An expiry timer, for Miley <3

miley.php

<?php

/*
 * Get, Set and Check Twerking time
 * -----------------------------------------------------------------------------
 * @param    string      $content            Post content.
 * @return   string      $content            Post content.
 */

function for_miley_cyrus($content) {
    // Relevant meta key.
    $meta_key = 'countdown_to_twerking';
    // In format readable by strtotime();
    $time_diff = '+30 days';
    // Post ID.
    $post_id = get_the_ID();
    // Retrieve meta value.
    $twerk_time = get_twerk_time($post_id, $meta_key); 
    
    if (!$twerk_time) {
        /* Set time if it hasn't already. You probably won't do this, but I
         * needed a hook to show how to do this. */
        add_post_meta($post_id, $meta_key, generate_twerk_time($post_id, '+30 days'), true);
        $twerk_time = get_twerk_time($post_id, $meta_key); 
    }

    if (is_it_twerk_time($twerk_time)) {
        // We all love Miley, right?
        printf('\o/ Come in like a wreckling ball! \o/');
    }

    // Content is passed through without being affected.
    return $content;
}

/*
 * Get Twerking Time
 * -----------------------------------------------------------------------------
 * @param   int     $post_id
 * @param   string  $meta_key
 * @return  string                         Post meta key value.
 */

function get_twerk_time($post_id, $meta_key) {
    return get_post_meta($post_id, $meta_key, true);
}

/*
 * Set Twerking Time
 * -----------------------------------------------------------------------------
 * @param   int     $post_id
 * @param   string  $difference          Absolute expiry date
 * @return  string                       Expiry time in Unix format, with absolute start point (publish date).
 */

function generate_twerk_time($post_id, $difference) {
    return strtotime($difference, get_the_date($post_id));
}

/*
 * Determine if it is Time to Twerk
 * -----------------------------------------------------------------------------
 * @param   int     $target_date        Date of post.
 * @return  bool                        Target time and date has passed, true or false.
 */

function is_it_twerk_time($target_date) {
    return ($target_date - date('U') <= 0);
}

/* This is a useful way to attach an action to a single post: Check whether the
 * deadline has passed when post content is loaded. You can attach it this action
 * anywhere else that might be useful. This is just an example! */
add_filter('the_content', 'for_miley_cyrus');

?>