type Privilege = "user" | "admin";
type UserPrivilege = {
  privilege: "user";
  login: () => void;
  logout: () => void;
};
type AdminPrivilege = {
  privilege: "admin";
  add: () => void;
  delete: () => void;
};
type AdminPanelUsers = {
  user: UserPrivilege;
  admin: AdminPrivilege;
};

function adminPanel<T extends Privilege>(
  privilege: T,
  user: AdminPanelUsers[T]
) {
  console.log(`${privilege} logined`);

  // Type safe.
  switch (user.privilege) {
    case "admin":
      user.add();
      break;
    case "user":
      user.login();
      break;
    default:
      throw new Error("Wrong type");
  }
}

const normalUser: UserPrivilege = {
  privilege: "user",
  login: () => {},
  logout: () => {}
};
const adminUser: AdminPrivilege = {
  privilege: "admin",
  add: () => {},
  delete: () => {}
};

adminPanel("admin", adminUser);
// Will be get error.
adminPanel("admin", normalUser);