Models.cs

using System;
using System.Collections.Generic;

using MongoDB.Bson;
using MongoDB.Driver;

namespace Travel.Modelling
{
    public sealed class Customer
    {
        public ObjectId Id { get; set; }

        public String FirstName { get; set; }

        public String LastName { get; set; }

        public String Email { get; set; }

        public DateTime BirthDate { get; set; }
    }

    public enum ProductType
    {
        Avia,
        Train,
        Hotel,
    }

    public sealed class Product
    {
        public ObjectId Id { get; set; }

        public ProductType ProductType { get; set; }

        public Single Price { get; set; }

        public String Details { get; set; }

        public List<MongoDBRef> Customers { get; set; }
    }

    public enum OrderStatus
    {
        Pending,
        Processing,
        PartiallyFinished,
        Finished,
        Failed,
    }

    public sealed class Order
    {
        public ObjectId Id { get; set; }

        public OrderStatus Status { get; set; }

        public List<MongoDBRef> Products { get; set; }
    }

    public interface ICustomerService
    {
        Customer AddCustomer(Customer customer);

        Customer UpdateCustomer(Customer customer);

        void DeleteCustomer(Customer customer);
    }

    public interface IProductService
    {
        Product FindProduct(ProductType type);
    }

    public interface IOrderService
    {
        Order CreateOrder(List<Product> products);

        Order AddProducts(ObjectId orderId, List<Product> products);

        Order RemoveProducts(ObjectId orderId, List<Product> products);

        void ProcessOrder(ObjectId orderId);

        void CancelOrder(ObjectId orderId);
    }

    public interface ITravelPlatform
    {
        ICustomerService CustomerService { get; set; }

        IProductService ProductService { get; set; }

        IOrderService OrderService { get; set; }
    }
}