#include <stdio.h>
#include <stdlib.h>
#include<string.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/wait.h>
#include<signal.h>
#define MAX 500  //Max Input
#define ARGS 20 //Max number of arguments
//handle the signal SIGCHLD when a child process is terminated
void signalHandler(int sig_num)
{
    FILE *fp;
    fp=fopen("shell_logfile.log","a+");// Open log file
    if(fp == NULL)
    {
        printf("\nerror:couldn't open file");
    }
    else fprintf(fp,"Child process was terminated\n");
    fclose(fp);

}
void ExecuteBackground(char *parsedArguments[]){
    pid_t pid = fork();
    if(pid>=0){
       if(pid==0){
       execvp(parsedArguments[0],parsedArguments);
       }
    else {
    printf("Error Parsing");
    }
    }
    }



int Parse(char line[], char *parsedArguments[]) //Parsing
{
    int i=0;

    if((parsedArguments[i] = strtok(line," \n\t"))==NULL) return 0;
    i=1;
    //tokenize the input line by space
    while((parsedArguments[i] = strtok(NULL, " \n\t")) != NULL) i++;
    parsedArguments[i]= NULL;
    return i;
}
int ExecuteProcess(char *parsedArguments[]){
    pid_t pid = fork();
    if(pid==-1){
        printf("\nFailed Fork");
        return ;
    }
    else if(pid==0) {
       if(execvp(parsedArguments[0],parsedArguments)<0){
        printf("Could not Execute Command");
       }
       exit(0);
    }
    else{
        wait(NULL);
    }
}
int main()
{
    char line[MAX]; // User Input
    char *parsedArgument[ARGS]; // Arguments in Command (tokens)
    int count=0;
    int status;
    int flag=1;
    struct sigaction sa;

    sa.sa_handler = signalHandler; // to call my signal handling functions
    sigemptyset(&sa.sa_mask);  //set sa with zeros
    sigaction(SIGCHLD,&sa,NULL);
    printf("Simple Shell");
    while(1)
    {
        printf("\n>>>");
        fgets(line, MAX, stdin);//Read Input from User
        count=Parse(line,parsedArgument);//Parsing Input
        if(count==0){
        continue;
        }
        if(strcmp(parsedArgument[0],"exit") == 0)
        {
                exit(0);
        }
        if(strcmp(parsedArgument[count-1],"&")==0){
        flag=2;
        }

        if(flag==1){
            ExecuteProcess(parsedArgument);
        }
        else{
            ExecuteBackground(parsedArgument);
        }
    }

    return 0;
}