/**
 *
 * Copyright 2003-2004 The Apache Software Foundation
 *
 *  Licensed 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 javax.cache;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Properties;

public class CacheManager {
    protected static CacheManager instance = new CacheManager();
    private final Map caches = Collections.synchronizedMap(new HashMap());

    public static CacheManager getInstance() {
        return instance;
    }

    public Cache getCache(String cacheName) {
        return (Cache) caches.get(cacheName);
    }

    public void registerCache(String cacheName, Cache cache) {
        caches.put(cacheName, cache);
    }

    public CacheFactory getCacheFactory() throws CacheException {
        String name = getImplementationClassName(CacheFactory.class.getName());
        if (name == null) {
            throw new CacheException("No implementation of JCache can be found on the classpath");
        }
        Class type = null;
        try {
            type = Thread.currentThread().getContextClassLoader().loadClass(name);
        }
        catch (ClassNotFoundException e) {
            try {
                type = getClass().getClassLoader().loadClass(name);
            }
            catch (ClassNotFoundException e1) {
                throw new CacheException("Could not find class name: " + name);
            }
        }
        try {
            return (CacheFactory) type.newInstance();
        }
        catch (Exception e) {
            throw new CacheException("Could not instantiate instance of: " + name + ". Reason: " + e, e);
        }
    }

    protected String getImplementationClassName(String interfaceType) {
        try {
            String name = System.getProperty(interfaceType);
            if (name != null && name.length() > 0)
                return name;
        }
        catch (SecurityException e) {
            // ignore security exceptions disallowing us from accessing 
            // system properties
        }

        // lets try META-INF/services
        try {
            InputStream in = getResourceAsStream("META-INF/services/" + interfaceType);
            if (in != null) {
                BufferedReader r = new BufferedReader(new InputStreamReader(in));
                try {
                    String line = r.readLine();
                    if (line != null) {
                        line = line.trim();
                        if (line.length() > 0) {
                            return line;
                        }
                    }
                }
                finally {
                    r.close();
                }
            }
        }
        catch (IOException e) {
            // ignore errors reading the file
        }
        return null;
    }

    protected InputStream getResourceAsStream(String name) {
        InputStream answer = Thread.currentThread().getContextClassLoader().getResourceAsStream(name);
        if (answer == null) {
            answer = getClass().getClassLoader().getResourceAsStream(name);
        }
        return answer;
    }
}