diff --git a/class/UserMgr.php b/class/UserMgr.php
new file mode 100644
index 0000000..e286b6d
--- /dev/null
+++ b/class/UserMgr.php
@@ -0,0 +1,221 @@
+<?php
+
+require_once "common_func.php";
+
+class User
+{
+    private int $id; // User's ID
+    private string $nickname; // User's nickname
+    private string $password; // User's password in it's encoded form or left empty
+    private string $realname; // User's real name displayed in their profile
+    private array $groups; // User's assigned groups
+    private string $privilege; // User's privilege
+    private UserMgr $userMgr; // UserManager object governing this object.
+
+    // -------------------------------------------
+
+    // Store modifications to the database.
+    private function storeMods(): void
+    {
+        $this->userMgr->updateUser($this);
+    }
+
+    // -------------------------------------------
+
+    function __construct(UserMgr &$usrmgr, int|array $id_serialized, string $nickname = null, string $password = null, string $realname = null, array $groups = null, string $privilege = null)
+    {
+        if (is_array($id_serialized)) {
+            $init = $id_serialized;
+            $this->id = $id_serialized["_id"] ?? "-1";
+            $this->nickname = $init["nickname"];
+            $this->password = $init["password"];
+            $this->realname = $init["realname"];
+            $this->groups = $init["groups"];
+            $this->privilege = $init["privilege"];
+        } else {
+            $this->id = $id_serialized;
+            $this->nickname = $nickname;
+            $this->password = $password;
+            $this->realname = $realname;
+            $this->groups = $groups;
+            $this->privilege = $privilege;
+        }
+
+        // save reference to user manager
+        $this->userMgr = &$usrmgr;
+    }
+
+    // Create user from an array
+    static function fromArray(UserMgr &$usrmgr, array $a): User
+    {
+        return new User($usrmgr, $a);
+    }
+
+    // Convert user to array
+    function toArray(array $omit = []): array
+    {
+        $a = [
+            "_id" => $this->id,
+            "nickname" => $this->nickname,
+            "password" => $this->password,
+            "realname" => $this->realname,
+            "groups" => $this->groups,
+            "privilege" => $this->privilege
+        ];
+
+        // omit specific fields
+        foreach ($omit as $field) {
+            unset($a[$field]);
+        }
+
+        return $a;
+    }
+
+    // Change user password. If $safe, then $old is checked.
+    function changePassword(string $new, string $old, bool $safe = true): bool
+    {
+        if (!$safe || password_verify($old, $this->password)) {
+            $this->password = password_hash($new, PASSWORD_DEFAULT);
+            $this->storeMods(); // store modifications
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    // Change user groups
+    function changeGroups(array $add, array $remove): void
+    {
+        alter_array_contents($this->groups, $add, $remove);
+        $this->storeMods(); // store modifications
+    }
+
+    // Get user's groups
+    function getGroups(): array
+    {
+        return $this->groups;
+    }
+
+    // Set user privilege level
+    function setPrivilege(string $privilege): void
+    {
+        $this->privilege = ($this->nickname === QUIZMASTER_NICKNAME) ? PRIVILEGE_QUIZMASTER : $privilege; // quizmaster's privilege mustn't be tampered with
+        $this->storeMods(); // store modifications
+    }
+
+    // Get user privilege level
+    function getPrivilege(): string
+    {
+        return $this->privilege;
+    }
+
+    // Get user's nickname.
+    function getNickname(): string
+    {
+        return $this->nickname;
+    }
+
+    // Set user's real name.
+    function setRealname(string $realname): void {
+        $this->realname = $realname;
+    }
+
+    // Get user's real name.
+    function getRealname(): string {
+        return $this->realname;
+    }
+
+    // Check against user credentials.
+    function checkPassword(string $password): bool
+    {
+        return password_verify($password, $this->password);
+    }
+}
+
+class UserMgr
+{
+    public \SleekDB\Store $db;
+
+    function __construct()
+    {
+        // create database
+        $this->db = new \SleekDB\Store(USERDB, DATADIR, ["timeout" => false]);
+    }
+
+    // Get user by nickname. Returns with a User object if found, null else.
+    function getUser(string $nickname): User|null
+    {
+        $user_data_array = $this->db->findBy(["nickname", "=", $nickname]);
+        return count($user_data_array) != 0 ? new User($this, $user_data_array[0]) : null;
+    }
+
+    // Update user.
+    function updateUser(User $user): void
+    {
+        $a = $user->toArray(); // convert to array
+        $this->db->update($a); // update using the extracted array
+    }
+
+    // checks if a nickname is taken
+    function isNicknameTaken(string $nickname): bool {
+        return !($this->db->findOneBy(["nickname", "=", $nickname]) == null);
+    }
+
+    // Add new user.
+    function addUser(string $nickname, string $password, string $realname, array $groupids = [], string $privilege = PRIVILEGE_PLAYER): bool
+    {
+        if ($this->isNicknameTaken($nickname)) { // user exists
+            return false;
+        }
+
+        $a = [
+            "nickname" => $nickname,
+            "password" => password_hash($password, PASSWORD_DEFAULT),
+            "realname" => $realname,
+            "groups" => $groupids,
+            "privilege" => $privilege
+        ];
+
+        // create user object
+        $user = new User($this, $a);
+
+        // add user to specific groups FIXME!!!!
+        foreach ($groupids as $groupid) {
+            change_group_user_assignments($groupid, $nickname, null);
+        }
+
+        $this->db->insert($user->toArray(["_id"]));
+
+        return true; // user registration successful
+    }
+
+    // Delete user from the storage
+    function deleteUser(string $nickname): void
+    {
+        // cannot delete quizmaster
+        if ($nickname == QUIZMASTER_NICKNAME) {
+            return;
+        }
+
+        $user = $this->getUser($nickname);
+        if ($user !== null) {
+            foreach ($user->getGroups() as $groupid) {
+                change_group_user_assignments($groupid, null, $nickname);
+            }
+            $this->db->deleteBy(["nickname", "=", $nickname]);
+        }
+    }
+
+    // Dump all users. Users come wrapped in User objects.
+    function getAllUsers(): array
+    {
+        return array_map(fn($a): User => new User($this, $a), $this->db->findAll());
+    }
+
+    // Get all nicknames.
+    function getAllNicknames(): array
+    {
+        $qb = $this->db->createQueryBuilder();
+        return array_map(fn($c): string => $c["nickname"], $qb->select(["nickname"])->getQuery()->fetch());
+    }
+}
\ No newline at end of file
diff --git a/install.php b/install.php
index 80b436d..20c089e 100644
--- a/install.php
+++ b/install.php
@@ -1,5 +1,7 @@
 <?php
 
+use Couchbase\UserManager;
+
 require_once "globals.php";
 
 # -dxdebug.default_enable=1 -dxdebug.remote_enable=1 -dxdebug.remote_autostart=1 -dxdebug.remote_port=9000 -dxdebug.remote_host=127.0.0.1 -dxdebug.idekey=PHPSTORM -dxdebug.mode=debug
@@ -16,10 +18,14 @@ require_once "usermgr.php";
 require_once "groupmgr.php";
 require_once "gamemgr.php";
 
+require_once "class/UserMgr.php";
+
 // create "quizmaster" (admin) user
 $pw = uniqid();
-add_user(QUIZMASTER_NICKNAME, $pw, "");
-change_privilege_level(QUIZMASTER_NICKNAME, PRIVILEGE_QUIZMASTER);
+$usrmgr = new UserMgr();
+$usrmgr->addUser(QUIZMASTER_NICKNAME, $pw, "");
+$qm = $usrmgr->getUser(QUIZMASTER_NICKNAME);
+$qm->setPrivilege(PRIVILEGE_QUIZMASTER);
 echo "Quizmaster account: quizmaster, $pw\n";
 
 // deploy install indicator
diff --git a/interface.php b/interface.php
index e691a5f..9341189 100644
--- a/interface.php
+++ b/interface.php
@@ -24,39 +24,47 @@ require_once "controller.php";
 
 require_once "class/ReqHandler.php";
 
-// ------------------------
-function patch_through_image(string $gameid, string $img_url)
-{
-    $game_dir = get_game_dir_by_gameid($gameid);
-    $image_fetch_url = $game_dir . DIRECTORY_SEPARATOR . $img_url;
-
-    $img_fp = fopen($image_fetch_url, "r");
-    if ($img_fp === false) {
-        $img_fp = fopen(MISSING_IMAGE_PLACEHOLDER, "r");
-    }
-    fpassthru($img_fp);
-    fclose($img_fp);
-}
+require_once "class/UserMgr.php";
 
 // ------------------------
 
-$action = $_REQUEST["action"];
+$userMgr = new UserMgr();
+
+// ------------------------
 
 $result = "";
 $success = false;
+
+// user-related variables
+$user = null;
+$nickname = "";
 $privilege = PRIVILEGE_NONE;
+$is_quizmaster = false;
+// --------
 
 // create request handler
 $rh = new ReqHandler();
 
+// action dump callback
+function dump_actions(ReqHandler &$rh, array $params): string {
+    return $rh->dump_actions();
+}
+
+$rh->add("dump_actions", [], PRIVILEGE_QUIZMASTER, "dump_actions", RESP_PLAIN, "Dump all registered actions.");
+
 /* ------------ ACTIONS AVAILABLE WITHOUT LOGGING IN ---------- */
 
 // login the user
 function login(ReqHandler &$rh, array $params): string
 {
+    global $userMgr;
+    global $user;
+
     $nickname = $params["nickname"];
     $password = $params["password"];
-    if (check_user_credentials($nickname, $password)) {
+
+    $user = $userMgr->getUser($nickname);
+    if (($user !== null) && $user->checkPassword($password)) {
         session_start();
         $_SESSION["nickname"] = $nickname;
         $result = "OK";
@@ -74,9 +82,9 @@ if ((session_status() != PHP_SESSION_ACTIVE) || (!isset($_SESSION["nickname"]))
     goto process_and_print;
 }
 
-$user_data = get_user($_SESSION["nickname"]);
-$nickname = $user_data["nickname"];
-$privilege = $user_data["privilege"];
+$user = $userMgr->getUser($_SESSION["nickname"]);
+$nickname = $user->getNickname();
+$privilege = $user->getPrivilege();
 $is_quizmaster = $privilege === PRIVILEGE_QUIZMASTER;
 
 /* ---------- ACTIONS REQUIRING BEING LOGGED IN ------------ */
@@ -90,17 +98,17 @@ function logout(ReqHandler &$rh, array $params): string
 
 function get_user_info(ReqHandler &$rh, array $params): array
 {
-    global $user_data;
-    $user_data_filtered = $user_data;
+    global $user;
+    $user_data_filtered = $user->toArray();
     unset($user_data_filtered["password"]);
     return $user_data_filtered;
 }
 
 function get_available_games(ReqHandler &$rh, array $params): array
 {
-    global $user_data;
+    global $user;
     $games_by_groups = [];
-    $groupids = $user_data["groups"];
+    $groupids = $user->getGroups();
     foreach ($groupids as $groupid) {
         $group_data = get_group($groupid);
         $game_collection = [
@@ -221,6 +229,19 @@ function submit_test(ReqHandler &$rh, array $params): string
     }
 }
 
+function patch_through_image(string $gameid, string $img_url)
+{
+    $game_dir = get_game_dir_by_gameid($gameid);
+    $image_fetch_url = $game_dir . DIRECTORY_SEPARATOR . $img_url;
+
+    $img_fp = fopen($image_fetch_url, "r");
+    if ($img_fp === false) {
+        $img_fp = fopen(MISSING_IMAGE_PLACEHOLDER, "r");
+    }
+    fpassthru($img_fp);
+    fclose($img_fp);
+}
+
 function get_image(ReqHandler &$rh, array $params): string
 {
     $img_url = trim($params["img_url"] ?? "");
@@ -248,6 +269,7 @@ $requester_nickname = $is_quizmaster ? "*" : $nickname; // "*" means every game
 
 function create_update_game(ReqHandler &$rh, array $params): array
 {
+    global $userMgr;
     global $nickname;
     global $is_quizmaster;
 
@@ -308,7 +330,8 @@ function create_update_game(ReqHandler &$rh, array $params): array
             if (($game_data["owner"] === $nickname) || $is_quizmaster) {
                 $game_data["owner"] = $owner;
             }
-            $game_data["contributors"] = array_intersect($contributors, get_all_nicknames());
+
+            $game_data["contributors"] = array_intersect($contributors, $usrMgr->getAllNicknames());
             $game_data["properties"]["time_limit"] = $properties["time_limit"];
             $game_data["properties"]["repeatable"] = $properties["repeatable"];
 
@@ -457,18 +480,15 @@ if ($privilege === PRIVILEGE_CREATOR) {
 
 function create_update_group(ReqHandler &$rh, array $params): string
 {
-    global $user_data;
+    global $user;
 
     $update = $params[ReqHandler::ACTION_KEY] === "update_group";
     $groupname = trim($params["groupname"]);
     $description = trim($params["description"]);
     $editors = (!$update) ? [] : explode_list(trim($params["editors"]));
-    $owner = (!$update) ? $user_data["nickname"] : trim($params["owner"]);
+    $owner = (!$update) ? $user->getNickname() : (trim($params["owner"]) ?: $user->getNickname());
 
     $result = "FAIL";
-    if ($owner === "") {
-        $owner = $user_data["nickname"];
-    }
     if ($groupname != "") {
         if (!$update) {
             create_group($groupname, $owner, $description);
@@ -511,6 +531,8 @@ function search_player_groups(ReqHandler &$rh, array $params): array
 
 function create_update_user(ReqHandler &$rh, array $params): string
 {
+    global $userMgr;
+
     $update = $params[ReqHandler::ACTION_KEY] === "update_user";
     $target_nickname = trim($params["nickname"]);
     $password = trim($params["password"]);
@@ -523,13 +545,13 @@ function create_update_user(ReqHandler &$rh, array $params): string
     $success = false;
     if (($target_nickname !== "")) {
         if ((!$update) && ($password !== "")) { // CREATE
-            $success = add_user($target_nickname, $password, $realname, $groupids, $privilege);
+            $success = $userMgr->addUser($target_nickname, $password, $realname, $groupids, $privilege);
         } else if ($update) { // UPDATE
-            $user_data = get_user($target_nickname); // load user data
-            if (count ($user_data) > 0) {
+            $tuser =  $userMgr->getUser($target_nickname); // load user data
+            if ($tuser !== null) {
 
                 // group management
-                $old_groupids = $user_data["groups"]; // retain old groupids
+                $old_groupids = $tuser->getGroups(); // retain old groupids
                 $new_groupids = $groupids; // get new groupids
                 $groupids_add = array_diff($new_groupids, $old_groupids); // groups this user needs to be added to
                 $groupids_remove = array_diff($old_groupids, $new_groupids); // groups this user need to be removed from
@@ -541,18 +563,18 @@ function create_update_user(ReqHandler &$rh, array $params): string
                 }
 
                 // re-fetch user
-                $user_data = get_user($target_nickname); // load user data
+                //$tuser = get_user($target_nickname); // load user data
 
                 // further field update
-                $user_data["realname"] = $realname;
-                $user_data["privilege"] = $privilege;
+                $tuser->setRealname($realname);
+                $tuser->setPrivilege($privilege);
 
                 // password replacement, if requested
                 if ($password !== "") {
-                    $user_data["password"] = password_hash($password, PASSWORD_DEFAULT);
+                    $tuser->changePassword(password_hash($password, PASSWORD_DEFAULT), "", false);
                 }
 
-                $success = update_user($user_data);
+                $success = true;
             }
         }
     }
@@ -561,18 +583,23 @@ function create_update_user(ReqHandler &$rh, array $params): string
 }
 
 function delete_users(ReqHandler &$rh, array $params): string {
-    $users = explode_list($params["users"]);
-    foreach ($users as $g) {
-        delete_user($g);
+    global $userMgr;
+    $nicknames = explode_list($params["users"]);
+    foreach ($nicknames as $nick) {
+        $userMgr->deleteUser($nick);
     }
     return "OK";
 }
 
 function get_all_game_users(ReqHandler &$rh, array $params): array {
-    $user_data_filtered = get_all_users();
-    for ($i = 0; $i < count($user_data_filtered); $i++) {
-        unset($user_data_filtered[$i]["password"]); // remove password from records
-        resolve_groupids($user_data_filtered[$i]["groups"]);  // resolve group IDs
+    global $userMgr;
+    $user_data_filtered = [];
+    $all_users = $userMgr->getAllUsers();
+    for ($i = 0; $i < count($all_users); $i++) {
+        $a = $all_users[$i]->toArray(); // convert user to array
+        unset($a["password"]); // remove password from records
+        resolve_groupids($a["groups"]);  // resolve group IDs
+        $user_data_filtered[] = $a;
     }
     return $user_data_filtered;
 }
@@ -595,11 +622,13 @@ $rh->add("delete_users", ["users"], PRIVILEGE_QUIZMASTER, "delete_users", RESP_P
 $rh->add("get_all_users", [], PRIVILEGE_QUIZMASTER, "get_all_game_users", RESP_JSON, "Get all users.");
 $rh->add("import_users_from_csv", [], PRIVILEGE_QUIZMASTER, "import_users_from_csv", RESP_JSON, "Get all users.");
 
-function dump_actions(ReqHandler &$rh, array $params): string {
-    return $rh->dump_actions();
+function test(ReqHandler &$rh, array $params): string {
+    $usrmgr = new UserMgr();
+    $nicknames = $usrmgr->getAllNicknames();
+    return join(", ", $nicknames);
 }
 
-$rh->add("dump_actions", [], PRIVILEGE_QUIZMASTER, "dump_actions", RESP_PLAIN, "Dump all registered actions.");
+$rh->add("test", [], PRIVILEGE_QUIZMASTER, "test", RESP_PLAIN, "Test.");
 
 // ----------
 
diff --git a/usermgr.php b/usermgr.php
index d0cd936..9d3fe54 100644
--- a/usermgr.php
+++ b/usermgr.php
@@ -12,42 +12,42 @@ const PRIVILEGE_PLAYER = "player";
 const PRIVILEGE_CREATOR = "creator";
 const PRIVILEGE_QUIZMASTER = "admin"; // TODO: refactor!
 
-function add_user(string $nickname, string $password, string $realname, array $groupids = [], string $privilege = PRIVILEGE_PLAYER): bool
-{
-    global $userdb;
-    if (count(get_user($nickname)) != 0) { // user exists
-        return false;
-    }
-
-    $user_data = [
-        "nickname" => $nickname,
-        "password" => password_hash($password, PASSWORD_DEFAULT),
-        "realname" => $realname,
-        "groups" => $groupids,
-        "privilege" => $privilege
-    ];
-    foreach ($groupids as $groupid) {
-        change_group_user_assignments($groupid, $nickname, null);
-    }
-    $userdb->insert($user_data);
-    return true; // user registration successful
-}
-
-function delete_user(string $nickname)
-{
-    global $userdb;
-    if ($nickname == QUIZMASTER_NICKNAME) {
-        return;
-    }
-
-    $user_data = get_user($nickname);
-    if (count($user_data) !== 0) {
-        foreach ($user_data["groups"] as $groupid) {
-            change_group_user_assignments($groupid, null, $nickname);
-        }
-        $userdb->deleteBy(["nickname", "=", $nickname]);
-    }
-}
+//function add_user(string $nickname, string $password, string $realname, array $groupids = [], string $privilege = PRIVILEGE_PLAYER): bool
+//{
+//    global $userdb;
+//    if (count(get_user($nickname)) != 0) { // user exists
+//        return false;
+//    }
+//
+//    $user_data = [
+//        "nickname" => $nickname,
+//        "password" => password_hash($password, PASSWORD_DEFAULT),
+//        "realname" => $realname,
+//        "groups" => $groupids,
+//        "privilege" => $privilege
+//    ];
+//    foreach ($groupids as $groupid) {
+//        change_group_user_assignments($groupid, $nickname, null);
+//    }
+//    $userdb->insert($user_data);
+//    return true; // user registration successful
+//}
+//
+//function delete_user(string $nickname)
+//{
+//    global $userdb;
+//    if ($nickname == QUIZMASTER_NICKNAME) {
+//        return;
+//    }
+//
+//    $user_data = get_user($nickname);
+//    if (count($user_data) !== 0) {
+//        foreach ($user_data["groups"] as $groupid) {
+//            change_group_user_assignments($groupid, null, $nickname);
+//        }
+//        $userdb->deleteBy(["nickname", "=", $nickname]);
+//    }
+//}
 
 function get_user(string $nickname): array
 {
@@ -62,18 +62,18 @@ function update_user(array $user_data)
     return $userdb->update($user_data);
 }
 
-function change_password(string $nickname, string $old, string $new): bool
-{
-    $user_data = get_user($nickname);
-    if (count($user_data) != 0) {
-        if (password_verify($old, $user_data["password"])) {
-            $user_data["password"] = password_hash($new, PASSWORD_DEFAULT);
-            update_user($user_data);
-            return true;
-        }
-    }
-    return false;
-}
+//function change_password(string $nickname, string $old, string $new): bool
+//{
+//    $user_data = get_user($nickname);
+//    if (count($user_data) != 0) {
+//        if (password_verify($old, $user_data["password"])) {
+//            $user_data["password"] = password_hash($new, PASSWORD_DEFAULT);
+//            update_user($user_data);
+//            return true;
+//        }
+//    }
+//    return false;
+//}
 
 function change_user_group_assignments(string $nickname, $groupname_add, $groupname_remove)
 {
@@ -84,36 +84,36 @@ function change_user_group_assignments(string $nickname, $groupname_add, $groupn
     }
 }
 
-function change_privilege_level(string $nickname, string $privilege)
-{
-    $user_data = get_user($nickname);
-    if (count($user_data) != 0) {
-        $user_data["privilege"] = $privilege;
-        update_user($user_data);
-    }
-}
-
-function check_user_credentials(string $nickname, string $password): bool
-{
-    $user_data = get_user($nickname);
-    if (count($user_data) != 0) {
-        return password_verify($password, $user_data["password"]);
-    } else {
-        return false;
-    }
-}
-
-function get_all_users(): array
-{
-    global $userdb;
-    return $userdb->findAll();
-}
-
-function get_all_nicknames() : array {
-    $nicknames = [];
-    $user_data_array = get_all_users();
-    foreach ($user_data_array as $user_data) {
-        $nicknames[] = $user_data["nickname"];
-    }
-    return $nicknames;
-}
\ No newline at end of file
+//function change_privilege_level(string $nickname, string $privilege)
+//{
+//    $user_data = get_user($nickname);
+//    if (count($user_data) != 0) {
+//        $user_data["privilege"] = $privilege;
+//        update_user($user_data);
+//    }
+//}
+//
+//function check_user_credentials(string $nickname, string $password): bool
+//{
+//    $user_data = get_user($nickname);
+//    if (count($user_data) != 0) {
+//        return password_verify($password, $user_data["password"]);
+//    } else {
+//        return false;
+//    }
+//}
+//
+//function get_all_users(): array
+//{
+//    global $userdb;
+//    return $userdb->findAll();
+//}
+//
+//function get_all_nicknames() : array {
+//    $nicknames = [];
+//    $user_data_array = get_all_users();
+//    foreach ($user_data_array as $user_data) {
+//        $nicknames[] = $user_data["nickname"];
+//    }
+//    return $nicknames;
+//}
\ No newline at end of file