public static async Task <IEnumerable <T> > ShuffleAsync <T>(this IEnumerable <T> source, IRandomizer randomizer)
{
var elements = source.ToArray();
// Note i > 0 to avoid final pointless iteration
for (var i = elements.Length - 1; i > 0; i--)
{
// Swap element "i" with a random earlier element it (or itself)
var swapIndex = await randomizer.NextAsync(i + 1);
var tmp = elements[i];
elements[i] = elements[swapIndex];
elements[swapIndex] = tmp;
}
return(elements);
}