/* TICK.C    do something periodically, v2
   BUILD:    make tick
   USE:      ./tick [seconds to wait]
   AUTHOR:   philip k. <philip [dot] kaludercic [at] fau [dot] de>
   SHARE:    in the public domain */

#define _GNU_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stropts.h>
#include <unistd.h>
#include <stdbool.h>
#include <errno.h>
#include <fcntl.h>

#define USAGE "usage: %s [interval]"

/* tries to read stdin, returns false if nothing was found, true if
 * anything was written to stdout. */
static bool
checkpipe(void)
{
     static char *line;
     static size_t len, cap;
     char *last, *new;
     int ret;

     for (char buf[BUFSIZ];;) {
          /* try to read from buffer */
          ssize_t n = read(STDIN_FILENO, buf, sizeof buf);

          if (n == -1) {
               if (errno == EAGAIN) {
                    break;
               } else {
                    perror("read");
                    exit(EXIT_FAILURE);
               }
          } else if (n == 0) {
               break;
          } else {
               /* append buf to line */
               if (n > (ssize_t) (cap - len)) {
                    line = realloc(line, cap += BUFSIZ);
                    if (!line) {
                         perror("realloc");
                         exit(EXIT_FAILURE)
                    }
               }
               memcpy(line + len, buf, (size_t) n);
               len += (size_t) n;
          }
     }

     /* check if anything was written */
     if (line == NULL) {
          return false;
     }
	 
     /* find last newline and print until there */
     last = memrchr(line, '\n', len);
     if (last == NULL) {
          return false;
     }
     ret = fwrite(line, sizeof(char), last - line + 1, stdout);
     if (ret == 0) {
          perror("fwrite");
          exit(EXIT_FAILURE);
     }

     /* relocate rest */
     len -= last - line + 1;
     cap = (len / BUFSIZ + 1) * BUFSIZ;
     new = malloc(cap);
     if (!new) {
          perror("malloc");
          exit(EXIT_FAILURE);
     }
     memcpy(new, last, len);
     free(line);
     line = new;

     return true;
}

int main(int argc, char *argv[]) {
     useconds_t msec;

     if (argc == 2) {
          if (!strcmp(argv[1], "-h")) {
               fprintf(stderr, USAGE "\n", argv[0]);
               exit(EXIT_SUCCESS);
          }
          msec = (useconds_t) (atof(argv[1]) * 1e6);
          if (msec <= 0) {
               fprintf(stderr, "Interval must be positive\n");
               exit(EXIT_FAILURE);
          }
     } else {
          fprintf(stderr, USAGE "\n", argv[0]);
          exit(EXIT_FAILURE);
     }

     /* activate non-blocking I/O on standard input */
     if (-1 == fcntl(STDIN_FILENO, F_SETFL, O_NONBLOCK)) {
          perror("fcntl");
          exit(EXIT_FAILURE);
     }

     /* input loop */
     for (;;) {
          if (!checkpipe())
               printf("\n");
          if (-1 == usleep(msec)) {
               perror("usleep");
               exit(EXIT_FAILURE);
          }
     }

     return EXIT_SUCCESS;
}

/* Local Variables: */
/* indent-tabs-mode: nil */
/* End: */