using System;

using System.Collections.Generic;

using System.Linq;

using System.Threading.Tasks;

​

namespace Hierarchy

{

    class Program

    {

        static void Main(string[] args)

        {

            var perpetualInventoryFlatList = new List<PerpetualInventoryList> {

                new PerpetualInventoryList { ItemId = 1,ItemName = "Apple",ItemCode = "IT-205", StorageCategory = "Fruit"},

                new PerpetualInventoryList { ItemId = 3,ItemName = "Banana",ItemCode = "IT-206", StorageCategory = "Fruit"},

                new PerpetualInventoryList { ItemId = 4,ItemName = "Pinapple",ItemCode = "IT-207", StorageCategory = "Fruit"},

                new PerpetualInventoryList { ItemId = 5,ItemName = "Orange",ItemCode = "IT-208", StorageCategory = "Fruit"},

                new PerpetualInventoryList { ItemId = 6,ItemName = "Mango",ItemCode = "IT-209", StorageCategory = "Fruit"},

                new PerpetualInventoryList { ItemId = 7,ItemName = "IT-210",ItemCode = "IT-210", StorageCategory = "Fruit"}

            };

            var result = GetFlatList<PerpetualInventoryList, PerpetualInventoryTreeListContract>(perpetualInventoryFlatList);

        }

​

        public static PerpetualInventoryTreeListContract GetContract(IntermediateResult intermediateResult)

        {

            var createdItem = new List<Object>();

            createdItem.Add(intermediateResult.Items.FirstOrDefault());

​

            var createdLink = new List<Object>();

            createdLink.Add(intermediateResult.Links);

            /*var data =  new PerpetualInventoryTreeListContract

                        {

                            ItemId = item.ItemId,

                            ItemName = ((PerpetualInventoryTreeListContract)intermediateResult.Items).ItemName,

                        };

            return data;*/

            return new PerpetualInventoryTreeListContract();

        }

        public static Task<List<TContract>> GetFlatList<TInput, TContract>(List<TInput> items)

              where TContract : IHierarchyContract<TContract>, new() // inherit from IItem

              where TInput : IHierarchyData

        {

            var itemIds = items.Select(s => s.ItemId).ToList();

            var otherList = new ItemLinkService().GetItemLink2(itemIds);

​

            var data = otherList.GroupJoin(

                        items,

                        o => o.ItemId, // otherList

                        i => i.ItemId, // items

                        (thisOther, thisItem) => new IntermediateResult

                        {

                            Links = thisOther,

                            Items = (IEnumerable<IHierarchyData>)thisItem

                        })

                  .Where(i => i.Items.Any())

                  .ToList();

​

            var list = data.SelectMany(

                              x => x.Items.DefaultIfEmpty(),

                              (x, item) => GetContract(x)).ToList();

​

            return (System.Threading.Tasks.Task<List<TContract>>)(object)list;

        }

    }

    public class IntermediateResult

    {

        public IHierarchyData Links { get; set; }

        public IEnumerable<IHierarchyData> Items { get; set; }

    }

​

    public interface IHierarchyData

    {

        int ItemId { get; set; }

    }

​

    public interface IHierarchyContract<TContract> : IHierarchyData

    {

        string ItemName { get; set; }

    }

​

    public class PerpetualInventoryList : IHierarchyData

    {

        public int ItemId { get; set; }

        public string ItemName { get; set; }

        public string ItemCode { get; set; }

        public string StorageCategory { get; set; }

    }

​

    public class ItemLinkList : IHierarchyData

    {

        public int ItemId { get; set; }

        public int ItemLinkId { get; set; }

        public int ParentItemId { get; set; }

        public int ChildItemId { get; set; }

    }

​

    public class PerpetualInventoryTreeListContract : IHierarchyContract<PerpetualInventoryTreeListContract>

    {

        public int ItemId { get; set; }

        public string ItemName { get; set; }

        public string ItemCode { get; set; }

        public string StorageCategory { get; set; }

        public int ItemLinkId { get; set; }

        public int ParentItemId { get; set; }

        public int ChildItemId { get; set; }

    }

    public class ItemLinkService

    {

        public IEnumerable<IHierarchyData> GetItemLink(IEnumerable<int> itemIds)

        {

            return new List<IHierarchyData> {

            new PerpetualInventoryTreeListContract { ItemId = 1, ItemName = "First"},

            new PerpetualInventoryTreeListContract { ItemId = 2, ItemName = "Second"},

            new PerpetualInventoryTreeListContract { ItemId = 3, ItemName = "Third"}

         };

        }

        public IEnumerable<IHierarchyData> GetItemLink2(IEnumerable<int> itemIds)

        {

            return new List<IHierarchyData> {

            new ItemLinkList { ItemId = 1,ItemLinkId = 10 , ChildItemId = 1 , ParentItemId = 2 },

            new ItemLinkList { ItemId = 2,ItemLinkId = 20 , ChildItemId = 2 , ParentItemId = 4 },

            new ItemLinkList { ItemId = 3,ItemLinkId = 30 , ChildItemId = 3 , ParentItemId = 2 },

            new ItemLinkList { ItemId = 4,ItemLinkId = 40 , ChildItemId = 4 , ParentItemId = 0 },

            new ItemLinkList { ItemId = 5,ItemLinkId = 50 , ChildItemId = 5 , ParentItemId = 3 },

            new ItemLinkList { ItemId = 6,ItemLinkId = 60 , ChildItemId = 6 , ParentItemId = 3 },

            new ItemLinkList { ItemId = 7,ItemLinkId = 70 , ChildItemId = 7 , ParentItemId = 3 },

         };

        }

    }

}

​