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

#define clear() printf("\033[H\033[J")
#define LINEMAX 500  // MAX LIMIT FOR USER CHARACTER INPUT
#define TOKENSMAX 20 // MAX LIMIT FOR COMMAND TOKEN
#define pwd 1
#define cd 2
#define ls 3


void signalHandler(int sig_num);  //FUNCTION TO RECORD THE SIGCHILD SIGNAL IN LOG FILE
void changeDir(char * args[]); //UTILITY FUNCTION TO CHANGE DIRECTORY
void printDir(); // UTILITY FUNCTION TO PRINT CURRENT DIRECTORY
void commandHandler(char * args[], int args_count); //FUNCTION TO HANDLE ENTERED COMMANDS
int parseInput(char line[], char * tokens[]); // PARSE INPUT BY SEPARATING WITH SPACE
char* getCurrentTime();

int main()
{
    char input[LINEMAX]; // USER INPUT
    char * commands[TOKENSMAX]; // COMMAND TOKENS
    int commands_count=0,exit_flag=1;
    struct sigaction sig; // DEFINING SIGACTION STRUCT TO HANDLE SIGNALS

    sig.sa_handler = signalHandler; // LINKING SA_HANDLER WITH IMPLEMENTATION OF SIGNAL HANDLER
    sigemptyset(&sig.sa_mask);  // SET ZEROES
    sigaction(SIGCHLD,&sig,NULL); // CALL SIGNAL HANDLER ON CHILD TERMINATION
    printf("\t\t\t\tWelcome @%s\n\n",getenv("USER")); // WELCOME MESSAGE
    printf("The aim of this project is to create a simple Unix Shell program\ncapable of launching child processes. The project was created as a partial\nsimulation of the actual Unix terminal\n");

    while(exit_flag==1)
    {

        printDir(); //PRINT CURRENT DIRECTORY AFTER EACH LOOP
        fgets(input, LINEMAX, stdin); // READ USER INPUT
        commands_count=parseInput(input,commands); // PARSE USER'S INPUT AND STORE TOKEN COUNT
        if(commands_count==0)
        {
            continue;
        }
        if(strcmp(commands[0],"exit()") == 0) // IF COMMAND IS EXT(), TERMINATE
            {
                exit_flag=0;
                exit(0);
            }
        commandHandler(commands,commands_count); // HANDLE THE PARSED COMMANDS
    }

    return 0;
}

//FUNCTION TO RECORD THE SIGCHILD SIGNAL IN LOG FILE
void signalHandler(int sig_num)
{
    FILE *fp;
    char time[40];
    strcpy(time,getCurrentTime());
    fp=fopen("MYSIMPLESHELL.log","a+");
    if(fp == NULL)
        printf("\nERROR: OPENING FILE FAILED");
    else fprintf(fp,"%sCHILD PROCESS TERMINATED SUCCESSFULLY SIGNUM %d\n",time,sig_num);
    fclose(fp);
}

char* getCurrentTime()
{
    time_t rawtime;
    struct tm * timeinfo;
    time ( &rawtime );
    timeinfo = localtime (&rawtime);
    return asctime (timeinfo);
}

// UTILITY FUNCTION TO PRINT CURRENT DIRECTORY
void printDir()
{
    char currentDir[1024];
    getcwd(currentDir, sizeof(currentDir));
    printf("\nDir: %s :~$ ", currentDir);
}

//UTILITY FUNCTION TO CHANGE DIRECTORY
void changeDir(char * args[])
{
    if (args[1] == NULL)
        chdir(getenv("HOME")); // ONLY CD written
    else
    {
        if (chdir(args[1]) == -1)
            printf(" %s: ERROR: DIRECTORY NOT AVAILABLE\n", args[1]);
    }
}

//FUNCTION TO HANDLE COMMANDS ENTERED
void commandHandler(char * args[], int args_count)
{
    int count = args_count;
    int back_flag = 0; //SET BACKGROUND FLAG TO NO

    if(!(strcmp(args[count-1],"&"))) //CHECK FOR BACKGROUND PROCESS INDICATOR '&'
    {
        back_flag=1; //SET BACKGROUND FLAG TO YES
        args[count-1]='\0'; //REMOVING *&
        count--;
    }
    // EXECUTE THE ENTERED COMMAND
    pid_t pid=fork(); //PROCESS ID
    if (pid >= 0) // FORKING SUCCESSFUL
    {
        if(pid == 0)    //CHILD EXECUTING
        {    if(execvp(args[0],args)<0)
            {
                printf("ERROR: COMMAND COULDN'T BE EXECUTED!");
            }
        }
        else
        {
            if(back_flag==1)
                return;
            else
            {
                wait(NULL);
                // SUSPEND PARENT TILL CHILD CHANGES STATE
            }
        }
    }
    else
        printf("\nFORKING FAILED!");
}

// PARSE INPUT BY SEPARATING BY WHITESPACES
int parseInput(char line[], char * command_tokens[])
{
    int i=0;
    if((command_tokens[i] = strtok(line," \n\t")) == NULL)
        return 0;     // CASE OF NO INPUT, RETURN 0
    i=1;
    while((command_tokens[i] = strtok(NULL, " \n\t")) != NULL) // SEPARATE USER INPUT BY SPACES
        i++;                // COUNTING TOKENS
    tokens[i]= NULL;        // MAKING SURE LAST ELEMENT IS NULL
    return i;
}