Prevent HoO user from downgrading their usergroup if they're the only HoO

Author: pylipp

include/cms_users_edit.php

@@ -74,10 +74,34 @@
             WHERE ug.id = :id AND (NOT ug.deleted OR ug.deleted IS NULL)', ['id' => $_POST['cms_usergroups_id'][0]]);
         $is_admin = $_SESSION['user']['is_admin'];
         $organisation_allowed = ($_SESSION['organisation']['id'] == $posteduser['organisation_id']);
-        // allow admins to create another admin account
+        // allow HoO to create another HoO account
         // related to this trello card https://trello.com/c/YAF3Az4P
         $userlevel_allowed = ($_SESSION['usergroup']['userlevel'] > $posteduser['userlevel']) || ($_SESSION['usergroup']['userlevel'] == $posteduser['userlevel'] && '100' == $_SESSION['usergroup']['userlevel']);
 
+        // Prevent HoO user from downgrading their usergroup if they're the only HoO
+        if (!$is_admin && $_POST['id'] == $_SESSION['user']['id'] && 100 == $_SESSION['usergroup']['userlevel'] && $posteduser['userlevel'] < $_SESSION['usergroup']['userlevel']) {
+            // Count how many HoO users exist in this organization
+            $hoo_count = db_value(
+                '
+                SELECT COUNT(DISTINCT u.id)
+                FROM cms_users AS u
+                LEFT JOIN cms_usergroups AS ug ON ug.id = u.cms_usergroups_id
+                LEFT JOIN cms_usergroups_levels AS ugl ON ugl.id = ug.userlevel
+                WHERE ug.organisation_id = :org_id
+                    AND ugl.level = :highest_level
+                    AND (NOT u.deleted OR u.deleted IS NULL)
+                    AND (NOT ug.deleted OR ug.deleted IS NULL)
+                    AND (NOT u.valid_lastday < CURDATE() OR UNIX_TIMESTAMP(u.valid_lastday) = 0)',
+                ['org_id' => $_SESSION['organisation']['id'], 'highest_level' => $highest_level]
+            );
+
+            // If this is the last HoO, prevent the change
+            if ($hoo_count <= 1) {
+                redirect('?action=cms_users_edit&id='.$_POST['id'].'&origin='.$_POST['_origin'].'&warning=1&message=You cannot downgrade yourself. Your organisation must have at least one Head of Operations user.');
+                trigger_error('You cannot downgrade yourself. Your organisation must have at least one Head of Operations user.', E_USER_NOTICE);
+            }
+        }
+
         if ($is_admin || ($organisation_allowed && $userlevel_allowed)) {
             $keys = ['naam', 'email', 'cms_usergroups_id', 'valid_firstday', 'valid_lastday'];
             $userId = db_transaction(function () use ($table, $keys, $userId) {