using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace RailFence
{
    class Program
    {

        public static string Encrypt(string plainText, int key)
        { 
        
            int plainTextLength = plainText.Length;
            

            while (plainTextLength % key != 0)
            {
                plainText = plainText + " ";
                plainTextLength++;
            }
            

            int idx = plainTextLength / key;
            int counterPart = 0;


            string[] part = new string[idx];

            for(int i = 0; i < plainTextLength; i = i + key)
            {
                part[counterPart] = plainText.Substring(i, key);
                counterPart++;

            }

            string enc = "";

            string spos = " ";
            for (int k = 0; k < key; k++)
            {
                int step = key;
                if (step % 2 != 0)
                {
                    if (k % 2 == 0) step++;
                    else step--;
                }

                for (int x = k; x < idx; x = x + step)
                {
                    spos = spos + x + " ";
                    enc = enc + part[x];
                }
                spos = " ";
            }

            return enc;
        }

        public static string Decrypt(string textoEncriptado, int key) {

            int textoEncriptadoLength = textoEncriptado.Length;

            int idx = textoEncriptadoLength / key;
            int counterPart = 0;

            string[] decPos = new string[idx];

            string[] part = new string[idx];

            for (int i = 0; i < textoEncriptadoLength; i = i + key)
            {
                part[counterPart] = textoEncriptado.Substring(i, key);
                counterPart++;

            }

            string dec = "";
            int encCounter = 0;
            string spos = " ";
            for (int k = 0; k < key; k++)
            {
                int step = key;
                if (step % 2 != 0)
                {
                    if (k % 2 == 0) step++;
                    else step--;
                }

                for (int x = k; x < idx; x = x + step)
                {
                    spos = spos + x + " ("+encCounter+")";
                    decPos[x] = part[encCounter];
                    encCounter++;
                }
                spos = " ";
            }

            for (int y = 0; y < idx; y++ )
            {
                dec = dec + decPos[y];
            }

            return dec;

            
        }

        static void Main(string[] args)
        {
            int key = 3;
            string plainText =  "History has taught us: never underestimate the amount of money, time, " +
                                "and effort someone will expend to thwart a security system. It's always " +
                                "better to assume the worst. Assume your adversaries are better than they " +
                                "are. Assume science and technology will soon be able to do things they " +
                                "cannot yet. Give yourself a margin for error. Give yourself more security " +
                                "than you need today. When the unexpected happens, you'll be glad you did. " +
                                "--Bruce Schneier";

            String textEncrypted = Encrypt(plainText, key);
            Console.WriteLine(textEncrypted+"\n");

            String textDecrypted = Decrypt(textEncrypted, key);
            Console.WriteLine(textDecrypted);

            Console.ReadLine();

        }    
    }
}