/*
 * 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 "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 tm *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;
}