(** Geographic vector module *)

type t = {
  dx : float;  (* km *)
  dy : float;  (* km *)
}

let deg_to_rad = Float.pi /. 180.0
let rad_to_deg = 180.0 /. Float.pi

let create_cartesian ~dx ~dy = { dx; dy }

let create_polar ~heading ~distance =
  (* Convert heading to mathematical angle (east = 0, counterclockwise) *)
  let angle = (90.0 -. heading) *. deg_to_rad in
  {
    dx = distance *. cos angle;
    dy = distance *. sin angle;
  }

let between p1 p2 =
  (* Calculate vector between two coordinates *)
  let dist = Coord.distance_haversine p1 p2 in
  let bearing = Coord.bearing p1 p2 in
  create_polar ~heading:bearing ~distance:dist

let dx t = t.dx
let dy t = t.dy

let heading t =
  (* Convert from mathematical angle to geographic heading *)
  let angle = atan2 t.dy t.dx *. rad_to_deg in
  mod_float (90.0 -. angle +. 360.0) 360.0

let distance t =
  sqrt (t.dx ** 2.0 +. t.dy ** 2.0)

let add v1 v2 = {
  dx = v1.dx +. v2.dx;
  dy = v1.dy +. v2.dy;
}

let sub v1 v2 = {
  dx = v1.dx -. v2.dx;
  dy = v1.dy -. v2.dy;
}

let scale v factor = {
  dx = v.dx *. factor;
  dy = v.dy *. factor;
}

let neg v = {
  dx = -.v.dx;
  dy = -.v.dy;
}

let rotate v degrees =
  let angle = degrees *. deg_to_rad in
  let cos_a = cos angle in
  let sin_a = sin angle in
  {
    dx = v.dx *. cos_a -. v.dy *. sin_a;
    dy = v.dx *. sin_a +. v.dy *. cos_a;
  }

let apply coord v =
  Coord.offset coord ~heading:(heading v) ~distance:(distance v)

let to_string t =
  Printf.sprintf "Vector(heading=%.2f°, distance=%.2fkm)" (heading t) (distance t)