/*
 * 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.sparql.core.describe;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import org.apache.jena.query.ARQ;
import org.apache.jena.sparql.ARQConstants;
import org.apache.jena.sparql.util.Context;

/** Registry of DescribeHandlers. */

public class DescribeHandlerRegistry {
    static private DescribeHandlerRegistry globalRegistry = null;

    private List<DescribeHandlerFactory> registry = new ArrayList<>();

    private DescribeHandlerRegistry() {}

    private static DescribeHandlerRegistry standardRegistry() {
        DescribeHandlerRegistry reg = new DescribeHandlerRegistry();
        reg.add(new DescribeBNodeClosureFactory());
        return reg;
    }

    public static DescribeHandlerRegistry get(Context context) {
        if ( context == null )
            return null;
        return (DescribeHandlerRegistry)ARQ.getContext().get(ARQConstants.registryDescribeHandlers);
    }

    public static void set(Context context, DescribeHandlerRegistry reg) {
        context.set(ARQConstants.registryDescribeHandlers, reg);
    }

    public static DescribeHandlerRegistry get() {
        // Initialize if there is no registry already set
        DescribeHandlerRegistry reg = get(ARQ.getContext());
        if ( reg == null ) {
            synchronized(DescribeHandlerRegistry.class) {
                if ( reg == null ) {
                    reg = standardRegistry();
                    set(ARQ.getContext(), reg);
                }
            }
        }
        return reg;
    }

    public void add(DescribeHandlerFactory handlerFactory) {
        registry.add(0, handlerFactory);
    }

    public void remove(DescribeHandlerFactory handlerFactory) {
        registry.remove(handlerFactory);
    }

    public void clear() {
        registry.clear();
    }

    public List<DescribeHandler> newHandlerList() {
        List<DescribeHandler> a = new ArrayList<>(registry.size());
        for ( Iterator<DescribeHandlerFactory> iter = handlers() ; iter.hasNext() ; ) {
            DescribeHandlerFactory f = iter.next();
            a.add(f.create());
        }
        return a;
    }

    public Iterator<DescribeHandlerFactory> handlers() {
        return registry.iterator();
    }
}
