public IEnumerable <Debt> GetDebts(IEnumerable <Action> actions)
{
if (actions?.Any() != true)
{
return(Enumerable.Empty <Debt>());
}
var debtAggregator = new DebtAggregator();
foreach (var action in actions.OrderBy(a => a.Date))
{
var totalAmountPaid = action.Sponsors.Sum(s => s.Amount);
var payersDict = action.Goods
.SelectMany(good => good.Consumers)
.ToLookup(consumer => consumer.Participant)
.ToDictionary(p => p.Key, p => p.Sum(consumer => consumer.Amount));
foreach (var sponsor in action.Sponsors)
{
var sponsorRate = sponsor.Amount / totalAmountPaid;
foreach (var pair in payersDict.Where(pair => pair.Key != sponsor.Participant))
{
var consumer = pair.Key;
var amount = pair.Value;
var debtAmount = Math.Round(amount * sponsorRate, 2);
var debtTransaction = new DebtTransaction(debtAmount, action.Description, action.Date);
debtAggregator.AddTransaction(sponsor.Participant, consumer, debtTransaction);
}
}
}
return(debtAggregator.GetDebts().Where(totalDebt => totalDebt.Amount != 0));
}
public void AddTransaction(string creditor, string debtor, DebtTransaction transaction)
{
if ((transaction?.Amount ?? 0m) < 0m)
{
throw new ArgumentException($"Cannot add transaction: amount must be > 0 but was {transaction?.Amount}.");
}
if (creditor.IsNullOrWhiteSpace() || debtor.IsNullOrWhiteSpace())
{
throw new ArgumentException($"Cannot add transaction: creditor = [{creditor}], debtor = [{debtor}].");
}
if ((transaction?.Amount ?? 0m) == 0m)
{
return;
}
var key = new DebtAggregatorKey(creditor, debtor);
if (!debts.ContainsKey(key))
{
debts.Add(key, new Debt {
Creditor = creditor, Debtor = debtor
});
}
var debt = debts[key];
if (key.Creditor == debt.Creditor)
{
debt.Transactions.Add(transaction);
}
else
{
debt.Transactions.Add(transaction.Reverse());
if (debt.Amount < 0)
{
debts[key] = debt.Reverse();
}
else if (debt.Amount == 0)
{
debts.Remove(key);
}
}
}