/*
 * Copyright (c) 2011 Petr Koupy
 * Copyright (c) 2011 Jiri Zarevucky
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup libposix
 * @{
 */
/** @file Time measurement support.
 */

#define LIBPOSIX_INTERNAL

/* Must be first. */
#include "stdbool.h"

#include "internal/common.h"
#include "time.h"

#include "ctype.h"
#include "errno.h"
#include "signal.h"

#include "libc/malloc.h"
#include "libc/task.h"
#include "libc/stats.h"
#include "libc/sys/time.h"

// TODO: test everything in this file

/* In some places in this file, phrase "normalized broken-down time" is used.
 * This means time broken down to components (year, month, day, hour, min, sec),
 * in which every component is in its proper bounds. Non-normalized time could
 * e.g. be 2011-54-5 29:13:-5, which would semantically mean start of year 2011
 * + 53 months + 4 days + 29 hours + 13 minutes - 5 seconds.
 */



/* Helper functions ***********************************************************/

#define HOURS_PER_DAY (24)
#define MINS_PER_HOUR (60)
#define SECS_PER_MIN (60)
#define MINS_PER_DAY (MINS_PER_HOUR * HOURS_PER_DAY)
#define SECS_PER_HOUR (SECS_PER_MIN * MINS_PER_HOUR)
#define SECS_PER_DAY (SECS_PER_HOUR * HOURS_PER_DAY)

/**
 * Checks whether the year is a leap year.
 *
 * @param year Year since 1900 (e.g. for 1970, the value is 70).
 * @return true if year is a leap year, false otherwise
 */
static bool _is_leap_year(time_t year)
{
	year += 1900;

	if (year % 400 == 0)
		return true;
	if (year % 100 == 0)
		return false;
	if (year % 4 == 0)
		return true;
	return false;
}

/**
 * Returns how many days there are in the given month of the given year.
 * Note that year is only taken into account if month is February.
 *
 * @param year Year since 1900 (can be negative).
 * @param mon Month of the year. 0 for January, 11 for December.
 * @return Number of days in the specified month.
 */
static int _days_in_month(time_t year, time_t mon)
{
	assert(mon >= 0 && mon <= 11);

	static int month_days[] =
		{ 31, 0, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

	if (mon == 1) {
		year += 1900;
		/* february */
		return _is_leap_year(year) ? 29 : 28;
	} else {
		return month_days[mon];
	}
}

/**
 * For specified year, month and day of month, returns which day of that year
 * it is.
 *
 * For example, given date 2011-01-03, the corresponding expression is:
 *     _day_of_year(111, 0, 3) == 2
 *
 * @param year Year (year 1900 = 0, can be negative).
 * @param mon Month (January = 0).
 * @param mday Day of month (First day is 1).
 * @return Day of year (First day is 0).
 */
static int _day_of_year(time_t year, time_t mon, time_t mday)
{
	static int mdays[] =
	    { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 };
	static int leap_mdays[] =
	    { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335 };

	return (_is_leap_year(year) ? leap_mdays[mon] : mdays[mon]) + mday - 1;
}

/**
 * Integer division that rounds to negative infinity.
 * Used by some functions in this file.
 *
 * @param op1 Divident.
 * @param op2 Divisor.
 * @return Rounded quotient.
 */
static time_t _floor_div(time_t op1, time_t op2)
{
	if (op1 >= 0 || op1 % op2 == 0) {
		return op1 / op2;
	} else {
		return op1 / op2 - 1;
	}
}

/**
 * Modulo that rounds to negative infinity.
 * Used by some functions in this file.
 *
 * @param op1 Divident.
 * @param op2 Divisor.
 * @return Remainder.
 */
static time_t _floor_mod(time_t op1, time_t op2)
{
	int div = _floor_div(op1, op2);

	/* (a / b) * b + a % b == a */
	/* thus, a % b == a - (a / b) * b */

	int result = op1 - div * op2;
	
	/* Some paranoid checking to ensure I didn't make a mistake here. */
	assert(result >= 0);
	assert(result < op2);
	assert(div * op2 + result == op1);
	
	return result;
}

/**
 * Number of days since the Epoch.
 * Epoch is 1970-01-01, which is also equal to day 0.
 *
 * @param year Year (year 1900 = 0, may be negative).
 * @param mon Month (January = 0).
 * @param mday Day of month (first day = 1).
 * @return Number of days since the Epoch.
 */
static time_t _days_since_epoch(time_t year, time_t mon, time_t mday)
{
	return (year - 70) * 365 + _floor_div(year - 69, 4) -
	    _floor_div(year - 1, 100) + _floor_div(year + 299, 400) +
	    _day_of_year(year, mon, mday);
}

/**
 * Seconds since the Epoch. see also _days_since_epoch().
 * 
 * @param tm Normalized broken-down time.
 * @return Number of seconds since the epoch, not counting leap seconds.
 */
static time_t _secs_since_epoch(const struct posix_tm *tm)
{
	return _days_since_epoch(tm->tm_year, tm->tm_mon, tm->tm_mday) *
	    SECS_PER_DAY + tm->tm_hour * SECS_PER_HOUR +
	    tm->tm_min * SECS_PER_MIN + tm->tm_sec;
}

/**
 * Which day of week the specified date is.
 * 
 * @param year Year (year 1900 = 0).
 * @param mon Month (January = 0).
 * @param mday Day of month (first = 1).
 * @return Day of week (Sunday = 0).
 */
static int _day_of_week(time_t year, time_t mon, time_t mday)
{
	/* 1970-01-01 is Thursday */
	return _floor_mod((_days_since_epoch(year, mon, mday) + 4), 7);
}

/**
 * Normalizes the broken-down time and optionally adds specified amount of
 * seconds.
 * 
 * @param tm Broken-down time to normalize.
 * @param sec_add Seconds to add.
 * @return 0 on success, -1 on overflow
 */
static int _normalize_time(struct posix_tm *tm, time_t sec_add)
{
	// TODO: DST correction

	/* Set initial values. */
	time_t sec = tm->tm_sec + sec_add;
	time_t min = tm->tm_min;
	time_t hour = tm->tm_hour;
	time_t day = tm->tm_mday - 1;
	time_t mon = tm->tm_mon;
	time_t year = tm->tm_year;

	/* Adjust time. */
	min += _floor_div(sec, SECS_PER_MIN);
	sec = _floor_mod(sec, SECS_PER_MIN);
	hour += _floor_div(min, MINS_PER_HOUR);
	min = _floor_mod(min, MINS_PER_HOUR);
	day += _floor_div(hour, HOURS_PER_DAY);
	hour = _floor_mod(hour, HOURS_PER_DAY);

	/* Adjust month. */
	year += _floor_div(mon, 12);
	mon = _floor_mod(mon, 12);

	/* Now the difficult part - days of month. */
	
	/* First, deal with whole cycles of 400 years = 146097 days. */
	year += _floor_div(day, 146097) * 400;
	day = _floor_mod(day, 146097);
	
	/* Then, go in one year steps. */
	if (mon <= 1) {
		/* January and February. */
		while (day > 365) {
			day -= _is_leap_year(year) ? 366 : 365;
			year++;
		}
	} else {
		/* Rest of the year. */
		while (day > 365) {
			day -= _is_leap_year(year + 1) ? 366 : 365;
			year++;
		}
	}
	
	/* Finally, finish it off month per month. */
	while (day >= _days_in_month(year, mon)) {
		day -= _days_in_month(year, mon);
		mon++;
		if (mon >= 12) {
			mon -= 12;
			year++;
		}
	}
	
	/* Calculate the remaining two fields. */
	tm->tm_yday = _day_of_year(year, mon, day + 1);
	tm->tm_wday = _day_of_week(year, mon, day + 1);
	
	/* And put the values back to the struct. */
	tm->tm_sec = (int) sec;
	tm->tm_min = (int) min;
	tm->tm_hour = (int) hour;
	tm->tm_mday = (int) day + 1;
	tm->tm_mon = (int) mon;
	
	/* Casts to work around libc brain-damage. */
	if (year > ((int)INT_MAX) || year < ((int)INT_MIN)) {
		tm->tm_year = (year < 0) ? ((int)INT_MIN) : ((int)INT_MAX);
		return -1;
	}
	
	tm->tm_year = (int) year;
	return 0;
}

/**
 * Which day the week-based year starts on, relative to the first calendar day.
 * E.g. if the year starts on December 31st, the return value is -1.
 *
 * @param Year since 1900.
 * @return Offset of week-based year relative to calendar year.
 */
static int _wbyear_offset(int year)
{
	int start_wday = _day_of_week(year, 0, 1);
	return _floor_mod(4 - start_wday, 7) - 3;
}

/**
 * Returns week-based year of the specified time.
 *
 * @param tm Normalized broken-down time.
 * @return Week-based year.
 */
static int _wbyear(const struct posix_tm *tm)
{
	int day = tm->tm_yday - _wbyear_offset(tm->tm_year);
	if (day < 0) {
		/* Last week of previous year. */
		return tm->tm_year - 1;
	}
	if (day > 364 + _is_leap_year(tm->tm_year)) {
		/* First week of next year. */
		return tm->tm_year + 1;
	}
	/* All the other days are in the calendar year. */
	return tm->tm_year;
}

/**
 * Week number of the year, assuming weeks start on sunday.
 * The first Sunday of January is the first day of week 1;
 * days in the new year before this are in week 0.
 *
 * @param tm Normalized broken-down time.
 * @return The week number (0 - 53).
 */
static int _sun_week_number(const struct posix_tm *tm)
{
	int first_day = (7 - _day_of_week(tm->tm_year, 0, 1)) % 7;
	return (tm->tm_yday - first_day + 7) / 7;
}

/**
 * Week number of the year, assuming weeks start on monday.
 * If the week containing January 1st has four or more days in the new year,
 * then it is considered week 1. Otherwise, it is the last week of the previous
 * year, and the next week is week 1. Both January 4th and the first Thursday
 * of January are always in week 1.
 *
 * @param tm Normalized broken-down time.
 * @return The week number (1 - 53).
 */
static int _iso_week_number(const struct posix_tm *tm)
{
	int day = tm->tm_yday - _wbyear_offset(tm->tm_year);
	if (day < 0) {
		/* Last week of previous year. */
		return 53;
	}
	if (day > 364 + _is_leap_year(tm->tm_year)) {
		/* First week of next year. */
		return 1;
	}
	/* All the other days give correct answer. */
	return (day / 7 + 1);
}

/**
 * Week number of the year, assuming weeks start on monday.
 * The first Monday of January is the first day of week 1;
 * days in the new year before this are in week 0. 
 *
 * @param tm Normalized broken-down time.
 * @return The week number (0 - 53).
 */
static int _mon_week_number(const struct posix_tm *tm)
{
	int first_day = (1 - _day_of_week(tm->tm_year, 0, 1)) % 7;
	return (tm->tm_yday - first_day + 7) / 7;
}

/******************************************************************************/

int posix_daylight;
long posix_timezone;
char *posix_tzname[2];

/**
 * Set timezone conversion information.
 */
void posix_tzset(void)
{
	// TODO: read environment
	posix_tzname[0] = (char *) "GMT";
	posix_tzname[1] = (char *) "GMT";
	posix_daylight = 0;
	posix_timezone = 0;
}

/**
 * Calculate the difference between two times, in seconds.
 * 
 * @param time1 First time.
 * @param time0 Second time.
 * @return Time in seconds.
 */
double posix_difftime(time_t time1, time_t time0)
{
	return (double) (time1 - time0);
}

/**
 * This function first normalizes the provided broken-down time
 * (moves all values to their proper bounds) and then tries to
 * calculate the appropriate time_t representation.
 *
 * @param tm Broken-down time.
 * @return time_t representation of the time, undefined value on overflow.
 */
time_t posix_mktime(struct posix_tm *tm)
{
	// TODO: take DST flag into account
	// TODO: detect overflow

	_normalize_time(tm, 0);
	return _secs_since_epoch(tm);
}

/**
 * Converts a time value to a broken-down UTC time.
 *
 * @param timer Time to convert.
 * @return Normalized broken-down time in UTC, NULL on overflow.
 */
struct posix_tm *posix_gmtime(const time_t *timer)
{
	assert(timer != NULL);

	static struct posix_tm result;
	return posix_gmtime_r(timer, &result);
}

/**
 * Converts a time value to a broken-down UTC time.
 * 
 * @param timer Time to convert.
 * @param result Structure to store the result to.
 * @return Value of result on success, NULL on overflow.
 */
struct posix_tm *posix_gmtime_r(const time_t *restrict timer,
    struct posix_tm *restrict result)
{
	assert(timer != NULL);
	assert(result != NULL);

	/* Set result to epoch. */
	result->tm_sec = 0;
	result->tm_min = 0;
	result->tm_hour = 0;
	result->tm_mday = 1;
	result->tm_mon = 0;
	result->tm_year = 70; /* 1970 */

	if (_normalize_time(result, *timer) == -1) {
		errno = EOVERFLOW;
		return NULL;
	}

	return result;
}

/**
 * Converts a time value to a broken-down local time.
 *
 * @param timer Time to convert.
 * @return Normalized broken-down time in local timezone, NULL on overflow.
 */
struct posix_tm *posix_localtime(const time_t *timer)
{
	static struct posix_tm result;
	return posix_localtime_r(timer, &result);
}

/**
 * Converts a time value to a broken-down local time.
 * 
 * @param timer Time to convert.
 * @param result Structure to store the result to.
 * @return Value of result on success, NULL on overflow.
 */
struct posix_tm *posix_localtime_r(const time_t *restrict timer,
    struct posix_tm *restrict result)
{
	// TODO: deal with timezone
	// currently assumes system and all times are in GMT
	return posix_gmtime_r(timer, result);
}

/**
 * Converts broken-down time to a string in format
 * "Sun Jan 1 00:00:00 1970\n". (Obsolete)
 *
 * @param timeptr Broken-down time structure.
 * @return Pointer to a statically allocated string.
 */
char *posix_asctime(const struct posix_tm *timeptr)
{
	static char buf[ASCTIME_BUF_LEN];
	return posix_asctime_r(timeptr, buf);
}

/**
 * Converts broken-down time to a string in format
 * "Sun Jan 1 00:00:00 1970\n". (Obsolete)
 *
 * @param timeptr Broken-down time structure.
 * @param buf Buffer to store string to, must be at least ASCTIME_BUF_LEN
 *     bytes long.
 * @return Value of buf.
 */
char *posix_asctime_r(const struct posix_tm *restrict timeptr,
    char *restrict buf)
{
	assert(timeptr != NULL);
	assert(buf != NULL);

	static const char *wday[] = {
		"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
	};
	static const char *mon[] = {
		"Jan", "Feb", "Mar", "Apr", "May", "Jun",
		"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
	};

	snprintf(buf, ASCTIME_BUF_LEN, "%s %s %2d %02d:%02d:%02d %d\n",
	    wday[timeptr->tm_wday],
	    mon[timeptr->tm_mon],
	    timeptr->tm_mday, timeptr->tm_hour,
	    timeptr->tm_min, timeptr->tm_sec,
	    1900 + timeptr->tm_year);

	return buf;
}

/**
 * Equivalent to asctime(localtime(clock)).
 * 
 * @param timer Time to convert.
 * @return Pointer to a statically allocated string holding the date.
 */
char *posix_ctime(const time_t *timer)
{
	struct posix_tm *loctime = posix_localtime(timer);
	if (loctime == NULL) {
		return NULL;
	}
	return posix_asctime(loctime);
}

/**
 * Reentrant variant of ctime().
 * 
 * @param timer Time to convert.
 * @param buf Buffer to store string to. Must be at least ASCTIME_BUF_LEN
 *     bytes long.
 * @return Pointer to buf on success, NULL on falure.
 */
char *posix_ctime_r(const time_t *timer, char *buf)
{
	struct posix_tm loctime;
	if (posix_localtime_r(timer, &loctime) == NULL) {
		return NULL;
	}
	return posix_asctime_r(&loctime, buf);
}

/**
 * Convert time and date to a string, based on a specified format and
 * current locale.
 * 
 * @param s Buffer to write string to.
 * @param maxsize Size of the buffer.
 * @param format Format of the output.
 * @param tm Broken-down time to format.
 * @return Number of bytes written.
 */
size_t posix_strftime(char *restrict s, size_t maxsize,
    const char *restrict format, const struct posix_tm *restrict tm)
{
	assert(s != NULL);
	assert(format != NULL);
	assert(tm != NULL);

	// TODO: use locale
	static const char *wday_abbr[] = {
		"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
	};
	static const char *wday[] = {
		"Sunday", "Monday", "Tuesday", "Wednesday",
		"Thursday", "Friday", "Saturday"
	};
	static const char *mon_abbr[] = {
		"Jan", "Feb", "Mar", "Apr", "May", "Jun",
		"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
	};
	static const char *mon[] = {
		"January", "February", "March", "April", "May", "June", "July",
		"August", "September", "October", "November", "December"
	};
	
	if (maxsize < 1) {
		return 0;
	}
	
	char *ptr = s;
	size_t consumed;
	size_t remaining = maxsize;
	
	#define append(...) { \
		/* FIXME: this requires POSIX-correct snprintf */ \
		/*        otherwise it won't work with non-ascii chars */ \
		consumed = snprintf(ptr, remaining, __VA_ARGS__); \
		if (consumed >= remaining) { \
			return 0; \
		} \
		ptr += consumed; \
		remaining -= consumed; \
	}
	
	#define recurse(fmt) { \
		consumed = posix_strftime(ptr, remaining, fmt, tm); \
		if (consumed == 0) { \
			return 0; \
		} \
		ptr += consumed; \
		remaining -= consumed; \
	}
	
	#define TO_12H(hour) (((hour) > 12) ? ((hour) - 12) : \
	    (((hour) == 0) ? 12 : (hour)))
	
	while (*format != '\0') {
		if (*format != '%') {
			append("%c", *format);
			format++;
			continue;
		}
		
		format++;
		if (*format == '0' || *format == '+') {
			// TODO: padding
			format++;
		}
		while (isdigit(*format)) {
			// TODO: padding
			format++;
		}
		if (*format == 'O' || *format == 'E') {
			// TODO: locale's alternative format
			format++;
		}
		
		switch (*format) {
		case 'a':
			append("%s", wday_abbr[tm->tm_wday]); break;
		case 'A':
			append("%s", wday[tm->tm_wday]); break;
		case 'b':
			append("%s", mon_abbr[tm->tm_mon]); break;
		case 'B':
			append("%s", mon[tm->tm_mon]); break;
		case 'c':
			// TODO: locale-specific datetime format
			recurse("%Y-%m-%d %H:%M:%S"); break;
		case 'C':
			append("%02d", (1900 + tm->tm_year) / 100); break;
		case 'd':
			append("%02d", tm->tm_mday); break;
		case 'D':
			recurse("%m/%d/%y"); break;
		case 'e':
			append("%2d", tm->tm_mday); break;
		case 'F':
			recurse("%+4Y-%m-%d"); break;
		case 'g':
			append("%02d", _wbyear(tm) % 100); break;
		case 'G':
			append("%d", _wbyear(tm)); break;
		case 'h':
			recurse("%b"); break;
		case 'H':
			append("%02d", tm->tm_hour); break;
		case 'I':
			append("%02d", TO_12H(tm->tm_hour)); break;
		case 'j':
			append("%03d", tm->tm_yday); break;
		case 'k':
			append("%2d", tm->tm_hour); break;
		case 'l':
			append("%2d", TO_12H(tm->tm_hour)); break;
		case 'm':
			append("%02d", tm->tm_mon); break;
		case 'M':
			append("%02d", tm->tm_min); break;
		case 'n':
			append("\n"); break;
		case 'p':
			append("%s", tm->tm_hour < 12 ? "AM" : "PM"); break;
		case 'P':
			append("%s", tm->tm_hour < 12 ? "am" : "PM"); break;
		case 'r':
			recurse("%I:%M:%S %p"); break;
		case 'R':
			recurse("%H:%M"); break;
		case 's':
			append("%ld", _secs_since_epoch(tm)); break;
		case 'S':
			append("%02d", tm->tm_sec); break;
		case 't':
			append("\t"); break;
		case 'T':
			recurse("%H:%M:%S"); break;
		case 'u':
			append("%d", (tm->tm_wday == 0) ? 7 : tm->tm_wday); break;
		case 'U':
			append("%02d", _sun_week_number(tm)); break;
		case 'V':
			append("%02d", _iso_week_number(tm)); break;
		case 'w':
			append("%d", tm->tm_wday); break;
		case 'W':
			append("%02d", _mon_week_number(tm)); break;
		case 'x':
			// TODO: locale-specific date format
			recurse("%Y-%m-%d"); break;
		case 'X':
			// TODO: locale-specific time format
			recurse("%H:%M:%S"); break;
		case 'y':
			append("%02d", tm->tm_year % 100); break;
		case 'Y':
			append("%d", 1900 + tm->tm_year); break;
		case 'z':
			// TODO: timezone
			break;
		case 'Z':
			// TODO: timezone
			break;
		case '%':
			append("%%");
			break;
		default:
			/* Invalid specifier, print verbatim. */
			while (*format != '%') {
				format--;
			}
			append("%%");
			break;
		}
		format++;
	}
	
	#undef append
	#undef recurse
	
	return maxsize - remaining;
}

/**
 * Get clock resolution. Only CLOCK_REALTIME is supported.
 *
 * @param clock_id Clock ID.
 * @param res Pointer to the variable where the resolution is to be written.
 * @return 0 on success, -1 with errno set on failure.
 */
int posix_clock_getres(posix_clockid_t clock_id, struct posix_timespec *res)
{
	assert(res != NULL);

	switch (clock_id) {
		case CLOCK_REALTIME:
			res->tv_sec = 0;
			res->tv_nsec = 1000; /* Microsecond resolution. */
			return 0;
		default:
			errno = EINVAL;
			return -1;
	}
}

/**
 * Get time. Only CLOCK_REALTIME is supported.
 * 
 * @param clock_id ID of the clock to query.
 * @param tp Pointer to the variable where the time is to be written.
 * @return 0 on success, -1 with errno on failure.
 */
int posix_clock_gettime(posix_clockid_t clock_id, struct posix_timespec *tp)
{
	assert(tp != NULL);

	switch (clock_id) {
		case CLOCK_REALTIME:
			;
			struct timeval tv;
			gettimeofday(&tv, NULL);
			tp->tv_sec = tv.tv_sec;
			tp->tv_nsec = tv.tv_usec * 1000;
			return 0;
		default:
			errno = EINVAL;
			return -1;
	}
}

/**
 * Set time on a specified clock. As HelenOS doesn't support this yet,
 * this function always fails.
 * 
 * @param clock_id ID of the clock to set.
 * @param tp Time to set.
 * @return 0 on success, -1 with errno on failure.
 */
int posix_clock_settime(posix_clockid_t clock_id,
    const struct posix_timespec *tp)
{
	assert(tp != NULL);

	switch (clock_id) {
		case CLOCK_REALTIME:
			// TODO: setting clock
			// FIXME: HelenOS doesn't actually support hardware
			//        clock yet
			errno = EPERM;
			return -1;
		default:
			errno = EINVAL;
			return -1;
	}
}

/**
 * Sleep on a specified clock.
 * 
 * @param clock_id ID of the clock to sleep on (only CLOCK_REALTIME supported).
 * @param flags Flags (none supported).
 * @param rqtp Sleep time.
 * @param rmtp Remaining time is written here if sleep is interrupted.
 * @return 0 on success, -1 with errno set on failure.
 */
int posix_clock_nanosleep(posix_clockid_t clock_id, int flags,
    const struct posix_timespec *rqtp, struct posix_timespec *rmtp)
{
	assert(rqtp != NULL);
	assert(rmtp != NULL);

	switch (clock_id) {
		case CLOCK_REALTIME:
			// TODO: interruptible sleep
			if (rqtp->tv_sec != 0) {
				sleep(rqtp->tv_sec);
			}
			if (rqtp->tv_nsec != 0) {
				usleep(rqtp->tv_nsec / 1000);
			}
			return 0;
		default:
			errno = EINVAL;
			return -1;
	}
}

/**
 * Get CPU time used since the process invocation.
 *
 * @return Consumed CPU cycles by this process or -1 if not available.
 */
posix_clock_t posix_clock(void)
{
	posix_clock_t total_cycles = -1;
	stats_task_t *task_stats = stats_get_task(task_get_id());
	if (task_stats) {
		total_cycles = (posix_clock_t) (task_stats->kcycles + task_stats->ucycles);
		free(task_stats);
		task_stats = 0;
	}

	return total_cycles;
}

/** @}
 */
