Encode secret messages into text using zero-width spaces

SecretMessage.exs

defmodule SecretMessage do

  @zero "\u200C"
  @one "\u200D"

  def encode(text, secret) when byte_size(text) > byte_size(secret) do
    secret
    |> obfuscate
    |> Stream.concat(Stream.repeatedly fn -> "" end)
    |> Stream.zip(String.codepoints text)
    |> Enum.map(fn {x, y} -> [y, x] end)
    |> IO.iodata_to_binary
  end
  def encode(_text, _secret) do
    raise "Text must be longer than secret"
  end

  def decode(text) do
    text
    |> String.codepoints
    |> Stream.filter(& &1 in [@zero, @one])
    |> Stream.map(fn @zero -> <<0::1>>; @one -> <<1::1>> end)
    |> Stream.chunk_every(8)
    |> Stream.map(&deobfuscate/1) 
    |> Enum.filter(& bit_size(&1) == 8)
    |> IO.iodata_to_binary
  end

  defp obfuscate(secret) do
    for << b::1 <- secret >> do
      case b do
        0 -> @zero
        1 -> @one
      end
    end
    |> Enum.chunk_every(8)
  end

  defp deobfuscate(bits) do
    bits |> Enum.reduce(<<>>, fn x, acc -> <<acc::bitstring, x::bitstring>> end)
  end
end

text = "This is a test, it is only a test"
secret = "Secret secret"
IO.puts "Text:"
IO.puts text
IO.puts "Secret:"
IO.puts secret
IO.puts "Encoded:"
SecretMessage.encode(text, secret) |> IO.puts
IO.puts "Decoded:"
SecretMessage.encode(text, secret) |> SecretMessage.decode |> IO.puts
IO.puts "String length:"
SecretMessage.encode(text, secret) |> String.length |> IO.puts
IO.puts "Byte size:"
SecretMessage.encode(text, secret) |> byte_size |> IO.puts
IO.puts "Codepoints:"
SecretMessage.encode(text, secret) |> String.codepoints |> IO.inspect(limit: 500)

# Run with `elixir SecretMessage.exs`