package launcher.client;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.nio.charset.StandardCharsets;
import java.time.Duration;
import java.time.Instant;
import java.util.regex.Pattern;

import com.eclipsesource.json.Json;
import com.eclipsesource.json.JsonObject;
import launcher.LauncherAPI;
import launcher.helper.IOHelper;
import launcher.helper.LogHelper;
import launcher.helper.VerifyHelper;
import launcher.serialize.HInput;
import launcher.serialize.HOutput;

public final class ServerPinger {
	// Constants
	private static final String LEGACY_PING_HOST_MAGIC = "ยง1";
	private static final String LEGACY_PING_HOST_CHANNEL = "MC|PingHost";
	private static final Pattern LEGACY_PING_HOST_DELIMETER = Pattern.compile("\0", Pattern.LITERAL);

	// Instance
	private final InetSocketAddress address;
	private final ClientProfile.Version version;

	// Cache
	private final Object cacheLock = new Object();
	private Result cache;
	private Instant cacheTime;

	@LauncherAPI
	public ServerPinger(InetSocketAddress address, ClientProfile.Version version) {
		this.address = address;
		this.version = version;
	}

	@LauncherAPI
	public Result ping() throws IOException {
		Instant now = Instant.now();
		synchronized (cacheLock) {
			if (cache == null || cacheTime == null || Duration.between(now, cacheTime).getSeconds() >= 30) {
				cache = doPing();
				cacheTime = now;
			}
			return cache;
		}
	}

	private Result doPing() throws IOException {
		try (Socket socket = IOHelper.newSocket()) {
			socket.connect(IOHelper.resolve(address), IOHelper.SOCKET_TIMEOUT);
			try (HInput input = new HInput(socket.getInputStream());
				 HOutput output = new HOutput(socket.getOutputStream())) {
				return version.compareTo(ClientProfile.Version.MC172) >= 0 ?
					modernPing(input, output) : legacyPing(input, output);
			}
		}
	}

	private Result legacyPing(HInput input, HOutput output) throws IOException {
		output.writeUnsignedByte(0xFE); // 254 packet ID, Server list ping
		output.writeUnsignedByte(0x01); // Server ping payload
		output.writeUnsignedByte(0xFA); // 250 packet ID, Custom payload
		writeUTF16String(output, LEGACY_PING_HOST_CHANNEL); // Custom payload name

		// Prepare custom payload packet
		byte[] customPayloadPacket;
		try (ByteArrayOutputStream packetArray = IOHelper.newByteArrayOutput()) {
			try (HOutput packetOutput = new HOutput(packetArray)) {
				packetOutput.writeUnsignedByte(version.protocol); // Protocol version
				writeUTF16String(packetOutput, address.getHostString()); // Server address
				packetOutput.writeInt(address.getPort()); // Server port
			}
			customPayloadPacket = packetArray.toByteArray();
		}

		// Write custom payload packet
		output.writeShort((short) customPayloadPacket.length);
		output.stream.write(customPayloadPacket);
		output.flush();

		// Raed kick (response) packet
		int kickPacketID = input.readUnsignedByte();
		if (kickPacketID != 0xFF) {
			throw new IOException("Illegal kick packet ID: " + kickPacketID);
		}

		// Read and parse response
		String response = readUTF16String(input);
		LogHelper.debug("Ping response (legacy): '%s'", response);
		String[] splitted = LEGACY_PING_HOST_DELIMETER.split(response);
		if (splitted.length != 6) {
			throw new IOException("Tokens count mismatch");
		}

		// Verify all parts
		String magic = splitted[0];
		if (!magic.equals(LEGACY_PING_HOST_MAGIC)) {
			throw new IOException("Magic string mismatch: " + magic);
		}
		int protocol = Integer.parseInt(splitted[1]);
		if (protocol != version.protocol) {
			throw new IOException("Protocol mismatch: " + protocol);
		}
		String clientVersion = splitted[2];
		if (!clientVersion.equals(version.name)) {
			throw new IOException(String.format("Version mismatch: '%s'", clientVersion));
		}
		String title = splitted[3];
		int onlinePlayers = VerifyHelper.verifyInt(Integer.parseInt(splitted[4]),
			VerifyHelper.NOT_NEGATIVE, "onlinePlayers can't be < 0");
		int maxPlayers = VerifyHelper.verifyInt(Integer.parseInt(splitted[5]),
			VerifyHelper.NOT_NEGATIVE, "maxPlayers can't be < 0");

		// Return ping status
		return new Result(onlinePlayers, maxPlayers, title, response);
	}

	private Result modernPing(HInput input, HOutput output) throws IOException {
		// Prepare handshake packet
		byte[] handshakePacket;
		try (ByteArrayOutputStream packetArray = IOHelper.newByteArrayOutput()) {
			try (HOutput packetOutput = new HOutput(packetArray)) {
				packetOutput.writeVarInt(0x0); // Handshake packet ID
				packetOutput.writeVarInt(version.protocol); // Protocol version
				packetOutput.writeString(address.getHostString(), 0); // Server address
				packetOutput.writeShort((short) address.getPort()); // Server port
				packetOutput.writeVarInt(0x1); // Next state - status
			}
			handshakePacket = packetArray.toByteArray();
		}

		// Write handshake packet
		output.writeByteArray(handshakePacket, IOHelper.BUFFER_SIZE);

		// Request status packet
		output.writeVarInt(1); // Status packet size (single byte)
		output.writeVarInt(0x0); // Status packet ID
		output.flush();

		// Read outer status response packet ID
		// ab is a dirty fix for some servers (noticed KCauldron 1.7.10)
		String response;
		int ab = IOHelper.verifyLength(input.readVarInt(), IOHelper.BUFFER_SIZE);
		byte[] statusPacket = ab == 0x0 ? input.readByteArray(IOHelper.BUFFER_SIZE) : input.readByteArray(-ab);
		try (HInput packetInput = new HInput(statusPacket)) {
			int statusPacketID = packetInput.readVarInt();
			if (statusPacketID != 0x0) {
				throw new IOException("Illegal status packet ID: " + statusPacketID);
			}
			response = packetInput.readString(IOHelper.BUFFER_SIZE);
			LogHelper.debug("Ping response (modern): '%s'", response);
		}

		// Parse JSON response
		JsonObject object = Json.parse(response).asObject();
		String description = object.get("description").asString();
		JsonObject playersObject = object.get("players").asObject();
		int online = playersObject.get("online").asInt();
		int max = playersObject.get("max").asInt();

		// Return ping status
		return new Result(online, max, description, response);
	}

	private static String readUTF16String(HInput input) throws IOException {
		int length = input.readUnsignedShort() << 1;
		byte[] encoded = input.readByteArray(-length);
		return new String(encoded, StandardCharsets.UTF_16BE);
	}

	private static void writeUTF16String(HOutput output, String s) throws IOException {
		output.writeShort((short) s.length());
		output.stream.write(s.getBytes(StandardCharsets.UTF_16BE));
	}

	public static final class Result {
		private static final Pattern CODES_PATTERN = Pattern.compile("ยง[0-9a-fkmnor]", Pattern.CASE_INSENSITIVE);

		// Instance
		@LauncherAPI public final int onlinePlayers;
		@LauncherAPI public final int maxPlayers;
		@LauncherAPI public final String description;
		@LauncherAPI public final String raw;

		public Result(int onlinePlayers, int maxPlayers, CharSequence description, String raw) {
			this.onlinePlayers = VerifyHelper.verifyInt(onlinePlayers,
				VerifyHelper.NOT_NEGATIVE, "onlinePlayers can't be < 0");
			this.maxPlayers = VerifyHelper.verifyInt(maxPlayers,
				VerifyHelper.NOT_NEGATIVE, "maxPlayers can't be < 0");
			this.description = stripColorCodes(description);
			this.raw = raw;
		}

		@LauncherAPI
		public boolean isOverfilled() {
			return onlinePlayers >= maxPlayers;
		}

		private static String stripColorCodes(CharSequence s) {
			return CODES_PATTERN.matcher(s).replaceAll("");
		}
	}
}