using System;

using System.Text;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var html = new HtmlBuilder("html");

        html.AddChild("head", string.Empty).AddChild("script", string.Empty);

        var body = html.AddChild("body", string.Empty);

        body.AddChild("h1", "hello world");

        var ulContainer = body.AddChild("p", "here is a list").AddChild("ul", string.Empty);

        for(int i=0; i < 4; i++)

        {

            ulContainer.AddChild("li", i.ToString());

        }

        Console.WriteLine(html.ToString());

    }

    public class HtmlElement

    {

        public string Name { get; set; }

        public string Text { get; set; }

        private StringBuilder sb = new StringBuilder();

        public List<HtmlElement> Children = new List<HtmlElement>();

        private int indent = 2;

        public HtmlElement(string name, string text)

        {

            Name = name;

            Text = text;

        }

        public HtmlElement AddChild(string name, string text)

        {

            var htmlElement = new HtmlElement(name, text);

            Children.Add(htmlElement);

            return htmlElement;

        }

        public string ToHtmlString(int level = 0)

        {

            var indentString = new string(' ', indent * level);

            sb.Append(indentString);

            sb.AppendLine($"<{Name}>").Append(indentString).Append(Text);

            foreach(var htmlElement in Children)

            {

                sb.Append(indentString);

                sb.AppendLine(htmlElement.ToHtmlString(level+1));

            }

            sb.Append(indentString);

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

            return sb.ToString();

        }

    }

    public class HtmlBuilder

    {

        private HtmlElement root;

        public HtmlBuilder(string rootName)

        {

            root = new HtmlElement(rootName, string.Empty);

        }

        public HtmlElement AddChild(string name, string text)

        {

            var htmlElement = new HtmlElement(name, text);

            root.Children.Add(htmlElement);

            return htmlElement;

        }

        public override string ToString()

        {

            return root.ToHtmlString();

        }

    }

}