#include <unistd.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <sys/stat.h>       // open()
#include <signal.h>         // signal()
#include <fcntl.h>          // open()
#include <stdio.h>          // printf(), ...
#include <time.h>               // time(), ...
#include <string.h>
#include <sstream>
#include <iostream>
#include <unistd.h> // strtok()
#define MAXLINE 100
#define MOD "exit with CTR C"

time_t start;

int read_command(char *command,char *parameters[]) { // prompt for user input and read a command line
    char dir[FILENAME_MAX];
    getcwd(dir,FILENAME_MAX); //get current dir and safe into dir
    fprintf(stdout, "%s >",dir); //Print out current dir
    int noParam=0;
    char linearray[MAXLINE];
    fgets(linearray, MAXLINE, stdin);

    char* pointer;

    pointer = strtok(linearray," \n"); //Delimit at blank and \n (Enter)
    while(pointer != NULL){
        if(noParam == 0)
            strcpy(command,pointer);

        parameters[noParam] = pointer;
        noParam++;
        pointer = strtok(NULL," \n");
    }

    parameters[noParam] = NULL;
    return(noParam);
} // read_command

void childhandler(int) {
    pid_t pid;
    int status;

    //waitpid(-1, &status, WNOHANG) checks if any zombie children exists
    //If yes, it will be reaped and return either 0 if another unterminated child exists
    //Or -1 when no more are left

    /* Aus Dokumentation pubs.opengroup.org:
     *WNOHANG
     *The waitpid() function shall not suspend execution of the calling thread
     *if status is not immediately available for one of the child processes specified by pid.
    */
    while((pid = waitpid(-1, &status, WNOHANG)) > 0);

}

void exithandler(int){
    time_t end = time(NULL); //nehme Zeit, wenn STRG+C gedrückt wird
    int seconds = difftime(end,start); //Differenz zwischen Start und Ende
    int minutes = seconds / 60;
    int hours = minutes / 60;
    seconds = seconds % 60;
    minutes = minutes % 60;
    fprintf(stdout,"\nTerminated\nTime elapsed:%dh %dm %ds\n",hours,minutes,seconds);
    exit(0);
}


int main(int argc, char *argv[]) {
    start = time(NULL); //Zeit bei Start des Programms

    signal(SIGINT, exithandler);


    int childPid;
    int status;
    char command[MAXLINE];
    char *parameters[MAXLINE];
    int noParams;

    while (1) {
        noParams = read_command(command, parameters); // read user input
        if(strncmp(command,"cd",2)==0){
            chdir(parameters[1]);
            continue;
        }

        if(strcmp(parameters[noParams-1],"&") == 0) {
            parameters[noParams-1] = NULL;
            noParams--;
            //SIGCHLD is the Signal when a Childprocess terminates
            signal(SIGCHLD,childhandler);

            if (noParams == 0) {
                fprintf(stderr, "no command ?!\n");
                exit(1);
            }
            if ((childPid = fork()) == -1) { // create process
                fprintf(stderr, "can't fork!\n");
                exit(2);
            } else if (childPid == 0) { // child process
                execvp(command, parameters); // executes command
                exit(3);
            }
            else { // father
                printf("[%d]\n",childPid);
            }

        } else {

            if (noParams == 0) {
                fprintf(stderr, "no command ?!\n");
                exit(1);
            }
            if ((childPid = fork()) == -1) { // create process
                fprintf(stderr, "can't fork!\n");
                exit(2);
            } else if (childPid == 0) { // child process
                execvp(command, parameters); // executes command
                exit(3);
            }
            else { // father
                waitpid(childPid, &status, WUNTRACED | WCONTINUED);
            }
        }
    }
}