/* SPDX-License-Identifier: LGPL-2.1-or-later */

#include <ctype.h>
#include <errno.h>
#include <limits.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/time.h>
#include <sys/timerfd.h>
#include <sys/types.h>
#include <unistd.h>

#include "alloc-util.h"
#include "fd-util.h"
#include "fileio.h"
#include "fs-util.h"
#include "io-util.h"
#include "log.h"
#include "macro.h"
#include "missing_timerfd.h"
#include "parse-util.h"
#include "path-util.h"
#include "process-util.h"
#include "stat-util.h"
#include "string-table.h"
#include "string-util.h"
#include "strv.h"
#include "time-util.h"

static clockid_t map_clock_id(clockid_t c) {

        /* Some more exotic archs (s390, ppc, …) lack the "ALARM" flavour of the clocks. Thus, clock_gettime() will
         * fail for them. Since they are essentially the same as their non-ALARM pendants (their only difference is
         * when timers are set on them), let's just map them accordingly. This way, we can get the correct time even on
         * those archs. */

        switch (c) {

        case CLOCK_BOOTTIME_ALARM:
                return CLOCK_BOOTTIME;

        case CLOCK_REALTIME_ALARM:
                return CLOCK_REALTIME;

        default:
                return c;
        }
}

usec_t now(clockid_t clock_id) {
        struct timespec ts;

        assert_se(clock_gettime(map_clock_id(clock_id), &ts) == 0);

        return timespec_load(&ts);
}

nsec_t now_nsec(clockid_t clock_id) {
        struct timespec ts;

        assert_se(clock_gettime(map_clock_id(clock_id), &ts) == 0);

        return timespec_load_nsec(&ts);
}

dual_timestamp* dual_timestamp_get(dual_timestamp *ts) {
        assert(ts);

        ts->realtime = now(CLOCK_REALTIME);
        ts->monotonic = now(CLOCK_MONOTONIC);

        return ts;
}

triple_timestamp* triple_timestamp_get(triple_timestamp *ts) {
        assert(ts);

        ts->realtime = now(CLOCK_REALTIME);
        ts->monotonic = now(CLOCK_MONOTONIC);
        ts->boottime = clock_boottime_supported() ? now(CLOCK_BOOTTIME) : USEC_INFINITY;

        return ts;
}

static usec_t map_clock_usec_internal(usec_t from, usec_t from_base, usec_t to_base) {

        /* Maps the time 'from' between two clocks, based on a common reference point where the first clock
         * is at 'from_base' and the second clock at 'to_base'. Basically calculates:
         *
         *         from - from_base + to_base
         *
         * But takes care of overflows/underflows and avoids signed operations. */

        if (from >= from_base) { /* In the future */
                usec_t delta = from - from_base;

                if (to_base >= USEC_INFINITY - delta) /* overflow? */
                        return USEC_INFINITY;

                return to_base + delta;

        } else { /* In the past */
                usec_t delta = from_base - from;

                if (to_base <= delta) /* underflow? */
                        return 0;

                return to_base - delta;
        }
}

usec_t map_clock_usec(usec_t from, clockid_t from_clock, clockid_t to_clock) {

        /* Try to avoid any inaccuracy needlessly added in case we convert from effectively the same clock
         * onto itself */
        if (map_clock_id(from_clock) == map_clock_id(to_clock))
                return from;

        /* Keep infinity as is */
        if (from == USEC_INFINITY)
                return from;

        return map_clock_usec_internal(from, now(from_clock), now(to_clock));
}

dual_timestamp* dual_timestamp_from_realtime(dual_timestamp *ts, usec_t u) {
        assert(ts);

        if (u == USEC_INFINITY || u == 0) {
                ts->realtime = ts->monotonic = u;
                return ts;
        }

        ts->realtime = u;
        ts->monotonic = map_clock_usec(u, CLOCK_REALTIME, CLOCK_MONOTONIC);
        return ts;
}

triple_timestamp* triple_timestamp_from_realtime(triple_timestamp *ts, usec_t u) {
        usec_t nowr;

        assert(ts);

        if (u == USEC_INFINITY || u == 0) {
                ts->realtime = ts->monotonic = ts->boottime = u;
                return ts;
        }

        nowr = now(CLOCK_REALTIME);

        ts->realtime = u;
        ts->monotonic = map_clock_usec_internal(u, nowr, now(CLOCK_MONOTONIC));
        ts->boottime = clock_boottime_supported() ?
                map_clock_usec_internal(u, nowr, now(CLOCK_BOOTTIME)) :
                USEC_INFINITY;

        return ts;
}

dual_timestamp* dual_timestamp_from_monotonic(dual_timestamp *ts, usec_t u) {
        assert(ts);

        if (u == USEC_INFINITY) {
                ts->realtime = ts->monotonic = USEC_INFINITY;
                return ts;
        }

        ts->monotonic = u;
        ts->realtime = map_clock_usec(u, CLOCK_MONOTONIC, CLOCK_REALTIME);
        return ts;
}

dual_timestamp* dual_timestamp_from_boottime_or_monotonic(dual_timestamp *ts, usec_t u) {
        clockid_t cid;
        usec_t nowm;

        if (u == USEC_INFINITY) {
                ts->realtime = ts->monotonic = USEC_INFINITY;
                return ts;
        }

        cid = clock_boottime_or_monotonic();
        nowm = now(cid);

        if (cid == CLOCK_MONOTONIC)
                ts->monotonic = u;
        else
                ts->monotonic = map_clock_usec_internal(u, nowm, now(CLOCK_MONOTONIC));

        ts->realtime = map_clock_usec_internal(u, nowm, now(CLOCK_REALTIME));
        return ts;
}

usec_t triple_timestamp_by_clock(triple_timestamp *ts, clockid_t clock) {

        switch (clock) {

        case CLOCK_REALTIME:
        case CLOCK_REALTIME_ALARM:
                return ts->realtime;

        case CLOCK_MONOTONIC:
                return ts->monotonic;

        case CLOCK_BOOTTIME:
        case CLOCK_BOOTTIME_ALARM:
                return ts->boottime;

        default:
                return USEC_INFINITY;
        }
}

usec_t timespec_load(const struct timespec *ts) {
        assert(ts);

        if (ts->tv_sec < 0 || ts->tv_nsec < 0)
                return USEC_INFINITY;

        if ((usec_t) ts->tv_sec > (UINT64_MAX - (ts->tv_nsec / NSEC_PER_USEC)) / USEC_PER_SEC)
                return USEC_INFINITY;

        return
                (usec_t) ts->tv_sec * USEC_PER_SEC +
                (usec_t) ts->tv_nsec / NSEC_PER_USEC;
}

nsec_t timespec_load_nsec(const struct timespec *ts) {
        assert(ts);

        if (ts->tv_sec < 0 || ts->tv_nsec < 0)
                return NSEC_INFINITY;

        if ((nsec_t) ts->tv_sec >= (UINT64_MAX - ts->tv_nsec) / NSEC_PER_SEC)
                return NSEC_INFINITY;

        return (nsec_t) ts->tv_sec * NSEC_PER_SEC + (nsec_t) ts->tv_nsec;
}

struct timespec *timespec_store(struct timespec *ts, usec_t u)  {
        assert(ts);

        if (u == USEC_INFINITY ||
            u / USEC_PER_SEC >= TIME_T_MAX) {
                ts->tv_sec = (time_t) -1;
                ts->tv_nsec = -1L;
                return ts;
        }

        ts->tv_sec = (time_t) (u / USEC_PER_SEC);
        ts->tv_nsec = (long) ((u % USEC_PER_SEC) * NSEC_PER_USEC);

        return ts;
}

struct timespec *timespec_store_nsec(struct timespec *ts, nsec_t n)  {
        assert(ts);

        if (n == NSEC_INFINITY ||
            n / NSEC_PER_SEC >= TIME_T_MAX) {
                ts->tv_sec = (time_t) -1;
                ts->tv_nsec = -1L;
                return ts;
        }

        ts->tv_sec = (time_t) (n / NSEC_PER_SEC);
        ts->tv_nsec = (long) (n % NSEC_PER_SEC);

        return ts;
}

usec_t timeval_load(const struct timeval *tv) {
        assert(tv);

        if (tv->tv_sec < 0 || tv->tv_usec < 0)
                return USEC_INFINITY;

        if ((usec_t) tv->tv_sec > (UINT64_MAX - tv->tv_usec) / USEC_PER_SEC)
                return USEC_INFINITY;

        return
                (usec_t) tv->tv_sec * USEC_PER_SEC +
                (usec_t) tv->tv_usec;
}

struct timeval *timeval_store(struct timeval *tv, usec_t u) {
        assert(tv);

        if (u == USEC_INFINITY ||
            u / USEC_PER_SEC > TIME_T_MAX) {
                tv->tv_sec = (time_t) -1;
                tv->tv_usec = (suseconds_t) -1;
        } else {
                tv->tv_sec = (time_t) (u / USEC_PER_SEC);
                tv->tv_usec = (suseconds_t) (u % USEC_PER_SEC);
        }

        return tv;
}

char *format_timestamp_style(
                char *buf,
                size_t l,
                usec_t t,
                TimestampStyle style) {

        /* The weekdays in non-localized (English) form. We use this instead of the localized form, so that our
         * generated timestamps may be parsed with parse_timestamp(), and always read the same. */
        static const char * const weekdays[] = {
                [0] = "Sun",
                [1] = "Mon",
                [2] = "Tue",
                [3] = "Wed",
                [4] = "Thu",
                [5] = "Fri",
                [6] = "Sat",
        };

        struct tm tm;
        time_t sec;
        size_t n;
        bool utc = false, us = false;

        assert(buf);

        switch (style) {
                case TIMESTAMP_PRETTY:
                        break;
                case TIMESTAMP_US:
                        us = true;
                        break;
                case TIMESTAMP_UTC:
                        utc = true;
                        break;
                case TIMESTAMP_US_UTC:
                        us = true;
                        utc = true;
                        break;
                default:
                        return NULL;
        }

        if (l < (size_t) (3 +                  /* week day */
                          1 + 10 +             /* space and date */
                          1 + 8 +              /* space and time */
                          (us ? 1 + 6 : 0) +   /* "." and microsecond part */
                          1 + 1 +              /* space and shortest possible zone */
                          1))
                return NULL; /* Not enough space even for the shortest form. */
        if (t <= 0 || t == USEC_INFINITY)
                return NULL; /* Timestamp is unset */

        /* Let's not format times with years > 9999 */
        if (t > USEC_TIMESTAMP_FORMATTABLE_MAX) {
                assert(l >= STRLEN("--- XXXX-XX-XX XX:XX:XX") + 1);
                strcpy(buf, "--- XXXX-XX-XX XX:XX:XX");
                return buf;
        }

        sec = (time_t) (t / USEC_PER_SEC); /* Round down */

        if (!localtime_or_gmtime_r(&sec, &tm, utc))
                return NULL;

        /* Start with the week day */
        assert((size_t) tm.tm_wday < ELEMENTSOF(weekdays));
        memcpy(buf, weekdays[tm.tm_wday], 4);

        /* Add the main components */
        if (strftime(buf + 3, l - 3, " %Y-%m-%d %H:%M:%S", &tm) <= 0)
                return NULL; /* Doesn't fit */

        /* Append the microseconds part, if that's requested */
        if (us) {
                n = strlen(buf);
                if (n + 8 > l)
                        return NULL; /* Microseconds part doesn't fit. */

                sprintf(buf + n, ".%06"PRI_USEC, t % USEC_PER_SEC);
        }

        /* Append the timezone */
        n = strlen(buf);
        if (utc) {
                /* If this is UTC then let's explicitly use the "UTC" string here, because gmtime_r() normally uses the
                 * obsolete "GMT" instead. */
                if (n + 5 > l)
                        return NULL; /* "UTC" doesn't fit. */

                strcpy(buf + n, " UTC");

        } else if (!isempty(tm.tm_zone)) {
                size_t tn;

                /* An explicit timezone is specified, let's use it, if it fits */
                tn = strlen(tm.tm_zone);
                if (n + 1 + tn + 1 > l) {
                        /* The full time zone does not fit in. Yuck. */

                        if (n + 1 + _POSIX_TZNAME_MAX + 1 > l)
                                return NULL; /* Not even enough space for the POSIX minimum (of 6)? In that case, complain that it doesn't fit */

                        /* So the time zone doesn't fit in fully, but the caller passed enough space for the POSIX
                         * minimum time zone length. In this case suppress the timezone entirely, in order not to dump
                         * an overly long, hard to read string on the user. This should be safe, because the user will
                         * assume the local timezone anyway if none is shown. And so does parse_timestamp(). */
                } else {
                        buf[n++] = ' ';
                        strcpy(buf + n, tm.tm_zone);
                }
        }

        return buf;
}

char *format_timestamp_relative(char *buf, size_t l, usec_t t) {
        const char *s;
        usec_t n, d;

        if (t <= 0 || t == USEC_INFINITY)
                return NULL;

        n = now(CLOCK_REALTIME);
        if (n > t) {
                d = n - t;
                s = "ago";
        } else {
                d = t - n;
                s = "left";
        }

        if (d >= USEC_PER_YEAR) {
                usec_t years = d / USEC_PER_YEAR;
                usec_t months = (d % USEC_PER_YEAR) / USEC_PER_MONTH;

                (void) snprintf(buf, l, USEC_FMT " %s " USEC_FMT " %s %s",
                                years,
                                years == 1 ? "year" : "years",
                                months,
                                months == 1 ? "month" : "months",
                                s);
        } else if (d >= USEC_PER_MONTH) {
                usec_t months = d / USEC_PER_MONTH;
                usec_t days = (d % USEC_PER_MONTH) / USEC_PER_DAY;

                (void) snprintf(buf, l, USEC_FMT " %s " USEC_FMT " %s %s",
                                months,
                                months == 1 ? "month" : "months",
                                days,
                                days == 1 ? "day" : "days",
                                s);
        } else if (d >= USEC_PER_WEEK) {
                usec_t weeks = d / USEC_PER_WEEK;
                usec_t days = (d % USEC_PER_WEEK) / USEC_PER_DAY;

                (void) snprintf(buf, l, USEC_FMT " %s " USEC_FMT " %s %s",
                                weeks,
                                weeks == 1 ? "week" : "weeks",
                                days,
                                days == 1 ? "day" : "days",
                                s);
        } else if (d >= 2*USEC_PER_DAY)
                (void) snprintf(buf, l, USEC_FMT " days %s", d / USEC_PER_DAY, s);
        else if (d >= 25*USEC_PER_HOUR)
                (void) snprintf(buf, l, "1 day " USEC_FMT "h %s",
                                (d - USEC_PER_DAY) / USEC_PER_HOUR, s);
        else if (d >= 6*USEC_PER_HOUR)
                (void) snprintf(buf, l, USEC_FMT "h %s",
                                d / USEC_PER_HOUR, s);
        else if (d >= USEC_PER_HOUR)
                (void) snprintf(buf, l, USEC_FMT "h " USEC_FMT "min %s",
                                d / USEC_PER_HOUR,
                                (d % USEC_PER_HOUR) / USEC_PER_MINUTE, s);
        else if (d >= 5*USEC_PER_MINUTE)
                (void) snprintf(buf, l, USEC_FMT "min %s",
                                d / USEC_PER_MINUTE, s);
        else if (d >= USEC_PER_MINUTE)
                (void) snprintf(buf, l, USEC_FMT "min " USEC_FMT "s %s",
                                d / USEC_PER_MINUTE,
                                (d % USEC_PER_MINUTE) / USEC_PER_SEC, s);
        else if (d >= USEC_PER_SEC)
                (void) snprintf(buf, l, USEC_FMT "s %s",
                                d / USEC_PER_SEC, s);
        else if (d >= USEC_PER_MSEC)
                (void) snprintf(buf, l, USEC_FMT "ms %s",
                                d / USEC_PER_MSEC, s);
        else if (d > 0)
                (void) snprintf(buf, l, USEC_FMT"us %s",
                                d, s);
        else
                (void) snprintf(buf, l, "now");

        buf[l-1] = 0;
        return buf;
}

char *format_timespan(char *buf, size_t l, usec_t t, usec_t accuracy) {
        static const struct {
                const char *suffix;
                usec_t usec;
        } table[] = {
                { "y",     USEC_PER_YEAR   },
                { "month", USEC_PER_MONTH  },
                { "w",     USEC_PER_WEEK   },
                { "d",     USEC_PER_DAY    },
                { "h",     USEC_PER_HOUR   },
                { "min",   USEC_PER_MINUTE },
                { "s",     USEC_PER_SEC    },
                { "ms",    USEC_PER_MSEC   },
                { "us",    1               },
        };

        char *p = buf;
        bool something = false;

        assert(buf);
        assert(l > 0);

        if (t == USEC_INFINITY) {
                strncpy(p, "infinity", l-1);
                p[l-1] = 0;
                return p;
        }

        if (t <= 0) {
                strncpy(p, "0", l-1);
                p[l-1] = 0;
                return p;
        }

        /* The result of this function can be parsed with parse_sec */

        for (size_t i = 0; i < ELEMENTSOF(table); i++) {
                int k = 0;
                size_t n;
                bool done = false;
                usec_t a, b;

                if (t <= 0)
                        break;

                if (t < accuracy && something)
                        break;

                if (t < table[i].usec)
                        continue;

                if (l <= 1)
                        break;

                a = t / table[i].usec;
                b = t % table[i].usec;

                /* Let's see if we should shows this in dot notation */
                if (t < USEC_PER_MINUTE && b > 0) {
                        signed char j = 0;

                        for (usec_t cc = table[i].usec; cc > 1; cc /= 10)
                                j++;

                        for (usec_t cc = accuracy; cc > 1; cc /= 10) {
                                b /= 10;
                                j--;
                        }

                        if (j > 0) {
                                k = snprintf(p, l,
                                             "%s"USEC_FMT".%0*"PRI_USEC"%s",
                                             p > buf ? " " : "",
                                             a,
                                             j,
                                             b,
                                             table[i].suffix);

                                t = 0;
                                done = true;
                        }
                }

                /* No? Then let's show it normally */
                if (!done) {
                        k = snprintf(p, l,
                                     "%s"USEC_FMT"%s",
                                     p > buf ? " " : "",
                                     a,
                                     table[i].suffix);

                        t = b;
                }

                n = MIN((size_t) k, l);

                l -= n;
                p += n;

                something = true;
        }

        *p = 0;

        return buf;
}

static int parse_timestamp_impl(const char *t, usec_t *usec, bool with_tz) {
        static const struct {
                const char *name;
                const int nr;
        } day_nr[] = {
                { "Sunday",    0 },
                { "Sun",       0 },
                { "Monday",    1 },
                { "Mon",       1 },
                { "Tuesday",   2 },
                { "Tue",       2 },
                { "Wednesday", 3 },
                { "Wed",       3 },
                { "Thursday",  4 },
                { "Thu",       4 },
                { "Friday",    5 },
                { "Fri",       5 },
                { "Saturday",  6 },
                { "Sat",       6 },
        };

        const char *k, *utc = NULL, *tzn = NULL;
        struct tm tm, copy;
        time_t x;
        usec_t x_usec, plus = 0, minus = 0, ret;
        int r, weekday = -1, dst = -1;
        size_t i;

        /* Allowed syntaxes:
         *
         *   2012-09-22 16:34:22
         *   2012-09-22 16:34     (seconds will be set to 0)
         *   2012-09-22           (time will be set to 00:00:00)
         *   16:34:22             (date will be set to today)
         *   16:34                (date will be set to today, seconds to 0)
         *   now
         *   yesterday            (time is set to 00:00:00)
         *   today                (time is set to 00:00:00)
         *   tomorrow             (time is set to 00:00:00)
         *   +5min
         *   -5days
         *   @2147483647          (seconds since epoch)
         */

        assert(t);

        if (t[0] == '@' && !with_tz)
                return parse_sec(t + 1, usec);

        ret = now(CLOCK_REALTIME);

        if (!with_tz) {
                if (streq(t, "now"))
                        goto finish;

                else if (t[0] == '+') {
                        r = parse_sec(t+1, &plus);
                        if (r < 0)
                                return r;

                        goto finish;

                } else if (t[0] == '-') {
                        r = parse_sec(t+1, &minus);
                        if (r < 0)
                                return r;

                        goto finish;

                } else if ((k = endswith(t, " ago"))) {
                        t = strndupa_safe(t, k - t);

                        r = parse_sec(t, &minus);
                        if (r < 0)
                                return r;

                        goto finish;

                } else if ((k = endswith(t, " left"))) {
                        t = strndupa_safe(t, k - t);

                        r = parse_sec(t, &plus);
                        if (r < 0)
                                return r;

                        goto finish;
                }

                /* See if the timestamp is suffixed with UTC */
                utc = endswith_no_case(t, " UTC");
                if (utc)
                        t = strndupa_safe(t, utc - t);
                else {
                        const char *e = NULL;
                        int j;

                        tzset();

                        /* See if the timestamp is suffixed by either the DST or non-DST local timezone. Note that we only
                         * support the local timezones here, nothing else. Not because we wouldn't want to, but simply because
                         * there are no nice APIs available to cover this. By accepting the local time zone strings, we make
                         * sure that all timestamps written by format_timestamp() can be parsed correctly, even though we don't
                         * support arbitrary timezone specifications. */

                        for (j = 0; j <= 1; j++) {

                                if (isempty(tzname[j]))
                                        continue;

                                e = endswith_no_case(t, tzname[j]);
                                if (!e)
                                        continue;
                                if (e == t)
                                        continue;
                                if (e[-1] != ' ')
                                        continue;

                                break;
                        }

                        if (IN_SET(j, 0, 1)) {
                                /* Found one of the two timezones specified. */
                                t = strndupa_safe(t, e - t - 1);
                                dst = j;
                                tzn = tzname[j];
                        }
                }
        }

        x = (time_t) (ret / USEC_PER_SEC);
        x_usec = 0;

        if (!localtime_or_gmtime_r(&x, &tm, utc))
                return -EINVAL;

        tm.tm_isdst = dst;
        if (!with_tz && tzn)
                tm.tm_zone = tzn;

        if (streq(t, "today")) {
                tm.tm_sec = tm.tm_min = tm.tm_hour = 0;
                goto from_tm;

        } else if (streq(t, "yesterday")) {
                tm.tm_mday--;
                tm.tm_sec = tm.tm_min = tm.tm_hour = 0;
                goto from_tm;

        } else if (streq(t, "tomorrow")) {
                tm.tm_mday++;
                tm.tm_sec = tm.tm_min = tm.tm_hour = 0;
                goto from_tm;
        }

        for (i = 0; i < ELEMENTSOF(day_nr); i++) {
                size_t skip;

                if (!startswith_no_case(t, day_nr[i].name))
                        continue;

                skip = strlen(day_nr[i].name);
                if (t[skip] != ' ')
                        continue;

                weekday = day_nr[i].nr;
                t += skip + 1;
                break;
        }

        copy = tm;
        k = strptime(t, "%y-%m-%d %H:%M:%S", &tm);
        if (k) {
                if (*k == '.')
                        goto parse_usec;
                else if (*k == 0)
                        goto from_tm;
        }

        tm = copy;
        k = strptime(t, "%Y-%m-%d %H:%M:%S", &tm);
        if (k) {
                if (*k == '.')
                        goto parse_usec;
                else if (*k == 0)
                        goto from_tm;
        }

        tm = copy;
        k = strptime(t, "%y-%m-%d %H:%M", &tm);
        if (k && *k == 0) {
                tm.tm_sec = 0;
                goto from_tm;
        }

        tm = copy;
        k = strptime(t, "%Y-%m-%d %H:%M", &tm);
        if (k && *k == 0) {
                tm.tm_sec = 0;
                goto from_tm;
        }

        tm = copy;
        k = strptime(t, "%y-%m-%d", &tm);
        if (k && *k == 0) {
                tm.tm_sec = tm.tm_min = tm.tm_hour = 0;
                goto from_tm;
        }

        tm = copy;
        k = strptime(t, "%Y-%m-%d", &tm);
        if (k && *k == 0) {
                tm.tm_sec = tm.tm_min = tm.tm_hour = 0;
                goto from_tm;
        }

        tm = copy;
        k = strptime(t, "%H:%M:%S", &tm);
        if (k) {
                if (*k == '.')
                        goto parse_usec;
                else if (*k == 0)
                        goto from_tm;
        }

        tm = copy;
        k = strptime(t, "%H:%M", &tm);
        if (k && *k == 0) {
                tm.tm_sec = 0;
                goto from_tm;
        }

        return -EINVAL;

parse_usec:
        {
                unsigned add;

                k++;
                r = parse_fractional_part_u(&k, 6, &add);
                if (r < 0)
                        return -EINVAL;

                if (*k)
                        return -EINVAL;

                x_usec = add;
        }

from_tm:
        if (weekday >= 0 && tm.tm_wday != weekday)
                return -EINVAL;

        x = mktime_or_timegm(&tm, utc);
        if (x < 0)
                return -EINVAL;

        ret = (usec_t) x * USEC_PER_SEC + x_usec;
        if (ret > USEC_TIMESTAMP_FORMATTABLE_MAX)
                return -EINVAL;

finish:
        if (ret + plus < ret) /* overflow? */
                return -EINVAL;
        ret += plus;
        if (ret > USEC_TIMESTAMP_FORMATTABLE_MAX)
                return -EINVAL;

        if (ret >= minus)
                ret -= minus;
        else
                return -EINVAL;

        if (usec)
                *usec = ret;
        return 0;
}

typedef struct ParseTimestampResult {
        usec_t usec;
        int return_value;
} ParseTimestampResult;

int parse_timestamp(const char *t, usec_t *usec) {
        char *last_space, *tz = NULL;
        ParseTimestampResult *shared, tmp;
        int r;

        last_space = strrchr(t, ' ');
        if (last_space != NULL && timezone_is_valid(last_space + 1, LOG_DEBUG))
                tz = last_space + 1;

        if (!tz || endswith_no_case(t, " UTC"))
                return parse_timestamp_impl(t, usec, false);

        shared = mmap(NULL, sizeof *shared, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0);
        if (shared == MAP_FAILED)
                return negative_errno();

        r = safe_fork("(sd-timestamp)", FORK_RESET_SIGNALS|FORK_CLOSE_ALL_FDS|FORK_DEATHSIG|FORK_WAIT, NULL);
        if (r < 0) {
                (void) munmap(shared, sizeof *shared);
                return r;
        }
        if (r == 0) {
                bool with_tz = true;
                char *colon_tz;

                /* tzset(3) says $TZ should be prefixed with ":" if we reference timezone files */
                colon_tz = strjoina(":", tz);

                if (setenv("TZ", colon_tz, 1) != 0) {
                        shared->return_value = negative_errno();
                        _exit(EXIT_FAILURE);
                }

                tzset();

                /* If there is a timezone that matches the tzname fields, leave the parsing to the implementation.
                 * Otherwise just cut it off. */
                with_tz = !STR_IN_SET(tz, tzname[0], tzname[1]);

                /* Cut off the timezone if we don't need it. */
                if (with_tz)
                        t = strndupa_safe(t, last_space - t);

                shared->return_value = parse_timestamp_impl(t, &shared->usec, with_tz);

                _exit(EXIT_SUCCESS);
        }

        tmp = *shared;
        if (munmap(shared, sizeof *shared) != 0)
                return negative_errno();

        if (tmp.return_value == 0 && usec)
                *usec = tmp.usec;

        return tmp.return_value;
}

static const char* extract_multiplier(const char *p, usec_t *multiplier) {
        static const struct {
                const char *suffix;
                usec_t usec;
        } table[] = {
                { "seconds", USEC_PER_SEC    },
                { "second",  USEC_PER_SEC    },
                { "sec",     USEC_PER_SEC    },
                { "s",       USEC_PER_SEC    },
                { "minutes", USEC_PER_MINUTE },
                { "minute",  USEC_PER_MINUTE },
                { "min",     USEC_PER_MINUTE },
                { "months",  USEC_PER_MONTH  },
                { "month",   USEC_PER_MONTH  },
                { "M",       USEC_PER_MONTH  },
                { "msec",    USEC_PER_MSEC   },
                { "ms",      USEC_PER_MSEC   },
                { "m",       USEC_PER_MINUTE },
                { "hours",   USEC_PER_HOUR   },
                { "hour",    USEC_PER_HOUR   },
                { "hr",      USEC_PER_HOUR   },
                { "h",       USEC_PER_HOUR   },
                { "days",    USEC_PER_DAY    },
                { "day",     USEC_PER_DAY    },
                { "d",       USEC_PER_DAY    },
                { "weeks",   USEC_PER_WEEK   },
                { "week",    USEC_PER_WEEK   },
                { "w",       USEC_PER_WEEK   },
                { "years",   USEC_PER_YEAR   },
                { "year",    USEC_PER_YEAR   },
                { "y",       USEC_PER_YEAR   },
                { "usec",    1ULL            },
                { "us",      1ULL            },
                { "µs",      1ULL            },
        };

        for (size_t i = 0; i < ELEMENTSOF(table); i++) {
                char *e;

                e = startswith(p, table[i].suffix);
                if (e) {
                        *multiplier = table[i].usec;
                        return e;
                }
        }

        return p;
}

int parse_time(const char *t, usec_t *usec, usec_t default_unit) {
        const char *p, *s;
        usec_t r = 0;
        bool something = false;

        assert(t);
        assert(default_unit > 0);

        p = t;

        p += strspn(p, WHITESPACE);
        s = startswith(p, "infinity");
        if (s) {
                s += strspn(s, WHITESPACE);
                if (*s != 0)
                        return -EINVAL;

                if (usec)
                        *usec = USEC_INFINITY;
                return 0;
        }

        for (;;) {
                usec_t multiplier = default_unit, k;
                long long l;
                char *e;

                p += strspn(p, WHITESPACE);

                if (*p == 0) {
                        if (!something)
                                return -EINVAL;

                        break;
                }

                if (*p == '-') /* Don't allow "-0" */
                        return -ERANGE;

                errno = 0;
                l = strtoll(p, &e, 10);
                if (errno > 0)
                        return -errno;
                if (l < 0)
                        return -ERANGE;

                if (*e == '.') {
                        p = e + 1;
                        p += strspn(p, DIGITS);
                } else if (e == p)
                        return -EINVAL;
                else
                        p = e;

                s = extract_multiplier(p + strspn(p, WHITESPACE), &multiplier);
                if (s == p && *s != '\0')
                        /* Don't allow '12.34.56', but accept '12.34 .56' or '12.34s.56' */
                        return -EINVAL;

                p = s;

                if ((usec_t) l >= USEC_INFINITY / multiplier)
                        return -ERANGE;

                k = (usec_t) l * multiplier;
                if (k >= USEC_INFINITY - r)
                        return -ERANGE;

                r += k;

                something = true;

                if (*e == '.') {
                        usec_t m = multiplier / 10;
                        const char *b;

                        for (b = e + 1; *b >= '0' && *b <= '9'; b++, m /= 10) {
                                k = (usec_t) (*b - '0') * m;
                                if (k >= USEC_INFINITY - r)
                                        return -ERANGE;

                                r += k;
                        }

                        /* Don't allow "0.-0", "3.+1", "3. 1", "3.sec" or "3.hoge" */
                        if (b == e + 1)
                                return -EINVAL;
                }
        }

        if (usec)
                *usec = r;
        return 0;
}

int parse_sec(const char *t, usec_t *usec) {
        return parse_time(t, usec, USEC_PER_SEC);
}

int parse_sec_fix_0(const char *t, usec_t *ret) {
        usec_t k;
        int r;

        assert(t);
        assert(ret);

        r = parse_sec(t, &k);
        if (r < 0)
                return r;

        *ret = k == 0 ? USEC_INFINITY : k;
        return r;
}

int parse_sec_def_infinity(const char *t, usec_t *ret) {
        t += strspn(t, WHITESPACE);
        if (isempty(t)) {
                *ret = USEC_INFINITY;
                return 0;
        }
        return parse_sec(t, ret);
}

static const char* extract_nsec_multiplier(const char *p, nsec_t *multiplier) {
        static const struct {
                const char *suffix;
                nsec_t nsec;
        } table[] = {
                { "seconds", NSEC_PER_SEC    },
                { "second",  NSEC_PER_SEC    },
                { "sec",     NSEC_PER_SEC    },
                { "s",       NSEC_PER_SEC    },
                { "minutes", NSEC_PER_MINUTE },
                { "minute",  NSEC_PER_MINUTE },
                { "min",     NSEC_PER_MINUTE },
                { "months",  NSEC_PER_MONTH  },
                { "month",   NSEC_PER_MONTH  },
                { "M",       NSEC_PER_MONTH  },
                { "msec",    NSEC_PER_MSEC   },
                { "ms",      NSEC_PER_MSEC   },
                { "m",       NSEC_PER_MINUTE },
                { "hours",   NSEC_PER_HOUR   },
                { "hour",    NSEC_PER_HOUR   },
                { "hr",      NSEC_PER_HOUR   },
                { "h",       NSEC_PER_HOUR   },
                { "days",    NSEC_PER_DAY    },
                { "day",     NSEC_PER_DAY    },
                { "d",       NSEC_PER_DAY    },
                { "weeks",   NSEC_PER_WEEK   },
                { "week",    NSEC_PER_WEEK   },
                { "w",       NSEC_PER_WEEK   },
                { "years",   NSEC_PER_YEAR   },
                { "year",    NSEC_PER_YEAR   },
                { "y",       NSEC_PER_YEAR   },
                { "usec",    NSEC_PER_USEC   },
                { "us",      NSEC_PER_USEC   },
                { "µs",      NSEC_PER_USEC   },
                { "nsec",    1ULL            },
                { "ns",      1ULL            },
                { "",        1ULL            }, /* default is nsec */
        };
        size_t i;

        for (i = 0; i < ELEMENTSOF(table); i++) {
                char *e;

                e = startswith(p, table[i].suffix);
                if (e) {
                        *multiplier = table[i].nsec;
                        return e;
                }
        }

        return p;
}

int parse_nsec(const char *t, nsec_t *nsec) {
        const char *p, *s;
        nsec_t r = 0;
        bool something = false;

        assert(t);
        assert(nsec);

        p = t;

        p += strspn(p, WHITESPACE);
        s = startswith(p, "infinity");
        if (s) {
                s += strspn(s, WHITESPACE);
                if (*s != 0)
                        return -EINVAL;

                *nsec = NSEC_INFINITY;
                return 0;
        }

        for (;;) {
                nsec_t multiplier = 1, k;
                long long l;
                char *e;

                p += strspn(p, WHITESPACE);

                if (*p == 0) {
                        if (!something)
                                return -EINVAL;

                        break;
                }

                if (*p == '-') /* Don't allow "-0" */
                        return -ERANGE;

                errno = 0;
                l = strtoll(p, &e, 10);
                if (errno > 0)
                        return -errno;
                if (l < 0)
                        return -ERANGE;

                if (*e == '.') {
                        p = e + 1;
                        p += strspn(p, DIGITS);
                } else if (e == p)
                        return -EINVAL;
                else
                        p = e;

                s = extract_nsec_multiplier(p + strspn(p, WHITESPACE), &multiplier);
                if (s == p && *s != '\0')
                        /* Don't allow '12.34.56', but accept '12.34 .56' or '12.34s.56' */
                        return -EINVAL;

                p = s;

                if ((nsec_t) l >= NSEC_INFINITY / multiplier)
                        return -ERANGE;

                k = (nsec_t) l * multiplier;
                if (k >= NSEC_INFINITY - r)
                        return -ERANGE;

                r += k;

                something = true;

                if (*e == '.') {
                        nsec_t m = multiplier / 10;
                        const char *b;

                        for (b = e + 1; *b >= '0' && *b <= '9'; b++, m /= 10) {
                                k = (nsec_t) (*b - '0') * m;
                                if (k >= NSEC_INFINITY - r)
                                        return -ERANGE;

                                r += k;
                        }

                        /* Don't allow "0.-0", "3.+1", "3. 1", "3.sec" or "3.hoge" */
                        if (b == e + 1)
                                return -EINVAL;
                }
        }

        *nsec = r;

        return 0;
}

static int get_timezones_from_zone1970_tab(char ***ret) {
        _cleanup_fclose_ FILE *f = NULL;
        _cleanup_strv_free_ char **zones = NULL;
        int r;

        assert(ret);

        f = fopen("/usr/share/zoneinfo/zone1970.tab", "re");
        if (!f)
                return -errno;

        for (;;) {
                _cleanup_free_ char *line = NULL, *cc = NULL, *co = NULL, *tz = NULL;

                r = read_line(f, LONG_LINE_MAX, &line);
                if (r < 0)
                        return r;
                if (r == 0)
                        break;

                const char *p = line;

                /* Line format is:
                 * 'country codes' 'coordinates' 'timezone' 'comments' */
                r = extract_many_words(&p, NULL, 0, &cc, &co, &tz, NULL);
                if (r < 0)
                        continue;

                /* Lines that start with # are comments. */
                if (*cc == '#')
                        continue;

                r = strv_extend(&zones, tz);
                if (r < 0)
                        return r;
        }

        *ret = TAKE_PTR(zones);
        return 0;
}

static int get_timezones_from_tzdata_zi(char ***ret) {
        _cleanup_fclose_ FILE *f = NULL;
        _cleanup_strv_free_ char **zones = NULL;
        int r;

        f = fopen("/usr/share/zoneinfo/tzdata.zi", "re");
        if (!f)
                return -errno;

        for (;;) {
                _cleanup_free_ char *line = NULL, *type = NULL, *f1 = NULL, *f2 = NULL;

                r = read_line(f, LONG_LINE_MAX, &line);
                if (r < 0)
                        return r;
                if (r == 0)
                        break;

                const char *p = line;

                /* The only lines we care about are Zone and Link lines.
                 * Zone line format is:
                 * 'Zone' 'timezone' ...
                 * Link line format is:
                 * 'Link' 'target' 'alias'
                 * See 'man zic' for more detail. */
                r = extract_many_words(&p, NULL, 0, &type, &f1, &f2, NULL);
                if (r < 0)
                        continue;

                char *tz;
                if (IN_SET(*type, 'Z', 'z'))
                        /* Zone lines have timezone in field 1. */
                        tz = f1;
                else if (IN_SET(*type, 'L', 'l'))
                        /* Link lines have timezone in field 2. */
                        tz = f2;
                else
                        /* Not a line we care about. */
                        continue;

                r = strv_extend(&zones, tz);
                if (r < 0)
                        return r;
        }

        *ret = TAKE_PTR(zones);
        return 0;
}

int get_timezones(char ***ret) {
        _cleanup_strv_free_ char **zones = NULL;
        int r;

        assert(ret);

        r = get_timezones_from_tzdata_zi(&zones);
        if (r == -ENOENT) {
                log_debug_errno(r, "Could not get timezone data from tzdata.zi, using zone1970.tab: %m");
                r = get_timezones_from_zone1970_tab(&zones);
                if (r == -ENOENT)
                        log_debug_errno(r, "Could not get timezone data from zone1970.tab, using UTC: %m");
        }
        if (r < 0 && r != -ENOENT)
                return r;

        /* Always include UTC */
        r = strv_extend(&zones, "UTC");
        if (r < 0)
                return -ENOMEM;

        strv_sort(zones);
        strv_uniq(zones);

        *ret = TAKE_PTR(zones);
        return 0;
}

int verify_timezone(const char *name, int log_level) {
        bool slash = false;
        const char *p, *t;
        _cleanup_close_ int fd = -1;
        char buf[4];
        int r;

        if (isempty(name))
                return -EINVAL;

        /* Always accept "UTC" as valid timezone, since it's the fallback, even if user has no timezones installed. */
        if (streq(name, "UTC"))
                return 0;

        if (name[0] == '/')
                return -EINVAL;

        for (p = name; *p; p++) {
                if (!(*p >= '0' && *p <= '9') &&
                    !(*p >= 'a' && *p <= 'z') &&
                    !(*p >= 'A' && *p <= 'Z') &&
                    !IN_SET(*p, '-', '_', '+', '/'))
                        return -EINVAL;

                if (*p == '/') {

                        if (slash)
                                return -EINVAL;

                        slash = true;
                } else
                        slash = false;
        }

        if (slash)
                return -EINVAL;

        if (p - name >= PATH_MAX)
                return -ENAMETOOLONG;

        t = strjoina("/usr/share/zoneinfo/", name);

        fd = open(t, O_RDONLY|O_CLOEXEC);
        if (fd < 0)
                return log_full_errno(log_level, errno, "Failed to open timezone file '%s': %m", t);

        r = fd_verify_regular(fd);
        if (r < 0)
                return log_full_errno(log_level, r, "Timezone file '%s' is not  a regular file: %m", t);

        r = loop_read_exact(fd, buf, 4, false);
        if (r < 0)
                return log_full_errno(log_level, r, "Failed to read from timezone file '%s': %m", t);

        /* Magic from tzfile(5) */
        if (memcmp(buf, "TZif", 4) != 0)
                return log_full_errno(log_level, SYNTHETIC_ERRNO(EBADMSG),
                                      "Timezone file '%s' has wrong magic bytes", t);

        return 0;
}

bool clock_boottime_supported(void) {
        static int supported = -1;

        /* Note that this checks whether CLOCK_BOOTTIME is available in general as well as available for timerfds()! */

        if (supported < 0) {
                int fd;

                fd = timerfd_create(CLOCK_BOOTTIME, TFD_NONBLOCK|TFD_CLOEXEC);
                if (fd < 0)
                        supported = false;
                else {
                        safe_close(fd);
                        supported = true;
                }
        }

        return supported;
}

clockid_t clock_boottime_or_monotonic(void) {
        if (clock_boottime_supported())
                return CLOCK_BOOTTIME;
        else
                return CLOCK_MONOTONIC;
}

bool clock_supported(clockid_t clock) {
        struct timespec ts;

        switch (clock) {

        case CLOCK_MONOTONIC:
        case CLOCK_REALTIME:
                return true;

        case CLOCK_BOOTTIME:
                return clock_boottime_supported();

        case CLOCK_BOOTTIME_ALARM:
                if (!clock_boottime_supported())
                        return false;

                _fallthrough_;
        default:
                /* For everything else, check properly */
                return clock_gettime(clock, &ts) >= 0;
        }
}

int get_timezone(char **ret) {
        _cleanup_free_ char *t = NULL;
        const char *e;
        char *z;
        int r;

        r = readlink_malloc("/etc/localtime", &t);
        if (r == -ENOENT) {
                /* If the symlink does not exist, assume "UTC", like glibc does */
                z = strdup("UTC");
                if (!z)
                        return -ENOMEM;

                *ret = z;
                return 0;
        }
        if (r < 0)
                return r; /* returns EINVAL if not a symlink */

        e = PATH_STARTSWITH_SET(t, "/usr/share/zoneinfo/", "../usr/share/zoneinfo/");
        if (!e)
                return -EINVAL;

        if (!timezone_is_valid(e, LOG_DEBUG))
                return -EINVAL;

        z = strdup(e);
        if (!z)
                return -ENOMEM;

        *ret = z;
        return 0;
}

time_t mktime_or_timegm(struct tm *tm, bool utc) {
        return utc ? timegm(tm) : mktime(tm);
}

struct tm *localtime_or_gmtime_r(const time_t *t, struct tm *tm, bool utc) {
        return utc ? gmtime_r(t, tm) : localtime_r(t, tm);
}

static uint32_t sysconf_clock_ticks_cached(void) {
        static thread_local uint32_t hz = 0;
        long r;

        if (hz == 0) {
                r = sysconf(_SC_CLK_TCK);

                assert(r > 0);
                hz = r;
        }

        return hz;
}

uint32_t usec_to_jiffies(usec_t u) {
        uint32_t hz = sysconf_clock_ticks_cached();
        return DIV_ROUND_UP(u, USEC_PER_SEC / hz);
}

usec_t jiffies_to_usec(uint32_t j) {
        uint32_t hz = sysconf_clock_ticks_cached();
        return DIV_ROUND_UP(j * USEC_PER_SEC, hz);
}

usec_t usec_shift_clock(usec_t x, clockid_t from, clockid_t to) {
        usec_t a, b;

        if (x == USEC_INFINITY)
                return USEC_INFINITY;
        if (map_clock_id(from) == map_clock_id(to))
                return x;

        a = now(from);
        b = now(to);

        if (x > a)
                /* x lies in the future */
                return usec_add(b, usec_sub_unsigned(x, a));
        else
                /* x lies in the past */
                return usec_sub_unsigned(b, usec_sub_unsigned(a, x));
}

bool in_utc_timezone(void) {
        tzset();

        return timezone == 0 && daylight == 0;
}

int time_change_fd(void) {

        /* We only care for the cancellation event, hence we set the timeout to the latest possible value. */
        static const struct itimerspec its = {
                .it_value.tv_sec = TIME_T_MAX,
        };

        _cleanup_close_ int fd = -1;

        assert_cc(sizeof(time_t) == sizeof(TIME_T_MAX));

        /* Uses TFD_TIMER_CANCEL_ON_SET to get notifications whenever CLOCK_REALTIME makes a jump relative to
         * CLOCK_MONOTONIC. */

        fd = timerfd_create(CLOCK_REALTIME, TFD_NONBLOCK|TFD_CLOEXEC);
        if (fd < 0)
                return -errno;

        if (timerfd_settime(fd, TFD_TIMER_ABSTIME|TFD_TIMER_CANCEL_ON_SET, &its, NULL) >= 0)
                return TAKE_FD(fd);

        /* So apparently there are systems where time_t is 64bit, but the kernel actually doesn't support
         * 64bit time_t. In that case configuring a timer to TIME_T_MAX will fail with EOPNOTSUPP or a
         * similar error. If that's the case let's try with INT32_MAX instead, maybe that works. It's a bit
         * of a black magic thing though, but what can we do?
         *
         * We don't want this code on x86-64, hence let's conditionalize this for systems with 64bit time_t
         * but where "long" is shorter than 64bit, i.e. 32bit archs.
         *
         * See: https://github.com/systemd/systemd/issues/14362 */

#if SIZEOF_TIME_T == 8 && ULONG_MAX < UINT64_MAX
        if (ERRNO_IS_NOT_SUPPORTED(errno) || errno == EOVERFLOW) {
                static const struct itimerspec its32 = {
                        .it_value.tv_sec = INT32_MAX,
                };

                if (timerfd_settime(fd, TFD_TIMER_ABSTIME|TFD_TIMER_CANCEL_ON_SET, &its32, NULL) >= 0)
                        return TAKE_FD(fd);
        }
#endif

        return -errno;
}

static const char* const timestamp_style_table[_TIMESTAMP_STYLE_MAX] = {
        [TIMESTAMP_PRETTY] = "pretty",
        [TIMESTAMP_US] = "us",
        [TIMESTAMP_UTC] = "utc",
        [TIMESTAMP_US_UTC] = "us+utc",
};

/* Use the macro for enum → string to allow for aliases */
_DEFINE_STRING_TABLE_LOOKUP_TO_STRING(timestamp_style, TimestampStyle,);

/* For the string → enum mapping we use the generic implementation, but also support two aliases */
TimestampStyle timestamp_style_from_string(const char *s) {
        TimestampStyle t;

        t = (TimestampStyle) string_table_lookup(timestamp_style_table, ELEMENTSOF(timestamp_style_table), s);
        if (t >= 0)
                return t;
        if (streq_ptr(s, "µs"))
                return TIMESTAMP_US;
        if (streq_ptr(s, "µs+utc"))
                return TIMESTAMP_US_UTC;
        return t;
}
