defmodule Phoenix.SessionProcess.SessionId do
  @moduledoc """
  Documentation for `Phoenix.SessionProcess.SessionId`.

  Add this after the `:fetch_session` plug to generate a unique session ID.

      plug :fetch_session
      plug Phoenix.SessionProcess.SessionId

  """
 @behaviour Plug

 import Plug.Conn

 @impl true
 def init(default), do: default

 @impl true
 def call(conn, _config) do
   case get_session(conn, :session_id) do
     nil ->
       session_id = generate_unique_session_id()
       put_session(conn, :session_id, session_id)

     _session_id ->
       conn
   end
 end

 @spec generate_unique_session_id() :: binary()
 def generate_unique_session_id() do
   :crypto.strong_rand_bytes(16) |> Base.encode16()
 end
end