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

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <time.h>

static time_t my_mktime(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--;
        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[] = {
        "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"
};

/*
 * 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"
 */
const char *show_date(unsigned long time, int tz)
{
        struct tm *tm;
        time_t t;
        static char timebuf[200];
        int minutes;

        minutes = tz < 0 ? -tz : tz;
        minutes = (tz / 100)*60 + (tz % 100);
        minutes = tz < 0 ? -minutes : minutes;
        t = time - minutes * 60;
        tm = gmtime(&t);
        if (!tm)
                return NULL;
        sprintf(timebuf, "%.3s %.3s %d %02d:%02d:%02d %d %+05d",
                weekday_names[tm->tm_wday],
                month_names[tm->tm_mon],
                tm->tm_mday,
                tm->tm_hour, tm->tm_min, tm->tm_sec,
                tm->tm_year + 1900, tz);
        return timebuf;
}

/*
 * 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) */

        { "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",  +11, 0, },    /* New Zealand */
        { "NZST", +11, 0, },    /* New Zealand Standard */
        { "NZDT", +11, 1, },    /* New Zealand Daylight */
        { "IDLE", +12, 0, },    /* International Date Line East */
};

#define NR_TZ (sizeof(timezone_names) / sizeof(timezone_names[0]))
        
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 < NR_TZ; i++) {
                int match = match_string(date, timezone_names[i].name);
                if (match >= 3) {
                        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) {
                if (tm->tm_hour > 0 && tm->tm_hour < 12)
                        tm->tm_hour += 12;
                return 2;
        }

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

static int is_date(int year, int month, int day, struct tm *tm)
{
        if (month > 0 && month < 13 && day > 0 && day < 32) {
                if (year == -1) {
                        tm->tm_mon = month-1;
                        tm->tm_mday = day;
                        return 1;
                }
                if (year >= 1970 && year < 2100) {
                        year -= 1900;
                } else if (year > 70 && year < 100) {
                        /* ok */
                } else if (year < 38) {
                        year += 100;
                } else
                        return 0;

                tm->tm_mon = month-1;
                tm->tm_mday = day;
                tm->tm_year = year;
                return 1;
        }
        return 0;
}

static int match_multi_number(unsigned long num, char c, char *date, char *end, struct tm *tm)
{
        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 '/':
                if (num > 70) {
                        /* yyyy-mm-dd? */
                        if (is_date(num, num2, num3, tm))
                                break;
                        /* yyyy-dd-mm? */
                        if (is_date(num, num3, num2, tm))
                                break;
                }
                /* mm/dd/yy ? */
                if (is_date(num3, num2, num, tm))
                        break;
                /* dd/mm/yy ? */
                if (is_date(num3, num, num2, tm))
                        break;
                return 0;
        }
        return end - date;
}

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

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

        /*
         * Seconds since 1970? We trigger on that for anything after Jan 1, 2000
         */
        if (num > 946684800) {
                time_t time = num;
                if (gmtime_r(&time, tm))
                        return end - date;
        }

        /*
         * Check for special formats: num[:-/]num[same]num
         */
        switch (*end) {
        case ':':
        case '/':
        case '-':
                if (isdigit(end[1])) {
                        int match = match_multi_number(num, *end, date, end, tm);
                        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 <= 1200 && *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;
        }

        /*
         * NOTE! We will give precedence to day-of-month over month or
         * year numebers 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 < 32) {
                tm->tm_mday = num;
        } else if (num > 1900) {
                tm->tm_year = num - 1900;
        } else if (num > 70) {
                tm->tm_year = num;
        } else if (num > 0 && num < 13) {
                tm->tm_mon = num-1;
        }
                
        return n;
}

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

        min = offset % 100;
        hour = offset / 100;

        /*
         * Don't accept any random crap.. At least 3 digits, and
         * a valid minute. We might want to check that the minutes
         * are divisible by 30 or something too.
         */
        if (min < 60 && n > 2) {
                offset = hour*60+min;
                if (*date == '-')
                        offset = -offset;

                *offp = offset;
        }
        return end - date;
}

/* 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. */
void parse_date(char *date, char *result, int maxlen)
{
        struct tm tm;
        int offset, sign;
        time_t then;

        memset(&tm, 0, sizeof(tm));
        tm.tm_year = -1;
        tm.tm_mon = -1;
        tm.tm_mday = -1;
        tm.tm_isdst = -1;
        offset = -1;

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

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

                date += match;
        }

        /* mktime uses local timezone */
        then = my_mktime(&tm); 
        if (offset == -1)
                offset = (then - mktime(&tm)) / 60;

        if (then == -1)
                return;

        then -= offset * 60;

        sign = '+';
        if (offset < 0) {
                offset = -offset;
                sign = '-';
        }

        snprintf(result, maxlen, "%lu %c%02d%02d", then, sign, offset/60, offset % 60);
}

void datestamp(char *buf, int bufsize)
{
        time_t now;
        int offset;

        time(&now);

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

        snprintf(buf, bufsize, "%lu %+05d", now, offset/60*100 + offset%60);
}