philomena/lib/camo/image.ex

defmodule Camo.Image do
  def image_url(input) do
    %{host: host} = URI.parse(input)

    if !host or String.ends_with?(host, cdn_host()) or is_nil(camo_key()) do
      input
    else
      camo_digest = :crypto.hmac(:sha, camo_key(), input) |> Base.encode16(case: :lower)

      camo_uri = %URI{
        host: camo_host(),
        path: "/" <> camo_digest,
        query: URI.encode_query(url: input),
        scheme: "https"
      }

      URI.to_string(camo_uri)
    end
  end

  defp cdn_host do
    Application.get_env(:philomena, :cdn_host)
  end

  defp camo_key do
    Application.get_env(:philomena, :camo_key)
  end

  defp camo_host do
    Application.get_env(:philomena, :camo_host)
  end
end