What filters to call to modify the output of the entire page?

Question

I want to write a simple plugin. For every time a page is viewed, it will write to the MySQL database. Then, if the current hour is odd, it will set a PHP variable of $is_odd to true;

<?php
  require_once('library-of-functions-to-support-this-plugin.php');
  function_to_write_to_mysql_db();
  $is_odd = false;
  if(current_hour_odd()) {
    $is_odd=true;
  }
  $is_odd_json = json_encode($is_odd);
?>

Then, it should embed the following JavaScript (note: I've already modified the theme's templates to put an on each page):

<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript">
   var odd = <?php echo $is_odd_json; ?>;
   if(odd) {
      $("#OddElement").html('Odd!');
   }
</script>

So basically, I have no idea where to put these code snippets. What filters do I want to apply? I know this plugin seems stupid, but it's laying the groundwork for something else I want to do.

Thanks so much!

Answer 1

You could attach the to wp_head action http://codex.wordpress.org/Plugin_API/Action_Reference/wp_head