geocalc

defmodule Geocalc do
  @moduledoc """
  Calculate distance, bearing and more between Latitude/Longitude points.
  """

  use Application

  alias Geocalc.Point
  alias Geocalc.Calculator

  # See http://elixir-lang.org/docs/stable/elixir/Application.html
  # for more information on OTP Applications
  def start(_type, _args) do
    Geocalc.Supervisor.start_link()
  end

  @doc """
  Calculates distance between 2 points.
  Return distance in meters.

  ## Example
      iex> berlin = [52.5075419, 13.4251364]
      iex> paris = [48.8588589, 2.3475569]
      iex> Geocalc.distance_between(berlin, paris)
      878327.4291149472
      iex> Geocalc.distance_between(paris, berlin)
      878327.4291149472

  ## Example
      iex> berlin = %{lat: 52.5075419, lon: 13.4251364}
      iex> london = %{lat: 51.5286416, lng: -0.1015987}
      iex> paris = %{latitude: 48.8588589, longitude: 2.3475569}
      iex> Geocalc.distance_between(berlin, paris)
      878327.4291149472
      iex> Geocalc.distance_between(paris, london)
      344229.88946533133
  """
  @spec distance_between(Point.t, Point.t) :: number
  def distance_between(point_1, point_2) do
    GenServer.call(calc_pid, {:distance_between, point_1, point_2})
  end

  @doc """
  Calculates bearing.
  Return radians.

  ## Example
      iex> berlin = {52.5075419, 13.4251364}
      iex> paris = {48.8588589, 2.3475569}
      iex> Geocalc.bearing(berlin, paris)
      -1.9739245359361486
      iex> Geocalc.bearing(paris, berlin)
      1.0178267866082613

  ## Example
      iex> berlin = %{lat: 52.5075419, lon: 13.4251364}
      iex> paris = %{latitude: 48.8588589, longitude: 2.3475569}
      iex> Geocalc.bearing(berlin, paris)
      -1.9739245359361486
  """
  @spec bearing(Point.t, Point.t) :: number
  def bearing(point_1, point_2) do
    GenServer.call(calc_pid, {:bearing, point_1, point_2})
  end

  @doc """
  Finds point between start and end points in direction to end point
  with given distance (in meters).
  Finds point from start point with given distance (in meters) and bearing.
  Return array with latitude and longitude.

  ## Example
      iex> berlin = [52.5075419, 13.4251364]
      iex> paris = [48.8588589, 2.3475569]
      iex> bearing = Geocalc.bearing(berlin, paris)
      iex> distance = 400_000
      iex> Geocalc.destination_point(berlin, bearing, distance)
      {:ok, [50.97658022467569, 8.165929595956982]}

  ## Example
      iex> zero_point = {0.0, 0.0}
      iex> equator_degrees = 90.0
      iex> equator_bearing = Geocalc.degrees_to_radians(equator_degrees)
      iex> distance = 1_000_000
      iex> Geocalc.destination_point(zero_point, equator_bearing, distance)
      {:ok, [5.484172965344896e-16, 8.993216059187306]}

  ## Example
      iex> berlin = %{lat: 52.5075419, lon: 13.4251364}
      iex> bearing = -1.9739245359361486
      iex> distance = 100_000
      iex> Geocalc.destination_point(berlin, bearing, distance)
      {:ok, [52.147030316318904, 12.076990111001148]}

  ## Example
      iex> berlin = [52.5075419, 13.4251364]
      iex> paris = [48.8588589, 2.3475569]
      iex> distance = 250_000
      iex> Geocalc.destination_point(berlin, paris, distance)
      {:ok, [51.578054644172525, 10.096282782248409]}
  """
  @spec destination_point(Point.t, Point.t, number) :: tuple
  @spec destination_point(Point.t, number, number) :: tuple
  def destination_point(point_1, point_2, distance) do
    GenServer.call(calc_pid, {:destination_point, point_1, point_2, distance})
  end

  @doc """
  Finds intersection point from start points with given bearings.
  Return array with latitude and longitude.
  Raise an exception if no intersection point found.

  ## Example
      iex> berlin = [52.5075419, 13.4251364]
      iex> berlin_bearing = -2.102
      iex> london = [51.5286416, -0.1015987]
      iex> london_bearing = 1.502
      iex> Geocalc.intersection_point(berlin, berlin_bearing, london, london_bearing)
      {:ok, [51.49271112601574, 10.735322818996854]}

  ## Example
      iex> berlin = {52.5075419, 13.4251364}
      iex> london = {51.5286416, -0.1015987}
      iex> paris = {48.8588589, 2.3475569}
      iex> Geocalc.intersection_point(berlin, london, paris, london)
      {:ok, [51.5286416, -0.10159869999999019]}

  ## Example
      iex> berlin = %{lat: 52.5075419, lng: 13.4251364}
      iex> bearing = Geocalc.degrees_to_radians(90.0)
      iex> Geocalc.intersection_point(berlin, bearing, berlin, bearing)
      {:error, "No intersection point found"}
  """
  @spec intersection_point(Point.t, Point.t, Point.t, Point.t) :: tuple
  @spec intersection_point(Point.t, Point.t, Point.t, number) :: tuple
  @spec intersection_point(Point.t, number, Point.t, Point.t) :: tuple
  @spec intersection_point(Point.t, number, Point.t, number) :: tuple
  def intersection_point(point_1, bearing_1, point_2, bearing_2) do
    args = {:intersection_point, point_1, bearing_1, point_2, bearing_2}
    try do
      GenServer.call(calc_pid, args)
    catch
      :exit, _ -> {:error, "No intersection point found"}
    end
  end

  @doc """
  Calculates a bounding box around a point with a radius in meters
  Returns an array with 2 points (list format). The bottom left point,
  and the top-right one

  ## Example
      iex> berlin = [52.5075419, 13.4251364]
      iex> radius = 10_000
      iex> Geocalc.bounding_box(berlin, radius)
      [[52.417520954378574, 13.277235453275123], [52.59756284562143, 13.573037346724874]]
  """
  @spec bounding_box(Point.t, number) :: list
  def bounding_box(point, radius_in_m) do
    GenServer.call(calc_pid, {:bounding_box, point, radius_in_m})
  end

  @doc """
  Compute the geographic center (aka geographic midpoint, center of gravity)
  for an array of geocoded objects and/or [lat,lon] arrays (can be mixed).
  Any objects missing coordinates are ignored. Follows the procedure
  documented at http://www.geomidpoint.com/calculation.html.

  ## Example
      iex> point_1 = [0, 0]
      iex> point_2 = [0, 3]
      iex> Geocalc.geographic_center([point_1, point_2])
      [0.0, 1.5]
  """
  @spec geographic_center(list) :: Point.t
  def geographic_center(points) do
    GenServer.call(calc_pid, {:geographic_center, points})
  end

  @doc """
  Converts radians to degrees.
  Return degrees.

  ## Example
      iex> Geocalc.radians_to_degrees(2.5075419)
      143.67156782221554

  ## Example
      iex> Geocalc.radians_to_degrees(-0.1015987)
      -5.821176714015797
  """
  @spec radians_to_degrees(number) :: number
  def radians_to_degrees(radians) do
    GenServer.call(calc_pid, {:radians_to_degrees, radians})
  end

  @doc """
  Converts degrees to radians.
  Return radians.

  ## Example
      iex> Geocalc.degrees_to_radians(143.67156782221554)
      2.5075419

  ## Example
      iex> Geocalc.degrees_to_radians(-10.735322818996854)
      -0.18736672945597435
  """
  @spec degrees_to_radians(number) :: number
  def degrees_to_radians(degrees) do
    GenServer.call(calc_pid, {:degrees_to_radians, degrees})
  end

  defp calc_pid do
    workers = Supervisor.which_children(Geocalc.Supervisor)
    {Calculator, pid, :worker, _} = hd(workers)
    pid
  end
end