using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        var a = new Category(){ Name = "A", Path = "A" };

        var b = new Category(){ Name = "B", Path = "A/B" };

        var c = new Category(){ Name = "C", Path = "A/B/C" };

        var vms = Map(new[]{a,b,c});    

        foreach(var vm in vms)

        {

            vm.Print(string.Empty);

        }

    }

    public class CategoryViewModel

    {

        public Guid Id { get; set; }

        public Guid DomainId { get; set; } 

        public string Name { get; set; } = default!;

        public string Path { get; set; } = default!;

        public CategoryViewModel? Parent { get; set; }

        public List<CategoryViewModel> Children { get; set; } = new List<CategoryViewModel>();

        public void Print(string root)

        {

            root += this.Name;

            Console.WriteLine(root);

            foreach(var children in this.Children)

            {

                children.Print(root);

            }

        }

    }

    public class Category

    {   

        public Guid Id { get; set; }

        public Guid DomainId { get; set; } 

        public string Name { get; set; } = default!;

        public string Path { get; set; } = default!;

    }

​

    public static List<CategoryViewModel> Map(IEnumerable<Category> input)

        {

            var source = input

                .GroupBy(p => p.Path, StringComparer.OrdinalIgnoreCase)

                .ToDictionary(g => g.Key, g => g.First(), StringComparer.OrdinalIgnoreCase);

​

            var destination = new Dictionary<string, CategoryViewModel>();

​

            CategoryViewModel RecursiveBuild(

                string[] parts,

                int index,

                CategoryViewModel parent)

            {

                var path = string.Join("/", parts.Take(index + 1));

​

                if (destination.ContainsKey(path) == false) // have we processed this?

                {

                    CategoryViewModel category = null;

​

                    if (source.ContainsKey(path))

                    {

                        category = Map(source[path]);

                    }

                    else

                    {

                        // we don't have an in data representation of this category so this is a placeholder

                        category = new CategoryViewModel

                        {

                            Name = parts[index],

                            Path = path,                            

                        };

                    }

​

                    destination[path] = category;

​

                    if (parent != null)

                    {

                        category.Parent = parent;

                        parent.Children.Add(category);

                    }

                }

​

                return index < parts.Length - 1 ? RecursiveBuild(parts, index + 1, destination[path]) : destination[path];

            }

​

            //link

            foreach (var item in input)

            {

                var path = item.Path;

                var parts = path.Split('/');

                RecursiveBuild(parts, 0, null);

            }

​

            var roots = destination.Values.Where(c => c.Parent == null).ToList();

            return new List<CategoryViewModel>(roots);

        }

​

        public static CategoryViewModel Map(Category source)

        {

            return new ()

            {

                Id = source.Id,

                DomainId = source.DomainId,

                Name = source.Name,

                Path = source.Path

            };

        }

​

}