#include <stdio.h>
#include <stdlib.h>
#include<string.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/wait.h>
#include<signal.h>
#define MAXL 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 Execute(char * args[], int args_count) //Executes Command
{
    int count=args_count;
    char cwd[1024];
    // status of the child
    int status;
    int background=0;

    //check if it's a background process or not
    if(!(strcmp(args[count-1],"&")))
    {
        //SET background flag to zero
        background=1;
        //remove the "&" so it could be executed
        args[count-1]='\0';
        count--;
    }

    // print the current directory
    if (strcmp(args[0],"pwd") == 0)
    {
        printf("%s\n", getcwd(cwd, sizeof(cwd)));
    }
    // change directory
    else if (strcmp(args[0],"cd") == 0)
    {
        changeDirectory(args);
    }
    //execute the command
    else
    {
        //process id
        pid_t pid=fork();

        // no error in forking
        if (pid >= 0)
        {
            // if it's a child process
            if(pid== 0)
            {
                execvp(args[0],args);

            }
            //if it's the parent process
            else
            {
                if(background==1) return;
                else
                {
                    //suspends execution until the child specified by pid change state
                    do
                    {
                    waitpid(pid,&status,WUNTRACED);
                   }
                   while(!WIFEXITED(status) && !WIFSIGNALED(status));
                    //wait(&status);
                }
            }
        }
        else
            printf("\nfailed to fork!");
    }
}

int Parse(char line[], char *parsedArguments[]) //Parsing
{
    int i=0;
    if((parsedArguments[i] = strtok(line," "))==NULL){
        printf("Please enter Command ");
        return 0;
    }
    int counter=1;
    while((parsedArguments[counter] = strtok(NULL, " ")) != NULL){ //Parse Using Spaces
        i++;
    }
    parsedArguments[i]= '\0';
    return i;
}
int ExecuteProcess(char *parsedArguments[]){
    pid_t pid = fork();
    if(pid==-1){
        printf("\nFailed Fork");
        return ;
    }
    else if(pid==0) {
       if(execvp(parsed[0],parsed)<0){
        printf("Couldnt Execute Command");
       }
       exit(0);
    }
    else{
        wait(Null);
    }
}
int main()
{
    char line[MAX]; // User Input
    char *parsedArguemnt[ARGS]; // Arguments in Command (tokens)
    int tokenCount=0;
    int status;
    int flag=1;

    struct sigaction sa;//Child Signal

    sa.sa_handler = signalHandler; // to call my signal handling functions
    sigemptyset(&sa.sa_mask);  //set sa with zeros
    sigaction(SIGCHLD,&sa,NULL);//call my signal handler when a child terinates
    printf("Simple Shell");
    while(1)
    {
        printf("\n>>");
        fgets(line, MAXLINE, stdin);//Read Input from User
        tokenCount=Parse(line,parsedArguemnt);//Parsing Input
        if(strcmp(parsedArguemnt[0],"exit") == 0){ //Exit Function
                exit(0);
        }
        if(flag==1){
            ExecuteProcess(parsedArguemnt);
        }
    }

    return 0;
}