/*
 * Copyright ©2025 Hannah C. Tang.  All rights reserved.
 *
 * Permission is hereby granted to students registered for University
 * of Washington CSE 351 for purposes of the course.  No other use, copying,
 * distribution, or modification is permitted without prior written
 * consent. Copyrights for third-party components of this work must be
 * honored.  Instructors interested in reusing these course materials
 * should contact the author.
 */

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

static const int kDefaultSleepSecs = 10;

int main(int argc, char **argv) {
  // If we want to to `ps aux` in a separate terminal to show the process
  // tree, then we should use a relatively generous sleep threshold.  A
  // "straight-shot" demo would benefit from passing in a value of "1".
  int sleep_secs = kDefaultSleepSecs;
  if (argc == 2) {
    if ((sleep_secs = atoi(argv[1])) < 0) {
      sleep_secs = kDefaultSleepSecs;
    }
  }

  pid_t parent_pid = getpid();
  printf("[parent:%d] about to fork...\n\n", parent_pid);
  sleep(sleep_secs);

  pid_t child_pid = fork();
  if (child_pid == 0) {
    // Child.  Its job is to wait a little bit, then exit.
    child_pid = getpid();
    printf("[child:%d] I'm alive!\n", child_pid);
    sleep(sleep_secs);
    printf("[child:%d] Exiting ... I'm becoming a zombie.\n", child_pid);
    return EXIT_SUCCESS;
  } else if (child_pid < 0) {
    // Parent (fork failed).
    fprintf(stderr, "[parent:%d] fork failed :(\n", parent_pid);
    return EXIT_FAILURE;
  } else {
    // Parent (fork succeeded).  Its job is to print the pid of the
    // child process, call waitpid() to ensure that the child has exited (per
    // its algorithm, described above), then exit.
    printf("[parent:%d] Child process (%d) is running!\n",
           parent_pid, child_pid);
    sleep(1.5 * sleep_secs);

    printf("\n[parent:%d] Waiting for child process to finish...\n",
           parent_pid);
    waitpid(child_pid, NULL, 0);

    printf("[parent:%d] Child process is done.\n", parent_pid);
    sleep(0.5 * sleep_secs);
    return EXIT_SUCCESS;
  }
}