#define _POSIX_C_SOURCE 2
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static void die(const char *message) {
  fputs(message, stderr);
  fputc('\n', stderr);
  exit(1);
}

static void die_err(const char *message) {
  perror(message);
  exit(1);
}

static void remove_logfile() {
  if (remove("tl.log") != 0) {
    if (errno != ENOENT) {
      die_err("Error removing log file");
    }
  }
}

static void write_to_tl_append(const char *content) {
  FILE *p = popen("./tl-append", "w");
  if (p == NULL)
    die_err("Couldn't run tl-append");
  if (fputs(content, p) == EOF)
    die("Couldn't write to pipe");
  int status = pclose(p);
  if (status < 0)
    die_err("Error closing pipe");
  if (status != 0)
    die("tl-append exited abnormally");
}

static void verify_log_contents(const char *contents) {
  char buf[10];

  FILE *f = fopen("tl.log", "r");
  if (f == NULL)
    die_err("Error opening log file");
  buf[fread(buf, 1, sizeof(buf), f)] = '\0';
  if (ferror(f))
    die("Error reading log file");
  if (strncmp(contents, buf, sizeof(buf)) != 0)
    die("Wrong contents in log file");
  if (fclose(f) != 0)
    die_err("Error closing log file");
}

static void write_and_read_line() {
  remove_logfile();
  write_to_tl_append("foo\n");
  verify_log_contents("foo\n");
}

static void write_and_read_two_lines() {
  remove_logfile();
  write_to_tl_append("foo\n");
  write_to_tl_append("bar\n");
  verify_log_contents("foo\nbar\n");
}

int main() {
  write_and_read_line();
  write_and_read_two_lines();
}