Store and Retrieve the Game State

We want to store the full state for each game in the :game_state table whenever it changes. We register each game process by the name of the first player, so the name makes a great key to store the state under.

Changes in the Game module

For game processes, some states will change whenever there is a successful reply, either in the game itself or in the state machine data. Luckily, we wrote a single function in the Game module to handle successful replies— reply_success/2. A call to :ets.insert/2 with the name :player1 as the key and the full game state as the value is all we need:

defp reply_success(state_data, reply) do
  :ets.insert(:game_state, {state_data.player1.name, state_data})
  {:reply, reply, state_data, @timeout}
end

Any time we start or restart a process, GenServer triggers the init/1 callback. That makes init/1 a good place to check the :game_state table for any state stored under the first player’s name.

If :ets.lookup/2 returns an empty list, we generate fresh state the way init/1 had done before. If :ets.lookup/2 returns some state, we use that instead.

We add a new private function that returns the state of a new game given the first player’s name:

defp fresh_state(name) do
  player1 = %{name: name, board: Board.new(), guesses: Guesses.new()}
  player2 = %{name: nil, board: Board.new(), guesses: Guesses.new()}
  %{player1: player1, player2: player2, rules: %Rules{}}
end

Then, we can use that new function in init/1:

def init(name) do
  state_data =
  case :ets.lookup(:game_state, name) do
    [] -> fresh_state(name)
    [{_key, state}] -> state
  end
  :ets.insert(:game_state, {name, state_data})
  {:ok, state_data, @timeout}
end