package eu.siacs.conversations.utils;

import android.annotation.TargetApi;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.LinkProperties;
import android.net.Network;
import android.net.RouteInfo;
import android.os.Build;

import java.io.IOException;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.List;
import java.util.TreeSet;
import java.util.regex.Pattern;

import de.measite.minidns.Client;
import de.measite.minidns.DNSMessage;
import de.measite.minidns.Record;
import de.measite.minidns.Record.CLASS;
import de.measite.minidns.Record.TYPE;
import de.measite.minidns.record.Data;
import de.measite.minidns.record.SRV;
import de.measite.minidns.util.NameUtil;
import de.thedevstack.android.logcat.Logging;
import de.thedevstack.conversationsplus.ConversationsPlusApplication;
import de.thedevstack.conversationsplus.dto.SrvRecord;
import eu.siacs.conversations.Config;
import eu.siacs.conversations.xmpp.jid.Jid;

public class DNSHelper {
    private static final String CLIENT_SRV_PREFIX = "_xmpp-client._tcp.";
    private static final String SECURE_CLIENT_SRV_PREFIX = "_xmpps-client._tcp.";
	private static final Pattern PATTERN_IPV4 = Pattern.compile("\\A(25[0-5]|2[0-4]\\d|[0-1]?\\d?\\d)(\\.(25[0-5]|2[0-4]\\d|[0-1]?\\d?\\d)){3}\\z");
	private static final Pattern PATTERN_IPV6_HEX4DECCOMPRESSED = Pattern.compile("\\A((?:[0-9A-Fa-f]{1,4}(?::[0-9A-Fa-f]{1,4})*)?) ::((?:[0-9A-Fa-f]{1,4}:)*)(25[0-5]|2[0-4]\\d|[0-1]?\\d?\\d)(\\.(25[0-5]|2[0-4]\\d|[0-1]?\\d?\\d)){3}\\z");
	private static final Pattern PATTERN_IPV6_6HEX4DEC = Pattern.compile("\\A((?:[0-9A-Fa-f]{1,4}:){6,6})(25[0-5]|2[0-4]\\d|[0-1]?\\d?\\d)(\\.(25[0-5]|2[0-4]\\d|[0-1]?\\d?\\d)){3}\\z");
	private static final Pattern PATTERN_IPV6_HEXCOMPRESSED = Pattern.compile("\\A((?:[0-9A-Fa-f]{1,4}(?::[0-9A-Fa-f]{1,4})*)?)::((?:[0-9A-Fa-f]{1,4}(?::[0-9A-Fa-f]{1,4})*)?)\\z");
	private static final Pattern PATTERN_IPV6 = Pattern.compile("\\A(?:[0-9a-fA-F]{1,4}:){7}[0-9a-fA-F]{1,4}\\z");

	protected static Client client = new Client();

    static {
        client.setTimeout(Config.PING_TIMEOUT * 1000);
    }

    /**
     * Queries the SRV record for the server JID.
     * This method uses all available Domain Name Servers.
     * @param jid the server JID
     * @return TreeSet with SrvRecords. If no SRV record is found for JID an empty TreeSet is returned.
     */
    public static final TreeSet<SrvRecord> querySrvRecord(Jid jid) {
        String host = jid.getDomainpart();
        TreeSet<SrvRecord> result = new TreeSet<>();

        final List<InetAddress> dnsServers = Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP ? getDnsServers() : getDnsServersPreLollipop();

        if (dnsServers != null) {
            for (InetAddress dnsServer : dnsServers) {
                result = querySrvRecord(host, dnsServer);
                if (!result.isEmpty()) {
                    break;
                }
            }
        }

        return result;
    }

	@TargetApi(21)
	private static List<InetAddress> getDnsServers() {
		List<InetAddress> servers = new ArrayList<>();
		ConnectivityManager connectivityManager = (ConnectivityManager) ConversationsPlusApplication.getInstance().getSystemService(Context.CONNECTIVITY_SERVICE);
		Network[] networks = connectivityManager == null ? null : connectivityManager.getAllNetworks();
		if (networks == null) {
			return getDnsServersPreLollipop();
		}
		for(int i = 0; i < networks.length; ++i) {
			LinkProperties linkProperties = connectivityManager.getLinkProperties(networks[i]);
			if (linkProperties != null) {
				if (hasDefaultRoute(linkProperties)) {
					servers.addAll(0, linkProperties.getDnsServers());
				} else {
					servers.addAll(linkProperties.getDnsServers());
				}
			}
		}
		if (servers.size() > 0) {
            Logging.d("dns", "used lollipop variant to discover dns servers in " + networks.length + " networks");
		}
		return servers.size() > 0 ? servers : getDnsServersPreLollipop();
	}

	@TargetApi(Build.VERSION_CODES.LOLLIPOP)
	private static boolean hasDefaultRoute(LinkProperties linkProperties) {
		for(RouteInfo route: linkProperties.getRoutes()) {
			if (route.isDefaultRoute()) {
				return true;
			}
		}
		return false;
	}

	private static List<InetAddress> getDnsServersPreLollipop() {
		List<InetAddress> servers = new ArrayList<>();
		String[] dns = client.findDNS();
		for(int i = 0; i < dns.length; ++i) {
			try {
				servers.add(InetAddress.getByName(dns[i]));
			} catch (UnknownHostException e) {
				//ignore
			}
		}
		return servers;
	}

    /**
     * Queries the SRV record for an host from the given Domain Name Server.
     * @param host the host to query for
     * @param dnsServerAddress the DNS to query on
     * @return TreeSet with SrvRecords.
     */
    private static final TreeSet<SrvRecord> querySrvRecord(String host, InetAddress dnsServerAddress) {
        TreeSet<SrvRecord> result = new TreeSet<>();
        querySrvRecord(host, dnsServerAddress, false, result);
        querySrvRecord(host, dnsServerAddress, true, result);
        return result;
    }

    private static final void querySrvRecord(String host, InetAddress dnsServerAddress, boolean tlsSrvRecord, TreeSet<SrvRecord> result) {
        String qname = (tlsSrvRecord ? SECURE_CLIENT_SRV_PREFIX : CLIENT_SRV_PREFIX) + host;
        String dnsServerHostAddress = dnsServerAddress.getHostAddress();
        Logging.d("dns", "using dns server: " + dnsServerHostAddress + " to look up " + qname);
        try {
            DNSMessage message = client.query(qname, TYPE.SRV, CLASS.IN, dnsServerHostAddress);
            Record[] rrset = message.getAnswers();
            for (Record rr : rrset) {
                Data d = rr.getPayload();
                if (d instanceof SRV && NameUtil.idnEquals(qname, rr.getName())) {
                    SRV srv = (SRV) d;
                    SrvRecord srvRecord = new SrvRecord(srv.getPriority(), srv.getName(), srv.getPort(), tlsSrvRecord);
                    result.add(srvRecord);
                }
            }
        } catch (IOException e) {
            Logging.d("dns", "Error while retrieving SRV record '" + qname + "' for '" + host + "' from DNS '" + dnsServerHostAddress + "': " + e.getMessage());
        }
    }

	public static boolean isIp(final String server) {
		return server != null && (
				PATTERN_IPV4.matcher(server).matches()
				|| PATTERN_IPV6.matcher(server).matches()
				|| PATTERN_IPV6_6HEX4DEC.matcher(server).matches()
				|| PATTERN_IPV6_HEX4DECCOMPRESSED.matcher(server).matches()
				|| PATTERN_IPV6_HEXCOMPRESSED.matcher(server).matches());
	}
}