Wordpress - Backdate scheduled posts

gistfile1.txt

//  Adds a meta box to the post editing screen for changing the post's publication
//  date and time after it has initially been published.
//  Only visible to administrators.
//  Place in functions.php file.

function cdap_add_meta_box() {
    // Check if the current user is an administrator
    if (current_user_can('administrator')) {
        add_meta_box(
            'cdap_meta_box',             // ID of the meta box
            'Backdate Scheduled Posts',  // Title of the meta box
            'cdap_meta_box_callback',    // Callback function
            'post',                      // Post type
            'side'                       // Context
        );
    }
}
add_action('add_meta_boxes', 'cdap_add_meta_box');

//  Outputs the HTML for the meta box.
function cdap_meta_box_callback($post) {
    // Add a nonce field so we can check for it later.
    wp_nonce_field('cdap_save_meta_box_data', 'cdap_meta_box_nonce');

    // Get the current value, if there is one.
    $value = get_post_meta($post->ID, '_cdap_new_date', true);

    // Output the datetime-local field
    echo '<label for="cdap_new_date">New Publication Date and Time:</label> ';
    echo '<input type="datetime-local" id="cdap_new_date" name="cdap_new_date" value="' . esc_attr($value ? date('Y-m-d\TH:i', strtotime($value)) : '') . '" style="width: 100%;">';
}

//  Saves the custom date and time selected in the meta box.
function cdap_save_meta_box_data($post_id) {
    // Check if our nonce is set.
    if (!isset($_POST['cdap_meta_box_nonce'])) {
        return;
    }

    // Verify that the nonce is valid.
    if (!wp_verify_nonce($_POST['cdap_meta_box_nonce'], 'cdap_save_meta_box_data')) {
        return;
    }

    // If this is an autosave, our form has not been submitted, so we don't want to do anything.
    if (defined('DOING_AUTOSAVE') && DOING_AUTOSAVE) {
        return;
    }

    // Check the user's permissions.
    if (isset($_POST['post_type']) && 'page' === $_POST['post_type']) {
        if (!current_user_can('edit_page', $post_id)) {
            return;
        }
    } else {
        if (!current_user_can('edit_post', $post_id)) {
            return;
        }
    }

    // Make sure that it is set.
    if (isset($_POST['cdap_new_date'])) {
        // Update the meta field in the database.
        update_post_meta($post_id, '_cdap_new_date', sanitize_text_field($_POST['cdap_new_date']));
    }
}
add_action('save_post', 'cdap_save_meta_box_data');


//  Updates the post's publish date and time after it is published, based on the
//  selected date and time in the meta box.

function cdap_update_post_date($new_status, $old_status, $post) {
    if ('publish' === $new_status && 'publish' !== $old_status && $new_date = get_post_meta($post->ID, '_cdap_new_date', true)) {
        // Check if the new date is set and valid
        if (!empty($new_date)) {
            $postarr = array(
                'ID' => $post->ID,
                'post_date' => $new_date,
                'post_date_gmt' => get_gmt_from_date($new_date)
            );
            // Update the post
            wp_update_post($postarr);
        }
    }
}
add_action('transition_post_status', 'cdap_update_post_date', 10, 3);