#include <cstdlib>
#include <cstring>
#include <cerrno>
#include <unistd.h>
#include <fcntl.h>
#include <string>
#include <iostream>

using namespace std;

extern char ** environ;
char * result[100];
bool wasNotBuiltIn = true;

char ** convert(string s)
{

  char * cstr = new char [s.length()+1];
  strcpy (cstr, s.c_str());

  // cstr now contains a c-string copy of str

  int counter = 0;
  char * p = strtok (cstr," ");
  while (p!=0)
  {
    result[counter] = p;
    p = std::strtok(NULL," ");
    counter++;
  }

  return result;
}

void execute(char ** c)
{
  if (execvp(c[0], c + 1) == -1) perror(c[0]);
}

int main()
{
  string line;

  string homeDir = getenv("HOME");
  string presentDir = getenv("PWD");
  string toPrint;
  if(strcmp(homeDir.c_str(), presentDir.substr(0, homeDir.length()).c_str()) == 0)
  {
    toPrint = "~" + presentDir.substr(homeDir.length(), presentDir.length());
  }
  else
  {
    toPrint = presentDir;
  }

  while(printf("1730sh:%s$ ", toPrint.c_str()) && getline(cin, line))
  {
    convert(line);

    string exit = "exit";
    if(strcmp(result[0],exit.c_str()) == 0)
    {
      return EXIT_SUCCESS;
    }

    string help = "help";
    string cd = "cd";
  if(strcmp(result[0],help.c_str()) == 0)
    {
      if(result[1] == nullptr)
      {
        cout << "Built-In Commands" << endl;
        cout << "cd [PATH] - Change the current directory to PATH. The environmental variable HOME is the default PATH." << endl;
        cout << "exit [N] - Cause the shell to exit with a status of N. If N is omitted, the exit status is that of the last job executed." << endl;
        cout << "help - Display helpful information about builtin commands." << endl;
      }
      else
      {
        if(strcmp(result[1],cd.c_str()) == 0)
        {
          cout << "Built-In Command " << result[1] <<  endl;
          cout << "cd [PATH] - Change the current directory to PATH. The environmental variable HOME is the default PATH." << endl;
        }
        else if(strcmp(result[1],exit.c_str()) == 0)
        {
          cout << "Built-In Command " << result[1] <<  endl;
          cout << "exit [N] - Cause the shell to exit with a status of N. If N is omitted, the exit status is that of the last job executed." << endl;
        }
        else if(strcmp(result[1],help.c_str()) == 0)
        {
          cout << "Built-In Command " << result[1] <<  endl;
          cout << "help - Display helpful information about builtin commands." << endl;
        }
  else
        {
          cout << "That built-in command does not exist." << endl;
        }
      }

      wasNotBuiltIn = false;
    }

    if(strcmp(result[0],cd.c_str()) == 0)
    {

      if(result[1] == nullptr)
      {
        chdir(getenv("HOME"));
      }
      else
      {
        chdir(result[1]);
      }
     homeDir = getenv("HOME");
      presentDir = get_current_dir_name();
      if(strcmp(homeDir.c_str(), presentDir.substr(0, homeDir.length()).c_str()) == 0)
      {
        toPrint = "~" + presentDir.substr(homeDir.length(), presentDir.length());
      }
      else
      {
        toPrint = presentDir;
      }

      wasNotBuiltIn = false;
    }

    if(wasNotBuiltIn)
    {
      execute(result);
    }
    wasNotBuiltIn = true;

    for(int i = 0; i < 100; i++)
    {
      result[i] = nullptr;
    }
  }

}