def encrypt(string, shift)
  string.map! do |char|
    if char.ord == 32
      char
    elsif (char.ord + shift) < 123
      (char.ord + shift).chr
    else
      (char.ord + shift - 26).chr
    end
  end
  string.join
end

def decrypt(string, shift)
  string.map! do |char|
    if char.ord == 32
      char
    elsif (char.ord - shift) > 96
      (char.ord - shift).chr
    else
      (char.ord - shift + 26).chr
    end
  end
  string.join
end

puts "Enter filename to encrypt and shift: "
filename = gets.chomp
shift = gets.to_i

encrypted = ""
File.open(filename, "r") do |f|
  f.each_line do |line|
    encrypted += encrypt(line.chomp.chars, shift) + "\n"
  end
end
puts encrypted

File.open(filename, "w") do |line|
  line.puts "\r" + encrypted
end

puts "Enter filename to decrypt and shift: "
filename = gets.chomp
shift = gets.to_i

decrypted = ""
File.open(filename, "r") do |f|
  f.each_line do |line|
    decrypted += decrypt(line.chomp.chars, shift) + "\n"
  end
end
puts decrypted