defmodule Vuforex.Signature do
  @moduledoc false

  @hex_digest "d41d8cd98f00b204e9800998ecf8427e"
  @server_secret_key Application.compile_env!(:vuforex, :server_secret_key)

  @spec generate(String.t(), String.t() | nil, String.t(), String.t()) :: any()
  @doc """
  Generates the signature based on path, body, http verb and time.

  ## Examples

    iex> Vuforex.Signature.generate("/summary", nil, "GET", "Sun, 25 Apr 2021 17:34:44 GMT")
    "JLJTY+J/6O6FpXsY4t3CbGRwmOc="
  """
  def generate(path, body, verb, time) when body in ["POST", "PUT"] do
    hex_digest =
      :crypto.hash(:md5, Jason.encode!(body))
      |> Base.encode16()

    to_digest = "#{verb}\n#{hex_digest}\napplication/json\n#{time}\n#{path}"

    to_digest |> do_generate_hash()
  end

  def generate(path, _body, verb, time) do
    to_digest = "#{verb}\n#{@hex_digest}\n\n#{time}\n#{path}"

    to_digest |> do_generate_hash()
  end

  defp do_generate_hash(to_digest) do
    :crypto.hmac(:sha, @server_secret_key, to_digest) |> Base.encode64()
  end
end