protected function load()
    {
        $this->children = [];
        $this->rules = [];
        $this->assignments = [];
        $this->items = [];

        $items = $this->loadFromFile($this->itemFile);
        $itemsMtime = @filemtime($this->itemFile);
        $assignments = $this->loadFromFile($this->assignmentFile);
        $assignmentsMtime = @filemtime($this->assignmentFile);
        $rules = $this->loadFromFile($this->ruleFile);

        foreach ($items as $name => $item) {
            $class = $item['type'] == Item::TYPE_PERMISSION ? Permission::class : Role::class;

            $this->items[$name] = new $class([
                'name' => $name,
                'description' => isset($item['description']) ? $item['description'] : null,
                'ruleName' => isset($item['ruleName']) ? $item['ruleName'] : null,
                'data' => isset($item['data']) ? $item['data'] : null,
                'createdAt' => $itemsMtime,
                'updatedAt' => $itemsMtime,
            ]);
        }

        foreach ($items as $name => $item) {
            if (isset($item['children'])) {
                foreach ($item['children'] as $childName) {
                    if (isset($this->items[$childName])) {
                        $this->children[$name][$childName] = $this->items[$childName];
                    }
                }
            }
        }

        foreach ($assignments as $userId => $roles) {
            foreach ($roles as $role) {
                $this->assignments[$userId][$role] = new Assignment([
                    'userId' => $userId,
                    'roleName' => $role,
                    'createdAt' => $assignmentsMtime,
                ]);
            }
        }

        foreach ($rules as $name => $ruleData) {
            $this->rules[$name] = unserialize($ruleData);
        }
    }