#define DEFAULT_MONITOR_SPEED 115200

#define MISCORS_IN_MILLIS 1000
#define MILLIS_IN_SEC 1000
#define SECS_IN_MIN 60
#define MINS_IN_HOUR 60
#define HOURS_IN_DAY 24

#include <Arduino.h>
#include <string.h>
#include <math.h>

struct Time
{
  unsigned short int days;
  byte hours;
  byte mins;
  byte secs;
  unsigned short int millis;
};

void tickTime(Time &time);
String getFormattedTime(Time &time);

Time time = {0, 0, 0, 0, 0};
Time oldTime = time;
unsigned long usTime;

void setup()
{
  Serial.begin(DEFAULT_MONITOR_SPEED);
  usTime = micros();
}

void loop()
{
  unsigned long currTime = micros();
  if (abs(currTime - usTime) >= MISCORS_IN_MILLIS)
  {
    tickTime(time);
    usTime = currTime;
  }

  if (oldTime.secs != time.secs)
  {
    Serial.println(getFormattedTime(time));
    oldTime = time;
  }
}

void tickTime(Time &time)
{
  time.millis += 1;

  // in range [0..24]
  if (time.hours >= (HOURS_IN_DAY - 1))
  {
    time.hours -= HOURS_IN_DAY - 1;
    time.days += 1;
  }

  // in range [0..59]
  if (time.mins >= (MINS_IN_HOUR - 1))
  {
    time.mins -= MINS_IN_HOUR - 1;
    time.hours += 1;
  }

  // in range [0..59]
  if (time.secs >= (SECS_IN_MIN - 1))
  {
    time.secs -= SECS_IN_MIN - 1;
    time.mins += 1;
  }

  // in range [0..999]
  if (time.millis >= (MILLIS_IN_SEC - 1))
  {
    time.millis -= MILLIS_IN_SEC - 1;
    time.secs += 1;
  }
}

String getFormattedTime(Time &time)
{
  String formattedTime = "Timer: ";
  formattedTime.concat(time.days);
  formattedTime.concat("d : ");
  formattedTime.concat(time.hours);
  formattedTime.concat("h : ");
  formattedTime.concat(time.mins);
  formattedTime.concat("m : ");
  formattedTime.concat(time.secs);
  formattedTime.concat("s. ");
  formattedTime.concat("System timer value: ");
  formattedTime.concat(usTime);
  formattedTime.concat("us");

  return formattedTime;
}