FluentOrderBuilder.cs

using System;
using System.Collections.Generic;

namespace Fluent
{
    public class OrderBuilder
    {
        private readonly Order _order;
        private OrderLine _currentLine;
        private int _currentLineNumber;
       
        public OrderBuilder()
        {
            _currentLineNumber = 0;
            _order = new Order
            {
                Lines = new List<OrderLine>(),
                BillingContact = new OrderContact(),
            };
        }

        public OrderBuilder AddLine(string description, int quantity, decimal unitPrice)
        {
            return WithLine(description, quantity, unitPrice);
        }

        public OrderBuilder AndLine(string description, int quantity, decimal unitPrice)
        {
            return WithLine(description, quantity, unitPrice);
        }

        private OrderBuilder WithLine(string description, int quantity, decimal unitPrice)
        {
            _currentLineNumber++;
            var toAdd = new OrderLine
            {
                Number = _currentLineNumber,
                Description = description,
                ExtendedPrice = quantity*unitPrice,
                Quantity = quantity,
                UnitPrice = unitPrice,
                AddOns = new List<OrderLineAddOn>()
            };

            _order.Lines.Add(toAdd);
            _currentLine = toAdd;

            return this;
        }

        public OrderBuilder WithAddOn(string description, int quantity, decimal unitPrice)
        {
            var toAdd = new OrderLineAddOn
            {
                Description = description,
                Quantity = quantity,
                UnitPrice = unitPrice,
                ExtendedPrice = quantity*unitPrice
            };

            _currentLine.AddOns.Add(toAdd);

            return this;
        }

        public OrderBuilder WithOrderCode(string value)
        {
            _order.Code = value;
            return this;
        }

        public OrderBuilder WithBillingContact(Action<OrderContactBuilder> contact)
        {
            var builder = new OrderContactBuilder();
            contact(builder);
            _order.BillingContact = builder.Build();
            
            return this;
        }

        public OrderBuilder WithShippingContact(Action<OrderContactBuilder> contact)
        {
            var builder = new OrderContactBuilder();
            contact(builder);
            _order.ShippingContact = builder.Build();

            return this;
        }

        public Order Build()
        {
            return _order;
        }
    }

    public class OrderContactBuilder
    {
        private readonly OrderContact _contact;
        public OrderContactBuilder()
        {
            _contact = new OrderContact();
        }

        public OrderContactBuilder FirstName(string value)
        {
            _contact.FirstName = value;
            return this;
        }

        public OrderContactBuilder LastName(string value)
        {
            _contact.LastName = value;
            return this;
        }

        public OrderContactBuilder Address1(string value)
        {
            _contact.Address1 = value;
            return this;
        }

        public OrderContactBuilder Address2(string value)
        {
            _contact.Address2 = value;
            return this;
        }

        public OrderContactBuilder City(string value)
        {
            _contact.City = value;
            return this;
        }

        public OrderContactBuilder State(string value)
        {
            _contact.State = value;
            return this;
        }

        public OrderContactBuilder ZipCode(string value)
        {
            _contact.ZipCode = value;
            return this;
        }

        public OrderContactBuilder PhoneNumber(string value)
        {
            _contact.PhoneNumber = value;
            return this;
        }

        public OrderContact Build()
        {
            return _contact;
        }
    }
    
    public class Order
    {
        public string Code { get; set; }

        public OrderContact BillingContact { get; set; }
        public OrderContact ShippingContact { get; set; }

        public IList<OrderLine> Lines { get; set; }
    }

    public class OrderLine
    {
        public int Number { get; set; }
        public string Description { get; set; }
        public int Quantity { get; set; }
        public decimal UnitPrice { get; set; }
        public decimal ExtendedPrice { get; set; }

        public IList<OrderLineAddOn> AddOns { get; set; }
    }

    public class OrderLineAddOn
    {
        public string Description { get; set; }
        public int Quantity { get; set; }
        public decimal UnitPrice { get; set; }
        public decimal ExtendedPrice { get; set; }
    }

    public class OrderContact
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Address1 { get; set; }
        public string Address2 { get; set; }
        public string City { get; set; }
        public string State { get; set; }
        public string ZipCode { get; set; }
        public string PhoneNumber { get; set; }
    }
}