/**
 * Copyright (c) 2022 Huawei Device Co., Ltd.
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <stdint.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include "libc.h"
#include "lock.h"
#include "time_impl.h"

#define __TZ_VERSION__ '2'

long  __timezone = 0;
int   __daylight = 0;
char *__tzname[2] = { 0, 0 };

weak_alias(__timezone, timezone);
weak_alias(__daylight, daylight);
weak_alias(__tzname, tzname);

static char std_name[TZNAME_MAX+1];
static char dst_name[TZNAME_MAX+1];
const char __utc[] = "UTC";
const char __gmt[] = "GMT";

static int dst_off;
static int r0[5], r1[5];

static const unsigned char *zi, *trans, *index, *types, *abbrevs, *abbrevs_end;
static size_t map_size;

static char old_tz_buf[32];
static char *old_tz = old_tz_buf;
static size_t old_tz_size = sizeof old_tz_buf;

static volatile int lock[1];

static int getint(const char **p)
{
    unsigned x;
    for (x=0; **p-'0'<10U; (*p)++) {
        x = **p-'0' + 10*x;
    }
    return x;
}

static int getoff(const char **p)
{
    int neg = 0;
    if (**p == '-') {
        ++*p;
        neg = 1;
    } else if (**p == '+') {
        ++*p;
    }
    int off = 3600*getint(p);
    if (**p == ':') {
        ++*p;
        off += 60*getint(p);
        if (**p == ':') {
            ++*p;
            off += getint(p);
        }
    }
    return neg ? -off : off;
}

static void getrule(const char **p, int rule[5])
{
    int r = rule[0] = **p;

    if (r!='M') {
        if (r=='J') {
            ++*p;
        } else {
            rule[0] = 0;
        }
        rule[1] = getint(p);
    } else {
        ++*p;
        rule[1] = getint(p);
        ++*p;
        rule[2] = getint(p);
        ++*p;
        rule[3] = getint(p);
    }

    if (**p=='/') {
        ++*p;
        rule[4] = getoff(p);
    } else {
        rule[4] = 7200;
    }
}

static void getname(char *d, const char **p)
{
    int i;
    if (**p == '<') {
        ++*p;
        for (i=0; (*p)[i]!='>' && i<TZNAME_MAX; i++)
            d[i] = (*p)[i];
        ++*p;
    } else {
        for (i=0; ((*p)[i]|32)-'a'<26U && i<TZNAME_MAX; i++)
            d[i] = (*p)[i];
    }
    *p += i;
    d[i] = 0;
}

#define VEC(...) ((const unsigned char[]) {__VA_ARGS__})

static uint32_t zi_read32(const unsigned char *z)
{
    return (unsigned)(z[0]<<24) | (z[1]<<16) | (z[2]<<8) | z[3];
}

static size_t zi_dotprod(const unsigned char *z, const unsigned char *v, size_t n)
{
    size_t y;
    uint32_t x;
    for (y=0; n; n--, z+=4, v++) {
        x = zi_read32(z);
        y += x * *v;
    }
    return y;
}

static void do_tzset()
{
    char buf[NAME_MAX+25], *pathname = buf+24;
    const char *try, *s, *p;
    const unsigned char *map = 0;
    size_t i;
    static const char search[] =
        "/etc/zoneinfo/\0/usr/share/zoneinfo/\0/share/zoneinfo/\0";

    s = getenv("TZ");
    if (!s) {
        s = "/etc/localtime";
    }
    if (!*s) {
        s = __utc;
    }

    if (old_tz && !strcmp(s, old_tz)) {
        return;
    }

    for (i=0; i<5; i++) {
        r0[i] = r1[i] = 0;
    }

    if (zi) {
        __munmap((void *)zi, map_size);
    }

    /* Cache the old value of TZ to check if it has changed. Avoid
     * free so as not to pull it into static programs. Growth
     * strategy makes it so free would have minimal benefit anyway. */
    i = strlen(s);
    if (i > PATH_MAX+1) s = __utc, i = 3;
    if (i >= old_tz_size) {
        old_tz_size *= 2;
        if (i >= old_tz_size) old_tz_size = i+1;
        if (old_tz_size > PATH_MAX+2) old_tz_size = PATH_MAX+2;
        old_tz = malloc(old_tz_size);
    }
    if (old_tz) memcpy(old_tz, s, i+1);

    /* Non-suid can use an absolute tzfile pathname or a relative
     * pathame beginning with "."; in secure mode, only the
     * standard path will be searched. */
    int flag = 1;
    if (*s == ':' || ((p=strchr(s, '/')) && !memchr(s, ',', p-s))) {
        if (*s == ':') s++;
        if (*s == '/' || *s == '.') {
            /* The path is invalid, use the default value. */
            flag = 0;
            if (!libc.secure || !strcmp(s, "/etc/localtime")) {
                map = __map_file(s, &map_size);
            }
        }
    }

    if (flag) {
        /* Adapt to time zone names, such as Asia/Shanghai or Shanghai*/
        size_t l = strlen(s);
        if (l <= NAME_MAX && !strchr(s, '.')) {
            memcpy(pathname, s, l+1);
            pathname[l] = 0;
            for (try=search; !map && *try; try+=l+1) {
                l = strlen(try);
                memcpy(pathname-l, try, l);
                map = __map_file(pathname-l, &map_size);
            }
        }
    }
    if (!map) {
        s = __utc;
    }

    if (map && (map_size < 44 || memcmp(map, "TZif", 4))) {
        __munmap((void *)map, map_size);
        map = 0;
        s = __utc;
    }

    zi = map;
    if (map) {
        int scale = 2;

        /*
         * map[0]-map[3]: magic, it is TZif
         * map[4]:        version, '\0' or '2' or '3' as of 2013
         * map[5]-map[19]: reserved; must be zero
         * map[20]-map[23]: The number of UT/local indicators stored in the file.
         * map[24]-map[27]: The number of standard/wall indicators stored in the file.
         * map[24]-map[31]: The number of leap seconds for which data entries are stored in the file.
         * map[32]-map[35]: The number of transition times for which data entries are stored in the file.
         * map[36]-map[39]: The number of local time types for which data entries are
         *                  stored in the file (must not be zero).
         * map[40]-map[43]: The number of bytes of time zone abbreviation strings stored in the file.

         * If map[4] is '2' or greater, the above is followed by a second instance
         * of tzhead and a second instance of the data in which each coded transition
         * time uses 8 rather than 4 chars,
         * then a POSIX-TZ-environment-variable-style string for use in handling
         * instants after the last transition time stored in the file
         * (with nothing between the newlines if there is no POSIX representation for
         * such instants).

         * If map[4] is '3' or greater, the above is extended as follows.
         * First, the POSIX TZ string's hour offset may range from -167
         * through 167 as compared to the POSIX-required 0 through 24.
         * Second, its DST start time may be January 1 at 00:00 and its stop
         * time December 31 at 24:00 plus the difference between DST and
         * standard time, indicating DST all year. */
        if (sizeof(time_t) > 4 && map[4] >= __TZ_VERSION__) {
            size_t skip = zi_dotprod(zi+20, VEC(1, 1, 8, 5, 6, 1), 6);
            trans = zi+skip+44+44;
            scale++;
        } else {
            trans = zi+44;
        }
        index = trans + (zi_read32(trans-12) << scale);
        types = index + zi_read32(trans-12);
        abbrevs = types + 6*zi_read32(trans-8);
        abbrevs_end = abbrevs + zi_read32(trans-4);
        if (zi[map_size-1] == '\n') {
            for (s = (const char *)zi+map_size-2; *s!='\n'; s--);
            s++;
        } else {
            const unsigned char *p;
            __tzname[0] = __tzname[1] = 0;
            __daylight = __timezone = dst_off = 0;
            for (p=types; p<abbrevs; p+=6) {
                if (!p[4] && !__tzname[0]) {
                    __tzname[0] = (char *)abbrevs + p[5];
                    __timezone = -zi_read32(p);
                }
                if (p[4] && !__tzname[1]) {
                    __tzname[1] = (char *)abbrevs + p[5];
                    dst_off = -zi_read32(p);
                    __daylight = 1;
                }
            }
            if (!__tzname[0]) __tzname[0] = __tzname[1];
            if (!__tzname[0]) __tzname[0] = (char *)__utc;
            if (!__daylight) {
                __tzname[1] = __tzname[0];
                dst_off = __timezone;
            }
            return;
        }
    }

    if (!s) s = __utc;
    getname(std_name, &s);
    __tzname[0] = std_name;
    __timezone = getoff(&s);
    getname(dst_name, &s);
    __tzname[1] = dst_name;
    if (dst_name[0]) {
        __daylight = 1;
        if (*s == '+' || *s=='-' || *s-'0'<10U)
            dst_off = getoff(&s);
        else
            dst_off = __timezone - 3600;
    } else {
        __daylight = 0;
        dst_off = __timezone;
    }

    if (*s == ',') s++, getrule(&s, r0);
    if (*s == ',') s++, getrule(&s, r1);
}

/* Search zoneinfo rules to find the one that applies to the given time,
 * and determine alternate opposite-DST-status rule that may be needed. */

static size_t scan_trans(long long t, int local, size_t *alt)
{
    int scale = 3 - (trans == zi+44);
    uint64_t x;
    int off = 0;

    size_t a = 0, n = (index-trans)>>scale, m;

    if (!n) {
        if (alt) *alt = 0;
        return 0;
    }

    /* Binary search for 'most-recent rule before t'. */
    while (n > 1) {
        m = a + n/2;
        x = zi_read32(trans + (m<<scale));
        if (scale == 3) x = (x<<32) | zi_read32(trans + (m<<scale) + 4);
        else x = (int32_t)x;
        if (local) off = (int32_t)zi_read32(types + 6 * index[m-1]);
        if (t - off < (int64_t)x) {
            n /= 2;
        } else {
            a = m;
            n -= n/2;
        }
    }

    /* First and last entry are special. First means to use lowest-index
     * non-DST type. Last means to apply POSIX-style rule if available. */
    n = (index-trans)>>scale;
    if (a == n-1) return -1;
    if (a == 0) {
        x = zi_read32(trans + (a<<scale));
        if (scale == 3) x = (x<<32) | zi_read32(trans + (a<<scale) + 4);
        else x = (int32_t)x;
        if (local) off = (int32_t)zi_read32(types + 6 * index[a-1]);
        if (t - off < (int64_t)x) {
            for (a=0; a<(abbrevs-types)/6; a++) {
                if (types[6*a+4] != types[4]) break;
            }
            if (a == (abbrevs-types)/6) a = 0;
            if (types[6*a+4]) {
                *alt = a;
                return 0;
            } else {
                *alt = 0;
                return a;
            }
        }
    }

    /* Try to find a neighboring opposite-DST-status rule. */
    if (alt) {
        if (a && types[6*index[a-1]+4] != types[6*index[a]+4])
            *alt = index[a-1];
        else if (a+1<n && types[6*index[a+1]+4] != types[6*index[a]+4])
            *alt = index[a+1];
        else
            *alt = index[a];
    }

    return index[a];
}

static int days_in_month(int m, int is_leap)
{
    if (m==2) return 28+is_leap;
    else return 30+((0xad5>>(m-1))&1);
}

/* Convert a POSIX DST rule plus year to seconds since epoch. */

static long long rule_to_secs(const int *rule, int year)
{
    int is_leap;
    long long t = __year_to_secs(year, &is_leap);
    int x, m, n, d;
    if (rule[0]!='M') {
        x = rule[1];
        if (rule[0]=='J' && (x < 60 || !is_leap)) x--;
        t += 86400 * x;
    } else {
        m = rule[1];
        n = rule[2];
        d = rule[3];
        t += __month_to_secs(m-1, is_leap);
        int wday = (int)((t + 4*86400) % (7*86400)) / 86400;
        int days = d - wday;
        if (days < 0) days += 7;
        if (n == 5 && days+28 >= days_in_month(m, is_leap)) n = 4;
        t += 86400 * (days + 7*(n-1));
    }
    t += rule[4];
    return t;
}

/* Determine the time zone in effect for a given time in seconds since the
 * epoch. It can be given in local or universal time. The results will
 * indicate whether DST is in effect at the queried time, and will give both
 * the GMT offset for the active zone/DST rule and the opposite DST. This
 * enables a caller to efficiently adjust for the case where an explicit
 * DST specification mismatches what would be in effect at the time. */

void __secs_to_zone(long long t, int local, int *isdst, long *offset, long *oppoff, const char **zonename)
{
    LOCK(lock);

    do_tzset();

    if (zi) {
        size_t alt, i = scan_trans(t, local, &alt);
        if (i != -1) {
            *isdst = types[6*i+4];
            *offset = (int32_t)zi_read32(types+6*i);
            *zonename = (const char *)abbrevs + types[6*i+5];
            if (oppoff) *oppoff = (int32_t)zi_read32(types+6*alt);
            UNLOCK(lock);
            return;
        }
    }

    if (!__daylight) goto std;

    long long y = t / 31556952 + 70;
    while (__year_to_secs(y, 0) > t) y--;
    while (__year_to_secs(y+1, 0) < t) y++;

    long long t0 = rule_to_secs(r0, y);
    long long t1 = rule_to_secs(r1, y);

    if (!local) {
        t0 += __timezone;
        t1 += dst_off;
    }
    if (t0 < t1) {
        if (t >= t0 && t < t1) goto dst;
        goto std;
    } else {
        if (t >= t1 && t < t0) goto std;
        goto dst;
    }
std:
    *isdst = 0;
    *offset = -__timezone;
    if (oppoff) {
        *oppoff = -dst_off;
    }
    *zonename = __tzname[0];
    UNLOCK(lock);
    return;
dst:
    *isdst = 1;
    *offset = -dst_off;
    if (oppoff) {
        *oppoff = -__timezone;
    }
    *zonename = __tzname[1];
    UNLOCK(lock);
}

static void __tzset()
{
    LOCK(lock);
    do_tzset();
    UNLOCK(lock);
}

weak_alias(__tzset, tzset);

const char *__tm_to_tzname(const struct tm *tm)
{
    const void *p = tm->__tm_zone;
    LOCK(lock);
    do_tzset();
    if (p != __utc && p != __tzname[0] && p != __tzname[1] &&
        (!zi || (uintptr_t)p-(uintptr_t)abbrevs >= abbrevs_end - abbrevs)) {
        p = "";
    }
    UNLOCK(lock);
    return p;
}
