defmodule ViaUtils.Location do
  @moduledoc """
  Documentation for `UtilsLocation`.
  """

  @doc """
  Hello world.

  ## Examples

      iex> UtilsLocation.hello()
      :world

  """
  require Logger
  require ViaUtils.Constants, as: VC

  @enforce_keys [:latitude_rad, :longitude_rad, :altitude_m]
  defstruct [:latitude_rad, :longitude_rad, :altitude_m]

  @spec new_location(number(), number(), number()) :: struct()
  def new_location(lat, lon, alt \\ 0) do
    %ViaUtils.Location{
      latitude_rad: lat,
      longitude_rad: lon,
      altitude_m: alt
    }
  end

  @spec new_location_input_degrees(number(), number(), number()) :: struct()
  def new_location_input_degrees(lat, lon, alt \\ 0) do
    new_location(ViaUtils.Math.deg2rad(lat), ViaUtils.Math.deg2rad(lon), alt)
  end

  @spec to_string(struct()) :: binary()
  def to_string(location) do
    lat_str = ViaUtils.Format.eftb(ViaUtils.Math.rad2deg(location.latitude_rad), 5)
    lon_str = ViaUtils.Format.eftb(ViaUtils.Math.rad2deg(location.longitude_rad), 5)
    alt_str = ViaUtils.Format.eftb(location.altitude_m, 1)
    "lat/lon/alt: #{lat_str}/#{lon_str}/#{alt_str}"
  end

  @spec dx_dy_between_points(struct(), struct()) :: tuple()
  def dx_dy_between_points(wp1, wp2) do
    dx_dy_between_points(wp1.latitude_rad, wp1.longitude_rad, wp2.latitude_rad, wp2.longitude_rad)
  end

  @spec dx_dy_between_points(float(), float(), float(), float()) :: tuple()
  def dx_dy_between_points(latitude1_rad, longitude1_rad, latitude2_rad, longitude2_rad) do
    dpsi =
      :math.log(
        :math.tan(VC.pi_4() + latitude2_rad / 2) / :math.tan(VC.pi_4() + latitude1_rad / 2)
      )

    dlat = latitude2_rad - latitude1_rad
    dlon = longitude2_rad - longitude1_rad

    q =
      if abs(dpsi) > 0.0000001 do
        dlat / dpsi
      else
        :math.cos(latitude1_rad)
      end

    {dlat * VC.earth_radius_m(), q * dlon * VC.earth_radius_m()}
  end

  @spec angle_between_points(struct(), struct()) :: float()
  def angle_between_points(location1, location2) do
    {dx, dy} = dx_dy_between_points(location1, location2)
    ViaUtils.Math.constrain_angle_to_compass(:math.atan2(dy, dx))
  end

  @spec location_from_point_with_dx_dy(struct(), float(), float()) :: struct()
  def location_from_point_with_dx_dy(starting_point, dx, dy) do
    lat1 = starting_point.latitude_rad
    lon1 = starting_point.longitude_rad
    dlat = dx / VC.earth_radius_m()
    lat2 = lat1 + dlat
    dpsi = :math.log(:math.tan(VC.pi_4() + lat2 / 2) / :math.tan(VC.pi_4() + lat1 / 2))

    q =
      if abs(dpsi) > 0.0000001 do
        dlat / dpsi
      else
        :math.cos(lat1)
      end

    dlon = dy / VC.earth_radius_m() / q
    lon2 = lon1 + dlon
    # {lat2, lon2}
    new_location(lat2, lon2, starting_point.altitude_m)
  end

  @spec location_from_point_with_distance_bearing(struct(), float(), float()) :: struct()
  def location_from_point_with_distance_bearing(starting_point, distance, bearing) do
    dx = distance * :math.cos(bearing)
    dy = distance * :math.sin(bearing)
    # Logger.debug("dx/dy: #{dx}/#{dy}")
    location_from_point_with_dx_dy(starting_point, dx, dy)
  end
end