Debounce

Debounce.cs

var source = Ints();
await foreach (var item in Debounce(source, TimeSpan.FromSeconds(0.5)))
{
    Console.WriteLine($"{DateTime.Now} {item}");
}

static async IAsyncEnumerable<int> Ints()
{
    for (int i = 0; i < 80; i += 5)
    {
        await Task.Delay(i * 10);
        yield return i;
    }

    for (int i = 80; i > 0; i -= 5)
    {
        await Task.Delay(i * 10);
        yield return i;
    }
}

static async IAsyncEnumerable<T> Debounce<T>(IAsyncEnumerable<T> source, TimeSpan time)
{
    await using var enumerator = source.GetAsyncEnumerator();
    if (!await enumerator.MoveNextAsync())
        yield break;

    while (true)
    {
        var item = enumerator.Current;
        var read = enumerator.MoveNextAsync().AsTask();
        var timeout = Task.Delay(time);
        if (await Task.WhenAny(read, timeout) == timeout)
            yield return item;

        if (!await read)
        {
            await timeout;
            yield return item; // last item
            yield break;
        }
    }
}