pivo

defmodule Pivo.Endpoint do
  @moduledoc """
  Endpoint behaviour module.

  Sets the endpoint configuration.

  This module is meant to be `use`'d in custom modules in order to support different
  endpoints of the Pivotal's Tracker API.

  Receives a `params` keyword list with the following keys:
  - Required
    + `path` - String
    + `http_methods` - list of triplets {action_verb, context, params}
  - Optional
    + `path_params` - keyword list

  ## Example

      defmodule Pivo.MeEndpoint do
        use Pivo.Endpoint,
          path: "/me",
          http_methods: [
              {:get, [resource: Me], []}
            ]
      end

  """

  @type t :: module()

  @typep params :: Keyword.t()

  @doc """
  Returns the current endpoint `path`.
  """
  @callback path() :: String.t()

  @doc """
  Returns the current endpoint `path_params`.
  """
  @callback path_params() :: params()

  defmacro __using__(options) do
    path = Keyword.get(options, :path, "/")
    path_params = Keyword.get(options, :path_params, [])
    http_methods = Keyword.get(options, :http_methods, [])

    quote bind_quoted: [
            path: path,
            path_params: path_params,
            http_methods: http_methods
          ],
          location: :keep do
      @behaviour Pivo.Endpoint

      @impl true
      def path, do: unquote(path)

      @impl true
      def path_params, do: unquote(path_params)
    end
  end

  @doc """
  Builds the `url_path` for a given `Pivo.Endpoint` using the provided parameters.
  """
  def build_path_with_params(endpoint, path_params) do
    string_path_params = stringify_path_params(endpoint.path_params(), path_params)

    Enum.reduce(string_path_params, endpoint.path(), fn {param_key, param_string_value}, url ->
      String.replace(url, ~r/({#{Atom.to_string(param_key)}})/, param_string_value)
    end)
  end

  defp stringify_path_params(params_def, params_val) do
    for {param_key, param_type} <- params_def do
      case Keyword.fetch(params_val, param_key) do
        {:ok, value} ->
          {param_key, path_param_to_string(param_type, value)}

        :error ->
          raise ArgumentError,
            message: "invalid argument path_params, missing required parameter: #{param_key}"
      end
    end
  end

  defp path_param_to_string(:integer, value) when is_integer(value) do
    Integer.to_string(value)
  end

  defp path_param_to_string(_, value) do
    to_string(value)
  end
end