Laravel generate Sequence number

public function generateCode(Request $request)

{

$year = date('y');

$SalesClosure = SalesClosure::orderBy('created_at', 'DESC')->withTrashed()->first();

if ($SalesClosure) {

$lastNumber = substr($SalesClosure->project_code, 6, 12);

$code = "GRG{$year}-" . str_pad($lastNumber + 1, 6, "0", STR_PAD_LEFT);

$isExist = SalesClosure::where('project_code', $code)->withTrashed()->first();

if ($isExist > 0) {

$lastNumber = substr($code, 6, 12);

$code = "GRG{$year}-" . str_pad($lastNumber + 1, 6, "0", STR_PAD_LEFT);

}

} else {

$code = "GRG{$year}-" . str_pad('100001', 6, "0", STR_PAD_LEFT);

}

return $code;

}