/* Author: Ruud Harmsen, September 2021.

   Explanation: https://rudhar.com/sfreview/siworin/siworin17.htm

   Further illustration of this bug:
   https://sourceware.org/bugzilla/show_bug.cgi?id=28258
 */

#include <stdio.h>
#include <stdlib.h>
#include <locale.h>
#include <wchar.h>
#include <wctype.h>
#include <ctype.h>
#include <errno.h>

#define REPERR(LINE, ERRNO) { \
   fprintf(stderr, "Line %3d, error %d ", (LINE), (ERRNO)); \
   perror(NULL);}

int main (int argc, char **argv)
{
   static char bytes1[] = u8"Bênção\n";
   static char bytes2[] =   "B\352n\347\343o\n";
   FILE *fp;
   wint_t wc;
   int c;
   long pos;
   long beforeread = 0;

   if (!setlocale(LC_ALL, "en_US.UTF-8"))
      REPERR(__LINE__, errno);

   /* Write the test string to disk. */
   fp = fopen("in", "w");
   fwrite(bytes1, 1, sizeof bytes1 - 1, fp);
   fwrite(bytes2, 1, sizeof bytes2 - 1, fp);
   fwrite(bytes1, 1, sizeof bytes1 - 1, fp);
   fclose(fp);

   /* Reopen for reading. */
   fp = fopen("in", "r");
   while (pos = ftell(fp), wc = fgetwc(fp), !feof(fp))
   {
      printf("Line %3d, ftell %3ld>%3ld. ",
          __LINE__, pos, ftell(fp));
      if (ferror(fp) && errno == EILSEQ)
      {
         clearerr(fp);
         /* Skip one byte and continue */
         if (argc > 1)
         {
            printf("...fseek"); fflush(stdout);
            if (fseek(fp, beforeread + 1, SEEK_SET))
               REPERR(__LINE__, errno);
            printf("... "); fflush(stdout);
         }
         else
         {
            c = fgetc(fp);
            printf("Line %3d, byte c %c %02x. ",
               __LINE__, isprint(c) ? c : '=', (int)c);
         }
      }
      printf("Line %3d, wide character %lc %04x\n",
         __LINE__, iswprint(wc) ? wc : '=', (int)wc);

      if (wc == WEOF)
         wc = '-';
      {
         char s[MB_CUR_MAX];
         beforeread += wctomb(s, wc);
      }
   }
   fclose(fp);
   return 0;
}