/*

 * 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

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package jdk.dns.client;

import jdk.dns.client.ex.DnsResolverException;

import jdk.dns.client.internal.DnsName;

import jdk.dns.client.internal.HostsFileResolver;

import jdk.dns.client.internal.Resolver;

import jdk.dns.client.internal.ResourceClassType;

import jdk.dns.client.internal.ResourceRecord;

import jdk.dns.client.internal.ResourceRecords;

import jdk.dns.conf.DnsResolverConfiguration;

import sun.net.util.IPAddressUtil;

import java.net.InetAddress;

import java.net.ProtocolFamily;

import java.net.UnknownHostException;

import java.security.PrivilegedAction;

import java.util.ArrayList;

import java.util.Collections;

import java.util.LinkedHashSet;

import java.util.List;

import java.util.Set;

import java.util.stream.Collectors;

public class NetworkNamesResolver {

    private final AddressFamily addressFamily;

    public static NetworkNamesResolver open() throws UnknownHostException {

        return new NetworkNamesResolver(AddressFamily.ANY);

    }

    public static NetworkNamesResolver open(ProtocolFamily protocolFamily) throws UnknownHostException {

        return new NetworkNamesResolver(AddressFamily.fromProtocolFamily(protocolFamily));

    }

    private NetworkNamesResolver(AddressFamily addressFamily) throws UnknownHostException {

        this.addressFamily = addressFamily;

        this.dnsResolver = new Resolver(dnsResolverConfiguration.nameservers(), 1000, 4);

    }

    /**

     * Lookup the IP address of a host.

     * The family of required address needed can be specified with {@code addressFamily} parameter.

     *

     * @param hostname the specified host name

     * @return first IP address that matches requested {@code addressFamily}

     * @throws UnknownHostException  if no IP address found for the specified host name and the specified address family

     */

    public InetAddress lookupHostAddr(String hostname) throws UnknownHostException {

        // First try hosts file

        // TODO: Add nsswitch.conf to select proper order

        try {

            return hostsFileResolver.getHostAddress(hostname, addressFamily);

        } catch (UnknownHostException uhe) {

            if (DEBUG) {

                System.err.printf("Hosts file doesn't know '%s' host with '%s' address family%n",

                        hostname, addressFamily.toString());

            }

        }

        // If no luck - try to ask name servers

        try {

            var results = lookup(hostname, addressFamily, true, true, 0);

            if (results.isEmpty()) {

                throw new UnknownHostException(hostname);

            }

            return results.get(0);

        } catch (DnsResolverException e) {

            UnknownHostException uhe = new UnknownHostException(hostname);

            uhe.initCause(e);

            throw uhe;

        }

    }

    /**

     * <p>Lookup a host mapping by name. Retrieve the IP addresses

     * associated with a host.

     *

     * @param hostname the specified hostname

     * @return array of IP addresses for the requested host

     * @throws UnknownHostException if no IP address for the {@code hostname} could be found

     */

    public List<InetAddress> lookupAllHostAddr(String hostname) throws UnknownHostException {

        // First try hosts file

        // TODO: Add nsswitch.conf ReloadTracker and parser to select proper order

        try {

            return List.of(hostsFileResolver.getHostAddress(hostname));

        } catch (UnknownHostException uhe) {

            if (DEBUG) {

                System.err.printf("Resolver API: Hosts file doesn't know '%s' host%n", hostname);

            }

        }

        try {

            var results = lookup(hostname, AddressFamily.ANY, false, true, 0);

            if (results.isEmpty()) {

                throw new UnknownHostException(hostname + " unknown host name");

            }

            return results;

        } catch (DnsResolverException e) {

            UnknownHostException uhe = new UnknownHostException(hostname);

            uhe.initCause(e);

            throw uhe;

        }

    }

    /**

     * Lookup the host name  corresponding to the IP address provided.

     *

     * @param address the specified IP address

     * @return {@code String} representing the host name

     * @throws UnknownHostException if no host found for the specified IP address

     */

    public String getHostByAddr(InetAddress address) throws UnknownHostException {

        var results = getAllHostsByAddr(address);

        return results.get(0);

    }

    /**

     * Lookup all known host names which correspond to the IP address provided

     *

     * @param address the specified IP address

     * @return array of {@code String} representing the host names

     * @throws UnknownHostException if no host found for the specified IP address

     */

    public List<String> getAllHostsByAddr(InetAddress address) throws UnknownHostException {

        // First try hosts file

        // TODO: Add nsswitch.conf to select proper order

        try {

            return List.of(hostsFileResolver.getByAddress(address));

        } catch (UnknownHostException uhe) {

            if (DEBUG) {

                System.err.printf("Resolver API: No host in hosts file with %s address%n", address);

            }

        }

        try {

            var literalIP = addressToLiteralIP(address);

            var family = AddressFamily.fromInetAddress(address);

            var results = rlookup(literalIP, family);

            if (results.isEmpty()) {

                throw new UnknownHostException();

            }

            // remove trailing dot

            return results.stream()

                    .map(host -> host.endsWith(".") ? host.substring(0, host.length() - 1) : host)

                    .collect(Collectors.toList());

        } catch (DnsResolverException dre) {

            UnknownHostException uhe = new UnknownHostException();

            uhe.initCause(dre);

            throw uhe;

        }

    }

    private Set<String> prepareDomainsSearchList() {

        var domainsToSearch = new LinkedHashSet<String>();

        var domain = dnsResolverConfiguration.domain();

        // First will try the domain

        if (!domain.isBlank()) {

            domainsToSearch.add(domain);

        }

        // Then will iterate over search list

        domainsToSearch.addAll(dnsResolverConfiguration.searchlist());

        if (DEBUG) {

            System.out.printf("Domains search list:%s%n", domainsToSearch);

        }

        return domainsToSearch;

    }

    private List<InetAddress> lookup(String host, AddressFamily addressFamily, boolean oneIsEnough, boolean checkDomains, int depth) throws UnknownHostException, DnsResolverException {

        if (DEBUG) {

            System.out.printf("Resolver API: internal lookup call - %s%n", host);

        }

        // Will remain the same during DNS queries execution

        ResourceClassType ct = ResourceClassType.fromAddressFamily(addressFamily);

        ResourceRecords rrs = null;

        // First try to get the resource records with the requested DNS host name if it is FQDN

        if (host.contains(".")) {

            rrs = execAddrResolutionQuery(new DnsName(host), ct);

        }

        // Non-FQDN or not known host address and domains still can be checked

        if ((rrs == null || rrs.answer.isEmpty()) && checkDomains) {

            for (String domain : prepareDomainsSearchList()) {

                String hostWithSuffix = host + "." + domain;

                if (DEBUG) {

                    System.err.printf("Resolver API: Trying to lookup:'%s'%n", hostWithSuffix);

                }

                rrs = execAddrResolutionQuery(new DnsName(hostWithSuffix), ct);

                if (rrs != null && !rrs.answer.isEmpty()) {

                    if (DEBUG) {

                        System.err.printf("Resolver API: Found host in '%s' domain%n", domain);

                    }

                    break;

                }

            }

        }

        // If no answers then host is not known in registered domain

        if (rrs == null || rrs.answer.isEmpty()) {

            throw new UnknownHostException(host);

        }

        // Parse answers

        List<InetAddress> results = new ArrayList<>();

        for (int i = 0; i < rrs.answer.size(); i++) {

            ResourceRecord rr = rrs.answer.elementAt(i);

            int answerType = rr.getType();

            String recordData = rr.getRdata().toString();

            if (DEBUG) {

                System.err.printf("Resolver API: Got %s type: %s%n", ResourceRecord.getTypeName(rr.getType()), rr.getRdata());

            }

            if (answerType == ResourceRecord.TYPE_CNAME) {

                // We've got CNAME entry - issue another request to resolve the canonical host name

                if (depth > MAX_CNAME_RESOLUTION_DEPTH) {

                    throw new UnknownHostException(host);

                }

                List<InetAddress> cnameResults = lookup(recordData, addressFamily, oneIsEnough, false, depth + 1);

                if (oneIsEnough) {

                    return cnameResults;

                } else {

                    results.addAll(cnameResults);

                }

            } else {

                byte[] addrBytes;

                if (answerType == ResourceRecord.TYPE_A && (addressFamily == AddressFamily.IPv4 || addressFamily == AddressFamily.ANY)) {

                    addrBytes = IPAddressUtil.textToNumericFormatV4(recordData);

                    if (addrBytes == null) {

                        if (DEBUG) {

                            System.err.println("Incorrect A resource record answer");

                        }

                        return Collections.emptyList();

                    }

                } else if (answerType == ResourceRecord.TYPE_AAAA && (addressFamily == AddressFamily.IPv6 || addressFamily == AddressFamily.ANY)) {

                    addrBytes = IPAddressUtil.textToNumericFormatV6(recordData);

                    if (addrBytes == null) {

                        if (DEBUG) {

                            System.err.println("Incorrect AAAA resource record answer");

                        }

                        return Collections.emptyList();

                    }

                } else {

                    continue;

                }

                // IPAddressUtil.textToNumeric can return null

                if (addrBytes == null) {

                    throw new RuntimeException("Internal error");

                }

                InetAddress address = InetAddress.getByAddress(host, addrBytes);

                results.add(address);

                if (oneIsEnough) {

                    break;

                }

            }

        }

        return results;

    }

    // Can return null if query failed

    private ResourceRecords execAddrResolutionQuery(DnsName name, ResourceClassType ct) {

        // Not supporting authoritative requests [for now?]

        try {

            ResourceRecords rrs = dnsResolver.query(name, ct.getRecordClass(), ct.getRecordType(),

                    true, false);

            return rrs.hasAddressOrAlias() ? rrs : null;

        } catch (DnsResolverException e) {

            if (DEBUG) {

                System.err.println("Query failed:" + e.getMessage());

                e.printStackTrace();

            }

            return null;

        }

    }

    private List<String> rlookup(String literalIP, AddressFamily family) throws DnsResolverException {

        switch (family) {

            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 name = new DnsName(request);

        var rrs = dnsResolver.query(name, ResourceRecord.CLASS_INTERNET,

                ResourceRecord.TYPE_PTR, true, false);

        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<>();

        DnsName name = new DnsName(literalIP + "IP6.ARPA.");

        ResourceRecords rrs = dnsResolver.query(name, ResourceRecord.CLASS_INTERNET,

                ResourceRecord.TYPE_PTR, true, false);

        /**

         * 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()) {

            name = new DnsName(literalIP + "IP6.INT.");

            rrs = dnsResolver.query(name, ResourceRecord.CLASS_INTERNET,

                    ResourceRecord.TYPE_PTR, true, false);

        }

        for (int i = 0; i < rrs.answer.size(); i++) {

            ResourceRecord rr = rrs.answer.elementAt(i);

            hostNames.add(rr.getRdata().toString());

        }

        return hostNames;

    }

    private static String addressToLiteralIP(InetAddress address) {

        byte[] bytes = address.getAddress();

        StringBuilder addressBuff = new StringBuilder();

        // IPv4 address

        if (bytes.length == 4) {

            for (int i = bytes.length - 1; i >= 0; i--) {

                addressBuff.append(bytes[i] & 0xff);

                addressBuff.append(".");

            }

        // IPv6 address

        } else if (bytes.length == 16) {

            for (int i = bytes.length - 1; i >= 0; i--) {

                addressBuff.append(Integer.toHexString((bytes[i] & 0x0f)));

                addressBuff.append(".");

                addressBuff.append(Integer.toHexString((bytes[i] & 0xf0) >> 4));

                addressBuff.append(".");

            }

        } else {

            return null;

        }

        return addressBuff.toString();

    }

    private static DnsResolverConfiguration dnsResolverConfiguration = new DnsResolverConfiguration();

    private static HostsFileResolver hostsFileResolver = new HostsFileResolver();

    // TODO: Add system property with the sequence of resolution OR nsswitch.conf location to get the order:

    //     file, name

    private final Resolver dnsResolver;

    private static final boolean DEBUG = java.security.AccessController.doPrivileged(

            (PrivilegedAction<Boolean>) () -> Boolean.getBoolean("jdk.dns.client.debug"));

    private static final int MAX_CNAME_RESOLUTION_DEPTH = 4;

}