JsonKeyedCollectionBase for JSON serialization/deserialization

JsonKeyedCollectionBase.cs

// Related: https://github.com/dotnet/runtime/issues/101003 -- [API Proposal]: New method HashSet<T>.Add that replaces an existing element if found
abstract class JsonKeyedCollectionBase<TKey, TItem> : ICollection<TItem>, IEqualityComparer<TItem>
{
    private readonly HashSet<TItem> _set;

    protected abstract TKey GetKeyForItem(TItem item);
    protected abstract TItem GetItemForKey(TKey key);

    protected virtual IEqualityComparer<TKey> KeyComparer => EqualityComparer<TKey>.Default;
    protected virtual IComparer<TItem> EnumerationComparer => null;

    protected JsonKeyedCollectionBase()
    {
        _set = new((IEqualityComparer<TItem>)this);
    }

    public bool TryGetItem(TKey key, out TItem item) => _set.TryGetValue(GetItemForKey(key), out item);

    public void Add(TItem item)
    {
        if (_set.Add(item)) return;
        bool removed = _set.Remove(item);
        bool added = _set.Add(item);
        Debug.Assert(removed);
        Debug.Assert(added);
    }

    public bool Remove(TKey key) => _set.Remove(GetItemForKey(key));

    public IEnumerator<TItem> GetEnumerator()
    {
        IComparer<TItem> comparer = EnumerationComparer;
        return comparer is null ? _set.GetEnumerator() : _set.Order(comparer).GetEnumerator();
    }
    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();

    bool IEqualityComparer<TItem>.Equals(TItem x, TItem y) => KeyComparer.Equals(GetKeyForItem(x), GetKeyForItem(y));
    int IEqualityComparer<TItem>.GetHashCode(TItem x) => KeyComparer.GetHashCode(GetKeyForItem(x));

    private ICollection<TItem> Collection => _set;
    int ICollection<TItem>.Count => Collection.Count;
    bool ICollection<TItem>.IsReadOnly => Collection.IsReadOnly;
    bool ICollection<TItem>.Contains(TItem item) => Collection.Contains(item);
    bool ICollection<TItem>.Remove(TItem item) => Collection.Remove(item);
    void ICollection<TItem>.Clear() => Collection.Clear();
    void ICollection<TItem>.CopyTo(TItem[] array, int arrayIndex) => Collection.CopyTo(array, arrayIndex);
}

/*
// Usage example
readonly record struct MediaRecord(string FileName, DateTime TimeStamp, double Volume, double SpeedRatio);

class JsonMediaCollection : JsonKeyedCollectionBase<string, MediaRecord>
{
    private static readonly Comparer<MediaRecord> s_EnumerationComparer
        = Comparer<MediaRecord>.Create((x, y) => x.TimeStamp.CompareTo(y.TimeStamp));

    protected override MediaRecord GetItemForKey(string key) => default(MediaRecord) with { FileName = key };
    protected override string GetKeyForItem(MediaRecord item) => item.FileName;

    protected override IEqualityComparer<string> KeyComparer => StringComparer.OrdinalIgnoreCase;
    protected override IComparer<MediaRecord> EnumerationComparer => s_EnumerationComparer;
}
*/