/*
 * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
 * 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
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */

package jdk.dns.client.internal;

import jdk.dns.client.ex.DnsResolverException;
import jdk.dns.conf.DnsResolverConfiguration;

import java.net.InetAddress;
import java.security.PrivilegedAction;
import java.util.ArrayList;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;

public class DnsResolver implements AutoCloseable {
    private DnsClient dnsClient;

    /*
     * Constructs a new Resolver given package oracle.dns.client.standalone;its servers and timeout parameters.
     * Each server is of the form "server[:port]".
     * IPv6 literal host names include delimiting brackets.
     * There must be at least one server.
     * "timeout" is the initial timeout interval (in ms) for UDP queries,
     * and "retries" gives the number of retries per server.
     */
    public DnsResolver() {
        dnsClient = new DnsClient(dnsResolverConfiguration.nameservers(), 1000, 4);
    }

    @Override
    public void close() {
        dnsClient.close();
        dnsClient = null;
    }

    public Set<String> getDomainsSearchList() {
        var domainsToSearch = new LinkedHashSet<String>();
        var domain = dnsResolverConfiguration.domain();
        // First, try the domain
        if (!domain.isBlank()) {
            domainsToSearch.add(domain);
        }
        // Then iterate over the search list
        domainsToSearch.addAll(dnsResolverConfiguration.searchlist());
        if (DEBUG) {
            System.out.printf("Domains search list:%s%n", domainsToSearch);
        }
        return domainsToSearch;
    }

    /*
     * Queries resource records of a particular class and type for a
     * given domain name.
     * Useful values of rrtype are ResourceRecord.[Q]TYPE_xxx.
     */
    public ResourceRecords query(String fqdn, int rrtype)
            throws DnsResolverException {
        return dnsClient.query(new DnsName(fqdn), ResourceRecord.CLASS_INTERNET, rrtype, true, false);
    }

    public List<String> rlookup(String literalIP, InetAddress address) throws DnsResolverException {

        switch (AddressFamily.fromInetAddress(address)) {
            case IPv4:
                return ipv4rlookup(literalIP);
            case IPv6:
                return ipv6rlookup(literalIP);
            default:
                throw new RuntimeException("Only IPv4 and IPv6 addresses are supported");
        }
    }

    private List<String> ipv4rlookup(String literalIP) throws DnsResolverException {
        var request = literalIP + "IN-ADDR.ARPA.";
        var hostNames = new ArrayList<String>();
        var rrs = query(request, ResourceRecord.TYPE_PTR);
        for (int i = 0; i < rrs.answer.size(); i++) {
            ResourceRecord rr = rrs.answer.elementAt(i);
            hostNames.add(rr.getRdata().toString());
        }
        return hostNames;
    }

    private List<String> ipv6rlookup(String literalIP) throws DnsResolverException {
        List<String> hostNames = new ArrayList<>();
        ResourceRecords rrs = query(literalIP + "IP6.ARPA.", ResourceRecord.TYPE_PTR);
        /**
         * Because RFC 3152 changed the root domain name for reverse
         * lookups from IP6.INT. to IP6.ARPA., we need to check
         * both. I.E. first the new one, IP6.ARPA, then if it fails
         * the older one, IP6.INT
         */
        if (rrs.answer.isEmpty()) {
            rrs = query(literalIP + "IP6.INT.", ResourceRecord.TYPE_PTR);
        }
        for (int i = 0; i < rrs.answer.size(); i++) {
            ResourceRecord rr = rrs.answer.elementAt(i);
            hostNames.add(rr.getRdata().toString());
        }
        return hostNames;
    }


    // Configuration file tracker
    private static DnsResolverConfiguration dnsResolverConfiguration = new DnsResolverConfiguration();
    private static final boolean DEBUG = java.security.AccessController.doPrivileged(
            (PrivilegedAction<Boolean>) () -> Boolean.getBoolean("jdk.dns.client.debug"));
}