API/src/StubAPI/Extensions.cs

namespace StubAPI;


public static class Extensions
{
    internal static Task<T?> AddItem<T>(this IList<T> collection, T? item)
    {
        if(item == null || collection.Contains(item))
        {
            return Task.FromResult<T?>(default(T));
        }
        collection.Add(item);
        return Task.FromResult<T?>(item);
    }

    internal static Task<bool> DeleteItem<T>(this IList<T> collection, T? item)
    {
        if(item == null)
        {
            return Task.FromResult(false);
        }
        bool result = collection.Remove(item!);
        return Task.FromResult(result);
    }

    internal static Task<T?> UpdateItem<T>(this IList<T> collection, T? oldItem, T? newItem)
    {
        if(oldItem == null || newItem == null) return Task.FromResult<T?>(default(T));

        if(!collection.Contains(oldItem))
        {
            return Task.FromResult<T?>(default(T));
        }

        collection.Remove(oldItem!);
        collection.Add(newItem!);
        return Task.FromResult<T?>(newItem);
    }
    
    public static IEnumerable<T> GetItemsWithFilterAndOrdering<T>(this IEnumerable<T> list, Func<T, bool> filter, int index, int count, Enum? orderCriterium, bool descending = false ) where T : class
    {
        var filteredList = list.Where(filter);
        
        if(orderCriterium != null)
        {
            filteredList = filteredList.OrderByCriteria(orderCriterium, descending);
        }        
        return filteredList
            .Skip(index * count)
            .Take(count);
    }

    public static IOrderedEnumerable<T> OrderByCriteria<T>(this IEnumerable<T> list, Enum orderCriterium, bool descending = false ) where T : class
    {
        var orderCriteriumString = orderCriterium.ToString();
        if (orderCriteriumString.StartsWith("By"))
        {
            orderCriteriumString = orderCriteriumString.Substring(2);
        }
        var propertyInfo = typeof(T).GetProperty(orderCriteriumString);
        if (propertyInfo == null)
        {
            throw new ArgumentException($"No property {orderCriterium} in type {typeof(T)}");
        }

        return descending ? list.OrderByDescending(x => propertyInfo.GetValue(x)) : list.OrderBy(x => propertyInfo.GetValue(x));
    }


}