#include "ml_date.h"

long now() {	// get-universal-time
	time_t t = std::time(nullptr);
	auto now = static_cast<long int>(t);

	return now;
}

long get_gmt_localtime_offset() {
	std::time_t current_time;
	std::time(&current_time);
	struct std::tm *timeinfo = std::localtime(&current_time);
	long offset = timeinfo->tm_gmtoff;
	return offset;
}

std::string date_to_string(const long datetime, const std::string& format) {
	// std::locale::global(std::locale("en-US.UTF8"));

	time_t timestamp = datetime;
	char mbstr[128];

	if (std::strftime(mbstr, sizeof(mbstr), format.c_str(), std::gmtime(&timestamp))) {
		std::string result = {mbstr};
		return result;
	}

	throw std::runtime_error("date_to_string, invalid date string or format (" + std::to_string(datetime) + ", " + format + ")" );
}

time_t time_to_epoch ( const struct tm *ltm, int utcdiff ) {
	const int mon_days [] = {0, 31, 31+28, 31+28+31,
							 31+28+31+30, 31+28+31+30+31, 31+28+31+30+31+30,
							 31+28+31+30+31+30+31, 31+28+31+30+31+30+31+31, 31+28+31+30+31+30+31+31+30,
							 31+28+31+30+31+30+31+31+30+31, 31+28+31+30+31+30+31+31+30+31+30, 31+28+31+30+31+30+31+31+30+31+30+31};

	long tyears, tdays, leaps, utc_hrs;

	tyears = ltm->tm_year - 70 ; // tm->tm_year is from 1900.
	leaps = (tyears + 2) / 4;
	// no of next two lines until year 2100.
	//int i = (ltm->tm_year – 100) / 100;
	//leaps -= ( (i/4)*3 + i%4 );

	tdays = mon_days[ltm->tm_mon];

	tdays += ltm->tm_mday-1; // days of month passed.
	tdays = tdays + (tyears * 365) + leaps;

	utc_hrs = ltm->tm_hour + utcdiff/3600; // for your time zone.
	return (tdays * 86400) + (utc_hrs * 3600) + (ltm->tm_min * 60) + ltm->tm_sec;
}

long string_to_date(const std::string &datestr, const std::string &format) {
	// format for example "%d.%m.%Y";

	struct tm tm{};
	memset(&tm, 0, sizeof(tm));
	if (strptime(datestr.c_str(), format.c_str(), &tm)) {
		time_t curTime;
		struct tm * timeinfo;

		time(&curTime );
		timeinfo = std::gmtime(&curTime);

		timeinfo->tm_year = tm.tm_year;
		timeinfo->tm_mon = tm.tm_mon;
		timeinfo->tm_mday = tm.tm_mday;
		timeinfo->tm_hour = tm.tm_hour;
		timeinfo->tm_min = tm.tm_min;
		timeinfo->tm_sec = tm.tm_sec;

		return time_to_epoch(timeinfo, 0);
	}

	throw std::runtime_error("string_to_date, invalid date string or format (" + datestr + ", " + format + ")" );
}


long add_to_date(const long datetime, const int quantity, const std::string &part) {
	// part is one of 'year', 'month', 'day', 'hour', 'minute' or 'second'

	// very basic implementation, just for now - no timezones DST etc
	time_t base = datetime;
	struct tm *tm = localtime(&base);

	if (part == "year") {
		tm->tm_year += quantity;
	} else if (part == "month") {
		tm->tm_mon += quantity;
	} else if (part == "day") {
		tm->tm_mday += quantity;
	} else if (part == "hour") {
		tm->tm_hour += quantity;
	} else if (part == "minute") {
		tm->tm_min += quantity;
	} else if (part == "second") {
		tm->tm_sec += quantity;
	} else {
		throw std::runtime_error("add_to_date, part to add (" + part + ")" );
	}

	return mktime(tm);	// mktime is quite slow!
}