#include <signal.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/wait.h>

#include "child.h"
#include "epty.h"

/* SIGTERM grace period before a child is sent SIGKILL.
 * Value is in microseconds (us), 1000us = 1ms */
#define CHILD_GRACE_US 100000

/* Check if a child is still alive by pid
 * by kill(3p) sending a null signal (0).
 */
static int is_alive(struct d_child *child) {
  return (kill(child->pid, 0) == 0);
}

/* Force a child to die, first by sending SIGTERM, otherwise SIGKILL.
 * NOTE: killchild() ASSUMES the child is LIVING at the start.
 * NOTE: Keep this in mind when threading!
 */
void killchild(struct d_child *child) {
  int stat;

  /* Request Death */
  kill(child->pid, SIGTERM);
  usleep(CHILD_GRACE_US);
  
  /* Force Death */
  if (is_alive(child))  
    kill(child->pid, SIGKILL);

  /* Reap */
  waitpid(child->pid, &stat, 0);
}

/* Fork to spawn a child process running bin/shfx in an "epty".
 */
int spawnchild(struct d_child *child) {
  *child = (struct d_child){ 0 };
  
  /* fork(2) and allocate an "error-piped pseudoterminal" (epty) */
  switch (child->pid = forkepty(&child->fdmx, &child->fderr)) {
  case -1:
    perror("forkepty");
    return EXIT_FAILURE;
  case 0:
    char *args[] = {"shfx", NULL};
    execvp("shfx", args);
    perror("execvp");
    exit(1);
  default:
    usleep(1000);
    char bufout[10];
    bufout[9] = '\0';
    read(child->fdmx, bufout, 9);
    printf("child stdout: \"%s\"\n", bufout);
    break;
  }
  return EXIT_SUCCESS;
}