/*

 Udp NTP Client

 Get the time from a Network Time Protocol (NTP) time server
 Demonstrates use of UDP sendPacket and ReceivePacket
 For more on NTP time servers and the messages needed to communicate with them,
 see http://en.wikipedia.org/wiki/Network_Time_Protocol

 created 4 Sep 2010
 by Michael Margolis
 modified 9 Apr 2012
 by Tom Igoe
 modified 02 Sept 2015
 by Arturo Guadalupi

 This code is in the public domain.

 */

#include "Arduino.h"
#include <SPI.h>
#include <Ethernet.h>
#include <EthernetUdp.h>
#include <Wire.h>
// #include <stdlib.h>
// #include <time.h>

const uint8_t daysArray [] PROGMEM = { 31,28,31,30,31,30,31,31,30,31,30,31 };
const uint8_t dowArray[] PROGMEM = { 0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4 };

// Enter a MAC address for your controller below.
// Newer Ethernet shields have a MAC address printed on a sticker on the shield
byte mac[] = {
  0xA8, 0x61, 0x0A, 0xAE, 0x78, 0xC2
};

unsigned int localPort = 8888;       // local port to listen for UDP packets

const char timeServer[] = "time.google.com"; // google

const int NTP_PACKET_SIZE = 48; // NTP time stamp is in the first 48 bytes of the message

byte packetBuffer[NTP_PACKET_SIZE]; //buffer to hold incoming and outgoing packets

unsigned long epoch;

#define DS3231_ADDRESS              (0x68)
#define DS3231_REG_TIME             (0x00)

// A UDP instance to let us send and receive packets over UDP
EthernetUDP Udp;

uint8_t dow(uint16_t y, uint8_t m, uint8_t d)
{
    uint8_t dow;

    y -= m < 3;
    dow = ((y + y/4 - y/100 + y/400 + pgm_read_byte(dowArray+(m-1)) + d) % 7);

    if (dow == 0)
    {
        return 7;
    }

    return dow;
}

uint8_t dec2bcd(uint8_t dec)
{
    return ((dec / 10) * 16) + (dec % 10);
}

// send an NTP request to the time server at the given address
void sendNTPpacket(const char * address) {
  // set all bytes in the buffer to 0
  memset(packetBuffer, 0, NTP_PACKET_SIZE);
  // Initialize values needed to form NTP request
  // (see URL above for details on the packets)
  packetBuffer[0] = 0b11100011;   // LI, Version, Mode
  packetBuffer[1] = 0;     // Stratum, or type of clock
  packetBuffer[2] = 6;     // Polling Interval
  packetBuffer[3] = 0xEC;  // Peer Clock Precision
  // 8 bytes of zero for Root Delay & Root Dispersion
  packetBuffer[12]  = 49;
  packetBuffer[13]  = 0x4E;
  packetBuffer[14]  = 49;
  packetBuffer[15]  = 52;

  // all NTP fields have been given values, now
  // you can send a packet requesting a timestamp:
  Udp.beginPacket(address, 123); // NTP requests are to port 123
  Udp.write(packetBuffer, NTP_PACKET_SIZE);
  Udp.endPacket();
}



void setup() {
  // You can use Ethernet.init(pin) to configure the CS pin
  //Ethernet.init(10);  // Most Arduino shields
  //Ethernet.init(5);   // MKR ETH shield
  //Ethernet.init(0);   // Teensy 2.0
  //Ethernet.init(20);  // Teensy++ 2.0
  //Ethernet.init(15);  // ESP8266 with Adafruit Featherwing Ethernet
  //Ethernet.init(33);  // ESP32 with Adafruit Featherwing Ethernet

  // Open serial communications and wait for port to open:
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }

  // start Ethernet and UDP
  if (Ethernet.begin(mac) == 0) {
    Serial.println("Failed to configure Ethernet using DHCP");
    // Check for Ethernet hardware present
    if (Ethernet.hardwareStatus() == EthernetNoHardware) {
      Serial.println("Ethernet shield was not found.  Sorry, can't run without hardware. :(");
    } else if (Ethernet.linkStatus() == LinkOFF) {
      Serial.println("Ethernet cable is not connected.");
    }
    // no point in carrying on, so do nothing forevermore:
    while (true) {
      delay(1);
    }
  }
  Udp.begin(localPort);
}

void loop() {
  sendNTPpacket(timeServer); // send an NTP packet to a time server

  // wait to see if a reply is available
  delay(1000);
  if (Udp.parsePacket()) {
    // We've received a packet, read the data from it
    Udp.read(packetBuffer, NTP_PACKET_SIZE); // read the packet into the buffer

    // the timestamp starts at byte 40 of the received packet and is four bytes,
    // or two words, long. First, extract the two words:

    unsigned long highWord = word(packetBuffer[40], packetBuffer[41]);
    unsigned long lowWord = word(packetBuffer[42], packetBuffer[43]);
    // combine the four bytes (two words) into a long integer
    // this is NTP time (seconds since Jan 1 1900):
    unsigned long secsSince1900 = highWord << 16 | lowWord;
    Serial.print("Seconds since Jan 1 1900 = ");
    Serial.println(secsSince1900);

    // now convert NTP time into everyday time:
    Serial.print("Unix time = ");
    // Unix time starts on Jan 1 1970. In seconds, that's 2208988800:
    const unsigned long seventyYears = 2208988800UL;
    // subtract seventy years:
    epoch = secsSince1900 - seventyYears;
    // print Unix time:
    Serial.println(epoch);
  }
// ************************* begin from DS3231.cpp *************************

    epoch -= 946684800;

    uint16_t year;
    uint8_t month;
    uint8_t day;
    uint8_t hour;
    uint8_t minute;
    uint8_t second;

    second = epoch % 60;
    epoch /= 60;

    minute = epoch % 60;
    epoch /= 60;

    hour = epoch % 24;
    uint16_t days = epoch / 24;
    uint8_t leap;

    for (year = 0; ; ++year)
    {
        leap = year % 4 == 0;
        if (days < 365 + leap)
        {
            break;
        }
        days -= 365 + leap;
    }

    for (month = 1; ; ++month)
    {
        uint8_t daysPerMonth = pgm_read_byte(daysArray + month - 1);

        if (leap && month == 2)
        {
            ++daysPerMonth;
        }

        if (days < daysPerMonth)
        {
            break;
        }
        days -= daysPerMonth;
    }

    day = days + 1;

    Serial.print(year+2000);
    Serial.print(" ");
    Serial.print(month);
    Serial.print(" ");
    Serial.print(day);
    Serial.print(" ");
    Serial.print(hour);
    Serial.print(" ");
    Serial.print(minute);
    Serial.print(" ");
    Serial.print(second);
    Serial.println();

    // setDateTime(year+2000, month, day, hour, minute, second);

    Wire.beginTransmission(DS3231_ADDRESS);

    #if ARDUINO >= 100
        Wire.write(DS3231_REG_TIME);
    #else
        Wire.send(DS3231_REG_TIME);
    #endif

    #if ARDUINO >= 100
        Wire.write(dec2bcd(second));
        Wire.write(dec2bcd(minute));
        Wire.write(dec2bcd(hour));

        Wire.write(dec2bcd(dow(year, month, day)));
        Wire.write(dec2bcd(day));
        Wire.write(dec2bcd(month));
        Wire.write(dec2bcd(year-2000));
    #else
        Wire.send(dec2bcd(second));
        Wire.send(dec2bcd(minute));
        Wire.send(dec2bcd(hour));
        Wire.send(dec2bcd(dow(year, month, day)));
        Wire.send(dec2bcd(day));
        Wire.send(dec2bcd(month));
        Wire.send(dec2bcd(year-2000));
    #endif

    #if ARDUINO >= 100
        Wire.write(DS3231_REG_TIME);
    #else
        Wire.send(DS3231_REG_TIME);
    #endif

    Wire.endTransmission();
    

// ************************* end from DS3231.cpp *************************

/*
    // print the hour, minute and second:
    Serial.print("The UTC time is ");       // UTC is the time at Greenwich Meridian (GMT)
    Serial.print((epoch  % 86400L) / 3600); // print the hour (86400 equals secs per day)
    Serial.print(':');
    if (((epoch % 3600) / 60) < 10) {
      // In the first 10 minutes of each hour, we'll want a leading '0'
      Serial.print('0');
    }
    Serial.print((epoch  % 3600) / 60); // print the minute (3600 equals secs per minute)
    Serial.print(':');
    if ((epoch % 60) < 10) {
      // In the first 10 seconds of each minute, we'll want a leading '0'
      Serial.print('0');
    }
    Serial.println(epoch % 60); // print the second
  }
*/
  
  // wait ten seconds before asking for the time again
  delay(10000);
  Ethernet.maintain();

  
}