#include <iostream>
#include <fstream>
#include <string>
#include <locale>

#define VERSION "1.0"
#define AUTHOR "Melvin Koopmans"

using namespace std;

string username;
string password;
string line;
int option;
char back;
char loginyn;

template < typename Iter >
void range_tolower ( Iter beg, Iter end ) {
for( Iter iter = beg; iter != end; ++iter ) {
*iter = tolower( *iter );
}
}

void string_tolower ( std::string & str ) {
range_tolower( str.begin(), str.end() );
}

int loginform()
{
    cout << "Login" << endl;
    cout << "Username: ";
    cin >> username;
    cout << "Password: ";
    cin >> password;
    string_tolower( username );
    ifstream datafile (username+".txt");
    if (datafile.is_open())
    {
    while (! datafile.eof() )
    {
      getline (datafile,line);
      if ( line == password )
      {
          cout << "Welcome " << username << "!" << endl;
      }
    }
    datafile.close();
    }
    else
    {
          cout << "Invalid login!" << endl;
    }
    return 0;
}

int registerform()
{
    cout << "Register" << endl;
    backregister:
    cout << "Username: ";
    cin >> username;
    cout << "Password: ";
    cin >> password;
    string_tolower( username );
    ofstream datafile;
    datafile.open (username+".txt");
    datafile << password;
    datafile.close();
    cout << "Registed Succesfuly!" << endl;
    loginynback:
    cout << "Login now[y/n]?: ";
    cin >> loginyn;

    if ( loginyn == 'y' )
    {
        loginform();
    }
    else if ( loginyn == 'n')
    {
    }

    else
    {
        cout << "Invalid option!" << endl;
        goto loginynback;
    }

    return 0;
}

int main()
{
    start:
    cout << "MyProgram " << VERSION << endl;
    cout << "1. Login" << endl;
    cout << "2. Register" << endl;
    cout << "3. Credits" << endl;
    cout << "4. Exit" << endl;
    cout << "Choose an option: ";
    cin >> option;

    if ( option == 1 )
    {
        loginform();
    }
    else if ( option == 2 )
    {
        registerform();
    }
    else if ( option == 3 )
    {
        cout << "Made by: Melvin Koopmans" << endl;
        cout << "Made in C++ " << endl;
        cout << " " << endl;
        back2:
        cout << "Back[y/n]?: ";
        cin >> back;

        if ( back == 'y' )
        {
            cout << " " << endl;
            goto start;
        }
        else if ( back == 'n' )
        {

        }
        else
        {
            cout << "Invalid option!" << endl;
            goto back2;
        }
    }

    else if ( option == 4 )
    {

    }
}