I hate time

/*
    Purpose:
    Author: Reece W.
    License: All Rights Reserved J. Reece Wilson (2018-01-12)
    License: Released under MIT License (https://en.wikipedia.org/wiki/MIT_License) (2018-06-26)
*/
#include <xenus_lazy.h>
#include <Utils\DateHelper.hpp>

const char * __month_names[] = {
	"January", "Febuary", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"
};

const char * __day_names[] = {
	"Monday", "Tuesday", "MedianDay", "Thursday", "Friday", "Saturday", "Sunday"
};

timezone * _sys_tz = nullptr;
uint64_t _tz_offset = -1;

bool __is_leap_year(int year);
void __get_year(uint64_t ms, int * years_passed, int * days_passed);
void __month_calc(int year, int day, int * out_month, int * out_days);

uint64_t DateHelpers::get_timezone_offset()
{
	if (!_sys_tz)
		_sys_tz = (timezone *)kallsyms_lookup_name("sys_tz");

	if (!_sys_tz)
		return 0;

	return _tz_offset = -_sys_tz->tz_minuteswest * 60000;
}

uint64_t DateHelpers::get_unix_time()
{
	return NS_TO_MS(ktime_get_with_offset(TK_OFFS_REAL));
}


void DateHelpers::parse_time(uint64_t ms, time_info & timeinfo)
{
	int year;
	int month;
	int days_start_month;
	int rem_days;
	int days_start_year;

	__get_year(ms, &year, &days_start_year);

	rem_days = (ms / 86400000) - days_start_year;

	__month_calc(year, rem_days, &month, &days_start_month);

	timeinfo.year				= year;

	timeinfo.month.index		= month;
	timeinfo.month.month		= month + 1;
	timeinfo.month.name			= __month_names[month];

	timeinfo.day.day_of_year	= rem_days;
	timeinfo.day.day_of_week	= ((ms % 604800000) / 86400000) - 3; //epoch starts on thursday
	timeinfo.day.day_of_month	= (rem_days - days_start_month) + 1;
	timeinfo.day.index			= timeinfo.day.day_of_week - 1;
	timeinfo.day.name			= __day_names[timeinfo.day.index];

	timeinfo.time.hours			= ((ms % 86400000) / 3600000);
	timeinfo.time.minutes		= ((ms % 3600000) / 60000);
	timeinfo.time.seconds		= ((ms % 60000) / 1000);
	timeinfo.time.milliseconds	= (ms % 1000);
}

size_t DateHelpers::ISO8601_format(char * str, size_t length, time_info & time)
{
	return snprintf(str, length,
		"%04d-%02d-%02dT%02d:%02d:%02d.%03dZ",
		time.year,
		time.month.month,
		time.day.day_of_month,

		time.time.hours,
		time.time.minutes,
		time.time.seconds,
		time.time.milliseconds);
}

size_t DateHelpers::ISO8601_format(char * str, size_t length, uint64_t ms)
{
	time_info time;
	DateHelpers::parse_time(ms, time);
	return ISO8601_format(str, length, time);
}

bool __is_leap_year(int year)
{
	return ((year % 400 == 0 || year % 100 != 0) && (year % 4 == 0));
}

void __get_days_in_months(int * months, int year)
{
	int month_cnt[] = {
		31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
	};

	if (__is_leap_year(year))
		month_cnt[1] = 29;

	memcpy(months, month_cnt, sizeof(month_cnt));
}

void __get_year(uint64_t ms, int * o_years_passed, int * o_days_passed)
{
	int i;
	int32_t fuck;
	int32_t you;
	int32_t year;

	fuck	= ms / 86400000;
	you		= 0;
	year	= 1970;
	while (fuck - (i = __is_leap_year(year) ? 366 : 365) >= 0)
	{
		fuck -= i;
		you  += i;
		year ++;
	}
	*o_years_passed	= year;
	*o_days_passed	= you;
}

void __month_calc(int year, int day, int * out_month, int * out_days)
{
	int months[12];
	int days = 0;
	int month = 0;

	__get_days_in_months((int *)&months, year);

	while (days + months[month] <= day)
		days += months[month++];

	*out_days	= days;
	*out_month	= month;
}