#include <cstdlib>
#include <cstring>
#include <cerrno>
#include <unistd.h>
#include <fcntl.h>
#include <string>
#include <iostream>
#include <sys/wait.h>
#include <stdlib.h>

using namespace std;

extern char ** environ;  //environmental variables
char * result[100]; //used to store user input
bool wasNotBuiltIn = true; //used to determine if you call execute or not
int exitStatus = 0; //stores the last process's exit status

//converts the string the user inputs to an array of characters
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;
}

//checks if there is at least one pipe
bool checkPipes(char ** c)
{
  int count = 0;
  while(result[count] != nullptr)
  {
    string pipe = "|";
    if((strcmp(result[count], pipe.c_str())) == 0)
      return true;
    count++;
  }

  return false;
}

//executes the user's input if it is not a builtin command
void execute(char ** c)
{
  pid_t  pid;
  int    status;

  //make child process
  if ((pid = fork()) < 0)
  {
    printf("*** ERROR: forking child process failed\n");
    exit(1);
  }
  //only in child
  else if (pid == 0)
  {
    //executes the command or prints error
    if (execvp(*c, c) < 0)
    {
      printf("*** ERROR: exec failed\n");
      exit(1);
    }
  }
  //only in parent
  else
  {
    //waiting for child to finish
    while (wait(&status) != pid);
  }

  //setting exitStatus to the exit status of last process
  exitStatus = status;

}

//deletes pipes
void close_pipe(int pipefd [2]) {
  if (close(pipefd[0]) == -1) {
    perror("close");
    exit(EXIT_FAILURE);
  } // if
  if (close(pipefd[1]) == -1) {
    perror("close");
    exit(EXIT_FAILURE);
  } // if
} // close_pipe

//execute logic if there are pipes
void executePipes(char ** c)
{
  int pipefd [2];
  int pid;

  // create pipe
  if (pipe(pipefd) == -1)
  {
     perror("pipe");
  } // if

  // create first child
  if ((pid = fork()) == -1) {
    perror("fork");
  } else if (pid == 0) {

    if (dup2(pipefd[1], STDOUT_FILENO) == -1) {
      perror("dup2");
    } // if

    close_pipe(pipefd);

    char ** args = new char * [3];
    args[0] = strdup(c[0]);
    args[1] = strdup(c[1]);
    args[2] = nullptr;

    execvp(args[0], args);

    perror("execvp");
    for (int i = 0; i < 3; ++i) free(args[i]);
    delete[] args;
    exit(EXIT_FAILURE);

  } // if

  // create second child
  if ((pid = fork()) == -1) {
    perror("fork");
  } else if (pid == 0) {

    if (dup2(pipefd[0], STDIN_FILENO) == -1) {
      perror("dup2");
    } // if

    close_pipe(pipefd);

    char ** args;
    if(c[4] == nullptr)
    {
      args = new char * [2];
      args[0] = strdup(c[3]);
      args[1] = nullptr;
    }
    else
    {
      args = new char * [3];
      args[0] = strdup(c[3]);
      args[1] = strdup(c[4]);
      args[2] = nullptr;
    }

    execvp(args[0], args);

    perror("execvp");
    for (int i = 0; i < 2; ++i) free(args[i]);
    delete[] args;
    exit(EXIT_FAILURE);

  } // if
  close_pipe(pipefd);

  // wait on last child
  waitpid(pid, nullptr, 0);

}

//creates the prompt, contains builtin logic, and calls the other two methods
int main()
{
  //user's input
  string line;

  //prompt logic
  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;
  }

  //looping prompt until user exits
  label:
  while(printf("1730sh:%s$ ", toPrint.c_str()) && getline(cin, line))
  {
    convert(line);


    //built in commands

    if(result[0] == nullptr)
    {
      goto label;
    }

    //exit
    string exit = "exit";
    if(strcmp(result[0],exit.c_str()) == 0)
    {
      //user just typed exit
      //return exit status of last executed process
      if(result[1] == nullptr)
      {
        return exitStatus;
      }
      //user typed exit and an exit status
      //return the exit status the user entered
      else
      {
        char * ep;
        return (int)strtol(result[1], &ep, 10);
      }
    }

    //help
    string help = "help";
    string cd = "cd";
    if(strcmp(result[0],help.c_str()) == 0)
    {
      //user typed just help
      //print info about all the builtin commands
      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;
      }
      //user typed help and a specific command
      //give info about that command
   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;
    }


    //cd
    if(strcmp(result[0],cd.c_str()) == 0)
    {
      //if just cd, return to home directory
      if(result[1] == nullptr)
      {
        chdir(getenv("HOME"));
      }
      //otherwise, change to target directory
      else
      {
        chdir(result[1]);
      }

      //changing prompt logic
      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 it wasn't a built in command, execute
    if(checkPipes(result))
    {
        executePipes(result);
    }
    else if(wasNotBuiltIn)
    {
      execute(result);
    }
    wasNotBuiltIn = true;


    //resetting the char array
    for(int i = 0; i < 100; i++)
    {
      result[i] = nullptr;
    }
  }

}