analytics/lib/plausible_web/refinspector.ex

defmodule PlausibleWeb.RefInspector do
  def parse(nil), do: nil

  def parse(ref) do
    case ref.source do
      :unknown ->
        uri = URI.parse(String.trim(ref.referer))

        if right_uri?(uri) do
          format_referrer_host(uri)
        end

      source ->
        source
    end
  end

  def format_referrer(uri) do
    path = String.trim_trailing(uri.path || "", "/")
    format_referrer_host(uri) <> path
  end

  def right_uri?(%URI{host: nil}), do: false

  def right_uri?(%URI{host: host, scheme: scheme})
      when scheme in ["http", "https", "android-app"] and byte_size(host) > 0,
      do: true

  def right_uri?(_), do: false

  defp format_referrer_host(uri) do
    protocol = if uri.scheme == "android-app", do: "android-app://", else: ""
    host = String.replace_prefix(uri.host, "www.", "")

    protocol <> host
  end
end