using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

​

namespace ConsoleApplication1

{

    class ListOfInsertPos

    {

        public int index;

        public int whitch; // in this case: true for: insertion1 = "<b>" and false for: string insertion2 = "</b>"

        public int Index

        {

            get { return index; }

            set{index = value;}

        }

        public int Whitch

        {

            get { return whitch; }

            set { whitch = value; }

        }

    }

    class Program

    {

        static void Main(string[] args)

        {

            string text1 = "The quick brown fox jumps over the lazy dog.";

            //string text2 = "The quick brown fox jumps";

            string insertion1 = "<b>"; // when whitch=0

            string insertion2 = "</b>"; // when whitch=1         

            int[][] Markers = new int[][] 

            {

                new int[] { 4, 15 },

                new int[] { 35, 8 },

            };

            string result = Insert(text1, Markers, insertion1, insertion2); //final method

            Console.WriteLine(result); 

        }

​

        public static List<ListOfInsertPos> Converter(int[][] Markers, string text) //coverts the original markers into a new system and sorts them in a decending order

        { 

            List<ListOfInsertPos> newMarkers = new List<ListOfInsertPos>();

            // original example is converted like this: {4,15} {35,8} -> {4,0} {4+15,1} {35,0} {8+35,1} {position whereto insert in original text, whether <b> or </b>}

            // using this sytem I can make my insertions going from end to front ignoring any problems that would be caused going front to end, by the text being pushed by the insertions and needing to take that into account

            for (int i = 0; i < Markers.Length; i++)

            {

                if (Markers[i][0] <= text.Length && Markers[i][0] + Markers[i][1] <= text.Length) //checks if both positions for insertion1 and insertion2 (<b> and </b>) exist, if not the marker is ignored(35,8 is ignored using text2)

                {

                    newMarkers.Add(new ListOfInsertPos() { Index = Markers[i][0], Whitch = 0 });

                    newMarkers.Add(new ListOfInsertPos() { Index = Markers[i][0] + Markers[i][1], Whitch = 1 });

                }

            }

            List<ListOfInsertPos> SortedList = newMarkers.OrderByDescending(o => o.index).ThenByDescending(c => c.whitch).ToList(); //list is sorted in a idex decending order: {43,1} {35,0} {19,1} {4,0}  ||| ThenByDescending is require if the positions are {0,0}       

            return SortedList;

        }

        public static string Inserter(string original, List<ListOfInsertPos> positions, string insertion1, string insertion2)

        {

            for (int i = 0; i < positions.Count; i++)

            {

                if (positions[i].whitch == 0)

                    original = original.Insert(positions[i].index, insertion1); // inserts insertion1 if true   

                if (positions[i].whitch == 1 ) 

                    original = original.Insert(positions[i].index, insertion2); // inserts insertion2 if false               

            }

            return original;

        }

        public static string Insert(string text, int [][] Markers, string insertion1, string insertion2)

        {

            List<ListOfInsertPos> SortedMarkers = Converter(Markers,text); 

            return Inserter(text, SortedMarkers, insertion1, insertion2); //returns the edited string;

        }

    }

}