package info.nightscout.androidaps.utils

import android.os.SystemClock
import javax.inject.Singleton
import javax.inject.Inject
import info.nightscout.androidaps.logging.AAPSLogger
import java.lang.Exception
import java.net.DatagramPacket
import java.net.DatagramSocket
import java.net.InetAddress

/*
 * Copyright (C) 2008 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */ /**
 * {@hide}
 *
 *
 * Simple SNTP client class for retrieving network time.
 *
 *
 * Sample usage:
 * <pre>SntpClient client = new SntpClient();
 * if (client.requestTime("time.foo.com")) {
 * long now = client.getNtpTime() + SystemClock.elapsedRealtime() - client.getNtpTimeReference();
 * }
</pre> *
 */
@Singleton
class SntpClient @Inject constructor(
    private val aapsLogger: AAPSLogger,
    private val dateUtil: DateUtil
) {

    companion object {
        //private final int REFERENCE_TIME_OFFSET = 16;
        private const val ORIGINATE_TIME_OFFSET = 24
        private const val RECEIVE_TIME_OFFSET = 32
        private const val TRANSMIT_TIME_OFFSET = 40
        private const val NTP_PACKET_SIZE = 48
        private const val NTP_PORT = 123
        private const val NTP_MODE_CLIENT = 3
        private const val NTP_VERSION = 3

        // Number of seconds between Jan 1, 1900 and Jan 1, 1970
        // 70 years plus 17 leap days
        private const val OFFSET_1900_TO_1970 = (365L * 70L + 17L) * 24L * 60L * 60L
    }

    /**
     * Returns the time computed from the NTP transaction.
     *
     * @return time value computed from NTP server response.
     */
    // system time computed from NTP server response
    private var ntpTime: Long = 0

    /**
     * Returns the reference clock value (value of SystemClock.elapsedRealtime())
     * corresponding to the NTP time.
     *
     * @return reference clock corresponding to the NTP time.
     */
    // value of SystemClock.elapsedRealtime() corresponding to mNtpTime
    private var ntpTimeReference: Long = 0

    /**
     * Returns the round trip time of the NTP transaction
     *
     * @return round trip time in milliseconds.
     */
    // round trip time in milliseconds
    private var roundTripTime: Long = 0

    abstract class Callback : Runnable {

        var networkConnected = false
        var success = false
        var time: Long = 0
    }

    @Synchronized fun ntpTime(callback: Callback, isConnected: Boolean) {
        callback.networkConnected = isConnected
        if (callback.networkConnected) {
            Thread { doNtpTime(callback) }.start()
        } else {
            callback.run()
        }
    }

    fun doNtpTime(callback: Callback) {
        aapsLogger.debug("Time detection started")
        callback.success = requestTime("time.google.com", 5000)
        callback.time = ntpTime + SystemClock.elapsedRealtime() - ntpTimeReference
        aapsLogger.debug("Time detection ended: " + callback.success + " " + dateUtil.dateAndTimeString(ntpTime))
        callback.run()
    }

    /**
     * Sends an SNTP request to the given host and processes the response.
     *
     * @param host    host name of the server.
     * @param timeout network timeout in milliseconds.
     * @return true if the transaction was successful.
     */
    @Suppress("SameParameterValue")
    @Synchronized private fun requestTime(host: String, timeout: Int): Boolean {
        try {
            val socket = DatagramSocket()
            socket.soTimeout = timeout
            val address = InetAddress.getByName(host)
            val buffer = ByteArray(NTP_PACKET_SIZE)
            val request = DatagramPacket(buffer, buffer.size, address, NTP_PORT)

            // set mode = 3 (client) and version = 3
            // mode is in low 3 bits of first byte
            // version is in bits 3-5 of first byte
            buffer[0] = (NTP_MODE_CLIENT or (NTP_VERSION shl 3)).toByte()

            // get current time and write it to the request packet
            val requestTime = System.currentTimeMillis()
            val requestTicks = SystemClock.elapsedRealtime()
            writeTimeStamp(buffer, TRANSMIT_TIME_OFFSET, requestTime)
            socket.send(request)

            // read the response
            val response = DatagramPacket(buffer, buffer.size)
            socket.receive(response)
            val responseTicks = SystemClock.elapsedRealtime()
            val responseTime = requestTime + (responseTicks - requestTicks)
            socket.close()

            // extract the results
            val originateTime = readTimeStamp(buffer, ORIGINATE_TIME_OFFSET)
            val receiveTime = readTimeStamp(buffer, RECEIVE_TIME_OFFSET)
            val transmitTime = readTimeStamp(buffer, TRANSMIT_TIME_OFFSET)
            val roundTripTime = responseTicks - requestTicks - (transmitTime - receiveTime)
            val clockOffset = (receiveTime - originateTime + (transmitTime - responseTime)) / 2

            // save our results - use the times on this side of the network latency
            // (response rather than request time)
            ntpTime = responseTime + clockOffset
            ntpTimeReference = responseTicks
            this.roundTripTime = roundTripTime
        } catch (e: Exception) {
            aapsLogger.debug("request time failed: $e")
            return false
        }
        return true
    }

    /**
     * Reads an unsigned 32 bit big endian number from the given offset in the buffer.
     */
    private fun read32(buffer: ByteArray, offset: Int): Long {
        val b0 = buffer[offset]
        val b1 = buffer[offset + 1]
        val b2 = buffer[offset + 2]
        val b3 = buffer[offset + 3]

        // convert signed bytes to unsigned values
        val i0 = if (b0.toInt() and 0x80 == 0x80) (b0.toInt() and 0x7F) + 0x80 else b0.toInt()
        val i1 = if (b1.toInt() and 0x80 == 0x80) (b1.toInt() and 0x7F) + 0x80 else b1.toInt()
        val i2 = if (b2.toInt() and 0x80 == 0x80) (b2.toInt() and 0x7F) + 0x80 else b2.toInt()
        val i3 = if (b3.toInt() and 0x80 == 0x80) (b3.toInt() and 0x7F) + 0x80 else b3.toInt()
        return (i0.toLong() shl 24) + (i1.toLong() shl 16) + (i2.toLong() shl 8) + i3.toLong()
    }

    /**
     * Reads the NTP time stamp at the given offset in the buffer and returns
     * it as a system time (milliseconds since January 1, 1970).
     */
    private fun readTimeStamp(buffer: ByteArray, offset: Int): Long {
        val seconds = read32(buffer, offset)
        val fraction = read32(buffer, offset + 4)
        return (seconds - OFFSET_1900_TO_1970) * 1000 + fraction * 1000L / 0x100000000L
    }

    /**
     * Writes system time (milliseconds since January 1, 1970) as an NTP time stamp
     * at the given offset in the buffer.
     */
    @Suppress("SameParameterValue")
    private fun writeTimeStamp(buffer: ByteArray, offsetParam: Int, time: Long) {
        var offset = offsetParam
        var seconds = time / 1000L
        val milliseconds = time - seconds * 1000L
        seconds += OFFSET_1900_TO_1970

        // write seconds in big endian format
        buffer[offset++] = (seconds shr 24).toByte()
        buffer[offset++] = (seconds shr 16).toByte()
        buffer[offset++] = (seconds shr 8).toByte()
        buffer[offset++] = (seconds shr 0).toByte()
        val fraction = milliseconds * 0x100000000L / 1000L
        // write fraction in big endian format
        buffer[offset++] = (fraction shr 24).toByte()
        buffer[offset++] = (fraction shr 16).toByte()
        buffer[offset++] = (fraction shr 8).toByte()
        // low order bits should be random data
        buffer[offset] = (Math.random() * 255.0).toInt().toByte()
    }
}