Use single bot per tournament

Author: vtm9

services/app/apps/codebattle/lib/codebattle/bot/context.ex

@@ -43,6 +43,14 @@ defmodule Codebattle.Bot.Context do
     |> Enum.map(&Map.merge(&1, params))
   end
 
+  @spec get(pos_integer()) :: User.t() | nil
+  def get(id) do
+    case Repo.get(User, id) do
+      %User{is_bot: true} = bot -> bot
+      _ -> nil
+    end
+  end
+
   defp bots_query(limit \\ 1) do
     from(
       user in User,

services/app/apps/codebattle/lib/codebattle/tournament/strategy/base.ex

@@ -888,6 +888,21 @@ defmodule Codebattle.Tournament.Base do
         game_params
       end
 
+      defp get_or_build_tournament_bot(tournament) do
+        meta = tournament.meta || %{}
+        bot_id = Map.get(meta, :bot_id)
+
+        case bot_id && Bot.Context.get(bot_id) do
+          %{} = bot ->
+            {tournament, Tournament.Player.new!(bot)}
+
+          _ ->
+            bot = Bot.Context.build()
+            meta = Map.put(meta, :bot_id, bot.id)
+            {update_struct(tournament, %{meta: meta}), Tournament.Player.new!(bot)}
+        end
+      end
+
       defp upsert_tournament_user_results(tournament) do
         Tournament.TournamentUserResult.upsert_results(tournament)
       end

services/app/apps/codebattle/lib/codebattle/tournament/strategy/swiss.ex

@@ -2,7 +2,6 @@ defmodule Codebattle.Tournament.Swiss do
   @moduledoc false
   use Codebattle.Tournament.Base
 
-  alias Codebattle.Bot
   alias Codebattle.Tournament
 
   @impl Tournament.Base
@@ -41,7 +40,7 @@ defmodule Codebattle.Tournament.Swiss do
   def build_round_pairs(tournament) do
     {player_pairs, unmatched_players, played_pair_ids} = build_player_pairs(tournament)
 
-    opponent_bot = Tournament.Player.new!(Bot.Context.build())
+    {tournament, opponent_bot} = get_or_build_tournament_bot(tournament)
 
     unmatched_pairs = Enum.map(unmatched_players, fn player -> [player, opponent_bot] end)