defmodule Microwaveprop.Rover.Elevation do
  @moduledoc """
  Bulk SRTM elevation lookup for a list of `{lat, lon}` points.

  Wraps `Microwaveprop.Terrain.Srtm.lookup/3`, which already opens and
  reads each tile per call. Cells whose tile is missing or whose value
  is the SRTM void sentinel are mapped to `nil`.
  """

  alias Microwaveprop.Terrain.Srtm

  @spec lookup_many([{float(), float()}]) :: %{{float(), float()} => integer() | nil}
  def lookup_many(points) when is_list(points) do
    tiles_dir = Application.get_env(:microwaveprop, :srtm_tiles_dir, "/data/srtm")

    Map.new(points, fn {lat, lon} = key ->
      case Srtm.lookup(lat, lon, tiles_dir) do
        {:ok, elev} -> {key, elev}
        {:error, _} -> {key, nil}
      end
    end)
  end
end