/*
 * GIT - The information manager from hell
 *
 * Copyright (C) Linus Torvalds, 2005
 */

#include "cache.h"

/*
 * This is like mktime, but without normalization of tm_wday and tm_yday.
 */
static time_t tm_to_time_t(const struct tm *tm)
{
        static const int mdays[] = {
            0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
        };
        int year = tm->tm_year - 70;
        int month = tm->tm_mon;
        int day = tm->tm_mday;

        if (year < 0 || year > 129) /* algo only works for 1970-2099 */
                return -1;
        if (month < 0 || month > 11) /* array bounds */
                return -1;
        if (month < 2 || (year + 2) % 4)
                day--;
        if (tm->tm_hour < 0 || tm->tm_min < 0 || tm->tm_sec < 0)
                return -1;
        return (year * 365 + (year + 1) / 4 + mdays[month] + day) * 24*60*60UL +
                tm->tm_hour * 60*60 + tm->tm_min * 60 + tm->tm_sec;
}

static const char *month_names[] = {
        "January", "February", "March", "April", "May", "June",
        "July", "August", "September", "October", "November", "December"
};

static const char *weekday_names[] = {
        "Sundays", "Mondays", "Tuesdays", "Wednesdays", "Thursdays", "Fridays", "Saturdays"
};

static time_t gm_time_t(timestamp_t time, int tz)
{
        int minutes;

        minutes = tz < 0 ? -tz : tz;
        minutes = (minutes / 100)*60 + (minutes % 100);
        minutes = tz < 0 ? -minutes : minutes;

        if (minutes > 0) {
                if (unsigned_add_overflows(time, minutes * 60))
                        die("Timestamp+tz too large: %"PRItime" +%04d",
                            time, tz);
        } else if (time < -minutes * 60)
                die("Timestamp before Unix epoch: %"PRItime" %04d", time, tz);
        time += minutes * 60;
        if (date_overflows(time))
                die("Timestamp too large for this system: %"PRItime, time);
        return (time_t)time;
}

/*
 * The "tz" thing is passed in as this strange "decimal parse of tz"
 * thing, which means that tz -0100 is passed in as the integer -100,
 * even though it means "sixty minutes off"
 */
static struct tm *time_to_tm(timestamp_t time, int tz)
{
        time_t t = gm_time_t(time, tz);
        return gmtime(&t);
}

static struct tm *time_to_tm_local(timestamp_t time)
{
        time_t t = time;
        return localtime(&t);
}

/*
 * Fill in the localtime 'struct tm' for the supplied time,
 * and return the local tz.
 */
static int local_time_tzoffset(time_t t, struct tm *tm)
{
        time_t t_local;
        int offset, eastwest;

        localtime_r(&t, tm);
        t_local = tm_to_time_t(tm);
        if (t_local == -1)
                return 0; /* error; just use +0000 */
        if (t_local < t) {
                eastwest = -1;
                offset = t - t_local;
        } else {
                eastwest = 1;
                offset = t_local - t;
        }
        offset /= 60; /* in minutes */
        offset = (offset % 60) + ((offset / 60) * 100);
        return offset * eastwest;
}

/*
 * What value of "tz" was in effect back then at "time" in the
 * local timezone?
 */
static int local_tzoffset(timestamp_t time)
{
        struct tm tm;

        if (date_overflows(time))
                die("Timestamp too large for this system: %"PRItime, time);

        return local_time_tzoffset((time_t)time, &tm);
}

static void get_time(struct timeval *now)
{
        const char *x;

        x = getenv("GIT_TEST_DATE_NOW");
        if (x) {
                now->tv_sec = atoi(x);
                now->tv_usec = 0;
        }
        else
                gettimeofday(now, NULL);
}

void show_date_relative(timestamp_t time,
                        const struct timeval *now,
                        struct strbuf *timebuf)
{
        timestamp_t diff;
        if (now->tv_sec < time) {
                strbuf_addstr(timebuf, _("in the future"));
                return;
        }
        diff = now->tv_sec - time;
        if (diff < 90) {
                strbuf_addf(timebuf,
                         Q_("%"PRItime" second ago", "%"PRItime" seconds ago", diff), diff);
                return;
        }
        /* Turn it into minutes */
        diff = (diff + 30) / 60;
        if (diff < 90) {
                strbuf_addf(timebuf,
                         Q_("%"PRItime" minute ago", "%"PRItime" minutes ago", diff), diff);
                return;
        }
        /* Turn it into hours */
        diff = (diff + 30) / 60;
        if (diff < 36) {
                strbuf_addf(timebuf,
                         Q_("%"PRItime" hour ago", "%"PRItime" hours ago", diff), diff);
                return;
        }
        /* We deal with number of days from here on */
        diff = (diff + 12) / 24;
        if (diff < 14) {
                strbuf_addf(timebuf,
                         Q_("%"PRItime" day ago", "%"PRItime" days ago", diff), diff);
                return;
        }
        /* Say weeks for the past 10 weeks or so */
        if (diff < 70) {
                strbuf_addf(timebuf,
                         Q_("%"PRItime" week ago", "%"PRItime" weeks ago", (diff + 3) / 7),
                         (diff + 3) / 7);
                return;
        }
        /* Say months for the past 12 months or so */
        if (diff < 365) {
                strbuf_addf(timebuf,
                         Q_("%"PRItime" month ago", "%"PRItime" months ago", (diff + 15) / 30),
                         (diff + 15) / 30);
                return;
        }
        /* Give years and months for 5 years or so */
        if (diff < 1825) {
                timestamp_t totalmonths = (diff * 12 * 2 + 365) / (365 * 2);
                timestamp_t years = totalmonths / 12;
                timestamp_t months = totalmonths % 12;
                if (months) {
                        struct strbuf sb = STRBUF_INIT;
                        strbuf_addf(&sb, Q_("%"PRItime" year", "%"PRItime" years", years), years);
                        strbuf_addf(timebuf,
                                 /* TRANSLATORS: "%s" is "<n> years" */
                                 Q_("%s, %"PRItime" month ago", "%s, %"PRItime" months ago", months),
                                 sb.buf, months);
                        strbuf_release(&sb);
                } else
                        strbuf_addf(timebuf,
                                 Q_("%"PRItime" year ago", "%"PRItime" years ago", years), years);
                return;
        }
        /* Otherwise, just years. Centuries is probably overkill. */
        strbuf_addf(timebuf,
                 Q_("%"PRItime" year ago", "%"PRItime" years ago", (diff + 183) / 365),
                 (diff + 183) / 365);
}

struct date_mode *date_mode_from_type(enum date_mode_type type)
{
        static struct date_mode mode;
        if (type == DATE_STRFTIME)
                BUG("cannot create anonymous strftime date_mode struct");
        mode.type = type;
        mode.local = 0;
        return &mode;
}

static void show_date_normal(struct strbuf *buf, timestamp_t time, struct tm *tm, int tz, struct tm *human_tm, int human_tz, int local)
{
        struct {
                unsigned int    year:1,
                                date:1,
                                wday:1,
                                time:1,
                                seconds:1,
                                tz:1;
        } hide = { 0 };

        hide.tz = local || tz == human_tz;
        hide.year = tm->tm_year == human_tm->tm_year;
        if (hide.year) {
                if (tm->tm_mon == human_tm->tm_mon) {
                        if (tm->tm_mday > human_tm->tm_mday) {
                                /* Future date: think timezones */
                        } else if (tm->tm_mday == human_tm->tm_mday) {
                                hide.date = hide.wday = 1;
                        } else if (tm->tm_mday + 5 > human_tm->tm_mday) {
                                /* Leave just weekday if it was a few days ago */
                                hide.date = 1;
                        }
                }
        }

        /* Show "today" times as just relative times */
        if (hide.wday) {
                struct timeval now;
                get_time(&now);
                show_date_relative(time, &now, buf);
                return;
        }

        /*
         * Always hide seconds for human-readable.
         * Hide timezone if showing date.
         * Hide weekday and time if showing year.
         *
         * The logic here is two-fold:
         *  (a) only show details when recent enough to matter
         *  (b) keep the maximum length "similar", and in check
         */
        if (human_tm->tm_year) {
                hide.seconds = 1;
                hide.tz |= !hide.date;
                hide.wday = hide.time = !hide.year;
        }

        if (!hide.wday)
                strbuf_addf(buf, "%.3s ", weekday_names[tm->tm_wday]);
        if (!hide.date)
                strbuf_addf(buf, "%.3s %d ", month_names[tm->tm_mon], tm->tm_mday);

        /* Do we want AM/PM depending on locale? */
        if (!hide.time) {
                strbuf_addf(buf, "%02d:%02d", tm->tm_hour, tm->tm_min);
                if (!hide.seconds)
                        strbuf_addf(buf, ":%02d", tm->tm_sec);
        } else
                strbuf_rtrim(buf);

        if (!hide.year)
                strbuf_addf(buf, " %d", tm->tm_year + 1900);

        if (!hide.tz)
                strbuf_addf(buf, " %+05d", tz);
}

const char *show_date(timestamp_t time, int tz, const struct date_mode *mode)
{
        struct tm *tm;
        struct tm human_tm = { 0 };
        int human_tz = -1;
        static struct strbuf timebuf = STRBUF_INIT;

        if (mode->type == DATE_UNIX) {
                strbuf_reset(&timebuf);
                strbuf_addf(&timebuf, "%"PRItime, time);
                return timebuf.buf;
        }

        if (mode->type == DATE_HUMAN) {
                struct timeval now;

                get_time(&now);

                /* Fill in the data for "current time" in human_tz and human_tm */
                human_tz = local_time_tzoffset(now.tv_sec, &human_tm);
        }

        if (mode->local)
                tz = local_tzoffset(time);

        if (mode->type == DATE_RAW) {
                strbuf_reset(&timebuf);
                strbuf_addf(&timebuf, "%"PRItime" %+05d", time, tz);
                return timebuf.buf;
        }

        if (mode->type == DATE_RELATIVE) {
                struct timeval now;

                strbuf_reset(&timebuf);
                get_time(&now);
                show_date_relative(time, &now, &timebuf);
                return timebuf.buf;
        }

        if (mode->local)
                tm = time_to_tm_local(time);
        else
                tm = time_to_tm(time, tz);
        if (!tm) {
                tm = time_to_tm(0, 0);
                tz = 0;
        }

        strbuf_reset(&timebuf);
        if (mode->type == DATE_SHORT)
                strbuf_addf(&timebuf, "%04d-%02d-%02d", tm->tm_year + 1900,
                                tm->tm_mon + 1, tm->tm_mday);
        else if (mode->type == DATE_ISO8601)
                strbuf_addf(&timebuf, "%04d-%02d-%02d %02d:%02d:%02d %+05d",
                                tm->tm_year + 1900,
                                tm->tm_mon + 1,
                                tm->tm_mday,
                                tm->tm_hour, tm->tm_min, tm->tm_sec,
                                tz);
        else if (mode->type == DATE_ISO8601_STRICT) {
                char sign = (tz >= 0) ? '+' : '-';
                tz = abs(tz);
                strbuf_addf(&timebuf, "%04d-%02d-%02dT%02d:%02d:%02d%c%02d:%02d",
                                tm->tm_year + 1900,
                                tm->tm_mon + 1,
                                tm->tm_mday,
                                tm->tm_hour, tm->tm_min, tm->tm_sec,
                                sign, tz / 100, tz % 100);
        } else if (mode->type == DATE_RFC2822)
                strbuf_addf(&timebuf, "%.3s, %d %.3s %d %02d:%02d:%02d %+05d",
                        weekday_names[tm->tm_wday], tm->tm_mday,
                        month_names[tm->tm_mon], tm->tm_year + 1900,
                        tm->tm_hour, tm->tm_min, tm->tm_sec, tz);
        else if (mode->type == DATE_STRFTIME)
                strbuf_addftime(&timebuf, mode->strftime_fmt, tm, tz,
                                !mode->local);
        else
                show_date_normal(&timebuf, time, tm, tz, &human_tm, human_tz, mode->local);
        return timebuf.buf;
}

/*
 * Check these. And note how it doesn't do the summer-time conversion.
 *
 * In my world, it's always summer, and things are probably a bit off
 * in other ways too.
 */
static const struct {
        const char *name;
        int offset;
        int dst;
} timezone_names[] = {
        { "IDLW", -12, 0, },    /* International Date Line West */
        { "NT",   -11, 0, },    /* Nome */
        { "CAT",  -10, 0, },    /* Central Alaska */
        { "HST",  -10, 0, },    /* Hawaii Standard */
        { "HDT",  -10, 1, },    /* Hawaii Daylight */
        { "YST",   -9, 0, },    /* Yukon Standard */
        { "YDT",   -9, 1, },    /* Yukon Daylight */
        { "PST",   -8, 0, },    /* Pacific Standard */
        { "PDT",   -8, 1, },    /* Pacific Daylight */
        { "MST",   -7, 0, },    /* Mountain Standard */
        { "MDT",   -7, 1, },    /* Mountain Daylight */
        { "CST",   -6, 0, },    /* Central Standard */
        { "CDT",   -6, 1, },    /* Central Daylight */
        { "EST",   -5, 0, },    /* Eastern Standard */
        { "EDT",   -5, 1, },    /* Eastern Daylight */
        { "AST",   -3, 0, },    /* Atlantic Standard */
        { "ADT",   -3, 1, },    /* Atlantic Daylight */
        { "WAT",   -1, 0, },    /* West Africa */

        { "GMT",    0, 0, },    /* Greenwich Mean */
        { "UTC",    0, 0, },    /* Universal (Coordinated) */
        { "Z",      0, 0, },    /* Zulu, alias for UTC */

        { "WET",    0, 0, },    /* Western European */
        { "BST",    0, 1, },    /* British Summer */
        { "CET",   +1, 0, },    /* Central European */
        { "MET",   +1, 0, },    /* Middle European */
        { "MEWT",  +1, 0, },    /* Middle European Winter */
        { "MEST",  +1, 1, },    /* Middle European Summer */
        { "CEST",  +1, 1, },    /* Central European Summer */
        { "MESZ",  +1, 1, },    /* Middle European Summer */
        { "FWT",   +1, 0, },    /* French Winter */
        { "FST",   +1, 1, },    /* French Summer */
        { "EET",   +2, 0, },    /* Eastern Europe, USSR Zone 1 */
        { "EEST",  +2, 1, },    /* Eastern European Daylight */
        { "WAST",  +7, 0, },    /* West Australian Standard */
        { "WADT",  +7, 1, },    /* West Australian Daylight */
        { "CCT",   +8, 0, },    /* China Coast, USSR Zone 7 */
        { "JST",   +9, 0, },    /* Japan Standard, USSR Zone 8 */
        { "EAST", +10, 0, },    /* Eastern Australian Standard */
        { "EADT", +10, 1, },    /* Eastern Australian Daylight */
        { "GST",  +10, 0, },    /* Guam Standard, USSR Zone 9 */
        { "NZT",  +12, 0, },    /* New Zealand */
        { "NZST", +12, 0, },    /* New Zealand Standard */
        { "NZDT", +12, 1, },    /* New Zealand Daylight */
        { "IDLE", +12, 0, },    /* International Date Line East */
};

static int match_string(const char *date, const char *str)
{
        int i = 0;

        for (i = 0; *date; date++, str++, i++) {
                if (*date == *str)
                        continue;
                if (toupper(*date) == toupper(*str))
                        continue;
                if (!isalnum(*date))
                        break;
                return 0;
        }
        return i;
}

static int skip_alpha(const char *date)
{
        int i = 0;
        do {
                i++;
        } while (isalpha(date[i]));
        return i;
}

/*
* Parse month, weekday, or timezone name
*/
static int match_alpha(const char *date, struct tm *tm, int *offset)
{
        int i;

        for (i = 0; i < 12; i++) {
                int match = match_string(date, month_names[i]);
                if (match >= 3) {
                        tm->tm_mon = i;
                        return match;
                }
        }

        for (i = 0; i < 7; i++) {
                int match = match_string(date, weekday_names[i]);
                if (match >= 3) {
                        tm->tm_wday = i;
                        return match;
                }
        }

        for (i = 0; i < ARRAY_SIZE(timezone_names); i++) {
                int match = match_string(date, timezone_names[i].name);
                if (match >= 3 || match == strlen(timezone_names[i].name)) {
                        int off = timezone_names[i].offset;

                        /* This is bogus, but we like summer */
                        off += timezone_names[i].dst;

                        /* Only use the tz name offset if we don't have anything better */
                        if (*offset == -1)
                                *offset = 60*off;

                        return match;
                }
        }

        if (match_string(date, "PM") == 2) {
                tm->tm_hour = (tm->tm_hour % 12) + 12;
                return 2;
        }

        if (match_string(date, "AM") == 2) {
                tm->tm_hour = (tm->tm_hour % 12) + 0;
                return 2;
        }

        /* BAD CRAP */
        return skip_alpha(date);
}

static int is_date(int year, int month, int day, struct tm *now_tm, time_t now, struct tm *tm)
{
        if (month > 0 && month < 13 && day > 0 && day < 32) {
                struct tm check = *tm;
                struct tm *r = (now_tm ? &check : tm);
                time_t specified;

                r->tm_mon = month - 1;
                r->tm_mday = day;
                if (year == -1) {
                        if (!now_tm)
                                return 1;
                        r->tm_year = now_tm->tm_year;
                }
                else if (year >= 1970 && year < 2100)
                        r->tm_year = year - 1900;
                else if (year > 70 && year < 100)
                        r->tm_year = year;
                else if (year < 38)
                        r->tm_year = year + 100;
                else
                        return 0;
                if (!now_tm)
                        return 1;

                specified = tm_to_time_t(r);

                /* Be it commit time or author time, it does not make
                 * sense to specify timestamp way into the future.  Make
                 * sure it is not later than ten days from now...
                 */
                if ((specified != -1) && (now + 10*24*3600 < specified))
                        return 0;
                tm->tm_mon = r->tm_mon;
                tm->tm_mday = r->tm_mday;
                if (year != -1)
                        tm->tm_year = r->tm_year;
                return 1;
        }
        return 0;
}

static int match_multi_number(timestamp_t num, char c, const char *date,
                              char *end, struct tm *tm, time_t now)
{
        struct tm now_tm;
        struct tm *refuse_future;
        long num2, num3;

        num2 = strtol(end+1, &end, 10);
        num3 = -1;
        if (*end == c && isdigit(end[1]))
                num3 = strtol(end+1, &end, 10);

        /* Time? Date? */
        switch (c) {
        case ':':
                if (num3 < 0)
                        num3 = 0;
                if (num < 25 && num2 >= 0 && num2 < 60 && num3 >= 0 && num3 <= 60) {
                        tm->tm_hour = num;
                        tm->tm_min = num2;
                        tm->tm_sec = num3;
                        break;
                }
                return 0;

        case '-':
        case '/':
        case '.':
                if (!now)
                        now = time(NULL);
                refuse_future = NULL;
                if (gmtime_r(&now, &now_tm))
                        refuse_future = &now_tm;

                if (num > 70) {
                        /* yyyy-mm-dd? */
                        if (is_date(num, num2, num3, NULL, now, tm))
                                break;
                        /* yyyy-dd-mm? */
                        if (is_date(num, num3, num2, NULL, now, tm))
                                break;
                }
                /* Our eastern European friends say dd.mm.yy[yy]
                 * is the norm there, so giving precedence to
                 * mm/dd/yy[yy] form only when separator is not '.'
                 */
                if (c != '.' &&
                    is_date(num3, num, num2, refuse_future, now, tm))
                        break;
                /* European dd.mm.yy[yy] or funny US dd/mm/yy[yy] */
                if (is_date(num3, num2, num, refuse_future, now, tm))
                        break;
                /* Funny European mm.dd.yy */
                if (c == '.' &&
                    is_date(num3, num, num2, refuse_future, now, tm))
                        break;
                return 0;
        }
        return end - date;
}

/*
 * Have we filled in any part of the time/date yet?
 * We just do a binary 'and' to see if the sign bit
 * is set in all the values.
 */
static inline int nodate(struct tm *tm)
{
        return (tm->tm_year &
                tm->tm_mon &
                tm->tm_mday &
                tm->tm_hour &
                tm->tm_min &
                tm->tm_sec) < 0;
}

/*
 * We've seen a digit. Time? Year? Date?
 */
static int match_digit(const char *date, struct tm *tm, int *offset, int *tm_gmt)
{
        int n;
        char *end;
        timestamp_t num;

        num = parse_timestamp(date, &end, 10);

        /*
         * Seconds since 1970? We trigger on that for any numbers with
         * more than 8 digits. This is because we don't want to rule out
         * numbers like 20070606 as a YYYYMMDD date.
         */
        if (num >= 100000000 && nodate(tm)) {
                time_t time = num;
                if (gmtime_r(&time, tm)) {
                        *tm_gmt = 1;
                        return end - date;
                }
        }

        /*
         * Check for special formats: num[-.:/]num[same]num
         */
        switch (*end) {
        case ':':
        case '.':
        case '/':
        case '-':
                if (isdigit(end[1])) {
                        int match = match_multi_number(num, *end, date, end, tm, 0);
                        if (match)
                                return match;
                }
        }

        /*
         * None of the special formats? Try to guess what
         * the number meant. We use the number of digits
         * to make a more educated guess..
         */
        n = 0;
        do {
                n++;
        } while (isdigit(date[n]));

        /* Four-digit year or a timezone? */
        if (n == 4) {
                if (num <= 1400 && *offset == -1) {
                        unsigned int minutes = num % 100;
                        unsigned int hours = num / 100;
                        *offset = hours*60 + minutes;
                } else if (num > 1900 && num < 2100)
                        tm->tm_year = num - 1900;
                return n;
        }

        /*
         * Ignore lots of numerals. We took care of 4-digit years above.
         * Days or months must be one or two digits.
         */
        if (n > 2)
                return n;

        /*
         * NOTE! We will give precedence to day-of-month over month or
         * year numbers in the 1-12 range. So 05 is always "mday 5",
         * unless we already have a mday..
         *
         * IOW, 01 Apr 05 parses as "April 1st, 2005".
         */
        if (num > 0 && num < 32 && tm->tm_mday < 0) {
                tm->tm_mday = num;
                return n;
        }

        /* Two-digit year? */
        if (n == 2 && tm->tm_year < 0) {
                if (num < 10 && tm->tm_mday >= 0) {
                        tm->tm_year = num + 100;
                        return n;
                }
                if (num >= 70) {
                        tm->tm_year = num;
                        return n;
                }
        }

        if (num > 0 && num < 13 && tm->tm_mon < 0)
                tm->tm_mon = num-1;

        return n;
}

static int match_tz(const char *date, int *offp)
{
        char *end;
        int hour = strtoul(date + 1, &end, 10);
        int n = end - (date + 1);
        int min = 0;

        if (n == 4) {
                /* hhmm */
                min = hour % 100;
                hour = hour / 100;
        } else if (n != 2) {
                min = 99; /* random crap */
        } else if (*end == ':') {
                /* hh:mm? */
                min = strtoul(end + 1, &end, 10);
                if (end - (date + 1) != 5)
                        min = 99; /* random crap */
        } /* otherwise we parsed "hh" */

        /*
         * Don't accept any random crap. Even though some places have
         * offset larger than 12 hours (e.g. Pacific/Kiritimati is at
         * UTC+14), there is something wrong if hour part is much
         * larger than that. We might also want to check that the
         * minutes are divisible by 15 or something too. (Offset of
         * Kathmandu, Nepal is UTC+5:45)
         */
        if (min < 60 && hour < 24) {
                int offset = hour * 60 + min;
                if (*date == '-')
                        offset = -offset;
                *offp = offset;
        }
        return end - date;
}

static void date_string(timestamp_t date, int offset, struct strbuf *buf)
{
        int sign = '+';

        if (offset < 0) {
                offset = -offset;
                sign = '-';
        }
        strbuf_addf(buf, "%"PRItime" %c%02d%02d", date, sign, offset / 60, offset % 60);
}

/*
 * Parse a string like "0 +0000" as ancient timestamp near epoch, but
 * only when it appears not as part of any other string.
 */
static int match_object_header_date(const char *date, timestamp_t *timestamp, int *offset)
{
        char *end;
        timestamp_t stamp;
        int ofs;

        if (*date < '0' || '9' < *date)
                return -1;
        stamp = parse_timestamp(date, &end, 10);
        if (*end != ' ' || stamp == TIME_MAX || (end[1] != '+' && end[1] != '-'))
                return -1;
        date = end + 2;
        ofs = strtol(date, &end, 10);
        if ((*end != '\0' && (*end != '\n')) || end != date + 4)
                return -1;
        ofs = (ofs / 100) * 60 + (ofs % 100);
        if (date[-1] == '-')
                ofs = -ofs;
        *timestamp = stamp;
        *offset = ofs;
        return 0;
}

/* Gr. strptime is crap for this; it doesn't have a way to require RFC2822
   (i.e. English) day/month names, and it doesn't work correctly with %z. */
int parse_date_basic(const char *date, timestamp_t *timestamp, int *offset)
{
        struct tm tm;
        int tm_gmt;
        timestamp_t dummy_timestamp;
        int dummy_offset;

        if (!timestamp)
                timestamp = &dummy_timestamp;
        if (!offset)
                offset = &dummy_offset;

        memset(&tm, 0, sizeof(tm));
        tm.tm_year = -1;
        tm.tm_mon = -1;
        tm.tm_mday = -1;
        tm.tm_isdst = -1;
        tm.tm_hour = -1;
        tm.tm_min = -1;
        tm.tm_sec = -1;
        *offset = -1;
        tm_gmt = 0;

        if (*date == '@' &&
            !match_object_header_date(date + 1, timestamp, offset))
                return 0; /* success */
        for (;;) {
                int match = 0;
                unsigned char c = *date;

                /* Stop at end of string or newline */
                if (!c || c == '\n')
                        break;

                if (isalpha(c))
                        match = match_alpha(date, &tm, offset);
                else if (isdigit(c))
                        match = match_digit(date, &tm, offset, &tm_gmt);
                else if ((c == '-' || c == '+') && isdigit(date[1]))
                        match = match_tz(date, offset);

                if (!match) {
                        /* BAD CRAP */
                        match = 1;
                }

                date += match;
        }

        /* do not use mktime(), which uses local timezone, here */
        *timestamp = tm_to_time_t(&tm);
        if (*timestamp == -1)
                return -1;

        if (*offset == -1) {
                time_t temp_time;

                /* gmtime_r() in match_digit() may have clobbered it */
                tm.tm_isdst = -1;
                temp_time = mktime(&tm);
                if ((time_t)*timestamp > temp_time) {
                        *offset = ((time_t)*timestamp - temp_time) / 60;
                } else {
                        *offset = -(int)((temp_time - (time_t)*timestamp) / 60);
                }
        }

        if (!tm_gmt)
                *timestamp -= *offset * 60;
        return 0; /* success */
}

int parse_expiry_date(const char *date, timestamp_t *timestamp)
{
        int errors = 0;

        if (!strcmp(date, "never") || !strcmp(date, "false"))
                *timestamp = 0;
        else if (!strcmp(date, "all") || !strcmp(date, "now"))
                /*
                 * We take over "now" here, which usually translates
                 * to the current timestamp.  This is because the user
                 * really means to expire everything she has done in
                 * the past, and by definition reflogs are the record
                 * of the past, and there is nothing from the future
                 * to be kept.
                 */
                *timestamp = TIME_MAX;
        else
                *timestamp = approxidate_careful(date, &errors);

        return errors;
}

int parse_date(const char *date, struct strbuf *result)
{
        timestamp_t timestamp;
        int offset;
        if (parse_date_basic(date, &timestamp, &offset))
                return -1;
        date_string(timestamp, offset, result);
        return 0;
}

static enum date_mode_type parse_date_type(const char *format, const char **end)
{
        if (skip_prefix(format, "relative", end))
                return DATE_RELATIVE;
        if (skip_prefix(format, "iso8601-strict", end) ||
            skip_prefix(format, "iso-strict", end))
                return DATE_ISO8601_STRICT;
        if (skip_prefix(format, "iso8601", end) ||
            skip_prefix(format, "iso", end))
                return DATE_ISO8601;
        if (skip_prefix(format, "rfc2822", end) ||
            skip_prefix(format, "rfc", end))
                return DATE_RFC2822;
        if (skip_prefix(format, "short", end))
                return DATE_SHORT;
        if (skip_prefix(format, "default", end))
                return DATE_NORMAL;
        if (skip_prefix(format, "human", end))
                return DATE_HUMAN;
        if (skip_prefix(format, "raw", end))
                return DATE_RAW;
        if (skip_prefix(format, "unix", end))
                return DATE_UNIX;
        if (skip_prefix(format, "format", end))
                return DATE_STRFTIME;
        /*
         * Please update $__git_log_date_formats in
         * git-completion.bash when you add new formats.
         */

        die("unknown date format %s", format);
}

void parse_date_format(const char *format, struct date_mode *mode)
{
        const char *p;

        /* "auto:foo" is "if tty/pager, then foo, otherwise normal" */
        if (skip_prefix(format, "auto:", &p)) {
                if (isatty(1) || pager_in_use())
                        format = p;
                else
                        format = "default";
        }

        /* historical alias */
        if (!strcmp(format, "local"))
                format = "default-local";

        mode->type = parse_date_type(format, &p);
        mode->local = 0;

        if (skip_prefix(p, "-local", &p))
                mode->local = 1;

        if (mode->type == DATE_STRFTIME) {
                if (!skip_prefix(p, ":", &p))
                        die("date format missing colon separator: %s", format);
                mode->strftime_fmt = xstrdup(p);
        } else if (*p)
                die("unknown date format %s", format);
}

void datestamp(struct strbuf *out)
{
        time_t now;
        int offset;

        time(&now);

        offset = tm_to_time_t(localtime(&now)) - now;
        offset /= 60;

        date_string(now, offset, out);
}

/*
 * Relative time update (eg "2 days ago").  If we haven't set the time
 * yet, we need to set it from current time.
 */
static time_t update_tm(struct tm *tm, struct tm *now, time_t sec)
{
        time_t n;

        if (tm->tm_mday < 0)
                tm->tm_mday = now->tm_mday;
        if (tm->tm_mon < 0)
                tm->tm_mon = now->tm_mon;
        if (tm->tm_year < 0) {
                tm->tm_year = now->tm_year;
                if (tm->tm_mon > now->tm_mon)
                        tm->tm_year--;
        }

        n = mktime(tm) - sec;
        localtime_r(&n, tm);
        return n;
}

/*
 * Do we have a pending number at the end, or when
 * we see a new one? Let's assume it's a month day,
 * as in "Dec 6, 1992"
 */
static void pending_number(struct tm *tm, int *num)
{
        int number = *num;

        if (number) {
                *num = 0;
                if (tm->tm_mday < 0 && number < 32)
                        tm->tm_mday = number;
                else if (tm->tm_mon < 0 && number < 13)
                        tm->tm_mon = number-1;
                else if (tm->tm_year < 0) {
                        if (number > 1969 && number < 2100)
                                tm->tm_year = number - 1900;
                        else if (number > 69 && number < 100)
                                tm->tm_year = number;
                        else if (number < 38)
                                tm->tm_year = 100 + number;
                        /* We screw up for number = 00 ? */
                }
        }
}

static void date_now(struct tm *tm, struct tm *now, int *num)
{
        *num = 0;
        update_tm(tm, now, 0);
}

static void date_yesterday(struct tm *tm, struct tm *now, int *num)
{
        *num = 0;
        update_tm(tm, now, 24*60*60);
}

static void date_time(struct tm *tm, struct tm *now, int hour)
{
        if (tm->tm_hour < hour)
                update_tm(tm, now, 24*60*60);
        tm->tm_hour = hour;
        tm->tm_min = 0;
        tm->tm_sec = 0;
}

static void date_midnight(struct tm *tm, struct tm *now, int *num)
{
        pending_number(tm, num);
        date_time(tm, now, 0);
}

static void date_noon(struct tm *tm, struct tm *now, int *num)
{
        pending_number(tm, num);
        date_time(tm, now, 12);
}

static void date_tea(struct tm *tm, struct tm *now, int *num)
{
        pending_number(tm, num);
        date_time(tm, now, 17);
}

static void date_pm(struct tm *tm, struct tm *now, int *num)
{
        int hour, n = *num;
        *num = 0;

        hour = tm->tm_hour;
        if (n) {
                hour = n;
                tm->tm_min = 0;
                tm->tm_sec = 0;
        }
        tm->tm_hour = (hour % 12) + 12;
}

static void date_am(struct tm *tm, struct tm *now, int *num)
{
        int hour, n = *num;
        *num = 0;

        hour = tm->tm_hour;
        if (n) {
                hour = n;
                tm->tm_min = 0;
                tm->tm_sec = 0;
        }
        tm->tm_hour = (hour % 12);
}

static void date_never(struct tm *tm, struct tm *now, int *num)
{
        time_t n = 0;
        localtime_r(&n, tm);
        *num = 0;
}

static const struct special {
        const char *name;
        void (*fn)(struct tm *, struct tm *, int *);
} special[] = {
        { "yesterday", date_yesterday },
        { "noon", date_noon },
        { "midnight", date_midnight },
        { "tea", date_tea },
        { "PM", date_pm },
        { "AM", date_am },
        { "never", date_never },
        { "now", date_now },
        { NULL }
};

static const char *number_name[] = {
        "zero", "one", "two", "three", "four",
        "five", "six", "seven", "eight", "nine", "ten",
};

static const struct typelen {
        const char *type;
        int length;
} typelen[] = {
        { "seconds", 1 },
        { "minutes", 60 },
        { "hours", 60*60 },
        { "days", 24*60*60 },
        { "weeks", 7*24*60*60 },
        { NULL }
};

static const char *approxidate_alpha(const char *date, struct tm *tm, struct tm *now, int *num, int *touched)
{
        const struct typelen *tl;
        const struct special *s;
        const char *end = date;
        int i;

        while (isalpha(*++end))
                ;

        for (i = 0; i < 12; i++) {
                int match = match_string(date, month_names[i]);
                if (match >= 3) {
                        tm->tm_mon = i;
                        *touched = 1;
                        return end;
                }
        }

        for (s = special; s->name; s++) {
                int len = strlen(s->name);
                if (match_string(date, s->name) == len) {
                        s->fn(tm, now, num);
                        *touched = 1;
                        return end;
                }
        }

        if (!*num) {
                for (i = 1; i < 11; i++) {
                        int len = strlen(number_name[i]);
                        if (match_string(date, number_name[i]) == len) {
                                *num = i;
                                *touched = 1;
                                return end;
                        }
                }
                if (match_string(date, "last") == 4) {
                        *num = 1;
                        *touched = 1;
                }
                return end;
        }

        tl = typelen;
        while (tl->type) {
                int len = strlen(tl->type);
                if (match_string(date, tl->type) >= len-1) {
                        update_tm(tm, now, tl->length * *num);
                        *num = 0;
                        *touched = 1;
                        return end;
                }
                tl++;
        }

        for (i = 0; i < 7; i++) {
                int match = match_string(date, weekday_names[i]);
                if (match >= 3) {
                        int diff, n = *num -1;
                        *num = 0;

                        diff = tm->tm_wday - i;
                        if (diff <= 0)
                                n++;
                        diff += 7*n;

                        update_tm(tm, now, diff * 24 * 60 * 60);
                        *touched = 1;
                        return end;
                }
        }

        if (match_string(date, "months") >= 5) {
                int n;
                update_tm(tm, now, 0); /* fill in date fields if needed */
                n = tm->tm_mon - *num;
                *num = 0;
                while (n < 0) {
                        n += 12;
                        tm->tm_year--;
                }
                tm->tm_mon = n;
                *touched = 1;
                return end;
        }

        if (match_string(date, "years") >= 4) {
                update_tm(tm, now, 0); /* fill in date fields if needed */
                tm->tm_year -= *num;
                *num = 0;
                *touched = 1;
                return end;
        }

        return end;
}

static const char *approxidate_digit(const char *date, struct tm *tm, int *num,
                                     time_t now)
{
        char *end;
        timestamp_t number = parse_timestamp(date, &end, 10);

        switch (*end) {
        case ':':
        case '.':
        case '/':
        case '-':
                if (isdigit(end[1])) {
                        int match = match_multi_number(number, *end, date, end,
                                                       tm, now);
                        if (match)
                                return date + match;
                }
        }

        /* Accept zero-padding only for small numbers ("Dec 02", never "Dec 0002") */
        if (date[0] != '0' || end - date <= 2)
                *num = number;
        return end;
}

static timestamp_t approxidate_str(const char *date,
                                   const struct timeval *tv,
                                   int *error_ret)
{
        int number = 0;
        int touched = 0;
        struct tm tm, now;
        time_t time_sec;

        time_sec = tv->tv_sec;
        localtime_r(&time_sec, &tm);
        now = tm;

        tm.tm_year = -1;
        tm.tm_mon = -1;
        tm.tm_mday = -1;

        for (;;) {
                unsigned char c = *date;
                if (!c)
                        break;
                date++;
                if (isdigit(c)) {
                        pending_number(&tm, &number);
                        date = approxidate_digit(date-1, &tm, &number, time_sec);
                        touched = 1;
                        continue;
                }
                if (isalpha(c))
                        date = approxidate_alpha(date-1, &tm, &now, &number, &touched);
        }
        pending_number(&tm, &number);
        if (!touched)
                *error_ret = 1;
        return (timestamp_t)update_tm(&tm, &now, 0);
}

timestamp_t approxidate_relative(const char *date, const struct timeval *tv)
{
        timestamp_t timestamp;
        int offset;
        int errors = 0;

        if (!parse_date_basic(date, &timestamp, &offset))
                return timestamp;
        return approxidate_str(date, tv, &errors);
}

timestamp_t approxidate_careful(const char *date, int *error_ret)
{
        struct timeval tv;
        timestamp_t timestamp;
        int offset;
        int dummy = 0;
        if (!error_ret)
                error_ret = &dummy;

        if (!parse_date_basic(date, &timestamp, &offset)) {
                *error_ret = 0;
                return timestamp;
        }

        get_time(&tv);
        return approxidate_str(date, &tv, error_ret);
}

int date_overflows(timestamp_t t)
{
        time_t sys;

        /* If we overflowed our timestamp data type, that's bad... */
        if ((uintmax_t)t >= TIME_MAX)
                return 1;

        /*
         * ...but we also are going to feed the result to system
         * functions that expect time_t, which is often "signed long".
         * Make sure that we fit into time_t, as well.
         */
        sys = t;
        return t != sys || (t < 1) != (sys < 1);
}