using System;

using System.Linq;

using System.Collections.ObjectModel;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var arch = new Archivable()

        {

            Ordinal = 1,

            IsArchived = true,

        };

        var dl = new OrderableDisplayList<Archivable>();

        // Fine

        dl.RestoreItem(arch);

        //  Not fine, can;t get method to compile

        dl.RestoreFirstItem();

    }

}

​

public class Archivable : IOrderable, IArchivable

{

    public bool IsArchived { get; set; }

    public int Ordinal { get; set; }

}

​

public interface IArchivable

{

    bool IsArchived { get; set; }

}

​

public interface IOrderable

{

    int Ordinal { get; set; }

}

​

public class OrderableDisplayList<TItem> where TItem : IOrderable

{

    private OrderableCollection<TItem> orderableItems { get; set; }

    public void RestoreItem<T>(T item) where T : TItem, IArchivable

    {

        if(orderableItems is not ArchivableOrderableCollection<T> items)

        {

            throw new InvalidOperationException();

        }

        items.Restore(item);

    }

    public void RestoreFirstItem()

    {

        RestoreItem(orderableItems.First());

    }

}

​

public class OrderableCollection<T> : Collection<T> where T : IOrderable

{

    public virtual IEnumerable<T> OrderedItems => Items.OrderBy(o => o.Ordinal);

​

    public virtual void MoveUp(T item)

    {

        int OrdinalOfCurrentRow = item.Ordinal;

​

        if (OrdinalOfCurrentRow > 1)

        {

            int OrdinalOfSwapRow = item.Ordinal--;

            OrderedItems.Where(o => o.Ordinal == OrdinalOfSwapRow).FirstOrDefault().Ordinal = OrdinalOfCurrentRow;

            item.Ordinal = OrdinalOfSwapRow;

        }

    }

}

​

public class ArchivableOrderableCollection<T> : OrderableCollection<T> where T : IOrderable, IArchivable

{

    public override IEnumerable<T> OrderedItems => Items.Where(_ => !_.IsArchived).OrderBy(_ => _.Ordinal);

​

    public void Archive(T Item)

    {

        Item.Ordinal = 0;

        Item.IsArchived = true;

    }

    public void Restore(T Item)

    {

        if (Item.IsArchived)

        {

            throw new InvalidOperationException();

        }

        Item.Ordinal = 0;

        OrderedItems.Where(o => o.Ordinal >= 1).ToList().ForEach(f => { f.Ordinal++; });

        Item.Ordinal = 1;

        Item.IsArchived = false;

    }

}