Booking train and hotel

booking.ts

book_train_and_hotel() : void {    // Needs 6 MANA.
    // 3 for train and callback and 3 for hotel and callback.
    // E.g. book_train and book_hotel doesn't need additional mana, so only 1 MANA for a call.
    // Callback may need 1 additional to cancel train or hotel booking if one of them failed.
    assert_has_mana(6); 
    
    let hotelBooking = bookHotel.withMana(3).withCoins(1000).book(sender());
    let trainBooking = bookTrain.withMana(3).withCoins(1000).book(sender());
    
    Promise.all(hotelBooking, trainBooking)
        .withMana(7)
            .catch(_bookingFailed.bind(sender(), /* whatever info about "session" needed */));
        .withMana(1)
            .then(_bookingCompleted.bind(sender(), /* whatever info about "session" needed */));
}

_bookingCompleted(client, /* session args */, hotel: HotelBookingResult, train: TrainBookingResult) {
    // This sends event to original caller
    client.onBookingCompleted(hotel, train);
}

_bookingFailed(client, /* session args */, errors: Array<Error>) {
    bookHotel.withMana(3).cancel(client);
    bookTrain.withMana(3).cancel(client);
    client.onBookingFailed(...);
}