#!/usr/bin/perl

use CGI;
use DBI;
use Digest::MD5 qw(md5 md5_hex md5_base64);

$DB = "dbi:mysql:demoOne:silo.cs.indiana.edu:port=16248";
$username = "dgerman"; $password = "sp00n";
$DB_TABLE = "aaron";

$SECRET = "something secret";
$EXPIRE = 30 * 24 * 3600; # one month
$MAX_TRIES = 10; 
$ID_LENGTH = 8; 

$q = new CGI;

# Open the database --------------------------------------------------------
$DBH = DBI->connect($DB, $username, $password, {PrintError => 0}) || die "Couldn't open database: ", $DBI::errstr; 

# get the current session ID, or make one ----------------------------------
my ($session_id, $note) = &get_session_id(); 

# retrieve the state -------------------------------------------------------
my $state = &get_state($session_id) unless $q->param('clear'); 

$message  = $state->{'message'};
$n1       = $state->{'n1'};
$n2       = $state->{'n2'};
$n3       = $state->{'n3'};
$user     = $state->{'user'};
$comp     = $state->{'comp'};
$turn     = $state->{'turn'};

$n1 = int(rand(100)) - 50;
$n2 = int(rand(100)) - 50;
$n3 = int(rand(100)) - 50;
      
if ($message) {  
  $message = "The score currently is $user - $comp.";  
  $turn = "computer";
} else {
  $user = 0;
  $comp = 0;
  $message = "Welcome, the score is $user - $comp. ";
  $turn = "computer";         
}

$state->{'message'}  = $message;
$state->{'n1'}       = $n1;
$state->{'n2'}       = $n2;
$state->{'n3'}       = $n3;
$state->{'user'}     = $user;
$state->{'comp'}     = $comp;
$state->{'turn'}     = $turn;

# save the modified state --------------------------------------------------
&save_state($state, $session_id); 

# start the page -----------------------------------------------------------
print $q->header, 
      $q->start_html(-title => 'Database Sessions with URL Rewriting',
                     -bgcolor => 'white'); 

print qq{<form method=POST action="/cgi-bin/aaron/two/$session_id"> 

  Your draw: <p> 
  <table border cellpadding=6>
    <tr><td> <font size=+3> $n1 </font> 
        <td> <font size=+3> $n2 </font> 
        <td> <font size=+3> $n3 </font> 
    <tr><td><input type=checkbox name=one> keep 
        <td><input type=checkbox name=two> keep 
        <td><input type=checkbox name=three> keep   
  </table> <p> 
  $message <p> 

  <input type="hidden" name="message" value="$message"> 
  <input type="hidden" name="n1"      value="$n1"> 
  <input type="hidden" name="n2"      value="$n2"> 
  <input type="hidden" name="n3"      value="$n3"> 
  <input type="hidden" name="turn"    value="$turn"> 
  <input type="hidden" name="user"    value="$user"> 
  <input type="hidden" name="comp"    value="$comp"> 

  Press <input type="submit" value="Proceed"> when you're ready to move on. 
</form> }; 

print $q->end_html; 

$DBH->disconnect; 

# save the state in the database ------------------------------save_state---
sub save_state {
  my ($state, $id) = @_; 
  my $sth = $DBH->prepare(<<END) || die "prepare: ", $DBH->errstr;
UPDATE $DB_TABLE
  SET message=?,n1=?,n2=?,n3=?,user=?,comp=?,turn=?
  WHERE session_id='$id'
END
  $sth->execute(@{$state}{qw(message n1 n2 n3 user comp turn)})
    || die "execute: ", $DBH->errstr;
  $sth->finish; 
} 

# get the state from the database ------------------------------get_state---
sub get_state {
  my $id = shift;  
  my $query = 
      "SELECT * FROM $DB_TABLE WHERE session_id = '$id'"; 
  my $sth = $DBH->prepare($query) || die "Prepare: ", $DBH->errstr;
  $sth->execute || die "Execute: ", $sth->errstr; 
  my $state = $sth->fetchrow_hashref; 
  $sth->finish; 
  return $state; 
}

# retrieve the session ID from the path info. if it's -----get_session_id---
# not already there, add it to the path info (more or less) with a redirect 
sub get_session_id {

  my (@result); 
  &expire_old_sessions(); 
  my ($id) = $q->path_info() =~ m:^/([a-h0-9]{$ID_LENGTH}):o;
  return @result if $id and @result = &check_id($id); 
  
  # if we get here, there's not already an ID in the path info 
  my $session_id = &generate_id(); 
  die "Couldn't make a new session id" unless $session_id; 
  print $q->redirect($q->script_name() . "/$session_id"); 
  exit 0; 
}

# find a new unique ID and insert it into the database -------generate_id---
sub generate_id {
  # create a new session id 
  my $tries = 0; 
  my $id = &hash($SECRET . rand()); 

  while ($tries++ < $MAX_TRIES) {
    last if $DBH->do("INSERT INTO $DB_TABLE (session_id) VALUES ('$id')"); 
    $id = &hash($id); 
  }

  return undef if $tries >= $MAX_TRIES; # we failed 
  return $id; 
}

# check to see that an old ID is valid --------------------------check_id---
sub check_id {

  my $id = shift; 

  return ($id, '') 

    if $DBH->do("SELECT 1 FROM $DB_TABLE WHERE session_id = '$id'") > 0; 

  return ($id, 'The record of your game may have expired. Restarting.')

    if $DBH->do("INSERT INTO $DB_TABLE (session_id) VALUES ('$id')"); 

  return (); 

}

# generate a hash value ---------------------------------------------hash---
sub hash {
  my $value = shift; 
  return substr(md5_hex($value), 0, $ID_LENGTH); 
}

sub expire_old_sessions { # --------------------------expire_old_sessions---
  $DBH->do(<<END); 
DELETE FROM $DB_TABLE
  WHERE (unix_timestamp() - unix_timestamp(modified)) > $EXPIRE
END
}