philomena/lib/philomena_web/controllers/search/reverse_controller.ex

defmodule PhilomenaWeb.Search.ReverseController do
  use PhilomenaWeb, :controller

  alias Philomena.Processors
  alias Philomena.DuplicateReports
  alias Philomena.Repo
  import Ecto.Query

  plug PhilomenaWeb.ScraperPlug, [params_key: "image", params_name: "image"] when action in [:create]

  def index(conn, _params) do
    render(conn, "index.html", images: nil)
  end

  def create(conn, %{"image" => image_params}) do
    images =
      image_params["image"].path
      |> mime()
      |> analyze()
      |> intensities()
      |> case do
        :error ->
          []

        {analysis, intensities} ->
          {width, height} = analysis.dimensions
          aspect = width / height
          dist = normalize_dist(image_params)

          DuplicateReports.duplicates_of(intensities, aspect, dist, dist)
          |> preload(:tags)
          |> Repo.all()
      end

    conn
    |> render("index.html", images: images)
  end

  defp mime(file) do
    {:ok, mime} = Philomena.Mime.file(file)

    {mime, file}
  end

  defp analyze({mime, file}) do
    case Processors.analyzers(mime) do
      nil -> :error
      a   -> {a.analyze(file), mime, file}
    end
  end

  defp intensities(:error), do: :error
  defp intensities({analysis, mime, file}) do
    {analysis, Processors.processors(mime).intensities(analysis, file)}
  end

  # The distance metric is taxicab distance, not Euclidean,
  # because this is more efficient to index.
  defp normalize_dist(%{"distance" => distance}) do
    distance
    |> String.to_float()
    |> max(0.01)
    |> min(1.0)
  end
end