# priv/repo/migrations/20210816141921_create_votes.exs
create table(:votes) do
  add :player_id, references(:players, type: :uuid, on_delete: :nothing)
  add :dealt_card_id, references(:dealt_cards, on_delete: :nothing)
  timestamps()
end

create index(:votes, [:player_id])
create index(:votes, [:dealt_card_id])
# MISSING: unique constraint on [:player_id, :dealt_card_id]

vote = get_vote(dealt_card, player)

if vote do
  # Time window for race condition here
  Copi.Repo.delete!(vote)
else
  # Multiple concurrent requests can both pass this check
  case Copi.Repo.insert(%Copi.Cornucopia.Vote{
    dealt_card_id: String.to_integer(dealt_card_id), 
    player_id: player.id
  }) do
    {:ok, _vote} -> # ...
    {:error, _changeset} -> # ...
  end
end

test "prevents duplicate votes from concurrent requests", %{game: game, player: player} do
  dealt_card = List.first(game.dealt_cards)
  
  # Simulate concurrent vote requests
  tasks = for _ <- 1..5 do
    Task.async(fn ->
      Repo.insert(%Vote{player_id: player.id, dealt_card_id: dealt_card.id})
    end)
  end
  
  results = Enum.map(tasks, &Task.await/1)
  successes = Enum.count(results, fn 
    {:ok, _} -> true
    _ -> false
  end)
  
  assert successes == 1, "Only one vote should succeed"
  assert Repo.aggregate(Vote, :count) == 1
end