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

#define PRINT

int main(void) {
    struct tm tm, *stm;
    time_t res;
    putenv("TZ=UTC");
    tm.tm_sec = tm.tm_min = 0; tm.tm_hour = 12;
    tm.tm_mday = 1; tm.tm_mon = 0; tm.tm_year = 120; tm.tm_isdst = 0;
    // test 2020-01-01
    res = mktime(&tm);
#ifdef PRINT
    printf("day %ld\n", res);
#else
    if(res != 1577880000L) exit(1);
#endif
    // and can we go back to POSIXlt?
#ifdef HAVE_GMTIME_R
    stm = gmtime_r(&res, &tm);
#else
    stm = gmtime(&res);
#endif
#ifdef PRINT
    printf("%d-%02d-%02d %02d:%02d:%02d\n",
	   1900+stm->tm_year, 1+stm->tm_mon, stm->tm_mday,
	   stm->tm_hour, stm->tm_min, stm->tm_sec);
#else
    if(stm->tm_year != 120 || stm->tm_mon != 0 || stm->tm_mday != 1
      || stm->tm_hour != 12 || stm-> tm_isdst != 0) exit(10);
#endif
    tm.tm_mon = 6; tm.tm_isdst = 0;
    // test 2020-07-01
    res = mktime(&tm);
#ifdef PRINT
    printf("res %ld\n", res);
#else
    if(res != 1593604800L) exit(2);
#endif
#ifdef HAVE_GMTIME_R
    stm = gmtime_r(&res, &tm);
#else
    stm = gmtime(&res);
#endif
#ifdef PRINT
    printf("%d-%02d-%02d %02d:%02d:%02d\n",
	   1900+stm->tm_year, 1+stm->tm_mon, stm->tm_mday,
	   stm->tm_hour, stm->tm_min, stm->tm_sec);
#else
    if(stm->tm_year != 120 || stm->tm_mon != 6 || stm->tm_mday != 1
      || stm->tm_hour != 12 || stm-> tm_isdst != 0) exit(20);
#endif

    putenv("TZ=Europe/London");
    tm.tm_sec = tm.tm_min = 0; tm.tm_hour = 12;
    tm.tm_mday = 1; tm.tm_mon = 0; tm.tm_year = 120; tm.tm_isdst = -1;
    // test 2020-01-01, whoch is assumed to be in GMT
    res = mktime(&tm);
#ifdef PRINT
    printf("res %ld\n", res);
#else
    if(res != 1577880000L) exit(3);
#endif
#ifdef HAVE_LOCALTIME_R
    stm = localtime_r(&res, &tm);
#else
    stm = localtime(&res);
#endif
#ifdef PRINT
    printf("%d-%02d-%02d %02d:%02d:%02d\n",
	   1900+stm->tm_year, 1+stm->tm_mon, stm->tm_mday,
	   stm->tm_hour, stm->tm_min, stm->tm_sec);
#else
    if(stm->tm_year != 120 || stm->tm_mon != 0 || stm->tm_mday != 1
       || stm->tm_hour != 12 || stm-> tm_isdst != 0) exit(30);
#endif
    tm.tm_mon = 6; tm.tm_isdst = -1;
    // test 2020-07-01 which is assumed to be in BST
    res = mktime(&tm);
#ifdef PRINT
    printf("res %ld\n", res);
#else
    if(res != 1593601200L) exit(4);
#endif
#ifdef HAVE_LOCALTIME_R
    stm = localtime_r(&res, &tm);
#else
    stm = localtime(&res);
#endif
#ifdef PRINT
    printf("%d-%02d-%02d %02d:%02d:%02d\n",
	   1900+stm->tm_year, 1+stm->tm_mon, stm->tm_mday,
	   stm->tm_hour, stm->tm_min, stm->tm_sec);
#else
    if(stm->tm_year != 120 || stm->tm_mon != 6 || stm->tm_mday != 1
      || stm->tm_hour != 12 || stm-> tm_isdst != 1) exit(40);
#endif
    putenv("TZ=Pacific/Auckland");
    tm.tm_sec = tm.tm_min = 0; tm.tm_hour = 12;
    tm.tm_mday = 1; tm.tm_mon = 0; tm.tm_year = 120; tm.tm_isdst = -1;
    res = mktime(&tm);
#ifdef PRINT
    printf("res %ld\n", res);
#else
    if(res != 1577833200L) exit(5);
#endif
#ifdef HAVE_LOCALTIME_R
    stm = localtime_r(&res, &tm);
#else
    stm = localtime(&res);
#endif
#ifdef PRINT
    printf("%d-%02d-%02d %02d:%02d:%02d\n",
	   1900+stm->tm_year, 1+stm->tm_mon, stm->tm_mday,
	   stm->tm_hour, stm->tm_min, stm->tm_sec);
#else
    if(stm->tm_year != 120 || stm->tm_mon != 0 || stm->tm_mday != 1
      || stm->tm_hour != 12 || stm-> tm_isdst != 1) exit(50);
#endif
    tm.tm_mon = 6; tm.tm_isdst = -1;
    res = mktime(&tm);
#ifdef PRINT
    printf("res %ld\n", res);
#else
    if(res != 1593561600L) exit(6);
#endif
#ifdef HAVE_LOCALTIME_R
    stm = localtime_r(&res, &tm);
#else
    stm = localtime(&res);
#endif
#ifdef PRINT
    printf("%d-%02d-%02d %02d:%02d:%02d\n",
	   1900+stm->tm_year, 1+stm->tm_mon, stm->tm_mday,
	   stm->tm_hour, stm->tm_min, stm->tm_sec);
#else
    if(stm->tm_year != 120 || stm->tm_mon != 6 || stm->tm_mday != 1
       || stm->tm_hour != 12 || stm-> tm_isdst != 0) exit(60);
#endif

    exit(0);
}