package eu.siacs.conversations.utils;

import android.content.ContentValues;
import android.database.Cursor;
import android.support.annotation.NonNull;
import android.util.Log;

import java.io.IOException;
import java.net.Inet4Address;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;

import de.measite.minidns.DNSClient;
import de.measite.minidns.DNSName;
import de.measite.minidns.Question;
import de.measite.minidns.Record;
import de.measite.minidns.dnssec.DNSSECResultNotAuthenticException;
import de.measite.minidns.dnsserverlookup.AndroidUsingExec;
import de.measite.minidns.hla.DnssecResolverApi;
import de.measite.minidns.hla.ResolverApi;
import de.measite.minidns.hla.ResolverResult;
import de.measite.minidns.record.A;
import de.measite.minidns.record.AAAA;
import de.measite.minidns.record.CNAME;
import de.measite.minidns.record.Data;
import de.measite.minidns.record.InternetAddressRR;
import de.measite.minidns.record.SRV;
import de.measite.minidns.util.MultipleIoException;
import eu.siacs.conversations.Config;
import eu.siacs.conversations.R;
import eu.siacs.conversations.services.XmppConnectionService;

public class Resolver {

	private static final String DIRECT_TLS_SERVICE = "_xmpps-client";
	private static final String STARTTLS_SERICE = "_xmpp-client";

	private static final String NETWORK_IS_UNREACHABLE = "Network is unreachable";

	private static XmppConnectionService SERVICE = null;


	public static void init(XmppConnectionService service) {
		Resolver.SERVICE = service;
		DNSClient.removeDNSServerLookupMechanism(AndroidUsingExec.INSTANCE);
		DNSClient.addDnsServerLookupMechanism(AndroidUsingExecLowPriority.INSTANCE);
		DNSClient.addDnsServerLookupMechanism(new AndroidUsingLinkProperties(service));
	}

	public static List<Result> resolve(String domain) throws NetworkIsUnreachableException {
		List<Result> results = new ArrayList<>();
		HashSet<String> messages = new HashSet<>();
		try {
			results.addAll(resolveSrv(domain, true));
		} catch (MultipleIoException e) {
			messages.addAll(extractMessages(e));
		} catch (Throwable throwable) {
			Log.d(Config.LOGTAG, Resolver.class.getSimpleName() + ": error resolving SRV record (direct TLS)", throwable);
		}
		try {
			results.addAll(resolveSrv(domain, false));
		} catch (MultipleIoException e) {
			messages.addAll(extractMessages(e));
		} catch (Throwable throwable) {
			Log.d(Config.LOGTAG, Resolver.class.getSimpleName() + ": error resolving SRV record (STARTTLS)", throwable);
		}
		if (results.size() == 0) {
			if (messages.size() == 1 && messages.contains(NETWORK_IS_UNREACHABLE)) {
				throw new NetworkIsUnreachableException();
			}
			results.addAll(resolveNoSrvRecords(DNSName.from(domain), true));
		}
		Collections.sort(results);
		Log.d(Config.LOGTAG, Resolver.class.getSimpleName() + ": " + results.toString());
		return results;
	}

	private static HashSet<String> extractMessages(MultipleIoException e) {
		HashSet<String> messages = new HashSet<>();
		for (Exception inner : e.getExceptions()) {
			if (inner instanceof MultipleIoException) {
				messages.addAll(extractMessages((MultipleIoException) inner));
			} else {
				messages.add(inner.getMessage());
			}
		}
		return messages;
	}

	private static List<Result> resolveSrv(String domain, final boolean directTls) throws IOException {
		if (Thread.currentThread().isInterrupted()) {
			return Collections.emptyList();
		}
		DNSName dnsName = DNSName.from((directTls ? DIRECT_TLS_SERVICE : STARTTLS_SERICE) + "._tcp." + domain);
		ResolverResult<SRV> result = resolveWithFallback(dnsName, SRV.class);
		List<Result> results = new ArrayList<>();
		for (SRV record : result.getAnswersOrEmptySet()) {
			if (record.name.length() == 0 && record.priority == 0) {
				continue;
			}
			final boolean addedIPv4 = results.addAll(resolveIp(record, A.class, result.isAuthenticData(), directTls));
			results.addAll(resolveIp(record, AAAA.class, result.isAuthenticData(), directTls));
			if (!addedIPv4 && !Thread.currentThread().isInterrupted()) {
				Result resolverResult = Result.fromRecord(record, directTls);
				resolverResult.authenticated = resolverResult.isAuthenticated();
				results.add(resolverResult);
			}
		}
		return results;
	}

	private static <D extends InternetAddressRR> List<Result> resolveIp(SRV srv, Class<D> type, boolean authenticated, boolean directTls) {
		if (Thread.currentThread().isInterrupted()) {
			return Collections.emptyList();
		}
		List<Result> list = new ArrayList<>();
		try {
			ResolverResult<D> results = resolveWithFallback(srv.name, type, authenticated);
			for (D record : results.getAnswersOrEmptySet()) {
				Result resolverResult = Result.fromRecord(srv, directTls);
				resolverResult.authenticated = results.isAuthenticData() && authenticated;
				resolverResult.ip = record.getInetAddress();
				list.add(resolverResult);
			}
		} catch (Throwable t) {
			Log.d(Config.LOGTAG, Resolver.class.getSimpleName() + ": error resolving " + type.getSimpleName() + " " + t.getMessage());
		}
		return list;
	}

	private static List<Result> resolveNoSrvRecords(DNSName dnsName, boolean withCnames) {
		List<Result> results = new ArrayList<>();
		try {
			for (A a : resolveWithFallback(dnsName, A.class, false).getAnswersOrEmptySet()) {
				results.add(Result.createDefault(dnsName, a.getInetAddress()));
			}
			for (AAAA aaaa : resolveWithFallback(dnsName, AAAA.class, false).getAnswersOrEmptySet()) {
				results.add(Result.createDefault(dnsName, aaaa.getInetAddress()));
			}
			if (results.size() == 0 && withCnames) {
				for (CNAME cname : resolveWithFallback(dnsName, CNAME.class, false).getAnswersOrEmptySet()) {
					results.addAll(resolveNoSrvRecords(cname.name, false));
				}
			}
		} catch (Throwable throwable) {
			Log.d(Config.LOGTAG, Resolver.class.getSimpleName() + "error resolving fallback records", throwable);
		}
		results.add(Result.createDefault(dnsName));
		return results;
	}

	private static <D extends Data> ResolverResult<D> resolveWithFallback(DNSName dnsName, Class<D> type) throws IOException {
		return resolveWithFallback(dnsName, type, validateHostname());
	}

	private static <D extends Data> ResolverResult<D> resolveWithFallback(DNSName dnsName, Class<D> type, boolean validateHostname) throws IOException {
		final Question question = new Question(dnsName, Record.TYPE.getType(type));
		if (!validateHostname) {
			return ResolverApi.INSTANCE.resolve(question);
		}
		try {
			return DnssecResolverApi.INSTANCE.resolveDnssecReliable(question);
		} catch (DNSSECResultNotAuthenticException e) {
			Log.d(Config.LOGTAG, Resolver.class.getSimpleName() + ": error resolving " + type.getSimpleName() + " with DNSSEC. Trying DNS instead.", e);
		} catch (IOException e) {
			throw e;
		} catch (Throwable throwable) {
			Log.d(Config.LOGTAG, Resolver.class.getSimpleName() + ": error resolving " + type.getSimpleName() + " with DNSSEC. Trying DNS instead.", throwable);
		}
		return ResolverApi.INSTANCE.resolve(question);
	}

	private static boolean validateHostname() {
		return SERVICE != null && SERVICE.getBooleanPreference("validate_hostname", R.bool.validate_hostname);
	}

	public static class Result implements Comparable<Result> {
		@Override
		public boolean equals(Object o) {
			if (this == o) return true;
			if (o == null || getClass() != o.getClass()) return false;

			Result result = (Result) o;

			if (port != result.port) return false;
			if (directTls != result.directTls) return false;
			if (authenticated != result.authenticated) return false;
			if (priority != result.priority) return false;
			if (ip != null ? !ip.equals(result.ip) : result.ip != null) return false;
			return hostname != null ? hostname.equals(result.hostname) : result.hostname == null;
		}

		@Override
		public int hashCode() {
			int result = ip != null ? ip.hashCode() : 0;
			result = 31 * result + (hostname != null ? hostname.hashCode() : 0);
			result = 31 * result + port;
			result = 31 * result + (directTls ? 1 : 0);
			result = 31 * result + (authenticated ? 1 : 0);
			result = 31 * result + priority;
			return result;
		}

		public static final String DOMAIN = "domain";

		public static final String IP = "ip";
		public static final String HOSTNAME = "hostname";
		public static final String PORT = "port";
		public static final String PRIORITY = "priority";
		public static final String DIRECT_TLS = "directTls";
		public static final String AUTHENTICATED = "authenticated";

		private InetAddress ip;
		private DNSName hostname;
		private int port = 5222;
		private boolean directTls = false;
		private boolean authenticated = false;
		private int priority;

		public InetAddress getIp() {
			return ip;
		}

		public int getPort() {
			return port;
		}

		public DNSName getHostname() {
			return hostname;
		}

		public boolean isDirectTls() {
			return directTls;
		}

		public boolean isAuthenticated() {
			return authenticated;
		}

		@Override
		public String toString() {
			return "Result{" +
					"ip='" + (ip == null ? null : ip.getHostAddress()) + '\'' +
					", hostame='" + hostname.toString() + '\'' +
					", port=" + port +
					", directTls=" + directTls +
					", authenticated=" + authenticated +
					", priority=" + priority +
					'}';
		}

		@Override
		public int compareTo(@NonNull Result result) {
			if (result.priority == priority) {
				if (directTls == result.directTls) {
					if (ip == null && result.ip == null) {
						return 0;
					} else if (ip != null && result.ip != null) {
						if (ip instanceof Inet4Address && result.ip instanceof Inet4Address) {
							return 0;
						} else {
							return ip instanceof Inet4Address ? -1 : 1;
						}
					} else {
						return ip != null ? -1 : 1;
					}
				} else {
					return directTls ? -1 : 1;
				}
			} else {
				return priority - result.priority;
			}
		}

		public static Result fromRecord(SRV srv, boolean directTls) {
			Result result = new Result();
			result.port = srv.port;
			result.hostname = srv.name;
			result.directTls = directTls;
			result.priority = srv.priority;
			return result;
		}

		public static Result createDefault(DNSName hostname, InetAddress ip) {
			Result result = new Result();
			result.port = 5222;
			result.hostname = hostname;
			result.ip = ip;
			return result;
		}

		public static Result createDefault(DNSName hostname) {
			return createDefault(hostname, null);
		}

		public static Result fromCursor(Cursor cursor) {
			final Result result = new Result();
			try {
				result.ip = InetAddress.getByAddress(cursor.getBlob(cursor.getColumnIndex(IP)));
			} catch (UnknownHostException e) {
				result.ip = null;
			}
			result.hostname = DNSName.from(cursor.getString(cursor.getColumnIndex(HOSTNAME)));
			result.port = cursor.getInt(cursor.getColumnIndex(PORT));
			result.priority = cursor.getInt(cursor.getColumnIndex(PRIORITY));
			result.authenticated = cursor.getInt(cursor.getColumnIndex(AUTHENTICATED)) > 0;
			result.directTls = cursor.getInt(cursor.getColumnIndex(DIRECT_TLS)) > 0;
			return result;
		}

		public ContentValues toContentValues() {
			final ContentValues contentValues = new ContentValues();
			contentValues.put(IP, ip == null ? null : ip.getAddress());
			contentValues.put(HOSTNAME, hostname.toString());
			contentValues.put(PORT, port);
			contentValues.put(PRIORITY, priority);
			contentValues.put(DIRECT_TLS, directTls ? 1 : 0);
			contentValues.put(AUTHENTICATED, authenticated ? 1 : 0);
			return contentValues;
		}
	}

	public static class NetworkIsUnreachableException extends Exception {

	}

}