Array Manipulator

/*
Write a program that reads an array of integers from the console and set of commands and executes them over the array.
The commands are as follows:
• add <index> <element> – adds element at the specified index (elements right from this position inclusively are shifted to the right).
• addMany <index> <element 1> <element 2> … <element n> – adds a set of elements at the specified index.
• contains <element> – prints the index of the first occurrence of the specified element (if exists) in the array
    or -1 if the element is not found.
• remove <index> – removes the element at the specified index.
• shift <positions> – shifts every element of the array the number of positions to the left (with rotation).
    o   For example, [1, 2, 3, 4, 5] -> shift 2 -> [3, 4, 5, 1, 2]
• sumPairs – sums the elements in the array by pairs (first + second, third + fourth, …).
    o   For example, [1, 2, 4, 5, 6, 7, 8] -> [3, 9, 13, 8].
• print – stop receiving more commands and print the last state of the array.

    input             output                       input                         output
  1 2 4 5 6 7      0                            1 2 3 4 5                  -1
  add 1 8          -1                           addMany 5 9 8 7 6 5        [2, 3, 5, 9, 8, 7, 6, 5, 1]
  contains 1       [1, 8, 2, 4, 5, 6, 7]        contains 15
  contains -3                                   remove 3
  print                                         shift 1
                                                print
*/

namespace Array_Manipulator
{
    using System;
    using System.Collections.Generic;
    using System.Linq;

    internal static class Program
    {
        private static void Main()
        {
            var numbers = Console.ReadLine()
                .Split()
                .Select(n => int.Parse(n))
                .ToList();

            var nextLine = Console.ReadLine();
            while (nextLine != "print")
            {
                if (nextLine == "sumPairs")
                {
                    SumElementsInListByPairs(numbers);
                }
                else
                {
                    var arguments = nextLine.Split();
                    switch (arguments[0])
                    {
                        case "add":
                            numbers.Insert(
                                int.Parse(arguments[1]), int.Parse(arguments[2]));
                            break;

                        case "addMany":
                            AddsSetOfElementsInListAtSpecificIndex(arguments, numbers);
                            break;

                        case "contains":
                            Console.WriteLine(numbers.IndexOf(int.Parse(arguments[1])));
                            break;

                        case "remove":
                            numbers.RemoveAt(int.Parse(arguments[1]));
                            break;

                        case "shift":
                            ShiftsEveryElementOfTheListWithNumberPositionsToTheLeft(
                                int.Parse(arguments[1]), numbers);
                            break;

                        default:
                            break;
                    }
                }

                nextLine = Console.ReadLine();
            }

            Console.WriteLine("[{0}]", string.Join(", ", numbers));
        }

        private static void AddsSetOfElementsInListAtSpecificIndex(
            string[] args, List<int> numbers)
        {
            var numbersToAdd = args.Skip(1).Select(n => int.Parse(n)).ToArray();
            for (int i = numbersToAdd.Length - 1; i > 0; i--)
            {
                numbers.Insert(numbersToAdd[0], numbersToAdd[i]);
            }
        }

        private static void ShiftsEveryElementOfTheListWithNumberPositionsToTheLeft(
            int positions, List<int> numbers)
        {
            for (int i = 0; i < positions; i++)
            {
                var movingNumber = numbers[0];
                numbers.RemoveAt(0);
                numbers.Add(movingNumber);
            }
        }

        private static void SumElementsInListByPairs(List<int> numbers)
        {
            var numbersArr = numbers.ToArray();
            numbers.Clear();
            for (int i = 0; i < numbersArr.Length; i += 2)
            {
                if (i + 1 >= numbersArr.Length)
                {
                    numbers.Add(numbersArr[i]);
                    break;
                }

                numbers.Add(numbersArr[i] + numbersArr[i + 1]);
            }
        }
    }
}