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

  alias CSV

  @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, :erik) do
      [_, place, _, _, _, _, _, _, _, _, _, _, _, _] ->
        {:ok, place |> String.split(" (") |> List.first()}

      _ ->
        :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."}

  def postal_code_to_location(postal_code)
      when is_binary(postal_code) and bit_size(postal_code) == 32 do
    case get_matching_postal_code(postal_code, :erik) do
      [_, _, _, _, _, _, _, _, _, latitude, longitude, _, _, _] ->
        {latitude, longitude}

      _ ->
        :no_results
    end
  end

  def postal_code_to_location(postal_code) when is_binary(postal_code),
    do: {:error, "Length must be 4."}

  def postal_code_to_location(_postal_code),
    do: {:error, "Invalid type of postal code, must be string"}

  @doc false
  defp get_erik_file do
    Path.join(File.cwd!(), "postnummer.csv")
    |> File.stream!([:encoding, :utf8])
    |> CSV.decode(encoding: :utf8)
    |> Enum.map(fn x ->
      case x do
        {:ok, list} ->
          Enum.at(
            Enum.map(list, fn y -> y |> String.replace("\r", "") |> String.split("\t") end),
            0
          )
      end
    end)
  end

  defp get_matching_postal_code(postal_code, :erik) do
    Enum.find(get_erik_file(), fn x -> Enum.at(x, 0) == postal_code end)
  end
end