Copyright 2014 Netflix, Inc.
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.
/**
 * Copyright 2014 Netflix, Inc.
 *
 * 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 com.netflix.config.sources;

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Properties;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.netflix.config.PollResult;
import com.netflix.config.PolledConfigurationSource;
import com.netflix.config.util.ConfigurationUtils;

A polled configuration source based on a set of URLs. For each poll,
it always returns the complete union of properties defined in all files. If one property
is defined in more than one URL, the value in file later on the list will override
the value in the previous one. The content of the URL should conform to the properties file format.
Author:
awang/**
 * A polled configuration source based on a set of URLs. For each poll,
 * it always returns the complete union of properties defined in all files. If one property
 * is defined in more than one URL, the value in file later on the list will override
 * the value in the previous one. The content of the URL should conform to the properties file format.
 * 
 * @author awang
 *
 */
public class URLConfigurationSource implements PolledConfigurationSource {

    private final URL[] configUrls;
    
    
System property name to define a set of URLs to be used by the
default constructor. 
/**
     * System property name to define a set of URLs to be used by the
     * default constructor. 
     */
    public static final String CONFIG_URL = "archaius.configurationSource.additionalUrls";
    
    
Default configuration file name to be used by default constructor. This file should be on the classpath. The file name can be overridden by the value of system property DEFAULT_CONFIG_FILE_PROPERTY. /**
     * Default configuration file name to be used by default constructor. This file should
     * be on the classpath. The file name can be overridden by the value of system property
     * {@link #DEFAULT_CONFIG_FILE_PROPERTY}.
     */
    public static final String DEFAULT_CONFIG_FILE_NAME = "config.properties";

    
System property name to be used to learn the location of the configuration file name
on the classpath.
/**
     * System property name to be used to learn the location of the configuration file name
     * on the classpath.
     */
    public static final String DEFAULT_CONFIG_FILE_PROPERTY = "archaius.configurationSource.defaultFileName";

    public static final String DEFAULT_CONFIG_FILE_FROM_CLASSPATH = System.getProperty(DEFAULT_CONFIG_FILE_PROPERTY, DEFAULT_CONFIG_FILE_NAME);

    private static final Logger logger = LoggerFactory.getLogger(URLConfigurationSource.class);

    
Create an instance with a list URLs to be used.
Params:
urls – list of URLs to be used/**
     * Create an instance with a list URLs to be used.
     * 
     * @param urls list of URLs to be used
     */
    public URLConfigurationSource(String... urls) {
       configUrls = createUrls(urls);
    }
    
    private static URL[] createUrls(String... urlStrings) {
        if (urlStrings == null || urlStrings.length == 0) {
            throw new IllegalArgumentException("urlStrings is null or empty");
        }
        URL[] urls = new URL[urlStrings.length];
        try {
            for (int i = 0; i < urls.length; i++) {
                urls[i] = new URL(urlStrings[i]);
            }
        } catch (Throwable e) {
            throw new RuntimeException(e);
        }
        return urls;        
    }
    
    
Create an instance with a list URLs to be used.
Params:
urls – list of URLs to be used/**
     * Create an instance with a list URLs to be used.
     * 
     * @param urls list of URLs to be used
     */
    public URLConfigurationSource(URL... urls) {
        configUrls = urls;
    }
    
    
Create the instance for the default list of URLs, which is composed by the following order

A configuration file (default name to be config.properties, see DEFAULT_CONFIG_FILE_NAME) on the classpath 
A list of URLs defined by system property "archaius.configurationSource.additionalUrls" with values separated by comma ",".

/**
     * Create the instance for the default list of URLs, which is composed by the following order
     * 
     * <ul>
     * <li>A configuration file (default name to be <code>config.properties</code>, see {@link #DEFAULT_CONFIG_FILE_NAME}) on the classpath
     * <li>A list of URLs defined by system property {@value #CONFIG_URL} with values separated by comma <code>","</code>.
     * </ul>
     */
    public URLConfigurationSource() {
        List<URL> urlList = new ArrayList<URL>();
        URL configFromClasspath = getConfigFileFromClasspath();
        if (configFromClasspath != null) {
            urlList.add(configFromClasspath);
        }
        String[] fileNames = getDefaultFileSources();
        if (fileNames.length != 0) {
            urlList.addAll(Arrays.asList(createUrls(fileNames)));                    
        } 
        if (urlList.size() == 0) { 
            configUrls = new URL[0];
            logger.warn("No URLs will be polled as dynamic configuration sources.");
            logger.info("To enable URLs as dynamic configuration sources, define System property " 
                    + CONFIG_URL + " or make " + DEFAULT_CONFIG_FILE_FROM_CLASSPATH + " available on classpath.");
        } else {
            configUrls = urlList.toArray(new URL[urlList.size()]);
            logger.info("URLs to be used as dynamic configuration source: " + urlList);
        }
    }
    
    private URL getConfigFileFromClasspath() {
        URL url = null;
        // attempt to load from the context classpath
        ClassLoader loader = Thread.currentThread().getContextClassLoader();
        if (loader != null) {
            url = loader.getResource(DEFAULT_CONFIG_FILE_FROM_CLASSPATH);
        }
        if (url == null) {
            // attempt to load from the system classpath
            url = ClassLoader.getSystemResource(DEFAULT_CONFIG_FILE_FROM_CLASSPATH);
        }
        if (url == null) {
            // attempt to load from the system classpath
            url = URLConfigurationSource.class.getResource(DEFAULT_CONFIG_FILE_FROM_CLASSPATH);
        }
        return url;
    }
    
    public List<URL> getConfigUrls() {
        return Collections.unmodifiableList(Arrays.asList(configUrls));
    }
    
    private static final String[] getDefaultFileSources() {
        String name = System.getProperty(CONFIG_URL);
        String[] fileNames;
        if (name != null) {
            fileNames = name.split(",");
        } else {
            fileNames = new String[0];
        }
        return fileNames;
    }
    
    
    
Retrieve the content of the property files. For each poll, it always
returns the complete union of properties defined in all URLs. If one
property is defined in content of more than one URL, the value in file later on the
list will override the value in the previous one. 
Params:
initial – this parameter is ignored by the implementation
checkPoint – this parameter is ignored by the implementation
Throws:
IOException – IOException occurred in file operation/**
     * Retrieve the content of the property files. For each poll, it always
     * returns the complete union of properties defined in all URLs. If one
     * property is defined in content of more than one URL, the value in file later on the
     * list will override the value in the previous one. 
     * 
     * @param initial this parameter is ignored by the implementation
     * @param checkPoint this parameter is ignored by the implementation
     * @throws IOException IOException occurred in file operation
     */
    @Override
    public PollResult poll(boolean initial, Object checkPoint)
            throws IOException {    
        if (configUrls == null || configUrls.length == 0) {
            return PollResult.createFull(null);
        }
        Map<String, Object> map = new HashMap<String, Object>();
        for (URL url: configUrls) {
            InputStream fin = url.openStream();
            Properties props = ConfigurationUtils.loadPropertiesFromInputStream(fin);
            for (Entry<Object, Object> entry: props.entrySet()) {
                map.put((String) entry.getKey(), entry.getValue());
            }
        }
        return PollResult.createFull(map);
    }

    @Override
    public String toString() {
        return "FileConfigurationSource [fileUrls=" + Arrays.toString(configUrls)
                + "]";
    }    
}