#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <langinfo.h>
#include <locale.h>
#include <ctype.h>
#include <time.h>
#include <limits.h>
#include "locale_impl.h"
#include "time_impl.h"

static int is_leap(int y)
{
        /* Avoid overflow */
        if (y>INT_MAX-1900) y -= 2000;
        y += 1900;
        return !(y%4) && ((y%100) || !(y%400));
}

static int week_num(const struct tm *tm)
{
        int val = (tm->tm_yday + 7U - (tm->tm_wday+6U)%7) / 7;
        /* If 1 Jan is just 1-3 days past Monday,
         * the previous week is also in this year. */
        if ((tm->tm_wday + 371U - tm->tm_yday - 2) % 7 <= 2)
                val++;
        if (!val) {
                val = 52;
                /* If 31 December of prev year a Thursday,
                 * or Friday of a leap year, then the
                 * prev year has 53 weeks. */
                {
                int dec31 = (tm->tm_wday + 7U - tm->tm_yday - 1) % 7;
                if (dec31 == 4 || (dec31 == 5 && is_leap(tm->tm_year%400-1)))
                        val++;
                }
        } else if (val == 53) {
                /* If 1 January is not a Thursday, and not
                 * a Wednesday of a leap year, then this
                 * year has only 52 weeks. */
                int jan1 = (tm->tm_wday + 371U - tm->tm_yday) % 7;
                if (jan1 != 4 && (jan1 != 3 || !is_leap(tm->tm_year)))
                        val = 1;
        }
        return val;
}

const char *__strftime_fmt_1(char (*s)[100], size_t *l, int f, const struct tm *tm, locale_t loc, int pad)
{
        nl_item item;
        long long val;
        const char *fmt = "-";
        int width = 2, def_pad = '0';

        switch (f) {
        case 'a':
                if (tm->tm_wday > 6U) goto string;
                item = ABDAY_1 + tm->tm_wday;
                goto nl_strcat;
        case 'A':
                if (tm->tm_wday > 6U) goto string;
                item = DAY_1 + tm->tm_wday;
                goto nl_strcat;
        case 'h':
        case 'b':
                if (tm->tm_mon > 11U) goto string;
                item = ABMON_1 + tm->tm_mon;
                goto nl_strcat;
        case 'B':
                if (tm->tm_mon > 11U) goto string;
                item = MON_1 + tm->tm_mon;
                goto nl_strcat;
        case 'c':
                item = D_T_FMT;
                goto nl_strftime;
        case 'C':
                val = (1900LL+tm->tm_year) / 100;
                goto number;
        case 'e':
                def_pad = '_';
        case 'd':
                val = tm->tm_mday;
                goto number;
        case 'D':
                fmt = "%m/%d/%y";
                goto recu_strftime;
        case 'F':
                fmt = "%Y-%m-%d";
                goto recu_strftime;
        case 'g':
        case 'G':
                val = tm->tm_year + 1900LL;
                if (tm->tm_yday < 3 && week_num(tm) != 1) val--;
                else if (tm->tm_yday > 360 && week_num(tm) == 1) val++;
                if (f=='g') val %= 100;
                else width = 4;
                goto number;
#ifdef __HAIKU__
        case 'k':
                def_pad = '_';
                // fallthrough
#endif
        case 'H':
                val = tm->tm_hour;
                goto number;
#ifdef __HAIKU__
        case 'l':
                def_pad = '_';
                // fallthrough
#endif
        case 'I':
                val = tm->tm_hour;
                if (!val) val = 12;
                else if (val > 12) val -= 12;
                goto number;
        case 'j':
                val = tm->tm_yday+1;
                width = 3;
                goto number;
        case 'm':
                val = tm->tm_mon+1;
                goto number;
        case 'M':
                val = tm->tm_min;
                goto number;
        case 'n':
                *l = 1;
                return "\n";
        case 'p':
                item = tm->tm_hour >= 12 ? PM_STR : AM_STR;
                goto nl_strcat;
        case 'r':
                item = T_FMT_AMPM;
                goto nl_strftime;
        case 'R':
                fmt = "%H:%M";
                goto recu_strftime;
        case 's':
                val = __tm_to_secs(tm) - tm->__tm_gmtoff;
                width = 1;
                goto number;
        case 'S':
                val = tm->tm_sec;
                goto number;
        case 't':
                *l = 1;
                return "\t";
        case 'T':
                fmt = "%H:%M:%S";
                goto recu_strftime;
        case 'u':
                val = tm->tm_wday ? tm->tm_wday : 7;
                width = 1;
                goto number;
        case 'U':
                val = (tm->tm_yday + 7U - tm->tm_wday) / 7;
                goto number;
        case 'W':
                val = (tm->tm_yday + 7U - (tm->tm_wday+6U)%7) / 7;
                goto number;
        case 'V':
                val = week_num(tm);
                goto number;
        case 'w':
                val = tm->tm_wday;
                width = 1;
                goto number;
        case 'x':
                item = D_FMT;
                goto nl_strftime;
        case 'X':
                item = T_FMT;
                goto nl_strftime;
        case 'y':
                val = (tm->tm_year + 1900LL) % 100;
                if (val < 0) val = -val;
                goto number;
        case 'Y':
                val = tm->tm_year + 1900LL;
                if (val >= 10000) {
                        *l = snprintf(*s, sizeof *s, "+%lld", val);
                        return *s;
                }
                width = 4;
                goto number;
        case 'z':
                if (tm->tm_isdst < 0) {
                        *l = 0;
                        return "";
                }
                *l = snprintf(*s, sizeof *s, "%+.4ld",
                        tm->__tm_gmtoff/3600*100 + tm->__tm_gmtoff%3600/60);
                return *s;
        case 'Z':
                if (tm->tm_isdst < 0) {
                        *l = 0;
                        return "";
                }
                fmt = __tm_to_tzname(tm);
                goto string;
        case '%':
                *l = 1;
                return "%";
        default:
                return 0;
        }
number:
        switch (pad ? pad : def_pad) {
        case '-': *l = snprintf(*s, sizeof *s, "%lld", val); break;
        case '_': *l = snprintf(*s, sizeof *s, "%*lld", width, val); break;
        case '0':
        default:  *l = snprintf(*s, sizeof *s, "%0*lld", width, val); break;
        }
        return *s;
nl_strcat:
        fmt = __nl_langinfo_l(item, loc);
string:
        *l = strlen(fmt);
        return fmt;
nl_strftime:
        fmt = __nl_langinfo_l(item, loc);
recu_strftime:
        *l = __strftime_l(*s, sizeof *s, fmt, tm, loc);
        if (!*l) return 0;
        return *s;
}

size_t __strftime_l(char *restrict s, size_t n, const char *restrict f, const struct tm *restrict tm, locale_t loc)
{
        size_t l, k;
        char buf[100];
        char *p;
        const char *t;
        int pad, plus;
        unsigned long width;
        for (l=0; l<n; f++) {
                if (!*f) {
                        s[l] = 0;
                        return l;
                }
                if (*f != '%') {
                        s[l++] = *f;
                        continue;
                }
                f++;
                pad = 0;
                if (*f == '-' || *f == '_' || *f == '0') pad = *f++;
                if ((plus = (*f == '+'))) f++;
                if (isdigit(*f)) {
                        width = strtoul(f, &p, 10);
                } else {
                        width = 0;
                        p = (void *)f;
                }
                if (*p == 'C' || *p == 'F' || *p == 'G' || *p == 'Y') {
                        if (!width && p!=f) width = 1;
                } else {
                        width = 0;
                }
                f = p;
                if (*f == 'E' || *f == 'O') f++;
                t = __strftime_fmt_1(&buf, &k, *f, tm, loc, pad);
                if (!t) break;
                if (width) {
                        /* Trim off any sign and leading zeros, then
                         * count remaining digits to determine behavior
                         * for the + flag. */
                        if (*t=='+' || *t=='-') t++, k--;
                        for (; *t=='0' && t[1]-'0'<10U; t++, k--);
                        if (width < k) width = k;
                        {
                        size_t d;
                        for (d=0; t[d]-'0'<10U; d++);
                        if (tm->tm_year < -1900) {
                                s[l++] = '-';
                                width--;
                        } else if (plus && d+(width-k) >= (*p=='C'?3:5)) {
                                s[l++] = '+';
                                width--;
                        }
                        for (; width > k && l < n; width--)
                                s[l++] = '0';
                        }
                }
                if (k > n-l) k = n-l;
                memcpy(s+l, t, k);
                l += k;
        }
        if (n) {
                if (l==n) l=n-1;
                s[l] = 0;
        }
        return 0;
}

size_t strftime(char *restrict s, size_t n, const char *restrict f, const struct tm *restrict tm)
{
        return __strftime_l(s, n, f, tm, CURRENT_LOCALE);
}

weak_alias(__strftime_l, strftime_l);