OpenWeatherMap API Basic Integration using Elixir

Weather.ex

defmodule Weather do
  @moduledoc """
    deps: [
      {:poison, "~> 4.0"},
      {:httpoison, "~> 1.7"}
    ]
  """
  @api_key "" # obtain for free at https://openweathermap.org/api
  @base_url "https://api.openweathermap.org/data/2.5"

  # Default coordinates of Atlanta, GA
  @default_latitude "33.7490"
  @default_longitude "-84.3880"

  defp prefix(str, prefix) do
    String.replace_prefix(str, "", prefix)
  end

  defp prefix(str, prefix, predicate) do
    cond do
      predicate.(str) -> prefix(str, prefix)
      true -> str
    end
  end

  defp map_to_params, do: ""

  defp map_to_params(map) do
    map
    |> Enum.map(fn {k, v} -> Atom.to_string(k) <> "=" <> v end)
    |> Enum.join("&")
    |> prefix("?", fn str -> byte_size(str) > 0 end)
  end

  def fetch(latitude \\ @default_latitude, longitude \\ @default_longitude) do
    %{
      lat: latitude,
      lon: longitude,
      units: "imperial",
      appid: @api_key
    }
    |> map_to_params()
    |> prefix(@base_url <> "/weather")
    |> HTTPoison.get!
    |> Map.get(:body)
    |> Poison.decode!(keys: :atoms)
  end

  def pretty_print(forecast) do
    with %{name: name, main: %{ temp: temperature, humidity: humidity }} = forecast,
      temp = Float.floor(temperature, 0) |> trunc() |> Integer.to_string() do
      "Currently in " <> name <> ", it is " <> temp <> "˚F, with a humidity of " <> Integer.to_string(humidity) <> "%."
    end
  end
end