How do I redirect a permalink for a Draft post to a custom 404 page?

Question

My users create posts with links to future posts which are in Draft status. We use Post Name as our permalink structure.

Eg.

 <a href="/future-draft-post">Here is our next fantastic post coming next week!</a>

Since they are logged in, our users click the links and are then redirected to the Drafts for editing. And as normal, when non-logged-in users click those links they get a nasty 404.

What I want is for non-logged-in users to click such links and be redirected to a custom page that says 'Coming Soon!'

How do I do that?

Two other optional features we would like.

1. Ideally, I would like to pass the scheduled publish date to the 'Coming Soon Page! (eg. 'Coming July 10, 2016!)

2. I would only like this behaviour for a certain category of posts. Other posts should redirect to a 404 as per usual.

So in addition to checking the status of the post we need a way to check the category and the publish date of the post in deciding whether to 404 or go to the custom page.

Answer 1

Here is what I came up with. Seems to be working. If anyone has suggestions for improvement, I'm all ears:

// Redirect links to future posts to Coming Soon page.
add_action('wp','redirect_coming_soon_posts', 0);
function redirect_coming_soon_posts(){
  global $wpdb; 
  if ($wpdb->last_result[0]->post_status == "future" &&
    $wpdb->last_result[0]->post_date_gmt != '0000-00-00 00:00:00' && 
    ! is_admin()  ):
      session_start();

     $_SESSION['next_post_id'] = $wpdb->last_result[0]->ID;         
     wp_redirect( '/coming-soon', 301 );
    exit();
   endif;
  }

function sess_start() {
  if (!session_id()) {
    session_start();
    }
 }
 add_action('init','sess_start');