// Programmer: Gabriel Fontaine

// Dates Worked On: Start Date: May 11 - End Date: 18

// Description: Make an encrytpion program and a decryption program to encrypt messages (note that this is with the concept of moving three characters to the right to encrypt them)

// Project: Simple Cryptography

using System;

public class Program

{

    public static void Main()

    {

        String message; // the sequence of words that the user is saying

        String encryptionStatus = ""; // the variable that determines if the user wants to encrypt or decrypt a message

        int asciiLetter = 0;

        Console.WriteLine("Welcome to the top secret Encryption Application:");

        recheckEncryption: // error checking for mispelling

        Console.WriteLine("Do you wish to Encrypt or Decrypt messages (Encrypt/Decrypt)");

        encryptionStatus = Console.ReadLine().ToLower().Substring(0, 1); // I use substring because I doubt most people can spell encrypt or decrypt flawlessly

        if (encryptionStatus != "e" && encryptionStatus != "d"){ // only need to check for the situation when the user does not type either encrypt or decrypt, as the same variable is used to declare that the user is encrypting or decrypting later in the code

            Console.WriteLine();

            Console.WriteLine("That is not an available option, please check over your answer");

            goto recheckEncryption; // making sure the user chooses an available option

        }

        Console.WriteLine("Enter in your secret message"); // note that this set of text will work with both encrypting and decrypting hidden messages

        message = Console.ReadLine(); // the encoded message that the user types

        if (encryptionStatus == "e"){ // the user has chosen to encrypt their message

            for (int position = 0; position < message.Length; position += 1){

                asciiLetter = char.ConvertToUtf32(message, position); // takes a certain letter from the alphabet within the message and converts that single character based on its position into an ascii numerical value

                // if this segment of code is not true the character will have been not a letter in the alphabet

                if ((asciiLetter > 64 && asciiLetter < 91) || (asciiLetter > 96 && asciiLetter < 123)){ // checks to see if it is within the range of the capital letters in the alphabet or if the letter is within the lower case portion of the alphabet, such as ABC or abc

                    asciiLetter += 3; // adds three letters for the encryption process

                    if (asciiLetter > 90 && asciiLetter < 97){ // if it passes the letter "Z" we want it to go back to the letter "A" (note that the range of numbers looks peculiar because it must also account for the other varification for the lower case and upper case letters)

                        asciiLetter -= 26; // goes back to first letters of the alphabet by subtracting all previous letters

                    } else if (asciiLetter > 122){ // if it passes the letter "z" we want it to go back to the letter "a"

                        asciiLetter -= 26;

                    }

                }

                Console.Write(char.ConvertFromUtf32(asciiLetter)); // prints the individual letter

            }

        } else { // only two options, so you are either encrypting messages, or decrypting them

            for (int position = 0; position < message.Length; position += 1){

                asciiLetter = char.ConvertToUtf32(message, position); // takes a certain letter from the alphabet within the message and converts that single character based on its position into an ascii numerical value

                // if this segment of code is not true the character will have been not a letter in the alphabet

                if ((asciiLetter > 64 && asciiLetter < 91) || (asciiLetter > 96 && asciiLetter < 123)){ // checks to see if it is within the range of the capital letters in the alphabet or if the letter is within the lower case portion of the alphabet, such as ABC or abc

                    asciiLetter -= 3; // removes three letters for the decryption process

                    if (asciiLetter < 65){ // if it passes the letter "A" we want it to go back to the letter "Z"

                        asciiLetter += 26; // goes back to the last letters of the alphabet by adding all previous letters

                    } else if (asciiLetter < 97 && asciiLetter > 90){ // if it passes the letter "z" we want it to go back to the letter "z" as this is a check to see if it ever leaves the range of the alphabet

                        asciiLetter += 26;

                    }

                }

                Console.Write(char.ConvertFromUtf32(asciiLetter)); // prints the individual letter

            }

        }

    }

}