using System;

using System.Linq;

using System.Collections.Generic;

using System.Threading.Tasks;

using System.Net.Http;

using Newtonsoft.Json;

using System.Text;

​

var client = new HttpClient() { BaseAddress = new Uri("https://api.jsonbin.io/b/5fb62f9404be4f05c9272f9b/2") };

client.DefaultRequestHeaders.Add("secret-key", "$2b$10$FRKBdPsyV27ReVeMpo83U.BYS0Jko5KUjctlj0A865qRkEYVf49ty");

​

var dataService = new DataService(client);

var items = await dataService.GetItemsAsync();

var nodes = items.ToTree();

​

var display = nodes.MakeFormattedString();

​

Console.WriteLine(display);

​

public static class NeedToImplementThis

{

    public static Node ToTree(this IEnumerable<Node> nodes)

    {

        var hashed = nodes.ToLookup(x => x.Parent);

        foreach (var node in nodes)

        {

            node.Childs = hashed[node.Id];

        }

        return hashed[-1].First();

    }

​

    public static StringBuilder MakeFormattedString(this Node node, StringBuilder sb = null, int level = 1)

    {

        sb = sb ?? new StringBuilder();

        var indent = new string('\t', level);

        sb.AppendLine($"{indent}<li>{node.Id}. {node.Text} ({level})</li>");

        if (node.Childs.Any())

        {

            sb.AppendLine($"{indent}<ul>");

            foreach (var child in node.Childs)

            {

                MakeFormattedString(child, sb, level + 1);

            }

            sb.AppendLine($"{indent}</ul>");

        }

        if (level == 1)

        {

            sb.Insert(0, "<ul>" + Environment.NewLine);

            sb.Append("</ul>");

        }

        return sb;

    }

}

​

public class Node

{

    public int Id { get; set; }

    public string Text { get; set; }

    public int Parent { get; set; }

    public IEnumerable<Node> Childs { get; set; }

​

    public bool IsRoot => Id == 0;

    public bool HasChilds => Childs != null && Childs.Any();

}

​

public class DataService

{

    private readonly HttpClient _httpClient;

    public DataService(HttpClient httpClient) => _httpClient = httpClient;

​

    public async Task<IEnumerable<Node>> GetItemsAsync()

    {

        using var resp = await _httpClient.GetAsync("");

        var json = await resp.Content.ReadAsStringAsync();

​

        Console.WriteLine(json);

        return JsonConvert.DeserializeObject<Node[]>(json);

    }

}

​