Improved RestClient (HTTPoison based), with support for passing config params as a single map

rest_client.ex

defmodule RestClient do 
  require Logger
  alias Poison, as: JSON

  def get_by_path(config, path, id, params)
    when (is_binary(id) or is_integer(id)) and is_list(params) do
    get_by_path(config, [path: path, id: id, params: params])
  end 

  def get_by_path(config, path, params) 
    when is_list(params) do  
    get_by_path(config, [path: path, params: params])
  end 

  def get_by_path(config, path, id) 
    when is_binary(id) or is_integer(id) do
    get_by_path(config, [path: path, id: id])
  end 

  def get_by_path(config, query) 
    when is_list(query) do
    get_by_path(config, format_path(query))
  end

  def get_by_path(config, fullpath) 
    when is_binary(fullpath) do
    uri = URI.encode(format_baseurl(config.baseurl) <> fullpath)
    get_by_url(config, uri)      
  end 

  def get_by_url(config, url) do
    content_type = "application/json"
    headers = [{"Accept", content_type}]
    headers = case auth_header(config.username, config.password) do
      nil -> headers
      auth -> [auth | headers]
    end 

    Logger.info "Request = {get, #{url}, #{inspect headers}}" 
    result = HTTPoison.get!(url, headers)
    %HTTPoison.Response{status_code: status_code, body: body} = result
    case status_code do
      200 ->
        JSON.decode!(body)
      _ ->
        {:error, status_code}
    end
  end

  def update_by_path(config, method, {path, id, params}, body) 
    when is_binary(path) and (is_binary(id) or is_integer(id)) and is_list(params) do
    query = [path: path, id: id, params: params]
    update_by_path(config, method, query, body)
  end

  def update_by_path(config, method, {path, id}, body) 
    when is_binary(path) and (is_binary(id) or is_integer(id)) do
    query = [path: path, id: id]
    update_by_path(config, method, query, body)
  end

  def update_by_path(config, method, {path, params}, body) 
    when is_binary(path) and is_list(params) do
    query = [path: path, params: params]
    update_by_path(config, method, query, body)
  end

  def update_by_path(config, method, query, body) 
    when is_list(query) do
    update_by_path(config, method, format_path(query), body)
  end

  def update_by_path(config, method, fullpath, body) 
    when is_binary(fullpath) do
    url = "#{format_baseurl(config.baseurl)}#{fullpath}" |> URI.encode()
    update_by_url(config, method, url, body)
  end

  def update_by_url(config, method, url, body) do
    content_type = "application/json"
    headers = [{"Content-Type", content_type},
              {"Accept", content_type}]
    headers = case auth_header(config.username, config.password) do
      nil -> headers
      auth -> [auth | headers]
    end 

    Logger.info "Request = {#{method}, #{url}, #{inspect body}}" 
    body2 = JSON.encode!(body)
    result = HTTPoison.request!(method, url, body2, headers)
    %HTTPoison.Response{status_code: status_code, body: body2} = result
    case status_code do
      200 ->
        JSON.decode!(body2)
      201 ->
        JSON.decode!(body2)
      _ ->
        {:error, {status_code, JSON.decode!(body2)}}
    end
  end

  defp format_baseurl(baseurl) do
    case String.ends_with?(baseurl, "/") do 
      true -> baseurl
      false -> "#{baseurl}/"
    end
  end

  defp auth_header(nil, nil) do
    nil
  end

  defp auth_header(username, password) do
    encoded = Base.encode64("#{username}:#{password}")
    {"Authorization", "Basic #{encoded}"}
  end

  defp format_path(path: path, params: params) do
    query = params
    |> Enum.reduce("", fn ({k, v}, acc) -> acc <> "#{k}=#{v}&" end)
    |> String.rstrip(?&)
    "#{path}/?#{query}"
  end 

  defp format_path(path: path, id: id) do
    "#{path}/#{id}"
  end   

  defp format_path(path: path, id: id, params: params) do
    query = params
    |> Enum.reduce("", fn ({k, v}, acc) -> acc <> "#{k}=#{v}&" end)
    |> String.rstrip(?&)
    "#{path}/#{id}/?#{query}"
  end 
end

defmodule RestApi1 do
  @baseurl Application.get_env(:rest_client, :rest_api1_baseurl)
  @username Application.get_env(:rest_client, :rest_api1_username)
  @password Application.get_env(:rest_client, :rest_api1_password)

  def config do 
    %{baseurl: @baseurl, username: @username, password: @password}
  end
end 

defmodule RestApi2 do
  @baseurl Application.get_env(:rest_client, :rest_api2_baseurl)
  @username Application.get_env(:rest_client, :rest_api2_username)
  @password Application.get_env(:rest_client, :rest_api2_password)

  def config do 
    %{baseurl: @baseurl, username: @username, password: @password}
  end
end