#include <string.h>

#include "stdio_impl.h"

#define MIN(a, b) ((a) < (b) ? (a) : (b))

char* fgets(char* restrict s, int n, FILE* restrict f) {
  char* p = s;
  unsigned char* z;
  size_t k;
  int c;

  FLOCK(f);

  if (n-- <= 1) {
    f->mode |= f->mode - 1;
    FUNLOCK(f);
    if (n)
      return 0;
    *s = 0;
    return s;
  }

  while (n) {
    if (f->rpos != f->rend) {
      // The buffer is nonempty, drain it up to the newline.
      // If the buffer doesn't contain a newline, then let
      // getc_unlocked do the heavy lifting and keep trying.
      z = memchr(f->rpos, '\n', f->rend - f->rpos);
      k = z ? z - f->rpos + 1 : f->rend - f->rpos;
      k = MIN(k, n);
      memcpy(p, f->rpos, k);
      f->rpos += k;
      p += k;
      n -= k;
      if (z || !n)
        break;
    }
    if ((c = getc_unlocked(f)) < 0) {
      if (p == s || !feof(f))
        s = 0;
      break;
    }
    n--;
    if ((*p++ = c) == '\n')
      break;
  }
  if (s)
    *p = 0;

  FUNLOCK(f);

  return s;
}

weak_alias(fgets, fgets_unlocked);