defmodule Pleroma.Web.OAuth.OAuthController do
  use Pleroma.Web, :controller

  alias Pleroma.Web.OAuth.{Authorization, Token, App}
  alias Pleroma.{Repo, User}
  alias Comeonin.Pbkdf2

  plug(:fetch_session)
  plug(:fetch_flash)

  action_fallback(Pleroma.Web.OAuth.FallbackController)

  def authorize(conn, params) do
    render(conn, "show.html", %{
      response_type: params["response_type"],
      client_id: params["client_id"],
      scope: params["scope"],
      redirect_uri: params["redirect_uri"],
      state: params["state"]
    })
  end

  def create_authorization(conn, %{
        "authorization" =>
          %{
            "name" => name,
            "password" => password,
            "client_id" => client_id,
            "redirect_uri" => redirect_uri
          } = params
      }) do
    with %User{} = user <- User.get_by_nickname_or_email(name),
         true <- Pbkdf2.checkpw(password, user.password_hash),
         %App{} = app <- Repo.get_by(App, client_id: client_id),
         {:ok, auth} <- Authorization.create_authorization(app, user) do
      if redirect_uri == "urn:ietf:wg:oauth:2.0:oob" do
        render(conn, "results.html", %{
          auth: auth
        })
      else
        connector = if String.contains?(redirect_uri, "?"), do: "&", else: "?"
        url = "#{redirect_uri}#{connector}code=#{auth.token}"

        url =
          if params["state"] do
            url <> "&state=#{params["state"]}"
          else
            url
          end

        redirect(conn, external: url)
      end
    end
  end

  # TODO
  # - proper scope handling
  def token_exchange(conn, %{"grant_type" => "authorization_code"} = params) do
    with %App{} = app <- get_app_from_request(conn, params),
         fixed_token = fix_padding(params["code"]),
         %Authorization{} = auth <-
           Repo.get_by(Authorization, token: fixed_token, app_id: app.id),
         {:ok, token} <- Token.exchange_token(app, auth) do
      response = %{
        token_type: "Bearer",
        access_token: token.token,
        refresh_token: token.refresh_token,
        expires_in: 60 * 10,
        scope: "read write follow"
      }

      json(conn, response)
    else
      _error -> json(conn, %{error: "Invalid credentials"})
    end
  end

  # TODO
  # - investigate a way to verify the user wants to grant read/write/follow once scope handling is done
  def token_exchange(
        conn,
        %{"grant_type" => "password", "name" => name, "password" => password} = params
      ) do
    with %App{} = app <- get_app_from_request(conn, params),
         %User{} = user <- User.get_cached_by_nickname(name),
         true <- Pbkdf2.checkpw(password, user.password_hash),
         {:ok, auth} <- Authorization.create_authorization(app, user),
         {:ok, token} <- Token.exchange_token(app, auth) do
      response = %{
        token_type: "Bearer",
        access_token: token.token,
        refresh_token: token.refresh_token,
        expires_in: 60 * 10,
        scope: "read write follow"
      }

      json(conn, response)
    else
      _error -> json(conn, %{error: "Invalid credentials"})
    end
  end

  defp fix_padding(token) do
    token
    |> Base.url_decode64!(padding: false)
    |> Base.url_encode64()
  end

  defp get_app_from_request(conn, params) do
    # Per RFC 6749, HTTP Basic is preferred to body params
    {client_id, client_secret} =
      with ["Basic " <> encoded] <- get_req_header(conn, "authorization"),
           {:ok, decoded} <- Base.decode64(encoded),
           [id, secret] <-
             String.split(decoded, ":")
             |> Enum.map(fn s -> URI.decode_www_form(s) end) do
        {id, secret}
      else
        _ -> {params["client_id"], params["client_secret"]}
      end

    if client_id && client_secret do
      Repo.get_by(
        App,
        client_id: client_id,
        client_secret: client_secret
      )
    else
      nil
    end
  end
end