date_format.c

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/*
 * This file is part of the Fun programming language.
 * https://fun-lang.xyz/
 *
 * Copyright 2025 Johannes Findeisen <you@hanez.org>
 * Licensed under the terms of the Apache-2.0 license.
 * https://opensource.org/license/apache-2-0
 */


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

case OP_DATE_FORMAT: {
 Value fmt = pop_value(vm);
 Value ms = pop_value(vm);
 if (ms.type != VAL_INT || fmt.type != VAL_STRING) {
 fprintf(stderr, "DATE_FORMAT expects (fmt:string, ms:int)\n");
 if (ms.type != VAL_NIL) free_value(ms);
 if (fmt.type != VAL_NIL) free_value(fmt);
 push_value(vm, make_string(""));
 break;
 }
 time_t secs = (time_t)(ms.i / 1000);
 struct tm tmv;
#if defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 1
 localtime_r(&secs, &tmv);
#else
 struct tm *ptm = localtime(&secs);
 if (!ptm) {
 free_value(ms);
 free_value(fmt);
 push_value(vm, make_string(""));
 break;
 }
 tmv = *ptm;
#endif
 /* Determine buffer size by attempting once with a reasonable size and retrying if needed */
 size_t cap = 128;
 char *buf = (char *)malloc(cap);
 size_t n = strftime(buf, cap, fmt.s, &tmv);
 if (n == 0) {
 /* try larger */
 cap = 512;
 buf = (char *)realloc(buf, cap);
 n = strftime(buf, cap, fmt.s, &tmv);
 }
 Value out;
 if (n == 0) {
 out = make_string("");
 } else {
 out = make_string(buf);
 }
 free(buf);
 free_value(ms);
 free_value(fmt);
 push_value(vm, out);
 break;
}