/* ctime.stp - Convert seconds to human readable date string.
 *
 * This code was adapted from the newlib mktm_r() and asctime_r()
 * functions.  In newlib, mktm_r.c states that it was adapted from
 * tzcode maintained by Arthur David Olson.  In newlib, asctime_r.c
 * doesn't have any author/copyright information.
 *
 * Changes copyright (C) 2006, 2008 Red Hat Inc.
 */

/**
 * sfunction ctime - Convert seconds since epoch into human readable date/time string.
 * @epochsecs: Number of seconds since epoch (as returned by gettimeofday_s()).
 *
 * Description: Takes an argument of seconds since the epoch as returned by
 * gettimeofday_s(). Returns a string of the form
 *
 *   "Wed Jun 30 21:49:08 1993"
 *
 * The string will always be exactly 24 characters. If the time would
 * be unreasonable far in the past (before what can be represented
 * with a 32 bit offset in seconds from the epoch) the returned string
 * will be "a long, long time ago...". If the time would be
 * unreasonable far in the future the returned string will be "far far
 * in the future..." (both these strings are also 24 characters wide).
 *
 * Note that the epoch (zero) corresponds to
 *
 *   "Thu Jan  1 00:00:00 1970"
 *
 * The earliest full date given by ctime, corresponding to epochsecs
 * -2147483648 is "Fri Dec 13 20:45:52 1901". The latest full date
 * given by ctime, corresponding to epochsecs 2147483647 is
 * "Tue Jan 19 03:14:07 2038".
 *
 * The abbreviations for the days of the week are ‘Sun’, ‘Mon’, ‘Tue’,
 * ‘Wed’, ‘Thu’, ‘Fri’, and ‘Sat’.  The abbreviations for the months
 * are ‘Jan’, ‘Feb’, ‘Mar’, ‘Apr’, ‘May’, ‘Jun’, ‘Jul’, ‘Aug’, ‘Sep’,
 * ‘Oct’, ‘Nov’, and ‘Dec’.
 *
 * Note that the real C library ctime() function puts a newline ('\n')
 * character at the end of the string that this function does not.
 * Also note that since the kernel has no concept of timezones, the
 * returned time is always in GMT.
 */
function ctime:string(epochsecs:long)
%{ /* pure */

#define SECSPERMIN	60L
#define MINSPERHOUR	60L
#define HOURSPERDAY	24L
#define SECSPERHOUR	(SECSPERMIN * MINSPERHOUR)
#define SECSPERDAY	(SECSPERHOUR * HOURSPERDAY)
#define DAYSPERWEEK	7
#define MONSPERYEAR	12

#define EPOCH_YEAR      1970
#define EPOCH_WDAY      4

#define isleap(y) ((((y) % 4) == 0 && ((y) % 100) != 0) || ((y) % 400) == 0)

    static const int mon_lengths[2][MONSPERYEAR] = {
	{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
	{31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
    } ;

    static const int year_lengths[2] = {
	365,
	366
    } ;

    static const char day_name[7][3] = {
	"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
    };
    static const char mon_name[12][3] = {
	"Jan", "Feb", "Mar", "Apr", "May", "Jun", 
	"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
    };

    long days, rem;
    time_t lcltime;
    int yleap;
    const int *ip;
    int tm_sec;         /* seconds */
    int tm_min;         /* minutes */
    int tm_hour;        /* hours */
    int tm_mday;        /* day of the month */
    int tm_mon;         /* month */
    int tm_year;        /* year */
    int tm_wday;        /* day of the week */

    // Check that the numer of seconds is "reasonable".
    // Otherwise (especially on 64bit machines) we will be spending
    // way too much time calculating the correct year, month and
    // day. Also we would like the returned string to always be 24 chars.
    // So cap to what can be represented normally on a 32bit machine.
    int64_t MAX_POS_SECS =  2147483647LL;
    int64_t MIN_NEG_SECS = -2147483648LL;

    if (THIS->epochsecs > MAX_POS_SECS)
      {
        strlcpy(THIS->__retvalue, "far far in the future...", MAXSTRINGLEN);
	return;
      }
    if (THIS->epochsecs < MIN_NEG_SECS)
      {
        strlcpy(THIS->__retvalue, "a long, long time ago...", MAXSTRINGLEN);
        return;
      }

    lcltime = THIS->epochsecs;
   
    days = ((long)lcltime) / SECSPERDAY;
    rem = ((long)lcltime) % SECSPERDAY;
    while (rem < 0) 
    {
	rem += SECSPERDAY;
	--days;
    }
    while (rem >= SECSPERDAY)
    {
	rem -= SECSPERDAY;
	++days;
    }
 
    /* compute hour, min, and sec */  
    tm_hour = (int) (rem / SECSPERHOUR);
    rem %= SECSPERHOUR;
    tm_min = (int) (rem / SECSPERMIN);
    tm_sec = (int) (rem % SECSPERMIN);

    /* compute day of week */
    if ((tm_wday = ((EPOCH_WDAY + days) % DAYSPERWEEK)) < 0)
	tm_wday += DAYSPERWEEK;

    /* compute year & day of year */
    tm_year = EPOCH_YEAR;
    if (days >= 0)
    {
	for (;;)
	{
	    yleap = isleap(tm_year);
	    if (days < year_lengths[yleap])
		break;
	    tm_year++;
	    days -= year_lengths[yleap];
	}
    }
    else
    {
	do
	{
	    --tm_year;
	    yleap = isleap(tm_year);
	    days += year_lengths[yleap];
	} while (days < 0);
    }

    ip = mon_lengths[yleap];
    for (tm_mon = 0; days >= ip[tm_mon]; ++tm_mon)
	days -= ip[tm_mon];
    tm_mday = days + 1;

    /*
     * At this point we have all our information.  Now we need to
     * convert it to an ascii representation.
     */

    snprintf (THIS->__retvalue, MAXSTRINGLEN, "%.3s %.3s%3d %.2d:%.2d:%.2d %d",
	      day_name[tm_wday], mon_name[tm_mon],
	      tm_mday, tm_hour, tm_min,
	      tm_sec, tm_year);
%}