implemented following users to receive (opt-in) email notifications when they publish an article.

functions/account_functions.php

@@ -4,6 +4,16 @@ require_once 'article_functions.php';
 
 use Postmark\PostmarkClient;
 
+function follow_user($follower_user_id, $following_user_id, $notify)
+{
+    exec_stmt('INSERT INTO follows (follower_user_id, following_user_id, notify_user) VALUES (?, ?, ?)', 'iii', $follower_user_id, $following_user_id, $notify);
+}
+
+function unfollow_user($follower_user_id, $following_user_id)
+{
+    exec_stmt('DELETE FROM follows WHERE follower_user_id = ? AND following_user_id = ?', 'ii', $follower_user_id, $following_user_id);
+}
+
 function user_id_exists($user_id)
 {
     $result = exec_stmt('SELECT user_id FROM user WHERE user_id = ?', 'i', $user_id)->fetch_assoc();