MoundHunters/lib/mound_hunters/ohio_lidar.ex

defmodule MoundHunters.OhioLidar do
  @moduledoc """
  Functions for querying Ohio's ArcGIS tile service and coordinate conversions.
  """
  require Logger

  # Ohio ArcGIS tile service
  @tile_service_url "https://maps.ohio.gov/arcgis/rest/services/OGRIP/3DepTiles/MapServer/0/query"

  # OGRIP download URL template
  @download_url_template "https://gis1.oit.ohio.gov/ZIPARCHIVES_III/ELEVATION/3DEP/LIDAR/{county}/{tile_name}.zip"

  @doc """
  Convert lon/lat (WGS84) to Web Mercator (EPSG:3857).
  
  Formula from: https://en.wikipedia.org/wiki/Web_Mercator_projection
  """
  def lonlat_to_webmercator(lon, lat) do
    # Earth radius in meters
    r = 6378137.0

    # Convert to radians
    lon_rad = lon * :math.pi() / 180.0
    lat_rad = lat * :math.pi() / 180.0

    # Web Mercator formulas
    x = r * lon_rad
    y = r * :math.log(:math.tan(:math.pi() / 4.0 + lat_rad / 2.0))

    {x, y}
  end

  @doc """
  Query Ohio ArcGIS service for tile information at given coordinates.
  
  Returns {:ok, tile_info} or {:error, reason}
  
  tile_info contains: %{
    tile_name: "BS19820747",
    county: "LIC",
    year: "2020",
    block: "4",
    note: "..."
  }
  """
  def query_tile_info(lon, lat) do
    {x, y} = lonlat_to_webmercator(lon, lat)

    geometry =
      Jason.encode!(%{
        x: x,
        y: y,
        spatialReference: %{wkid: 3857}
      })

    params = %{
      "f" => "json",
      "returnGeometry" => "false",
      "spatialRel" => "esriSpatialRelIntersects",
      "geometry" => geometry,
      "geometryType" => "esriGeometryPoint",
      "inSR" => "3857",
      "outFields" => "*",
      "outSR" => "3857"
    }

    Logger.debug("Querying ArcGIS for tile at (#{lon}, #{lat}) -> WebMercator (#{x}, #{y})")

    case HTTPoison.get(@tile_service_url, [], params: params, timeout: 10_000) do
      {:ok, %HTTPoison.Response{status_code: 200, body: body}} ->
        parse_tile_response(body)

      {:ok, %HTTPoison.Response{status_code: status}} ->
        Logger.error("ArcGIS returned status #{status}")
        {:error, "ArcGIS service returned status #{status}"}

      {:error, %HTTPoison.Error{reason: reason}} ->
        Logger.error("Failed to query ArcGIS: #{inspect(reason)}")
        {:error, "Network error: #{inspect(reason)}"}
    end
  end

  defp parse_tile_response(body) do
    case Jason.decode(body) do
      {:ok, %{"features" => []}} ->
        {:error, :no_tile_found}

      {:ok, %{"features" => [feature | _]}} ->
        attrs = feature["attributes"]

        tile_info = %{
          tile_name: attrs["TileName"],
          county: attrs["County"],
          year: attrs["Year"],
          block: attrs["Block"],
          note: attrs["note"]
        }

        {:ok, tile_info}

      {:ok, _} ->
        {:error, :invalid_response}

      {:error, _} ->
        {:error, :json_parse_error}
    end
  end

  @doc """
  Get the download URL for a tile.
  """
  def get_download_url(tile_name, county) do
    @download_url_template
    |> String.replace("{county}", county)
    |> String.replace("{tile_name}", tile_name)
  end

  @doc """
  Download a tile ZIP file from OGRIP.
  
  Returns {:ok, file_path} or {:error, reason}
  """
  def download_tile(tile_name, county, output_path) do
    url = get_download_url(tile_name, county)
    Logger.info("Downloading #{tile_name} from #{url}")

    # Ensure output directory exists
    output_path
    |> Path.dirname()
    |> File.mkdir_p!()

    case HTTPoison.get(url, [], timeout: 60_000, recv_timeout: 60_000, stream_to: self()) do
      {:ok, %HTTPoison.AsyncResponse{id: id}} ->
        receive_download(id, output_path, 0)

      {:error, %HTTPoison.Error{reason: reason}} ->
        Logger.error("Failed to start download: #{inspect(reason)}")
        {:error, "Download failed: #{inspect(reason)}"}
    end
  end

  defp receive_download(id, output_path, bytes_received) do
    receive do
      %HTTPoison.AsyncStatus{id: ^id, code: 200} ->
        Logger.debug("Download started, status 200")
        receive_download(id, output_path, bytes_received)

      %HTTPoison.AsyncStatus{id: ^id, code: status} ->
        Logger.error("Download failed with status #{status}")
        {:error, "HTTP status #{status}"}

      %HTTPoison.AsyncHeaders{id: ^id} ->
        # Start writing to file
        File.open(output_path, [:write, :binary], fn file ->
          receive_download_chunks(id, file, bytes_received)
        end)

      %HTTPoison.AsyncEnd{id: ^id} ->
        Logger.error("Download ended prematurely")
        {:error, :unexpected_end}

      {:error, reason} ->
        Logger.error("Download error: #{inspect(reason)}")
        {:error, reason}
    after
      70_000 ->
        {:error, :timeout}
    end
  end

  defp receive_download_chunks(id, file, bytes_received) do
    receive do
      %HTTPoison.AsyncChunk{id: ^id, chunk: chunk} ->
        IO.binwrite(file, chunk)
        new_bytes = bytes_received + byte_size(chunk)

        # Log progress every 10MB
        if div(new_bytes, 10_485_760) > div(bytes_received, 10_485_760) do
          Logger.debug("Downloaded #{div(new_bytes, 1_048_576)} MB")
        end

        receive_download_chunks(id, file, new_bytes)

      %HTTPoison.AsyncEnd{id: ^id} ->
        size_mb = bytes_received / 1_048_576
        Logger.info("Download complete: #{Float.round(size_mb, 2)} MB")
        {:ok, bytes_received}

      {:error, reason} ->
        {:error, reason}
    after
      70_000 ->
        {:error, :timeout}
    end
  end
end