defmodule Cnum.Brands do
  @moduledoc false

  # Brands is an in-memory table that stores supported credit cards'
  # Bank Identification Numbers according to their credit card brands.

  use GenServer

  @table_name :bins

  # Client

  def start_link(_arg) do
    GenServer.start_link(__MODULE__, nil, name: __MODULE__)
  end

  def get(key) do
    GenServer.call(__MODULE__, {:get, key})
  end

  # Ets methods

  def init(_) do
    :ets.new(@table_name, [:named_table])
    populate()
    {:ok, @table_name}
  end

  def handle_call({:get, key}, _from, state) do
    reply =
      case :ets.lookup(@table_name, key) do
        [] -> nil
        [{_key, value}] -> value
      end
      {:reply, reply, state}
  end

  # -------------------------------------------------- #

  defp brands() do
    [
      {"amex", ["34", "37"]},
      {"diners club", [300..305, "3095", "36", 38..39 ]},
      {"discover", ["6011", 622126..622925, 624000..626999, 628200..628899, "64", "65"]},
      {"jcb", [3528..3589]},
      {"maestro", ["6304", "6759", "6761", "6763", "676770", "676774"]},
      {"master card", [2221..2720, 51..55]},
      {"visa", ["4"]},
      {"visa electron", ["4026", "417500", "4405", "4508", "4844", "4913", "4917"]},
    ]
  end

  defp populate do
    for {brand, values} <- brands() do
      for first_digits <- values, do: seed_data(brand, first_digits)
    end
  end

  defp seed_data(brand, %Range{} = range) do
    for first_digits <- range do
      :ets.insert(@table_name, {"#{first_digits}", brand})
    end
  end

  defp seed_data(brand, first_digits) when is_binary(first_digits) do
    :ets.insert(@table_name, {first_digits, brand})
  end
end