defmodule PostalCode do
  @moduledoc """
  Postal code parser for the Norwegian postal code system.
  """

  @doc """
  Accepts a postal code in string format, and returns the postal place.

  ## Examples

    iex> PostalCode.postal_code_to_place("0186")
    {:ok, "OSLO"}

    iex> PostalCode.postal_code_to_place("0638")
    :no_results

    iex> PostalCode.postal_code_to_place(0186)
    {:error, "Invalid type of postal code, must be string."}

    iex> PostalCode.postal_code_to_place("018")
    {:error, "Length must be 4."}
  """
  def postal_code_to_place(postal_code) when is_binary(postal_code) and bit_size(postal_code) == 32 do
    case get_matching_postal_code(postal_code) do
      [_postal_code, place, _county_code, _county_name, _category] ->
        {:ok, place}

      nil ->
        :no_results
    end
  end
  def postal_code_to_place(postal_code) when is_binary(postal_code), do: {:error, "Length must be 4."}
  def postal_code_to_place(_postal_code), do: {:error, "Invalid type of postal code, must be string."}

  @doc false
  defp get_postal_codes do
    Path.join(File.cwd!(), "postal_codes.csv")
    |> Path.expand(__DIR__)
    |> File.read!()
    |> String.split("\n")
    |> Enum.map(fn x -> x |> String.replace("\r", "") |> String.split("\t") end)
  end

  @doc false
  defp get_matching_postal_code(postal_code) do
    Enum.find(get_postal_codes(), fn x -> Enum.at(x, 0) == postal_code end)
  end

end