#include <iostream>
#include <unistd.h>   // fork
#include <sys/wait.h> // for wait, waitpid
#include <time.h>     // for nanosleep, sleep
#include <signal.h>   // for kill
#include <stdio.h>   // perror

using namespace std;

void SleepChild(int sec) {
    int sleeptime;
    int exitStatus;

    cout << "\tHello from the child, I have pid " << getpid() << endl;

    sleeptime = sec;


    do {
        cout << "\tChild going to sleep  for " << sleeptime << " sec" << endl;
        sleeptime = sleep(sleeptime);
    } while (sleeptime > 0);

    // generate a random exit status.
    exitStatus = 1+rand()%255;
    cout <<"\tChild is exiting with value " << exitStatus << endl;

    // why exit here, not a return?
    exit(exitStatus);
}

void WaitChild(pid_t childPID) {
    pid_t tmp;
    int status;

    cout << "Parent waiting " << endl;
    cout << endl;

    //tmp = wait(&status);
    tmp = waitpid(-1,&status,WCONTINUED|WUNTRACED);
    
    if (tmp != -1) {

        cout << "Wait returned " << tmp << " which should be "
	     << childPID << endl;
        cout << "The status was " << status << endl;

        if (WIFEXITED(status)) {
           cout << "The exit status was " << WEXITSTATUS(status) << endl;
        } else if (WIFSIGNALED(status)) {
           cout << "Killed by signal " << WTERMSIG(status) << endl;
        } else if (WIFSTOPPED(status) ) {
           cout << "The process was stopped " << endl;
        } else if (WIFCONTINUED(status) ) {
           cout << "The process was continued " << endl;
        }

        cout << endl ;
    } else {
        perror("Wait or waitpid");
    }

    return;
}


int main() {

    srand(time(nullptr));

    pid_t childPID;

    cout << " The parent will wait before the child exits. " << endl;
    childPID = fork();
    if (childPID == 0) {
        SleepChild(2);
    }

    WaitChild(childPID);

    cout << endl << endl;
    cout << "Try that again." << endl;
    cout << "This time the child will exit before the parent waits" << endl;

    childPID = fork();
    if (childPID == 0) {
        SleepChild(1);
    }

    cout << "Parent sleeping for 2" << endl;
    sleep(2);
    cout << "Parent going to wait" << endl;
    cout << endl;

    WaitChild(childPID);

    cout << endl << endl;
    cout << "One more time" << endl;
    cout << "This time parent will send the child signals." << endl;

    childPID = fork();
    if (childPID == 0) {
        SleepChild(10);
    }

    sleep(1);

    cout << endl;
    cout << "\t\tSending SIGSTOP (" << SIGSTOP << ")" << endl;
    cout << endl;
    kill(childPID, SIGSTOP);
    WaitChild(childPID);

    cout << endl;
    cout << "\t\tSending SIGCONT (" << SIGCONT << ")" << endl;
    cout << endl;
    kill(childPID, SIGCONT);
    WaitChild(childPID);

    cout << endl;
    cout << "\t\tSending SIGUSR1 (" << SIGUSR1 << ")" << endl;
    cout << endl;
    kill(childPID, SIGUSR1);

    WaitChild(childPID);

    return 0;
}