distributed_system_coursework/lib/server.ex

defmodule ServerMacros do

  def create_create_loop(name, do: match_exp, else: process_exp, after: after_exp) do
    function_name = :"#{name}_loop"

    ast1 = quote do
      {:timeout} -> :timeout
    end
    ast2 = quote do
      value ->
        log("Got unexpected value: #{inspect(value)}")
        Process.send_after(self(), value, t + 2000)
        unquote(function_name)(v, t)
    end

    ast3 = ast1 ++ match_exp ++ ast2

    if after_exp != nil do
      quote do
        def unquote(function_name)(v, t) do
          var!(v) = v
          unquote(process_exp)
          receive do
            unquote(ast3)
          after
            unquote(after_exp)
          end
        end
      end
    else
      quote do
        def unquote(function_name)(v, t) do
          var!(v) = v
          unquote(process_exp)
          receive do
            unquote(ast3)
          after
            t -> :timeout
          end
        end
      end
    end
  end

  def create_create_loop(name, do: exp, else: else_exp) do
    create_create_loop(name, do: exp, else: else_exp, after: nil)
  end

  def create_create_loop(name, do: exp, after: after_exp) do
    create_create_loop(name, do: exp, else: nil, after: after_exp)
  end

  def create_create_loop(name, do: exp) do
    create_create_loop(name, do: exp, else: nil, after: nil)
  end

  defmacro create_loop(name, clauses) do
  	create_create_loop(name, clauses)
  end

  defmacro try_propose(val, do: ready, else: recal_do) do
    ast1 = quote do
      {:timeout} ->  unquote(recal_do)
      {:abort} ->   unquote(recal_do)
    end
    ast2 = quote do
      {:decision, v} ->
        var!(state) = apply_game(var!(state), v)
        unquote(recal_do)

      v ->
        raise "Unknown message on try_propose #{inspect(v)}"
    end

    ast3 = ast1 ++ ready ++ ast2

    quote do
      v = Paxos.propose(var!(state).paxos, var!(state).instance, unquote(val), 1000)
      case v do
        unquote(ast3)
      end
    end
  end

end

defmodule Server do
  require ServerMacros
  import ServerMacros
  require Utils
  import Utils

  create_log 3

  def start(name, participants) do
    log("starting server")

    pid = spawn(Server, :init, [name, participants])
    register_name(name, pid, false)
  end

  def init(name, participants) do
    paxos = Paxos.start(alter_name(name, "_paxos"), Enum.map(participants, fn name -> alter_name(name, "_paxos") end), true)
    state = %{
      name: name,
      procs: participants,
      games: %{},
      paxos: paxos,
      instance: 0,
    }

    run(state)
  end

  runfn do
    {:start_game, participants, pid_to_inform} ->
      {state, game_id} = try_to_create_game(state, participants)
      safecast(pid_to_inform, {:start_game_ans, game_id})
      state

    {:get_game_state, game_id, pid_to_inform} ->
      get_game_state(state, game_id, pid_to_inform)
  end

  def get_game_state(state, game_id, pid_to_inform, repeat \\ false) do
    cond do 
      state.games[game_id] == :not_playing_in_game ->
        safecast(pid_to_inform, {:game_state, game_id, :not_playing})
        state

      state.games[game_id] == nil ->
        if repeat do
          safecast(pid_to_inform, {:game_state, game_id, :game_does_not_exist})
          state
        else
          state = qurey_status(state)
          get_game_state(state, game_id, pid_to_inform, true)
        end

      true ->
        state = qurey_status(state)
        safecast(pid_to_inform, {:game_state, game_id, state.games[game_id].game_state, state.games[game_id].hand})
        state
    end
  end


  def try_to_create_game(state, participants) do
    game_ids = Map.keys(state.games)
    latest = Enum.at(Enum.sort(game_ids), length(game_ids) - 1)
    new_game_id = if latest do latest else 0 end + 1

    # TODO: randomize game state
    new_game_state = [1, 1]
    # TODO: randomize Initial hand value
    hand = Enum.reduce(participants, %{}, fn p, acc -> Map.put(acc, p, 1) end)

    try_propose {:start_game, new_game_id, participants, new_game_state, hand}
    do
      {:decision, {:start_game, ^new_game_id, ^participants, ^new_game_state, ^hand}} ->
        state = apply_game(state, {:start_game, new_game_id, participants, new_game_state, hand})
        {state, new_game_id}
    else
      try_to_create_game(state, participants)
    end
  end

  #
  # Utils
  #
  
  def qurey_status(state) do
    v = Paxos.get_decision(state.paxos, state.instance, 100)
    or_state v != nil do
      state = apply_game(state, v)
      qurey_status(state)
    end
  end

  #
  # Apply Game States
  #
  def apply_game(state, {:start_game, game_id, participants, new_game_state, hand}) do
    cond do
      state.games[game_id] ->
        raise :game_already_exists
      state.name in participants ->
        %{state | 
          games: Map.put(state.games, game_id, %{
            game_state: new_game_state,
            participants: participants,
            hand: hand[state.name],
          }),
          instance: state.instance + 1
        }
      true ->
        %{state | 
          games: Map.put(state.games, game_id, :not_playing_in_game),
          instance: state.instance + 1,
        }
    end
  end

  def apply_game(_, _), do: raise :do_not_know_how_to_apply_game_state

  ############
  # Interface 
  ############

  create_loop :start_game do
     {:start_game_ans, game_id} ->
       log("Started a game #{game_id}")
       {:start_game, game_id}
  end

  def start_game(name, participants) do
    safecast(name, {:start_game, participants, self()})
    start_game_loop(nil, 1000)
  end

  create_loop :get_game_state do
    {:game_state, ^v, :not_playing} ->
      IO.puts("Not Playing in that game")
      :not_playing
    {:game_state, ^v, game_state, hand} ->
      IO.puts("Got game state, #{inspect(game_state)}, hand: #{inspect(hand)}")
      {game_state, hand}
    {:game_state, ^v, :game_does_not_exist} ->
      IO.puts("Got game does not exist")
      nil
  end

  def get_game_state(name, game_id) do
    safecast(name, {:get_game_state, game_id, self()})
    get_game_state_loop(game_id, 1000)
  end


  ############
  # Debug 
  ############

  def spinup(number_of_participants) do
    procs = Enum.to_list(0..number_of_participants) |> Enum.map(fn n -> :"p#{n}" end)
    Enum.map(procs, fn proc -> Server.start(proc, procs) end)
  end

  def kill (pids) do
    pids |> Enum.map(fn m -> Process.exit(m, :kill) end)
  end
end