fakephone

defmodule Fakephone do
  @moduledoc """
    A GenServer fake phone number process.
  """

  use GenServer

  # Client API

  def start_link(opts \\ []) do
    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
  end

  def init(_opts) do
    {:ok, %{}}
  end

  # Server Callbacks

  def get_new_phone(phone) do
    GenServer.call(__MODULE__, {:get_new_phone, phone})
  end

  def get_current_phone(phone) do
    GenServer.call(__MODULE__, {:get_current_phone, phone})
  end

  def get_real_phone_by_fake_number(phone) do
    GenServer.call(__MODULE__, {:get_real_phone, phone})
  end

  def get_fake_phone_by_real_phone(phone) do
    GenServer.call(__MODULE__, {:get_fake_phone, phone})
  end

  # Callbacks
  def handle_call({:get_new_phone, phone_number}, _from, state) do
    new_number = generate_random_phone_number()
    updated_state = Map.put(state, phone_number, new_number)
    {:reply, new_number, updated_state}
  end

  def handle_call({:get_current_phone, phone_number}, _from, state) do
    fake_number = Map.get(state, phone_number, generate_random_phone_number())
    new_state = Map.put(state, phone_number, fake_number)
    {:reply, fake_number, new_state}
  end

  def handle_call({:get_fake_phone, real_number}, _from, state) do
    fake_number = Map.get(state, real_number, generate_random_phone_number())
    new_state = Map.put(state, real_number, fake_number)
    {:reply, fake_number, new_state}
  end

  def handle_call({:get_real_phone, fake_number}, _from, state) do
    real_number = filter_by_value(state, fake_number)
    {:reply, real_number, state}
  end

  # Helpers

  defp generate_random_phone_number do
    country_code = "52"

    area_code = "55"

    remaining_digits = Enum.join(Enum.map(1..7, fn _ -> Integer.to_string(Enum.random(0..9)) end))

    phone_number = "#{country_code}#{area_code}#{remaining_digits}"

    phone_number
  end

  defp filter_by_value(map, fake_number) do
    map
    |> Enum.filter(fn {_key, value} -> value == fake_number end)
    |> Enum.map(fn {key, _value} -> key end)
    |> case do
      [] -> fake_number
      [key] -> key
    end
  end
end