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

typedef struct expectation {
  time_t a, b;
  const char *message;
} ex_t;

const ex_t END = {((time_t)-1), ((time_t)-1), NULL};
static int is_end(ex_t exp) {
  return exp.a == END.a && exp.b == END.b && exp.message == END.message;
}
static ex_t expectation(time_t a, time_t b, const char *message) {
  ex_t exp;
  exp.a = a;
  exp.b = b;
  exp.message = message;
  return exp;
}

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

static void verify_log_contents(ex_t exps[]) {

  FILE *f = fopen("tl.log", "r");
  if (f == NULL)
    die_err("Error opening log file");
  for (size_t i = 0; !is_end(exps[i]); i++) {
    size_t len = strlen(exps[i].message);
    char *buf = (char *)malloc(len + 2);
    if (fgets(buf, len + 1, f) == NULL)
      die("Error reading log file");
    if (ferror(f))
      die("Error reading log file");
    if (strncmp(exps[i].message, buf, len + 1) != 0)
      die("Wrong contents in log file");
    free(buf);
  }
  if (fclose(f) != 0)
    die_err("Error closing log file");
}

static void write_and_read_line() {
  remove_logfile();
  ex_t e = write_to_tl_append("foo\n");
  verify_log_contents((ex_t[]){e, END});
}

static void write_and_read_two_lines() {
  remove_logfile();
  ex_t e1 = write_to_tl_append("foo\n");
  ex_t e2 = write_to_tl_append("bar\n");
  verify_log_contents((ex_t[]){e1, e2, END});
}

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