**** BEGIN LICENSE BLOCK *****
Version: EPL 2.0/GPL 2.0/LGPL 2.1
The contents of this file are subject to the Eclipse Public
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.eclipse.org/legal/epl-v20.html
Software distributed under the License is distributed on an "AS
IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
implied. See the License for the specific language governing
rights and limitations under the License.
Copyright (C) 2009 Yoko Harada 
Alternatively, the contents of this file may be used under the terms of
either of the GNU General Public License Version 2 or later (the "GPL"),
or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
in which case the provisions of the GPL or the LGPL are applicable instead
of those above. If you wish to allow use of your version of this file only
under the terms of either the GPL or the LGPL, and not to allow others to
use your version of this file under the terms of the EPL, indicate your
decision by deleting the provisions above and replace them with the notice
and other provisions required by the GPL or the LGPL. If you do not delete
the provisions above, a recipient may use your version of this file under
the terms of any one of the EPL, the GPL or the LGPL.
 **** END LICENSE BLOCK *****
/**
 * **** BEGIN LICENSE BLOCK *****
 * Version: EPL 2.0/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Eclipse Public
 * 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.eclipse.org/legal/epl-v20.html
 *
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 *
 * Copyright (C) 2009 Yoko Harada <yokolet@gmail.com>
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either of the GNU General Public License Version 2 or later (the "GPL"),
 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the EPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the EPL, the GPL or the LGPL.
 * **** END LICENSE BLOCK *****
 */
package org.jruby.embed.jsr223;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.StringTokenizer;

Finds SPI based services from classpath.
Author:
Yoko Harada /**
 * Finds SPI based services from classpath.
 *
 * @author Yoko Harada <yokolet@gmail.com>
 */
class ServiceFinder<T> {

    private final Set<T> services;

    ServiceFinder(final String serviceName, ClassLoader loader) throws IOException {
        final Enumeration<URL> urls;

        if (loader == null) {
            loader = ClassLoader.getSystemClassLoader();
            urls = ClassLoader.getSystemResources(serviceName);
        } else {
            urls = loader.getResources(serviceName);
        }

        List<String> classNames = readClassNames(urls);
        services = instantiateClasses(classNames, loader);
    }

    Collection<T> getServices() { return services; }

    private static List<String> readClassNames(Enumeration<URL> urls) {
        String encoding = System.getProperty("file.encoding");
        ArrayList<String> names = new ArrayList<String>();
        while ( urls.hasMoreElements() ) {
            URL url = null;
            try {
                url = urls.nextElement();
                BufferedReader reader =
                        new BufferedReader(new InputStreamReader(url.openStream(), encoding));
                String line;
                while ((line = reader.readLine()) != null) {
                    if ((line = deleteComments(line)) != null) {
                        names.add(line);
                    }
                }
            }
            catch (IOException e) {
                System.err.println("Failed to get a class name from " + url);
                continue;
            }
        }
        return names;
    }

    private static String deleteComments(final String line) {
        if ( line.startsWith("#") ) return null;
        if ( line.length() < 1 ) return null;
        StringTokenizer st = new StringTokenizer(line, "#");
        return ((String) st.nextElement()).trim();
    }

    private Set<T> instantiateClasses(final Collection<String> names,
        final ClassLoader loader) {
        HashSet<T> instances = new HashSet<T>( names.size() );
        for (String name : names) {
            try {
                @SuppressWarnings("unchecked")
                Class<T> clazz = (Class<T>) Class.forName(name, true, loader);
                instances.add( clazz.newInstance() );
            }
            catch (ClassNotFoundException e) {
                System.err.println(name + " was not found");
                continue;
            }
            catch (InstantiationException e) {
                System.err.println(name + " was not instantiated");
                continue;
            }
            catch (IllegalAccessException e) {
                System.err.println(name + " committed illegal access");
                continue;
            }
            catch (Throwable e) {
                System.err.println("failed to instantiate " + name);
                continue;
            }
        }
        return instances;
    }

}