/*
 * 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"
};

/*
 * 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;
} timezone_names[] = {
        { "IDLW", -12 },        /* International Date Line West */
        { "NT",   -11 },        /* Nome */
        { "CAT",  -10 },        /* Central Alaska */
        { "HST",  -10 },        /* Hawaii Standard */
        { "HDT",   -9 },        /* Hawaii Daylight */
        { "YDT",   -8 },        /* Yukon Daylight */
        { "YST",   -9 },        /* Yukon Standard */
        { "PST",   -8 },        /* Pacific Standard */
        { "PDT",   -7 },        /* Pacific Daylight */
        { "MST",   -7 },        /* Mountain Standard */
        { "MDT",   -6 },        /* Mountain Daylight */
        { "CST",   -6 },        /* Central Standard */
        { "CDT",   -5 },        /* Central Daylight */
        { "EST",   -5 },        /* Eastern Standard */
        { "EDT",   -4 },        /* Eastern Daylight */
        { "AST",   -3 },        /* Atlantic Standard */
        { "ADT",   -2 },        /* Atlantic Daylight */
        { "WAT",   -1 },        /* West Africa */

        { "GMT",    0 },        /* Greenwich Mean */
        { "UTC",    0 },        /* Universal (Coordinated) */

        { "WET",    0 },        /* Western European */
        { "BST",    0 },        /* British Summer */
        { "CET",   +1 },        /* Central European */
        { "MET",   +1 },        /* Middle European */
        { "MEWT",  +1 },        /* Middle European Winter */
        { "MEST",  +2 },        /* Middle European Summer */
        { "CEST",  +2 },        /* Central European Summer */
        { "MESZ",  +1 },        /* Middle European Summer */
        { "FWT",   +1 },        /* French Winter */
        { "FST",   +2 },        /* French Summer */
        { "EET",   +2 },        /* Eastern Europe, USSR Zone 1 */
        { "WAST",  +7 },        /* West Australian Standard */
        { "WADT",  +8 },        /* West Australian Daylight */
        { "CCT",   +8 },        /* China Coast, USSR Zone 7 */
        { "JST",   +9 },        /* Japan Standard, USSR Zone 8 */
        { "EAST", +10 },        /* Eastern Australian Standard */
        { "EADT", +11 },        /* Eastern Australian Daylight */
        { "GST",  +10 },        /* Guam Standard, USSR Zone 9 */
        { "NZT",  +11 },        /* New Zealand */
        { "NZST", +11 },        /* New Zealand Standard */
        { "NZDT", +12 },        /* New Zealand Daylight */
        { "IDLE", +12 },        /* 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;
}

/*
* 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) {
                        *offset = 60*timezone_names[i].offset;
                        return match;
                }
        }

        /* BAD CRAP */
        return 0;
}

static int match_digit(char *date, struct tm *tm, int *offset)
{
        char *end, c;
        unsigned long num, num2, num3;

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

        /* Time? num:num[:num] */
        if (num < 24 && end[0] == ':' && isdigit(end[1])) {
                tm->tm_hour = num;
                num = strtoul(end+1, &end, 10);
                if (num < 60) {
                        tm->tm_min = num;
                        if (end[0] == ':' && isdigit(end[1])) {
                                num = strtoul(end+1, &end, 10);
                                if (num < 61)
                                        tm->tm_sec = num;
                        }
                }
                return end - date;
        }

        /* Year? Day of month? Numeric date-string?*/
        c = *end;
        switch (c) {
        default:
                if (num > 0 && num < 32) {
                        tm->tm_mday = num;
                        break;
                }
                if (num > 1900) {
                        tm->tm_year = num - 1900;
                        break;
                }
                if (num > 70) {
                        tm->tm_year = num;
                        break;
                }
                break;

        case '-':
        case '/':
                if (num && num < 32 && isdigit(end[1])) {
                        num2 = strtoul(end+1, &end, 10);
                        if (!num2 || num2 > 31)
                                break;
                        if (num > 12) {
                                if (num2 > 12)
                                        break;
                                num3 = num;
                                num  = num2;
                                num2 = num3;
                        }
                        tm->tm_mon = num - 1;
                        tm->tm_mday = num2;
                        if (*end == c && isdigit(end[1])) {
                                num3 = strtoul(end, &end, 10);
                                if (num3 > 1900)
                                        num3 -= 1900;
                                tm->tm_year = num3;
                        }
                        break;
                }
        }
                
        return end - date;
                        
}

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

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

        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;
        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;

        snprintf(result, maxlen, "%lu %+03d%02d", then, 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);
}