/*
 * 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.tuscany.sca.extensibility;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

/**
 * Service discovery for Tuscany based on J2SE Jar service provider spec.
 * Services are described using configuration files in META-INF/services.
 * Service description specifies a class name followed by optional properties.
 *
 *
 * @version $Rev$ $Date$
 */
public final class ServiceDiscovery implements ServiceDiscoverer {
    private final static ServiceDiscovery INSTANCE = new ServiceDiscovery();

    private ServiceDiscoverer discoverer;

    private ServiceDiscovery() {
        super();
    }
    /**
     * Get an instance of Service discovery, one instance is created per
     * ClassLoader that this class is loaded from
     *
     * @return
     */
    public static ServiceDiscovery getInstance() {
        return INSTANCE;
    }

    public ServiceDiscoverer getServiceDiscoverer() {
        if (discoverer != null) {
            return discoverer;
        }
        try {
            // FIXME: This is a hack to trigger the activation of the extensibility-equinox bundle in OSGi
            Class.forName("org.apache.tuscany.sca.extensibility.equinox.EquinoxServiceDiscoverer");
            if (discoverer != null) {
                return discoverer;
            }
        } catch (Throwable e) {
        }
        discoverer = new ContextClassLoaderServiceDiscoverer();
        return discoverer;
    }

    public void setServiceDiscoverer(ServiceDiscoverer sd) {
        if (discoverer != null) {
            throw new IllegalStateException("The ServiceDiscoverer cannot be reset");
        }
        discoverer = sd;
    }

    public Collection<ServiceDeclaration> getServiceDeclarations(String name) throws IOException {
        return getServiceDeclarations(name, false);
    }

    public Collection<ServiceDeclaration> getServiceDeclarations(String name, boolean byRanking) throws IOException {
        Collection<ServiceDeclaration> declarations = getServiceDiscoverer().getServiceDeclarations(name);
        if (!byRanking) {
            return declarations;
        }
        if (!declarations.isEmpty()) {
            List<ServiceDeclaration> declarationList = new ArrayList<ServiceDeclaration>(declarations);
            Collections.sort(declarationList, ServiceComparator.DESCENDING_ORDER);
            return declarationList;
        } else {
            return Collections.emptyList();
        }
    }

    /**
     * Get the service declaration. If there are more than one services, the one with highest ranking will
     * be returned.
     */
    public ServiceDeclaration getServiceDeclaration(final String name) throws IOException {
        //        ServiceDeclaration service = getServiceDiscoverer().getFirstServiceDeclaration(name);
        //        return service;
        Collection<ServiceDeclaration> declarations = getServiceDeclarations(name, true);
        if (!declarations.isEmpty()) {
            List<ServiceDeclaration> declarationList = new ArrayList<ServiceDeclaration>(declarations);
            Collections.sort(declarationList, ServiceComparator.DESCENDING_ORDER);
            return declarationList.get(0);
        } else {
            return null;
        }
    }

    /**
     * Compare service declarations by ranking
     */
    private static class ServiceComparator implements Comparator<ServiceDeclaration> {
        private final static Comparator<ServiceDeclaration> DESCENDING_ORDER = new ServiceComparator();

        public int compare(ServiceDeclaration o1, ServiceDeclaration o2) {
            int rank1 = 0;
            String r1 = o1.getAttributes().get("ranking");
            if (r1 != null) {
                rank1 = Integer.parseInt(r1);
            }
            int rank2 = 0;
            String r2 = o2.getAttributes().get("ranking");
            if (r2 != null) {
                rank2 = Integer.parseInt(r2);
            }
            return rank2 - rank1; // descending
        }
    }

}