using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace bnhtrade.Core.Logic.Stock
{
    public class StatusBalance
    {
        private string sqlConnectionString;

        public StatusBalance(string sqlConnectionString)
        {
            this.sqlConnectionString = sqlConnectionString;
        }

        /// <summary>
        /// Return the avaliable balance of a status. Uses a more efficent sql/code. However, balance requests should
        /// generally also involve a date/time (i.e. the system does allow a stock transaction in the future, therefore
        /// this method may give an available quantity, but transfers before that date wouod not be possible).
        /// </summary>
        /// <param name="sku">SKU number</param>
        /// <param name="statusId">Status ID</param>
        /// <returns>Balance as quantity</returns>
        private int GetAvailableBalanceBySku(string sku, int statusId)
        {
            return new Data.Database.Stock.ReadStatusBalance(sqlConnectionString).BySku(sku, statusId);
        }

        /// <summary>
        /// Return the avaliable balance of a status at a specified date and time. Useful for checking availability before
        /// moving stock/sku retrospectivly
        /// </summary>
        /// <param name="sku">SKU number</param>
        /// <param name="statusId">Status ID</param>
        /// <param name="atDate">Date and time you would like to know the balance at</param>
        /// <returns></returns>
        public Model.Stock.StatusBalance GetBySku(string sku, int statusId)
        {
            if (string.IsNullOrWhiteSpace(sku))
            {
                throw new Exception("SKU number is null, empty, or whitespace");
            }

            // get list of transactions for availale stock
            var stockTransaction = new Data.Database.Stock.ReadStatusTransaction(sqlConnectionString);
            var transList = stockTransaction.BySku(statusId, sku);

            // create quantity list
            List<int> qtyList = new List<int>();
            for (int i = 0; i < transList.TransactionList.Count; i++)
            {
                qtyList.Add(transList.TransactionList[i].Quantity);
            }

            // tally list
            // loop, in reverse, to find credits to tally with debits
            for (int iCr = qtyList.Count - 1; iCr > -1; iCr--)
            {
                if (qtyList[iCr] < 0)
                {
                    int crStockNumber = transList.TransactionList[iCr].StockNumber;
                    DateTime crDate = transList.TransactionList[iCr].EntryDate;

                    // loop, in reverse, to find debits
                    for (int iDr = qtyList.Count - 1; iDr > -1; iDr--)
                    {
                        // find debits, last in first out (filter by date)
                        if (transList.TransactionList[iDr].StockNumber == crStockNumber
                            && transList.TransactionList[iDr].EntryDate <= crDate 
                            && qtyList[iDr] > 0)
                        {
                            // credit fully assigned
                            if ((qtyList[iCr] + qtyList[iDr]) >= 0)
                            {
                                qtyList[iDr] = qtyList[iDr] + qtyList[iCr];
                                qtyList[iCr] = 0;
                                break;
                            }
                            // credit partially assigned
                            else
                            {
                                qtyList[iCr] = qtyList[iDr] + qtyList[iCr];
                                qtyList[iDr] = 0;
                            }
                        }
                    }
                }
            }

            // build result list from tally results
            var result = new Model.Stock.StatusBalance();
            result.Sku = transList.Sku;
            result.StockStatusId = transList.StockStatusId;

            for (int i = 0; i < qtyList.Count; i++)
            {
                if (qtyList[i] != 0)
                {
                    result.AddBalanceTransaction(
                            transList.TransactionList[i].EntryDate,
                            transList.TransactionList[i].StockNumber,
                            qtyList[i]);
                }
            }

            return result;
        }
    }
}