/// <summary>
/// Process the uploaded file contents and return a list of records with completed calculations
/// </summary>
/// <param name="fileContents"></param>
/// <returns></returns>
public IEnumerable <CashRegisterRecord> ProcessFile(string fileContents)
{
// Parse the file contents to get a list of records
IEnumerable <CashRegisterRecord> records = ParseFileContents(fileContents);
// Calculate change and denominations for each record
foreach (CashRegisterRecord record in records)
{
try
{
record.Change = CalculateChange(record.Owed, record.Paid);
// Client's "twist"
// If amount owed is divisible by 3, use random algorithm to determine bills and coins
BillsAndCoinsAlgorithm algorithm = BillsAndCoinsAlgorithm.Greedy;
if ((record.Owed * 100) % 3 == 0)
{
algorithm = BillsAndCoinsAlgorithm.Random;
}
record.ChangeText = GetBillsAndCoins(record.Change, algorithm);
}
catch (Exception ex)
{
// Label this record as having an error
// Continue processing the rest of the records
record.Error = true;
}
}
return(records);
}
/// <summary>
/// Determine how many of each currency denomination is needed to make the provided amount
/// </summary>
/// <param name="amount"></param>
protected virtual string GetBillsAndCoins(decimal amount, BillsAndCoinsAlgorithm algorithm = BillsAndCoinsAlgorithm.Greedy)
{
try
{
// Get all denominations (ordered by value descending)
Denomination[] denominations = GetDenominations();
// String with bills and change written out
StringBuilder sb = new StringBuilder();
if (amount < 0)
{
// Data isn't right...
sb.Append("Customer still owes $" + (0 - amount));
}
else if (amount == 0)
{
// There is nothing to calculate
sb.Append("No change");
}
else
{
// Starting amount, when a matching bill or coin is found, their value will be subtracted from this amount
decimal amountLeft = amount;
switch (algorithm)
{
case BillsAndCoinsAlgorithm.Greedy:
// Use greedy algorithm to determine the minimum amount of bills and change
// If I recall correctly, in this case, greedy algorithm will always produce the best result
// Start with the highest denomination
foreach (Denomination denomination in denominations)
{
decimal value = denomination.Value;
string name = denomination.Name;
// Calculate how many times this denomination fits in amount left
int count = Convert.ToInt32(Math.Truncate(amountLeft / value));
if (count > 0)
{
// Append the amount to the result string
sb.Append((sb.Length > 1 ? ", " : "") + count + " " + (count > 1 ? name.ToPlural() : name));
// Substract the amount from the running amount left
amountLeft -= count * value;
}
}
break;
case BillsAndCoinsAlgorithm.Random:
// Random algorithm
// To make sure that bills and coins add up correctly and implementation is efficient and easy,
// follow the same pattern as greedy algorithm, but randomly choose the number of bills / coins at each step.
// At the end, get all the available pennies (or lowest denomination)
// This will produce a correct result, but will add a degree of randomess
Random rng = new Random();
// Start with the highest denomination
for (int i = 0; i < denominations.Length; i++)
{
decimal value = denominations[i].Value;
string name = denominations[i].Name;
// Calculate how many times this denomination fits in amount left
int count = Convert.ToInt32(Math.Truncate(amountLeft / value));
// Randomize if this is not the lowest denomination (penny)
if (i < denominations.Length - 1)
{
count = rng.Next(count);
}
if (count > 0)
{
// Append the amount to the result string
sb.Append((sb.Length > 1 ? ", " : "") + count + " " + (count > 1 ? name.ToPlural() : name));
// Substract the amount from the running amount left
amountLeft -= count * value;
}
}
break;
default:
throw new Exception("Unknown algorithm to determine bills and coins.");
}
// Note any amount that we were unable to process
// This could only happen if user entered values under 1 cent (or similar situation)
if (amountLeft > 0)
{
sb.Append((sb.Length > 1 ? " " : "") + "($" + amountLeft + " that cannot be given in change)");
}
}
return(sb.ToString());
}
catch (Exception ex)
{
throw new Exception("Unable to determine bills and change for " + amount + ".", ex);
}
}