/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * particular file as subject to the "Classpath" exception as provided

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 */

package com.sun.jndi.dns;

import java.net.MalformedURLException;

import java.util.ArrayList;

import java.util.Hashtable;

import java.util.List;

import javax.naming.*;

import javax.naming.spi.*;

import com.sun.jndi.toolkit.url.UrlUtil;

import sun.net.dns.ResolverConfiguration;       // available since 1.4.1

/**

 * A DnsContextFactory serves as the initial context factory for DNS.

 *

 * <p> When an initial context is being created, the environment

 * property "java.naming.provider.url" should contain a DNS pseudo-URL

 * (see DnsUrl) or a space-separated list of them.  Multiple URLs must

 * all have the same domain value.

 * If the property is not set, the default "dns:" is used.

 *

 * @author Scott Seligman

 */

public class DnsContextFactory implements InitialContextFactory {

    private static final String DEFAULT_URL = "dns:";

    public Context getInitialContext(Hashtable<?,?> env) throws NamingException {

        if (env == null) {

            env = new Hashtable(5);

        }

        return urlToContext(getInitCtxUrl(env), env);

    }

    public static DnsContext getContext(String domain,

                                        String[] servers, Hashtable<?,?> env)

            throws NamingException {

        return new DnsContext(domain, servers, env);

    }

    /*

     * "urls" are used to determine the servers, but any domain

     * components are overridden by "domain".

     */

    public static DnsContext getContext(String domain,

                                        DnsUrl[] urls, Hashtable env)

            throws NamingException {

        String[] servers = serversForUrls(urls);

        DnsContext ctx = getContext(domain, servers, env);

        if (platformServersUsed(urls)) {

            ctx.setProviderUrl(constructProviderUrl(domain, servers));

        }

        return ctx;

    }

    /*

     * Public for use by product test suite.

     */

    public static boolean platformServersAvailable() {

        return !ResolverConfiguration.open().nameservers().isEmpty();

    }

    private static Context urlToContext(String url, Hashtable env)

            throws NamingException {

        DnsUrl[] urls;

        try {

            urls = DnsUrl.fromList(url);

        } catch (MalformedURLException e) {

            throw new ConfigurationException(e.getMessage());

        }

        if (urls.length == 0) {

            throw new ConfigurationException(

                    "Invalid DNS pseudo-URL(s): " + url);

        }

        String domain = urls[0].getDomain();

        // If multiple urls, all must have the same domain.

        for (int i = 1; i < urls.length; i++) {

            if (!domain.equalsIgnoreCase(urls[i].getDomain())) {

                throw new ConfigurationException(

                        "Conflicting domains: " + url);

            }

        }

        return getContext(domain, urls, env);

    }

    /*

     * Returns all the servers specified in a set of URLs.

     * If a URL has no host (or port), the servers configured on the

     * underlying platform are used if possible.  If no configured

     * servers can be found, then fall back to the old behavior of

     * using "localhost".

     * There must be at least one URL.

     */

    private static String[] serversForUrls(DnsUrl[] urls)

            throws NamingException {

        if (urls.length == 0) {

            throw new ConfigurationException("DNS pseudo-URL required");

        }

        List servers = new ArrayList();

        for (int i = 0; i < urls.length; i++) {

            String server = urls[i].getHost();

            int port = urls[i].getPort();

            if (server == null && port < 0) {

                // No server or port given, so look to underlying platform.

                // ResolverConfiguration does some limited caching, so the

                // following is reasonably efficient even if called rapid-fire.

                List platformServers =

                    ResolverConfiguration.open().nameservers();

                if (!platformServers.isEmpty()) {

                    servers.addAll(platformServers);

                    continue;  // on to next URL (if any, which is unlikely)

                }

            }

            if (server == null) {

                server = "localhost";

            }

            servers.add((port < 0)

                        ? server

                        : server + ":" + port);

        }

        return (String[]) servers.toArray(

                                        new String[servers.size()]);

    }

    /*

     * Returns true if serversForUrls(urls) would make use of servers

     * from the underlying platform.

     */

    private static boolean platformServersUsed(DnsUrl[] urls) {

        if (!platformServersAvailable()) {

            return false;

        }

        for (int i = 0; i < urls.length; i++) {

            if (urls[i].getHost() == null &&

                urls[i].getPort() < 0) {

                return true;

            }

        }

        return false;

    }

    /*

     * Returns a value for the PROVIDER_URL property (space-separated URL

     * Strings) that reflects the given domain and servers.

     * Each server is of the form "server[:port]".

     * There must be at least one server.

     * IPv6 literal host names include delimiting brackets.

     */

    private static String constructProviderUrl(String domain,

                                               String[] servers) {

        String path = "";

        if (!domain.equals(".")) {

            try {

                path = "/" + UrlUtil.encode(domain, "ISO-8859-1");

            } catch (java.io.UnsupportedEncodingException e) {

                // assert false : "ISO-Latin-1 charset unavailable";

            }

        }

        StringBuffer buf = new StringBuffer();

        for (int i = 0; i < servers.length; i++) {

            if (i > 0) {

                buf.append(' ');

            }

            buf.append("dns://").append(servers[i]).append(path);

        }

        return buf.toString();

    }

    /*

     * Reads environment to find URL(s) of initial context.

     * Default URL is "dns:".

     */

    private static String getInitCtxUrl(Hashtable env) {

        String url = (String) env.get(Context.PROVIDER_URL);

        return ((url != null) ? url : DEFAULT_URL);

    }

}