/* Originally released by the musl project (http://www.musl-libc.org/) under the
 * MIT license. Taken from the file /src/time/__secs_to_tm.c */

#include <limits.h>
#include "libc_time.h"

/* 2000-03-01 (mod 400 year, immediately after feb29 */
#define LEAPOCH (946684800LL + 86400*(31+29))

#define DAYS_PER_400Y (365*400 + 97)
#define DAYS_PER_100Y (365*100 + 24)
#define DAYS_PER_4Y   (365*4   + 1)

int __secs_to_tm(long long t, struct mytm *tm) {
    long long days, secs, years;
    int remdays, remsecs, remyears;
    int qc_cycles, c_cycles, q_cycles;
    int months;
    int wday, yday, leap;
    static const char days_in_month[] = {31,30,31,30,31,31,30,31,30,31,31,29};

    /* Reject time_t values whose year would overflow int */
    if (t < INT_MIN * 31622400LL || t > INT_MAX * 31622400LL)
        return -1;

    secs = t - LEAPOCH;
    days = secs / 86400LL;
    remsecs = (int)(secs % 86400);
    if (remsecs < 0) {
        remsecs += 86400;
        --days;
    }

    wday = (int)((3+days)%7);
    if (wday < 0) wday += 7;

    qc_cycles = (int)(days / DAYS_PER_400Y);
    remdays = (int)(days % DAYS_PER_400Y);
    if (remdays < 0) {
        remdays += DAYS_PER_400Y;
        --qc_cycles;
    }

    c_cycles = remdays / DAYS_PER_100Y;
    if (c_cycles == 4) --c_cycles;
    remdays -= c_cycles * DAYS_PER_100Y;

    q_cycles = remdays / DAYS_PER_4Y;
    if (q_cycles == 25) --q_cycles;
    remdays -= q_cycles * DAYS_PER_4Y;

    remyears = remdays / 365;
    if (remyears == 4) --remyears;
    remdays -= remyears * 365;

    leap = !remyears && (q_cycles || !c_cycles);
    yday = remdays + 31 + 28 + leap;
    if (yday >= 365+leap) yday -= 365+leap;

    years = remyears + 4*q_cycles + 100*c_cycles + 400LL*qc_cycles;

    for (months=0; days_in_month[months] <= remdays; ++months)
        remdays -= days_in_month[months];

    if (years+100 > INT_MAX || years+100 < INT_MIN)
        return -1;

    tm->tm_year = (int)(years + 100);
    tm->tm_mon = months + 2;
    if (tm->tm_mon >= 12) {
        tm->tm_mon -=12;
        ++tm->tm_year;
    }
    tm->tm_mday = remdays + 1;
    tm->tm_wday = wday;
    tm->tm_yday = yday;

    tm->tm_hour = remsecs / 3600;
    tm->tm_min = remsecs / 60 % 60;
    tm->tm_sec = remsecs % 60;

    return 0;
}

int __month_to_secs(int month, int is_leap)
{
	static const int secs_through_month[] = {
		0, 31*86400, 59*86400, 90*86400,
		120*86400, 151*86400, 181*86400, 212*86400,
		243*86400, 273*86400, 304*86400, 334*86400 };
	int t = secs_through_month[month];
	if (is_leap && month >= 2) t+=86400;
	return t;
}

long long __year_to_secs(long long year, int *is_leap)
{
	if (year-(int)2ULL <= 136) {
		long long y = (int)year;
		long long leaps = (y-68)>>2;
		if (!((y-8)&3)) {
			leaps--;
			if (is_leap) *is_leap = 1;
		} else if (is_leap) *is_leap = 0;
		return 31536000*(y-70) + 86400*leaps;
	}

	int cycles, centuries, leaps, rem;

        //if (!is_leap) is_leap = &(int){0};
        int is_leap_val = 0;
	if (!is_leap){
            is_leap = &is_leap_val;
        }
	cycles = (int)((year-100) / 400);
	rem = (int)((year-100) % 400);
	/* Comparison is always false because rem >= 0.
	if (rem < 0) {
		cycles--;
		rem += 400;
	} */
	if (!rem) {
		*is_leap = 1;
		centuries = 0;
		leaps = 0;
	} else {
		if (rem >= 200) {
			if (rem >= 300) centuries = 3, rem -= 300;
			else centuries = 2, rem -= 200;
		} else {
			if (rem >= 100) centuries = 1, rem -= 100;
			else centuries = 0;
		}
		if (!rem) {
			*is_leap = 0;
			leaps = 0;
		} else {
			leaps = (rem / (int)4U);
			rem %= (int)4U;
			*is_leap = !rem;
		}
	}

	leaps += 97*cycles + 24*centuries - *is_leap;

	return (year-100) * 31536000LL + leaps * 86400LL + 946684800 + 86400;
}

long long __tm_to_secs(const struct mytm *tm)
{
	int is_leap;
	long long year = tm->tm_year;
	int month = tm->tm_mon;
	if (month >= 12 || month < 0) {
		int adj = month / 12;
		month %= 12;
		if (month < 0) {
			adj--;
			month += 12;
		}
		year += adj;
	}
	long long t = __year_to_secs(year, &is_leap);
	t += __month_to_secs(month, is_leap);
	t += 86400LL * (tm->tm_mday-1);
	t += 3600LL * tm->tm_hour;
	t += 60LL * tm->tm_min;
	t += tm->tm_sec;
	return t;
}