using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    private static readonly Random _random = new Random();

    public static void Main(string[] args)

    {

        var data = new List<byte>();

        var lookup = new Dictionary<int, PairInfo>();

        for (var i = 0; i < 30; i++)

        {

            var a = GenerateA();

            var b = GenerateB();

            var newPairInfo = new PairInfo();

            for (var j = 0; j < 2; j++)

            {

                var position = 0;

                // Choose a random place if we have data

                if (lookup.Count > 0)

                {

                    var randomIndex = _random.Next(0, lookup.Count); // we want to insert the data on a random place between arrays

                    var useA = _random.Next(0, 2) == 0; // 0 = a , 1 = b - also random if between a&b

                    position = useA ? lookup[randomIndex].A.Offset : lookup[randomIndex].B.Offset;

                }

​

                // First iteration is a and second is b

                var dataToInsert = j == 0 ? a : b;

                // Insert the data

                data.InsertRange(position, dataToInsert);

                var entriesNeedToUpdate = lookup.Values

                    .SelectMany(pair => new[] { pair.A, pair.B }) // Create a array of all EntryInfo

                    .Where(entry => entry.Offset >= position); // We only need entries which are behind the new data to update their offsets

                foreach (var entry in entriesNeedToUpdate)

                    entry.Offset += dataToInsert.Length;

                // Since we search a random place for A and B

                // and the pair didn't get added to the lookup yet

                // it could happen that B gets placed before the new A data

                if (newPairInfo.A?.Offset >= position)

                    newPairInfo.A.Offset += dataToInsert.Length;

                // Add the new EntryInfo to the pair

                if (j == 0)

                    newPairInfo.A = new EntryInfo(position, dataToInsert.Length);

                else

                    newPairInfo.B = new EntryInfo(position, dataToInsert.Length);

            }

​

            // Add the pair info to the lookup

            lookup.Add(i, newPairInfo);

        }

​

        // Quick check if everything is ok

        foreach (var pair in lookup.Values)

        {

            var a = data.Skip(pair.A.Offset).Take(pair.A.Length).ToArray();

            if (!a.SequenceEqual(new byte[] { 1, 2, 3 }))

                throw new Exception("Something is wrong :/ - A");

            var b = data.Skip(pair.B.Offset).Take(pair.B.Length).ToArray();

            if (!b.SequenceEqual(new byte[]{ 9, 8, 7 }))

                throw new Exception("Something is wrong :/ - B");

        }

        // Print data to the console

        foreach (var entry in lookup.Values.SelectMany(pair => new[] { pair.A, pair.B }).OrderBy(entry => entry.Offset))

        {

            var array = data.Skip(entry.Offset).Take(entry.Length).ToArray();

            PrintArray(array);

        }

    }

​

    private static byte[] GenerateA()

    {

        return new byte[] { 1, 2, 3 };

    }

​

    private static byte[] GenerateB()

    {

        return new byte[] { 9, 8, 7 };

    }

    private static void PrintArray(byte[] array)

    {

        Console.Write("[");

        for(var i=0; i<array.Length; i++)

        {

            Console.Write(array[i]);

            if(i < (array.Length -1))

                Console.Write(",");

        }

        Console.Write("] ");

    }

}

​

class EntryInfo

{

    public int Offset { get; set; }

    public int Length { get; set; }

​

    public EntryInfo(int offset, int length)

    {

        Offset = offset;

        Length = length;

    }

}

​

class PairInfo

{

    public EntryInfo A { get; set; }

    public EntryInfo B { get; set; }

}