phash

defmodule PHash do
  alias PHash.NIFs

  @doc """
  Reads an image from a path and produces a hash that can be compared
  with another hash via `PHash.image_hash_distance/2`.
  """
  def image_file_hash(image_path) when is_binary(image_path) do
    if File.exists?(image_path) do
      NIFs.image_hash(image_path)
    else
      {:error, :enoent}
    end
  end

  @doc """
  Write the image binary data to a temporary file and produces the same result
  as `PHash.image_file_hash/1` using that file.
  """
  def image_binary_hash(image_data) when is_binary(image_data) do
    Temp.track!()

    result =
      with {:ok, file_path} <- Temp.open([prefix: "phash"], &IO.binwrite(&1, image_data)) do
        image_file_hash(file_path)
      end

    Temp.cleanup()

    result
  end

  @doc """
  Calculates the hamming distance between two image hashes.
  """
  def image_hash_distance(hash_a, hash_b)
      when is_integer(hash_a) and is_integer(hash_b) and hash_a > 0 and hash_b > 0 do
    NIFs.image_hash_distance(hash_a, hash_b)
  end
end