defmodule ExFirebaseAuth.KeySource.Google do
  @moduledoc false

  @endpoint_url "https://www.googleapis.com/robot/v1/metadata/x509/securetoken@system.gserviceaccount.com"

  @behaviour ExFirebaseAuth.KeySource

  def fetch_certificates do
    with {:ok, %Finch.Response{body: body}} <-
           Finch.build(:get, @endpoint_url) |> Finch.request(ExFirebaseAuthFinch),
         {:ok, json_data} <- Jason.decode(body) do
      {:ok, convert_to_jose_keys(json_data)}
    else
      _ ->
        :error
    end
  end

  defp convert_to_jose_keys(json_data) do
    json_data
    |> Enum.map(fn {key, value} ->
      case JOSE.JWK.from_pem(value) do
        [] -> {key, nil}
        jwk -> {key, jwk}
      end
    end)
    |> Enum.filter(fn {_, value} -> not is_nil(value) end)
  end
end