defmodule LocationSimulator.Gps do
  @moduledoc """
  Generate a random location. Get next gps from a location.
  """

  require Logger

  alias :math, as: Math

  @doc """
  Generates a random location.
  """
  @spec generate_pos :: {float, float}
  def generate_pos() do
    :rand.seed(System.monotonic_time(:nanosecond))
    {:rand.uniform(90), :rand.uniform(180)}
  end

  @doc """
  Gets next location from current location.
  """
  @spec generate_next_pos(float, float, integer, integer) :: {float, float}
  def generate_next_pos(lati, long, step_lati \\ 1, step_long \\ 1)
      when is_number(long) and is_number(lati) do
    new_lati = lati + step_lati * meter_in_degree()
    new_long = long + step_long * meter_in_degree() / Math.cos(lati * (Math.pi() / 180))
    {new_lati, new_long}
  end

  @spec meter_in_degree() :: float
  defp meter_in_degree() do
    # Radius of the earth (km)
    earth_radius = 6378.137
    pi = Math.pi()
    r = 2 * pi / 360
    r = 1 / (r * earth_radius)
    r / 1000
  end
end