// A helper function for avsserting products in the collection are correct.
private void AssertProductAmountIsEqual(IProductAmountCollection collection, Mock <IProduct> product, double value)
{
Assert.That(collection.GetProductValue(product.Object), Is.EqualTo(value));
}
/// <summary>
/// Given a set of cash and a desired price, get the amount of the cash
/// to meet the price (rounded up for safety)
/// </summary>
/// <param name="AvailableCash">The amount of cash avaliable.</param>
/// <param name="price">The price to meet (roughly)</param>
/// <returns>The appropriate cash for the price.</returns>
/// <exception cref="ArgumentNullException">If <paramref name="AvailableCash"/> is null.</exception>
/// <exception cref="ArgumentOutOfRangeException">If <paramref name="price"/> is less than or equal to 0.</exception>
public IProductAmountCollection ChangeForPrice(IProductAmountCollection AvailableCash, double price)
{
// ensure cash is not null.
if (AvailableCash is null)
{
throw new ArgumentNullException(nameof(AvailableCash));
}
// ensure that the price is greater than 0
if (price <= 0) // TODO, allow this to savely give change for 0. It's not that hard.
{
throw new ArgumentOutOfRangeException("Price must be greater than 0.");
}
// first, check that all available cash can meet the price.
var totalCash = AvailableCash.Sum(x => x.Item2 * ProductPrices.GetProductValue(x.Item1));
// If the total cash available is less than the price sought, return a copy of the available cash.
if (totalCash < price)
{
return(AvailableCash.Copy());
}
// since we have more than we need,
var result = new ProductAmountCollection();
// start from the best and start making change, highest to lowest value.
foreach (var coin in AvailableCash.OrderByDescending(x => ProductPrices.GetProductValue(x.Item1)))
{
// if none of that coin exist
if (coin.Item2 == 0)
{
// add it as zero
result.AddProducts(coin.Item1, 0);
// and skip to the next loop
continue;
}
// coin type
var curr = coin.Item1;
// coin value
var val = ProductPrices.GetProductValue(curr);
// if value is higher then remaining price.
if (val > price)
{
// add it as zero
result.AddProducts(curr, 0);
// and skip
continue;
}
// coin amount
var amt = coin.Item2;
// how many whole coins can fit into the price.
var count = Math.Floor(price / val);
// select cap coins at the available level.
count = Math.Min(count, amt);
// add to our change
result.AddProducts(curr, count);
// subtract the value we took out
price -= val * count;
// then go to the next coin.
}
// if there is a remainder
if (price > 0)
{
// find the smallest coin available
foreach (var coin in AvailableCash.OrderBy(x => ProductPrices.GetProductValue(x.Item1)))
{
// if we have any available
if (result.GetProductValue(coin.Item1) < AvailableCash.GetProductValue(coin.Item1))
{
// add one
result.AddProducts(coin.Item1, 1);
// and move on.
break;
// by logic, only one should be needed as we guaranteed have
// more value in coins then the requested price and the
// remainder should be smaller than the smallest coin.
}
}
}
// return the change.
return(result);
}