/*
 * Copyright 2015 Red Hat, Inc. and/or its affiliates.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 *
 *      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.kie.internal.runtime.manager;

import java.util.Collection;
import java.util.Collections;
import java.util.concurrent.ConcurrentHashMap;

import org.kie.api.runtime.manager.RuntimeManager;

public class RuntimeManagerRegistry {

    private static RuntimeManagerRegistry INSTANCE = new RuntimeManagerRegistry();

    protected volatile ConcurrentHashMap<String, RuntimeManager> registeredManager = new ConcurrentHashMap<String, RuntimeManager>();

    private RuntimeManagerRegistry() {

    }

    public static RuntimeManagerRegistry get() {
        return INSTANCE;
    }

    public synchronized void register(RuntimeManager manager) {
        if (registeredManager.containsKey(manager.getIdentifier())) {
            throw new IllegalStateException("RuntimeManager is already registered with id " + manager.getIdentifier());
        }
        this.registeredManager.put(manager.getIdentifier(), manager);
    }

    public synchronized void remove(RuntimeManager manager) {

        this.registeredManager.remove(manager.getIdentifier());
    }

    public synchronized void remove(String identifier) {

        this.registeredManager.remove(identifier);
    }

    public RuntimeManager getManager(String id) {
        return this.registeredManager.get(id);
    }

    public boolean isRegistered(String id) {
        return this.registeredManager.containsKey(id);
    }

    public Collection<String> getRegisteredIdentifiers() {
        // Using "registeredManager.keySet()" directly would result in issues when compiling with JDK 8+. The "keySet()"
        // method returns type ConcurrentHashMap$KeySetView which is only available in Java 8+. That means
        // the bytecode would contain reference to that type, which does not exist in Java 6 and Java 7 and thus
        // clients would get NoSuchMethodError at runtime. The "keys()" method is fully backwards compatible, but it
        // requires wrapping inside additional collection as "unmodifiableCollection()" does not accept Enumerations.
        return Collections.unmodifiableCollection(Collections.list(this.registeredManager.keys()));
    }

}