Fix isNotA filter code in ValueSet expander

[mmsmits]

fixes #2801

[Kasdejong]

Right now we have side effects: we remove items, but we return the collection because we want to keep the fluent syntax. We should really be making this pure, that way the signature makes sense.

[mmsmits]

You are suggesting to make this a void you mean?

[Kasdejong]

We iterate 3 times now. We can get away with only doing this once, by just putting all the calls in a foreach loop, or better yet: a select (if we are going pure)

[mmsmits]

I was hoping to do this in a single forloop (or linq statement), but I couldn't figure it out without duplicating collections, and making it a mess.
You have a suggestion?

[Kasdejong]

In this case duplicating subsets of collections is a fact of life I think. The most optimized version is a big chain call, since the compiler can chain the methods together into a single loop. I will suggest a commit (once I find out how to)

[Kasdejong]

Alright, it seems like i'm not able to suggest it the way I wanted to. I would like to suggest something along the lines of:

internal static List<CSDC> RemoveCode(this ICollection<CSDC> concepts, string code)
{
    return concepts.getNonMatchingCodes(c => c.Code == code);
}

private static List<CSDC> getNonMatchingCodes(this ICollection<CSDC> concepts, Predicate<CSDC> predicate)
{
    var filtered = concepts.Where(c => !predicate(c)).ToList();
    
    foreach (var concept in filtered.Where(concept => concept.Concept?.Count is > 0))
    {
        concept.Concept = concept.Concept.getNonMatchingCodes(predicate).ToList();
    }
    
    return filtered;
}