Get Post ID within wp_set_comment_status hook

You should consider removing the average_ratingfn() function definition out of there and call it with an input argument for the post ID.

You can try to fetch the comment object with (untested):

$comment = get_comment( $comment_ID );

and then make sure it’s not null or you have an actual comment object with:

if( $comment instanceof \WP_Comment )
    $post_id = $comment->comment_post_ID;

You should be able to get the comment_post_ID field from that object.

I think you could also use the hooks within the wp_transition_comment_status() function, where the comment object is among the input arguments.

For example the hooks:

• comment_{$new_status}_{$comment->comment_type}

• comment_{$old_status}_to_{$new_status}

• transition_comment_status