using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFLol.DBDataManager
{
	static class ExtensionsDataManager
	{
		internal static Task<IEnumerable<T?>> GetItemsWithFilterAndOrdering<T>(this IEnumerable<T> collection,
			Func<T, bool> filter, int index, int count, string? orderingPropertyName = null, bool descending = false)
		{
			IEnumerable<T> temp = collection;
			temp = temp.Where(item => filter(item));
			if (orderingPropertyName != null)
			{
				var prop = typeof(T).GetProperty(orderingPropertyName!);
				if (prop != null)
				{
					temp = descending
						? temp.OrderByDescending(item => prop.GetValue(item))
						: temp.OrderBy(item => prop.GetValue(item));
				}
			}

			return Task.FromResult<IEnumerable<T?>>(temp.Skip(index * count).Take(count));
		}

		internal static Task<int> GetNbItemsWithFilter<T>(this IEnumerable<T> collection, Func<T, bool> filter)
		{
			return Task.FromResult(collection.Count(item => filter(item)));
		}

		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);
		}
	}
}