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add_action( 'init', 'my_script_enqueuer' );

function my_script_enqueuer() {
   wp_register_script( "my_voter_script", WP_PLUGIN_URL.'/my_plugin/my_voter_script.js', array('jquery') );
   wp_localize_script( 'my_voter_script', 'myAjax', array( 'ajaxurl' => admin_url( 'admin-ajax.php' )));        

   wp_enqueue_script( 'jquery' );
   wp_enqueue_script( 'my_voter_script' );

}


add_action("wp_ajax_my_user_vote", "my_user_vote");
add_action("wp_ajax_nopriv_my_user_vote", "my_must_login");

function my_user_vote() {

   if ( !wp_verify_nonce( $_REQUEST['nonce'], "my_user_vote_nonce")) {
      exit("No naughty business please");
   }   

   $vote_count = get_post_meta($_REQUEST["post_id"], "votes", true);
   $vote_count = ($vote_count == ’) ? 0 : $vote_count;
   $new_vote_count = $vote_count + 1;

   $vote = update_post_meta($_REQUEST["post_id"], "votes", $new_vote_count);

   if($vote === false) {
      $result['type'] = "error";
      $result['vote_count'] = $vote_count;
   }
   else {
      $result['type'] = "success";
      $result['vote_count'] = $new_vote_count;
   }

   if(!empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest') {
      $result = json_encode($result);
      echo $result;
   }
   else {
      header("Location: ".$_SERVER["HTTP_REFERER"]);
   }

   die();

}

function my_must_login() {
   echo "You must log in to vote";
   die();
}

jQuery(document).ready( function() {

   jQuery(".user_vote").click( function(e) {
      e.preventDefault(); 
      post_id = jQuery(this).attr("data-post_id")
      nonce = jQuery(this).attr("data-nonce")

      jQuery.ajax({
         type : "post",
         dataType : "json",
         url : myAjax.ajaxurl,
         data : {action: "my_user_vote", post_id : post_id, nonce: nonce},
         success: function(response) {
            if(response.type == "success") {
               jQuery("#vote_counter").html(response.vote_count)
            }
            else {
               alert("Your vote could not be added")
            }
         }
      })   

   })

})