<?php
  $data =& $_POST;
  if (!empty ($data)) {
    if (isset($data['date']) &&
        isset($data['price']) &&
        isset($data['gallons']) &&
        isset($data['odometer'])) {
      
      $file = 'data/lastodo';
      $lastodo = unserialize(file_get_contents($file));
    
      echo 'Added:'.
           'Date: ' . $data['date'] . ',' .   
           'Price: ' . $data['price'] . ',' .   
           'Gallons: ' . $data['gallons'] . ',' .   
           'Odometer: ' . $data['odometer']. ',' .
           'Miles = '.((int)$data['odometer'] - (int)$lastodo). '<br />';
      
      $lastodo = serialize($data['odometer']);
      file_put_contents($file, $lastodo);

    } else {
      echo "missing values\n";
    }
  } else {
      echo "empty form";
  }
?>
