Datetime/Datetime.h

#include <iostream>
#include <iomanip>
#include <string>
#include <math.h>

class Datetime
{
    private:
    double julian_days = 0;


    void init(int days)
    {
        julian_days = days;
    }


    void init(int year, int month, int days)
    {
        int a = int(14 - month) / 12;
        int y = year + 4800 - a;
        int m = month + 12*a - 3;
        julian_days = days + int((153*m + 2) / 5) + 365*y + int(y/4) - int(y/100) + int(y/400) - 32045;
    }

    void init(int year, int month, int days, int hours, int minuts, int seconds)
    {
        int a = int(14 - month) / 12;
        int y = year + 4800 - a;
        int m = month + 12*a - 3;
        julian_days = days + int((153*m + 2) / 5) + 365*y + int(y/4) - int(y/100) + int(y/400) - 32045;

        julian_days += double(hours - 12) / 24.0 + double(minuts) / 1440.0 + double(seconds) / 86400.0;
    }

    public:
    Datetime(int days)
    {
        init(days);
    }

    Datetime(int year, int month, int days)
    {
        init(year, month, days);
    }

    Datetime(int year, int month, int days, int hours, int minuts, int seconds)
    {
        init(year, month, days, hours, minuts, seconds);
    }

    Datetime(std::string data)
    {
        int current = 0;
        int dates[6] = {0,0,0,0,0,0};
        int date_index = 0;
        for (int i = 0; i < data.length(); i++) {
            if (data[i] == ':' or data[i] == '-' or data[i] == '.' or data[i] == ' ') {
                if (date_index > 5)
                    throw "Неправильный формат даты";
                dates[date_index] = current ;
                date_index++;
                current = 0;
                continue;
            }
            current = current*10 + int(data[i] - '0');
        }
        dates[date_index] = current;

        init(dates[0], dates[1], dates[2], dates[3], dates[4], dates[5]);
    }

    friend std::ostream &operator <<(std::ostream &os, Datetime &dt)
    {
        int a = dt.julian_days + 32044;
        int b = (4*a + 3) / 146097;
        int c = a - ((146097*b) / 4);
        int d = (4*c + 3) / 1461;
        int e = c - ((1461*d) / 4);
        int m = (5*e + 2) / 153;

        int days = e - ((153*m + 2) / 5) + 1;
        int month = m + 3 - 12 * (m/10);
        int years = 100*b + d - 4800 + (m/10);


        int hours = ((dt.julian_days - double(int(dt.julian_days)))*24 + 12*24) / 24; 
        int minuts = ((dt.julian_days - double(int(dt.julian_days))) * 1440) - int(dt.julian_days - double(int(dt.julian_days)))*24;
        int seconds = (dt.julian_days - double(int(dt.julian_days))) * 86400 - minuts*60 - int(dt.julian_days - double(int(dt.julian_days)))*24;  

        os << std::setw(4) << std::setfill('0') << years << ':' 
        << std::setw(2) << std::setfill('0') << month << ':' 
        << std::setw(2) << std::setfill('0') << days << 'T'
        << std::setw(2) << std::setfill('0') << hours << ':'
        << std::setw(2) << std::setfill('0') << minuts << ':'
        << std::setw(2) << std::setfill('0') << seconds;
        return os;
    }

    Datetime& operator += (const Datetime& r)
    {
        julian_days += r.julian_days;
        return *this;
    }

    Datetime operator + (const Datetime& r) const
    {
        Datetime res(*this);
        return res += r;
    }

    Datetime& operator -= (const Datetime& r)
    {
        julian_days -= r.julian_days;
        return *this;
    }

    Datetime operator - (const Datetime& r) const
    {
        Datetime res(*this);
        return res -= r;
    }
};