defmodule Maxwell.Middleware.Rels do
  @moduledoc """
  Decode reponse's body's rels.

  ## Examples

         # Client.ex
         use Maxwell.Builder ~(get)a
         middleware Maxwell.Middleware.Rels

  """
  use Maxwell.Middleware

  def response(%Maxwell.Conn{} = conn, _opts) do
    link = conn.resp_headers['Link'] || conn.resp_headers["Link"]

    if link do
      rels =
        link
        |> to_string
        |> String.split(",")
        |> Enum.map(&String.trim/1)
        |> Enum.reduce(%{}, fn e, acc ->
          case Regex.named_captures(~r/(?<value>(.+)); rel=(?<key>(.+))/, e) do
            nil -> acc
            result -> Map.put(acc, result["key"], result["value"])
          end
        end)

      Map.put(conn, :rels, rels)
    else
      conn
    end
  end
end