srtm

defmodule SRTM.Source.AWS do
  use SRTM.Source
  @moduledoc false

  alias SRTM.Client

  @base_url "https://s3.amazonaws.com/elevation-tiles-prod/skadi"

  @impl true
  def fetch(%Client{client: client, cache_path: cache_path}, {lat, lng}) do
    <<dir::binary-size(3)>> <> _ = name = name(lat, lng)
    url = "#{@base_url}/#{dir}/#{name}.hgt.gz"
    path = Path.join([cache_path, name <> ".hgt"])

    with {:ok, zipped_data} <- get(client, url),
         data = :zlib.gunzip(zipped_data),
         :ok <- write(path, data) do
      {:ok, path}
    end
  end

  defp write(path, data) do
    with {:error, reason} <- File.write(path, data) do
      {:error, %Error{reason: :io_error, message: "Writing hgt data failed: #{inspect(reason)}"}}
    end
  end
end