/* NetworkManager -- Network link manager
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301 USA.
 *
 * (C) Copyright 2018 Red Hat, Inc.
 */

#include "nm-default.h"

#include "nm-time-utils.h"

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

typedef struct {
	/* the offset to the native clock, in seconds. */
	gint64 offset_sec;
	clockid_t clk_id;
} GlobalState;

static const GlobalState *volatile p_global_state;

static const GlobalState *
_t_init_global_state (void)
{
	static GlobalState global_state = { };
	static gsize init_once = 0;
	const GlobalState *p;
	clockid_t clk_id;
	struct timespec tp;
	gint64 offset_sec;
	int r;

	clk_id = CLOCK_BOOTTIME;
	r = clock_gettime (clk_id, &tp);
	if (r == -1 && errno == EINVAL) {
		clk_id = CLOCK_MONOTONIC;
		r = clock_gettime (clk_id, &tp);
	}

	/* The only failure we tolerate is that CLOCK_BOOTTIME is not supported.
	 * Other than that, we rely on kernel to not fail on this. */
	g_assert (r == 0);
	g_assert (tp.tv_nsec >= 0 && tp.tv_nsec < NM_UTILS_NS_PER_SECOND);

	/* Calculate an offset for the time stamp.
	 *
	 * We always want positive values, because then we can initialize
	 * a timestamp with 0 and be sure, that it will be less then any
	 * value nm_utils_get_monotonic_timestamp_*() might return.
	 * For this to be true also for nm_utils_get_monotonic_timestamp_s() at
	 * early boot, we have to shift the timestamp to start counting at
	 * least from 1 second onward.
	 *
	 * Another advantage of shifting is, that this way we make use of the whole 31 bit
	 * range of signed int, before the time stamp for nm_utils_get_monotonic_timestamp_s()
	 * wraps (~68 years).
	 **/
	offset_sec = (- ((gint64) tp.tv_sec)) + 1;

	if (!g_once_init_enter (&init_once)) {
		/* there was a race. We expect the pointer to be fully initialized now. */
		p = g_atomic_pointer_get (&p_global_state);
		g_assert (p);
		return p;
	}

	global_state.offset_sec = offset_sec;
	global_state.clk_id = clk_id;
	p = &global_state;
	g_atomic_pointer_set (&p_global_state, p);
	g_once_init_leave (&init_once, 1);

	_nm_utils_monotonic_timestamp_initialized (&tp,
	                                           p->offset_sec,
	                                           p->clk_id == CLOCK_BOOTTIME);

	return p;
}

#define _t_get_global_state() \
	({ \
		const GlobalState *_p; \
		\
		_p = g_atomic_pointer_get (&p_global_state); \
		(G_LIKELY (_p) ? _p : _t_init_global_state ()); \
	})

#define _t_clock_gettime_eval(p, tp) \
	({ \
		struct timespec *const _tp = (tp); \
		const GlobalState *const _p2 = (p); \
		int _r; \
		\
		nm_assert (_tp); \
		\
		_r = clock_gettime (_p2->clk_id, _tp); \
		\
		nm_assert (_r == 0); \
		nm_assert (_tp->tv_nsec >= 0 && _tp->tv_nsec < NM_UTILS_NS_PER_SECOND); \
		\
		_p2; \
	})

#define _t_clock_gettime(tp) \
	_t_clock_gettime_eval (_t_get_global_state (), tp);

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

/**
 * nm_utils_get_monotonic_timestamp_ns:
 *
 * Returns: a monotonically increasing time stamp in nanoseconds,
 * starting at an unspecified offset. See clock_gettime(), %CLOCK_BOOTTIME.
 *
 * The returned value will start counting at an undefined point
 * in the past and will always be positive.
 *
 * All the nm_utils_get_monotonic_timestamp_*s functions return the same
 * timestamp but in different scales (nsec, usec, msec, sec).
 **/
gint64
nm_utils_get_monotonic_timestamp_ns (void)
{
	const GlobalState *p;
	struct timespec tp;

	p = _t_clock_gettime (&tp);

	/* Although the result will always be positive, we return a signed
	 * integer, which makes it easier to calculate time differences (when
	 * you want to subtract signed values).
	 **/
	return (((gint64) tp.tv_sec) + p->offset_sec) * NM_UTILS_NS_PER_SECOND +
	       tp.tv_nsec;
}

/**
 * nm_utils_get_monotonic_timestamp_us:
 *
 * Returns: a monotonically increasing time stamp in microseconds,
 * starting at an unspecified offset. See clock_gettime(), %CLOCK_BOOTTIME.
 *
 * The returned value will start counting at an undefined point
 * in the past and will always be positive.
 *
 * All the nm_utils_get_monotonic_timestamp_*s functions return the same
 * timestamp but in different scales (nsec, usec, msec, sec).
 **/
gint64
nm_utils_get_monotonic_timestamp_us (void)
{
	const GlobalState *p;
	struct timespec tp;

	p = _t_clock_gettime (&tp);

	/* Although the result will always be positive, we return a signed
	 * integer, which makes it easier to calculate time differences (when
	 * you want to subtract signed values).
	 **/
	return (((gint64) tp.tv_sec) + p->offset_sec) * ((gint64) G_USEC_PER_SEC) +
	       (tp.tv_nsec / (NM_UTILS_NS_PER_SECOND/G_USEC_PER_SEC));
}

/**
 * nm_utils_get_monotonic_timestamp_ms:
 *
 * Returns: a monotonically increasing time stamp in milliseconds,
 * starting at an unspecified offset. See clock_gettime(), %CLOCK_BOOTTIME.
 *
 * The returned value will start counting at an undefined point
 * in the past and will always be positive.
 *
 * All the nm_utils_get_monotonic_timestamp_*s functions return the same
 * timestamp but in different scales (nsec, usec, msec, sec).
 **/
gint64
nm_utils_get_monotonic_timestamp_ms (void)
{
	const GlobalState *p;
	struct timespec tp;

	p = _t_clock_gettime (&tp);

	/* Although the result will always be positive, we return a signed
	 * integer, which makes it easier to calculate time differences (when
	 * you want to subtract signed values).
	 **/
	return (((gint64) tp.tv_sec) + p->offset_sec) * ((gint64) 1000) +
	       (tp.tv_nsec / (NM_UTILS_NS_PER_SECOND/1000));
}

/**
 * nm_utils_get_monotonic_timestamp_s:
 *
 * Returns: nm_utils_get_monotonic_timestamp_ms() in seconds (throwing
 * away sub second parts). The returned value will always be positive.
 *
 * This value wraps after roughly 68 years which should be fine for any
 * practical purpose.
 *
 * All the nm_utils_get_monotonic_timestamp_*s functions return the same
 * timestamp but in different scales (nsec, usec, msec, sec).
 **/
gint32
nm_utils_get_monotonic_timestamp_s (void)
{
	const GlobalState *p;
	struct timespec tp;

	p = _t_clock_gettime (&tp);

	return (((gint64) tp.tv_sec) + p->offset_sec);
}

/**
 * nm_utils_monotonic_timestamp_as_boottime:
 * @timestamp: the monotonic-timestamp that should be converted into CLOCK_BOOTTIME.
 * @timestamp_ns_per_tick: How many nano seconds make one unit of @timestamp? E.g. if
 * @timestamp is in unit seconds, pass %NM_UTILS_NS_PER_SECOND; @timestamp in nano
 * seconds, pass 1; @timestamp in milli seconds, pass %NM_UTILS_NS_PER_SECOND/1000; etc.
 *
 * Returns: the monotonic-timestamp as CLOCK_BOOTTIME, as returned by clock_gettime().
 * The unit is the same as the passed in @timestamp basd on @timestamp_ns_per_tick.
 * E.g. if you passed @timestamp in as seconds, it will return boottime in seconds.
 * If @timestamp is a non-positive, it returns -1. Note that a (valid) monotonic-timestamp
 * is always positive.
 *
 * On older kernels that don't support CLOCK_BOOTTIME, the returned time is instead CLOCK_MONOTONIC.
 **/
gint64
nm_utils_monotonic_timestamp_as_boottime (gint64 timestamp, gint64 timestamp_ns_per_tick)
{
	const GlobalState *p;
	gint64 offset;

	/* only support ns-per-tick being a multiple of 10. */
	g_return_val_if_fail (timestamp_ns_per_tick == 1
	                      || (timestamp_ns_per_tick > 0 &&
	                          timestamp_ns_per_tick <= NM_UTILS_NS_PER_SECOND &&
	                          timestamp_ns_per_tick % 10 == 0),
	                      -1);

	/* Check that the timestamp is in a valid range. */
	g_return_val_if_fail (timestamp >= 0, -1);

	/* if the caller didn't yet ever fetch a monotonic-timestamp, he cannot pass any meaningful
	 * value (because he has no idea what these timestamps would be). That would be a bug. */
	nm_assert (g_atomic_pointer_get (&p_global_state));

	p = _t_get_global_state ();

	/* calculate the offset of monotonic-timestamp to boottime. offset_s is <= 1. */
	offset = p->offset_sec * (NM_UTILS_NS_PER_SECOND / timestamp_ns_per_tick);

	/* check for overflow. */
	g_return_val_if_fail (offset > 0 || timestamp < G_MAXINT64 + offset, G_MAXINT64);

	return timestamp - offset;
}