bnhtrade/src/bnhtrade.Core/Logic/Account/CurrencyService.cs

using bnhtrade.Core.Data.Database.UnitOfWork;
using FikaAmazonAPI.AmazonSpApiSDK.Models.FulfillmentInbound;
using FikaAmazonAPI.ConstructFeed.Messages;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Data.SqlClient;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Xml.Linq;
using static bnhtrade.Core.Model.Account.PurchaseInvoice;

namespace bnhtrade.Core.Logic.Account
{
    public class CurrencyService
    {
        private readonly IUnitOfWork _providedUnitOfWork = null;
        private readonly bool _ownsUnitOfWork = false;
        private List<Model.Account.CurrencyExchangeRate> _exchangeRateList = new List<Model.Account.CurrencyExchangeRate>();

        Log.LogEvent _log = new Log.LogEvent();

        public string ErrorMessage { get; private set; } = null;

        public bool ErrorMessageIsSet
        {
            get
            {
                return !string.IsNullOrEmpty(ErrorMessage);
            }
        }

        public CurrencyService()
        {
            _ownsUnitOfWork = true;
        }

        internal CurrencyService(IUnitOfWork unitOfWork)
        {
            _providedUnitOfWork = unitOfWork ?? throw new ArgumentNullException(nameof(unitOfWork));
            _ownsUnitOfWork = false;
        }

        private void Init()
        {
            ErrorMessage = null;
        }

        public bool ConvertInvoiceToGbp(Model.Account.IInvoice invoice)
        {
            Init();

            //checks
            if (invoice == null)
            {
                ErrorMessage = "Invoice cannot be null";
                return false;
            }
            if (invoice.InvoiceCurrencyCode == Model.Account.CurrencyCode.GBP)
            {
                return true; // no conversion needed
            }
            if (invoice.InvoiceDate == null)
            {
                ErrorMessage = "Invoice date cannot be null";
                return false;
            }

            //validate the invoice
            var validate = new Logic.Validate.Invoice();
            // Fix for CS1503: Cast 'invoice' to 'Model.Account.Invoice' explicitly
            if (validate.IsValidExportInvoice(new List<Model.Account.Invoice> { (Model.Account.Invoice)invoice }) == false)
            {
                ErrorMessage = "Invoice failed validation. See logs for further details.";
                _log.LogError(ErrorMessage);
                return false;
            }

            // check if exchange rate is already in list
            Model.Account.CurrencyExchangeRate existingRate = null;
            foreach (var exchangeRate in _exchangeRateList)
            {
                if (exchangeRate.CurrencyCode == invoice.InvoiceCurrencyCode && exchangeRate.DateTimeWithinPeriodCheck(invoice.InvoiceDate.Value))
                {
                    existingRate = exchangeRate;
                    break;
                }
            }

            // get rates from db and add to field list if not in list already
            var rateList = GetExchangeRateObjectList(
                new List<Model.Account.CurrencyCode> { invoice.InvoiceCurrencyCode }, invoice.InvoiceDate.Value);

            if (rateList == null || rateList.Count == 0)
            {
                ErrorMessage =
                    "Exchange rate for currency code '" + invoice.InvoiceCurrencyCode + "' and date " + invoice.InvoiceDate.Value.ToShortDateString() + "' does not exist in the Exchange Rate table";
                return false;
            }

            _exchangeRateList.AddRange(rateList);
            existingRate = rateList[0];

            // do the conversion
            // convert header information 
            decimal invoiceOriginalTotalAmount = invoice.InvoiceTotalAmount.Value;
            invoice.InvoiceTotalAmount = existingRate.ConvertToGbp(invoice.InvoiceTotalAmount.Value);
            invoice.InvoiceCurrencyCode = Model.Account.CurrencyCode.GBP;

            // convert line items
            var lineWeighting = new List<(int, decimal)>();
            var lineCalculatedTotalByWeighting = new List<(int, decimal)>();
            decimal convertedLineListSum = 0;
            int i = 0;
            foreach (var line in invoice.InvoiceLineList)
            {
                decimal weighting = line.LineTotalAmount / invoiceOriginalTotalAmount;
                decimal lineConvertedTotal = existingRate.ConvertToGbp(invoiceOriginalTotalAmount * weighting);
                lineWeighting.Add(new(i, weighting));
                lineCalculatedTotalByWeighting.Add(new(i, lineConvertedTotal));

                // edit line
                if (line.TaxAmountAdjust != 0)
                {
                    line.TaxAmountAdjust = existingRate.ConvertToGbp(line.TaxAmountAdjust);
                }
                line.UnitAmount = null;
                line.SetUnitAmountByLineTotal(decimal.Round(lineConvertedTotal, 2));
                convertedLineListSum += line.LineTotalAmount;

                i++;
            }

            // there may be rounding errors
            // section untested - may have to fix some bugs in here when I've got some invoice to test on
            if (invoice.InvoiceTotalAmount != convertedLineListSum)
            {
                decimal amountRemainingToDistribute = invoice.InvoiceTotalAmount.Value - convertedLineListSum;
                lineWeighting = lineWeighting.OrderByDescending(i => i.Item2).ToList();

                foreach (var line in lineWeighting)
                {
                    // distribute the amount remaining to the lines
                    decimal amountToDistribute = amountRemainingToDistribute * line.Item2;
                    if (amountToDistribute > 0 && amountToDistribute < 0.01m)
                    {
                        amountToDistribute = 0.01m; // minimum amount to distribute
                    }
                    else if (amountToDistribute < 0 && amountToDistribute > -0.01m)
                    {
                        amountToDistribute = -0.01m; // minimum amount to distribute
                    }
                    else
                    {
                        amountToDistribute = Math.Round(amountToDistribute, 2);
                    }

                    amountRemainingToDistribute = amountRemainingToDistribute - amountToDistribute;
                    invoice.InvoiceLineList[line.Item1].SetUnitAmountByLineTotal(
                        invoice.InvoiceLineList[line.Item1].LineTotalAmount + amountToDistribute
                        );

                    if (amountRemainingToDistribute == 0)
                    {
                        break;
                    }
                }

                if (amountRemainingToDistribute > 0.01m || amountRemainingToDistribute < -0.01m)
                {
                    // check if the amount remaining to distribute is too large
                    // this should not happen, but if it does, you'll have to manually fix the invoice or do more coding
                    ErrorMessage = "Rounding error when converting invoice to GBP. Amount remaining to distribute: " + amountRemainingToDistribute.ToString("C", CultureInfo.CurrentCulture);
                    _log.LogError(ErrorMessage);
                    return false;
                }
                else if (amountRemainingToDistribute != 0 && amountRemainingToDistribute < 0.01m && amountRemainingToDistribute > -0.01m)
                {
                    invoice.InvoiceLineList[lineWeighting[0].Item1].SetUnitAmountByLineTotal(
                        invoice.InvoiceLineList[lineWeighting[0].Item1].LineTotalAmount + amountRemainingToDistribute
                        );
                }
            }

            // Fix for CS1950: Ensure the list contains valid 'Model.Account.Invoice' objects
            if (validate.IsValidExportInvoice(new List<Model.Account.Invoice> { (Model.Account.Invoice)invoice }) == false)
            {
                ErrorMessage = "Invoice failed validation after conversion to GBP. See logs for further details.";
                _log.LogError(ErrorMessage);
                return false;
            }
            else
            {
                return true;
            }
        }

        public List<Model.Account.CurrencyExchangeRate> GetExchangeRateObjectList(List<Model.Account.CurrencyCode> currencyCodeList, DateTime conversionDate)
        {
            Init();

            IUnitOfWork currentUow = null;
            if (_ownsUnitOfWork)
            {
                currentUow = new UnitOfWork();
            }
            else
            {
                currentUow = _providedUnitOfWork;
            }

            using (currentUow != null && _ownsUnitOfWork ? currentUow : null)
            {
                return currentUow.CurrencyRepository.ReadExchangeRate(currencyCodeList, conversionDate);
            }
        }

        public decimal CurrencyConvertToGbp(string currencyCode, decimal amount, DateTime conversionDate)
        {
            Init();

            if (string.IsNullOrEmpty(currencyCode) || currencyCode.Length != 3)
            {
                throw new Exception("Invalid currency code '" + currencyCode + "'");
            }

            Enum.TryParse(currencyCode, out Model.Account.CurrencyCode enumCurrencyCode);

            return CurrencyConvertToGbp(enumCurrencyCode, amount, conversionDate);
        }

        public decimal CurrencyConvertToGbp(Model.Account.CurrencyCode currencyCode, decimal amount, DateTime conversionDate)
        {
            Init();

            //checks
            if (currencyCode == Model.Account.CurrencyCode.GBP || amount == 0M)
            {
                return amount;
            }

            // read db
            IUnitOfWork currentUow = null;
            if (_ownsUnitOfWork)
            {
                currentUow = new UnitOfWork();
            }
            else
            {
                currentUow = _providedUnitOfWork;
            }

            using (currentUow != null && _ownsUnitOfWork ? currentUow : null)
            {
                var exchageRate = currentUow.CurrencyRepository.ReadExchangeRate(currencyCode, conversionDate);

                if (exchageRate != null)
                {
                    return amount / Convert.ToDecimal(exchageRate);
                }
                else
                {
                    throw new Exception("Currency code '" + currencyCode + "' or date " + conversionDate.ToShortDateString() + " " + conversionDate.ToLongTimeString() + "' does not exist in the Exchange Rate table");
                }
            }
        }

        private DateTime GetHmrcMaxPeriodAvaible()
        {
            // HMRC monthly exchange rates are published on the penultimate Thursday of the month before
            // For some leeeeeeeeway we'll use the penultimate Friday

            // find penultimate Friday for current month
            var ukTimeNow = new Logic.Utilities.DateTime().ConvertUtcToUk(DateTime.UtcNow);
            var monthDayCount = DateTime.DaysInMonth(ukTimeNow.Year, ukTimeNow.Month);
            var thisMonthPenultimateFriday = DateTime.SpecifyKind(new DateTime(ukTimeNow.Year, ukTimeNow.Month, monthDayCount), DateTimeKind.Unspecified);
            int count = 0;
            int fridayCount = 0;
            while (count != 15)
            {
                if (thisMonthPenultimateFriday.DayOfWeek == DayOfWeek.Friday)
                {
                    fridayCount++;
                    if (fridayCount == 2)
                    {
                        break;
                    }
                }
                thisMonthPenultimateFriday = thisMonthPenultimateFriday.AddDays(-1);
                count++;
            }

            if (count == 15)
            {
                throw new Exception("Something went wrong here ErrorID:ef7f5d8f-0f7b-4014-aa65-421ecd5d7367");
            }

            var mostRecentPeriodAvaible = DateTime.SpecifyKind(new DateTime(ukTimeNow.Year, ukTimeNow.Month, 1), DateTimeKind.Unspecified); ;
            if (ukTimeNow >= thisMonthPenultimateFriday)
            {
                mostRecentPeriodAvaible = mostRecentPeriodAvaible.AddMonths(1);
            }

            return mostRecentPeriodAvaible;
        }

        public void UpdateHmrcExchageRates()
        {
            Init();

            _log.LogInformation("Starting update database HMRC exchange rates");

            int exchangeRateSourceId = 1; // id for hmrc

            // retrive most recent data from db
            IUnitOfWork currentUow = null;
            if (_ownsUnitOfWork)
            {
                currentUow = new UnitOfWork();
            }
            else
            {
                currentUow = _providedUnitOfWork;
            }

            using (currentUow != null && _ownsUnitOfWork ? currentUow : null)
            {
                var dbLatestRates = currentUow.CurrencyRepository.ReadExchangeRateLatest();

                // sanity check, make sure there are no duplicates
                int count = 0;
                foreach (var exchageRate in dbLatestRates)
                {
                    count = 0;
                    var currency = exchageRate.CurrencyCode;
                    foreach (var subExchageRate in dbLatestRates)
                    {
                        if (exchageRate.CurrencyCode == subExchageRate.CurrencyCode)
                        {
                            count = 1;
                        }
                    }
                    if (count > 1)
                    {
                        throw new FormatException("Datebase returned duplicate information");
                    }
                }

                // test for no data (first time running)
                var hmrcMonthToRetrive = new DateTime();
                if (dbLatestRates.Any() == false)
                {
                    hmrcMonthToRetrive = Data.Database.Constants.GetBusinessStartUk();
                }

                // set first/earliest month to retrive from hmrc website
                foreach (var exchageRate in dbLatestRates)
                {
                    var dbEndDateTime = exchageRate.DateTimeEndUk;

                    if (hmrcMonthToRetrive == default(DateTime))
                    {
                        hmrcMonthToRetrive = dbEndDateTime;
                    }
                    else
                    {
                        if (dbEndDateTime < hmrcMonthToRetrive)
                        {
                            hmrcMonthToRetrive = dbEndDateTime;
                        }
                    }
                }

                // check - more coding required to retrive periods before 2021-01-01
                if (hmrcMonthToRetrive < DateTime.SpecifyKind(new DateTime(2021, 1, 1), DateTimeKind.Unspecified))
                {
                    throw new Exception("This function does not currently retirve exchange rates from HMRC for dates before 2021-01-01");
                }

                // check if retrival from hmrc is required
                var hmrcMaxMonthAvaible = GetHmrcMaxPeriodAvaible();
                if (hmrcMonthToRetrive.Year == hmrcMaxMonthAvaible.Year && hmrcMonthToRetrive.Month > hmrcMaxMonthAvaible.Month)
                {
                    // nothing to retrive
                    _log.LogInformation("Exchange rates curretly up to date, exiting.");
                    return;
                }

                // get info from hmrc and insert data in db
                while (hmrcMonthToRetrive <= hmrcMaxMonthAvaible)
                {
                    count = 0;

                    var url = new string(
                        "https://www.trade-tariff.service.gov.uk/api/v2/exchange_rates/files/monthly_xml_"
                        + hmrcMonthToRetrive.Year.ToString()
                        + "-"
                        + hmrcMonthToRetrive.Month.ToString()
                        + ".xml"
                        );
                    var xd = new XDocument();
                    xd = XDocument.Load(url);

                    foreach (var exchageRate in dbLatestRates)
                    {
                        if (exchageRate.DateTimeStartUtc < hmrcMonthToRetrive)
                        {
                            //retrive exchange rate from xml
                            XElement node = xd.Root.Elements("exchangeRate").Where(e => e.Element("currencyCode").Value == exchageRate.CurrencyCode.ToString()).FirstOrDefault();
                            decimal rate = decimal.Parse(node.Element("rateNew").Value);
                            rate = decimal.Round(rate, 4);

                            // insert into db
                            currentUow.CurrencyRepository.InsertExchangeRate(
                                exchangeRateSourceId
                                , exchageRate.CurrencyCode
                                , rate
                                , new Utilities.DateTime().ConvertUkToUtc(hmrcMonthToRetrive)
                                , new Utilities.DateTime().ConvertUkToUtc(hmrcMonthToRetrive.AddMonths(1))
                                );

                            count++;
                        }
                    }

                    _log.LogInformation(
                        count + " new exchange rate(s) added to database for " + hmrcMonthToRetrive.ToString("MMMM") + " " + hmrcMonthToRetrive.Year.ToString()
                        );

                    hmrcMonthToRetrive = hmrcMonthToRetrive.AddMonths(1);
                }

                if (_ownsUnitOfWork)
                {
                    currentUow.Commit();
                }

                _log.LogInformation("Updating database currency exchange rates complete.");
            }
        }
    }
}