FastSpring/Xero integration

InvoiceBuilder.cs

// This class takes the records from FastSpring and turns them into a Xero invoice for saving

using System;
using System.Collections.Generic;
using System.Linq;
using XeroApi.Model;
using XeroFastSpring.FastSpring;

namespace XeroFastSpring.Xero
{
    public class InvoiceBuilder
    {
        private readonly DateTime month;
        private readonly decimal total;
        private readonly TaxRate gstFreeExports;
        private readonly TaxRate gstExempt;
        readonly Invoice invoice = new Invoice();

        public InvoiceBuilder(DateTime month, Contact contact, decimal total, List<TaxRate> tax)
        {
            var startOfMonth = new DateTime(month.Year, month.Month, 1);
            var endOfMonth = new DateTime(month.Year, month.Month, DateTime.DaysInMonth(month.Year, month.Month));

            this.month = month;
            this.total = total;
            gstFreeExports = tax.Single(t => t.Name == "BAS Excluded");
            gstExempt = tax.Single(t => t.Name == "BAS Excluded");
            invoice.CurrencyCode = "USD";
            invoice.Reference = "Sales for " + startOfMonth.ToString("MMMM yyyy");
            invoice.SentToContact = true;
            invoice.Date = endOfMonth;
            invoice.Type = "ACCREC";
            invoice.DueDate = FastSpringRules.GetAnticipatedPaymentDate(endOfMonth);
            invoice.LineItems = new LineItems();
            invoice.Contact = contact;
            invoice.TotalTax = 0;
            invoice.LineAmountTypes = LineAmountType.Inclusive;
            invoice.InvoiceNumber = "FS-" + month.Year + "/" + month.Month;
        }

        public InvoiceBuilder AddLines(IEnumerable<FastSpringSalesRecord> records)
        {
            var ordered =
                from record in records
                orderby record.Description descending
                where record.Units > 0
                group record by record.Description into g
                select g;

            var sales = new List<LineItem>();
            var fees = new List<LineItem>();

            foreach (var grouped in ordered)
            {
                var totalIncome = grouped.Sum(t => t.Income);
                var totalExpense = grouped.Sum(t => t.Expense);
                var units = grouped.Sum(t => t.Units);

                sales.Add(new LineItem
                {
                    AccountCode = "201", // Octopus Sales
                    ItemCode = Configuration.ProductMapping[grouped.Key],
                    Description = grouped.Key,
                    Quantity = units,
                    TaxAmount = 0,
                    UnitAmount = Round((totalIncome / units)),
                    TaxType = gstFreeExports.TaxType
                });

                fees.Add(new LineItem
                {
                    AccountCode = "403", // FastSpring Fees
                    ItemCode = "FastSpring Fees",
                    Description = "Fees: " + grouped.Key,
                    Quantity = units,
                    TaxAmount = 0,
                    UnitAmount = -Round((totalExpense / units)),
                    TaxType = gstExempt.TaxType
                });
            }

            invoice.LineItems.AddRange(sales);
            invoice.LineItems.AddRange(fees);

            return this;
        }

        public Invoice Build()
        {
            var totalOnInvoice = Round(invoice.LineItems.Sum(i => (i.UnitAmount ?? 0M) * (i.Quantity ?? 0)));
            var totalExpected = Round(total);
            var correction = totalOnInvoice - totalExpected;

            invoice.LineItems.Add(new LineItem
            {
                AccountCode = "403", // FastSpring Fees
                ItemCode = "FastSpring Fees",
                Description = "Rounding correction",
                Quantity = 1,
                TaxAmount = 0,
                UnitAmount = -correction,
                TaxType = gstExempt.TaxType
            });

            return invoice;
        }

        decimal Round(decimal? value)
        {
            return decimal.Round(value ?? 0M, 2);
        }
    }
}