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

#define READLINE_BUFFER 1024
#define BUFSIZE 64
#define DELIMITER " \t\r\n\a"

char* buffer = NULL;

int startFunc(char **args){
    pid_t pid, wpid;
    int process_status;

    pid = fork();
    if(pid == 0){
                         //Child process
        if(execvp(args[0], args) < 0){
            perror(args[0]);
            free(args);
            free(buffer);
            buffer = NULL;
            exit(1);
        }
    } else if(pid < 0){
                            //Error forking
            perror("fork");
      } else{
                        //Parent process
            waitpid(pid, &process_status, 0);

        }
    return 1;
}

int executeFunc(char **args){

    if(args[0] == NULL){
        return 1;  //An empty command was entered
    }

    return startFunc(args);
}


char *readLine(){
    int bufsize = READLINE_BUFFER;
    int position = 0;
    buffer = malloc(sizeof(char) * bufsize);
    int c;

    if(!buffer){
        fprintf(stderr, "No such file or directory\n");
        exit(EXIT_FAILURE);   // an unsuccessfull termination status is returned to the host env
    }

    while(1){
                     //reads character
        c = getchar();
        if(c == EOF){
            free(buffer);
            buffer = NULL;
            exit(0);
        }
        if(c == '\n'){
            buffer[position] = '\0';
            return buffer;
        } else{
                buffer[position] = c;
            }
        position++;

        if(position >= bufsize){
            bufsize += READLINE_BUFFER;
            buffer = realloc(buffer, bufsize);
            if(!buffer){
                fprintf(stderr, "No such file or directory");
                exit(EXIT_FAILURE); // an unsuccessfull termination status is returned to the host env
            }
        }
    }

}


char **parse_cmdline(const char *line){
    int bufsize = BUFSIZE, pos = 0;
    char **tokens = malloc(bufsize * sizeof(char*));
    char *token;

    if(!tokens){
        fprintf(stderr, "No such file or directory\n");
        exit(EXIT_FAILURE); // an unsuccessfull termination status is returned to the host env
    }
    token = strtok((char*)line, DELIMITER); //breaks string str into a series of tokens using the delimiter delim.
    while(token != NULL){
        tokens[pos] = token;
        pos++;

        if(pos >= bufsize){
            bufsize += BUFSIZE;
            tokens = realloc(tokens, bufsize * sizeof(char*));
            if(!tokens){
                fprintf(stderr, "Permission denied");
            }
        }
        token = strtok(NULL , DELIMITER);
    }
    tokens[pos] = NULL;
    return tokens;
}

void Cyclecommands(){
    int tmpexe;
    char *cmdline;
    char **arg;

    while(tmpexe){
    write(0, "$ ", 2);
        cmdline = readLine();
        arg = parse_cmdline(cmdline);
        tmpexe = executeFunc(arg);

        free(cmdline);
    free(arg);
        buffer = NULL;

    }

}

int main(int argc, char **argv){
Cyclecommands();

return 0;
}