/**************************************************************************
 * Student name and No.: Ho Hilary 3035229306
 * Development platform: Ubuntu 14.04 VM
 * Last modified date:
 * Compilation: gcc myshell.c -o myshell
 */

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

//signal handler declaration
void sigint_handler(int signum) {
    if(signum ==SIGUSR1){
        printf("Received SIGUSR1!\n");
    }else {
    printf(" Program terminated\n");
    }
}

int main() {
  //variable declaration

    //for timeX print out statisticc
    char str[50];
    FILE * file;
    int z;
    //unsigned long long i, x;
    unsigned long h, ut, st;

    char input[1024];   //store user input
    char *split[1024];  //split the input into
    int a=0;

      int childtype=0; //to indicate if it is background(1) or foreground(2) child process
    int result;     //store result of waitid() from parent process
    siginfo_t info; //signal type



  //start of program

    //prompt ##myshell $ and get the input from user and store in "input"
    printf("##myshell $");
    fgets(input, 1024,stdin);

    //loop until "exit" command appears
    while(strcmp(input,"exit\n")!=0){

        //remove the newline character at the end of the input
        if (input[strlen(input) - 1] == '\n') {
                input[strlen(input) - 1] = '\0';
        }

        //check if the input has the character '&'
        if(strstr(input,"&")!=NULL){
            if(input[strlen(input)-1]!='&'){  //the input has '&' but not at the end position
                 printf("'&' should not appear in the middle of the command line\n");
            }else{  //the input has '&' at the end
                childtype =1;  //define it as background child process
            }

        //get process statistics
      }else if(strcmp(input,"timeX")==0){   //the input is exactly "timeX"

                printf("myshell: \"timeX\" cannot be a standalone command\n");


                sprintf(str, "/proc/%d/stat", (int)getpid());
                file = fopen(str, "r");
                if (file == NULL) {
                    printf("Error in open my proc file\n");
                    exit(0);
                }
                fscanf(file, "%d %s %c %d %d %d %d %d %u %lu %lu %lu %lu %lu %lu", &z, str, &str[0], &z, &z, &z, &z, &z,
                       (unsigned *)&z, &h, &h, &h, &h, &ut, &st);
                fclose(file);
                printf("PID \t CMD \t UTIME \t STIME\n");
                    //remove the newline character of the input
                    if (input[strlen(input) - 1] == '\n') {
                        input[strlen(input) - 1] = '\0';
                    }
                printf("%d\t %s\t %.2lfs\t %.2lfs\n",(int)getpid(),input, ut*2.0f/sysconf(_SC_CLK_TCK),st*1.0f/sysconf(_SC_CLK_TCK));


          }else if ((strstr(input,"timeX")!=NULL) & (input[strlen(input)-1]=='&')){    //"timeX" command ends with '&'
                printf("myshell: \"timeX\" cannot be run in background mode\n");
            }
        else {

        //create child process to execute command
           int pid = fork();
               if (pid < 0) {
                printf("Cannot create child process successfully!");
            } else if (pid == 0) {  //run child process
              childtype =2;  ////define it as foreground child process

                // printf("It is a foreground process with type %d\n", childtype);
                //printf("I am a child process, with pid: %d\n", (int) getpid());

          //split the input into small pieces with delimiter of a space " "
          split[a] = strtok(input," ");
            while(split[a]!=NULL)
            {
               split[++a] = strtok(NULL," ");
            }

            if ((strcmp(split[0],"exit")==0)&& split[1]!=NULL){    //there are other input after "exit" command
                printf("myshell: \"exit\" with other arguments!!!\n");
            }
            else{
            //locate and execute program with aboslute
                execvp(split[0],split);
            char *path[] = {"HOME=/home","LOGNAME=home",(char *)0};
                execve(split[0],split,path);

            //input path cannot be found
            if (execvp (split[0], split) == -1) {
                printf("myshell: \'%s \': No such file or directory\n", input);
                exit(-1);
            }
            printf("These lines should never be printed\n");
            exit(0);
          }

          } else {
            //run parent process
            pid_t child_pid;
            child_pid = waitpid(pid,NULL,0);
              if(child_pid>0){}
            //printf("I am a parent process, with pid: %d and my child's pid is %d\n",(int) getpid(), (int) pid);
                //printf("Parent: OK\n");

              if(childtype==1) { // if it is a background child process.
                        signal(SIGCHLD,sigint_handler);// handle SIGCHLD signal
                    }

                    if(childtype ==2){ //if it is a foreground child process
                        result = waitid(P_ALL,0,&info,WCONTINUED);
                        if(result ==-1){ //error
                        //printf("Program terminated.%d\n",status.si_signo);
                    }

                                }
                }
          }
          //prompt the user and get input from user
             printf("##myshell $");
           fgets(input, 1024,stdin);
    }//end of while loop

  //"exit" command is typed
    printf("myshell: Terminated\n");
  return 0;
}