#!/usr/bin/perl

use strict;
use warnings;
use CGI::Carp qw(fatalsToBrowser);
use CGI qw(:standard);
use DBD::mysql;
use POSIX qw(strftime);

my @param_errors = ();

my $dbh = DBI->connect('DBI:mysql:nikos_db', 'root', 'password', {RaiseError=>1});

if ( param( 'Σύνδεση' )) {  # user hit the "login" button
    # check that username, password and email are filled in,
    # query database to see if these values are okay ...

    # if login is okay, redirect and exit
    # otherwise, push an error message onto @param_errors
}

elsif ( param( 'Εγγραφή' )) {  # user hit "new user" button
    # check whether all necessary params are present,
    # query database to see if user-supplied username has been used ...

    # if okay, insert new user record into database, redirect and exit
    # otherwise, push error message(s) onto @param_errors
}

# get here if there was no redirection -- that is, just one of
# the following is true for this run of the script:

#  -- user came directly to the login page (no params were set), or
#  -- user hit the "login" submit button, but login fields were invalid, or
#  -- user hit the "new user" submit button, but params were incomplete or
#      username was already in use

print header(...);
print start_html(...);

if ( @param_errors ) {
    # show error message(s)
}
# print the form...