs, triples)
 *  can be used.  There is no guarantee that processing Nodes (e.g. writing) will handle
 *  extensions.
 */
public abstract class Node_Ext<X> extends Node {

    private final X object;

    protected Node_Ext(X object) {
        this.object = Objects.requireNonNull(object);
    }

    @Override
    public Object visitWith(NodeVisitor v) {
        return null;
    }

    // If the extension wants the node to match in memory graphs, this must be true
    // and extension type X must support value-based .equals() and .hashCode().
    @Override
    public boolean isConcrete() {
        return false;
    }

    public X get() {
        return object;
    }

    @Override
    public boolean isExt() {
        return true;
    }

    @Override
    public int hashCode() {
        if ( object == null )
            return Node.hashExt;
        return object.hashCode();
    }

    @Override
    public boolean equals(Object obj) {
        if ( this == obj )
            return true;
        if ( !( obj instanceof Node_Ext<?> other ) )
            return false;
        return Objects.equals(object, other.object);
    }
}
