defmodule Proxy do
  import Plug.Conn

  def init(options) do
    options
  end

  def call(conn, options) do
    conn
    |> put_forward_for
    |> call_upstream(options)
    |> handle_response(conn)
  end

  defp call_upstream(conn, options) do
    method = ProxyRequest.method(conn)
    url = ProxyRequest.url(options.upstream, conn)
    body = ProxyRequest.body(conn)
    headers = ProxyRequest.headers(conn)

    Upstream.request(method, url, body, headers, timeout: options.timeout)
  end

  defp handle_response({:error, response}, conn) do
    conn
    |> Plug.Conn.send_resp(502, "Bad Gateway")
  end
  defp handle_response({_, response}, conn) do
    conn
    |> put_resp_headers(response.headers)
    |> Plug.Conn.send_resp(response.status_code, response.body)
  end

  defp put_forward_for(conn) do
    ip = conn.remote_ip
    |> ProxyRequest.ipToString

    Plug.Conn.put_req_header(conn, "x-forwarded-for", ip)
  end

  defp put_resp_headers(conn, []), do: conn
  defp put_resp_headers(conn, [{header, value} | tail]) do
    conn
    |> Plug.Conn.put_resp_header(header |> String.downcase, value)
    |> put_resp_headers(tail)
  end
end