feat: slots minigame

data/slots.csv

@@ -0,0 +1,7 @@
+probability,multiplier
+0.3,1.0
+0.08,2.0
+0.04,3.0
+0.025,5.0
+0.00499,10.0
+0.00001,100.0

lib/mix/tasks/gen.slots_payouts.ex

@@ -0,0 +1,59 @@
+defmodule Mix.Tasks.Gen.Payouts do
+  @shortdoc "Generates slot machine payouts from a CSV"
+  @moduledoc """
+  This CSV is waiting for:
+    probability,multiplier
+  """
+  use Mix.Task
+
+  alias NimbleCSV.RFC4180, as: CSV
+
+  def run(args) do
+    if Enum.empty?(args) do
+      Mix.shell().info("Needs to receive a file URL.")
+    else
+      args |> List.first() |> create
+    end
+  end
+
+  defp create(path) do
+    Mix.Task.run("app.start")
+
+    path
+    |> parse_csv()
+    |> validate_probabilities()
+    |> insert_payouts()
+  end
+
+  defp parse_csv(path) do
+    path
+    |> File.stream!()
+    |> CSV.parse_stream()
+    |> Enum.map(fn [probability, muliplier] ->
+      %{
+        probability: String.to_float(probability),
+        multiplier: String.to_float(muliplier)
+      }
+    end)
+  end
+
+  defp validate_probabilities(list) do
+    list
+    |> Enum.map_reduce(0, fn payout, acc -> {payout, payout.probability + acc} end)
+    |> case do
+      {_, x} ->
+        if x < 1 do
+          list
+        else
+          raise "The sum of all payout probabilities is bigger 1."
+        end
+    end
+  end
+
+  defp insert_payouts(list) do
+    list
+    |> Enum.map(fn payout ->
+      Safira.Slots.create_payout(payout)
+    end)
+  end
+end

lib/safira/roulette/roulette.ex

@@ -241,9 +241,9 @@ defmodule Safira.Roulette do
   end
 
   @doc """
-  Transaction that take a number of tokens from an attendee,
-  apply a probability-based function for "spinning the wheel",
-  and give the price to the attendee.
+  Transaction that takes a number of tokens from an attendee,
+  and applies a probability-based function for "spinning the wheel",
+  and give the prize to the attendee.
   """
   def spin_transaction(attendee) do
     Multi.new()

lib/safira/slots/attendee_payout.ex

@@ -0,0 +1,32 @@
+defmodule Safira.Slots.AttendeePayout do
+  @moduledoc """
+  Intermediate schema to register slot payouts won by attendees or losses.
+  """
+  use Ecto.Schema
+  import Ecto.Changeset
+
+  alias Safira.Accounts.Attendee
+  alias Safira.Slots.Payout
+
+  schema "attendees_payouts" do
+    field :bet, :integer
+    field :tokens, :integer
+
+    belongs_to :attendee, Attendee, foreign_key: :attendee_id, type: :binary_id
+    belongs_to :payout, Payout
+
+    timestamps()
+  end
+
+  @doc false
+  def changeset(attendee_prize, attrs) do
+    attendee_prize
+    |> cast(attrs, [:bet, :tokens, :attendee_id, :payout_id])
+    |> validate_required([:bet, :tokens, :attendee_id])
+    |> unique_constraint(:unique_attendee_payout)
+    |> validate_number(:bet, greater_than: 0)
+    |> validate_number(:tokens, greater_than_or_equal_to: 0)
+    |> foreign_key_constraint(:attendee_id)
+    |> foreign_key_constraint(:payout_id)
+  end
+end

lib/safira/slots/payout.ex

@@ -0,0 +1,24 @@
+defmodule Safira.Slots.Payout do
+  @moduledoc """
+  Payouts listed in the pay table that can be won by playing slots.
+  """
+  use Ecto.Schema
+  use Arc.Ecto.Schema
+  import Ecto.Changeset
+
+  schema "payouts" do
+    field :probability, :float
+    # supports float multipliers like 1.5x
+    field :multiplier, :float
+
+    timestamps()
+  end
+
+  def changeset(payout, attrs) do
+    payout
+    |> cast(attrs, [:probability, :multiplier])
+    |> validate_required([:probability, :multiplier])
+    |> validate_number(:multiplier, greater_than: 0)
+    |> validate_number(:probability, greater_than: 0, less_than_or_equal_to: 1)
+  end
+end

lib/safira/slots/slots.ex

@@ -0,0 +1,158 @@
+defmodule Safira.Slots do
+  @moduledoc """
+  The Slots context.
+  """
+
+  import Ecto.Query, warn: false
+
+  alias Ecto.Multi
+
+  alias Safira.Repo
+
+  alias Safira.Accounts.Attendee
+  alias Safira.Contest
+  alias Safira.Contest.DailyToken
+  alias Safira.Slots.AttendeePayout
+  alias Safira.Slots.Payout
+
+  @doc """
+  Creates a payout.
+
+  ## Examples
+
+      iex> create_payout(%{field: value})
+      {:ok, %Payout{}}
+
+      iex> create_payout(%{field: bad_value})
+      {:error, %Ecto.Changeset{}}
+
+  """
+  def create_payout(attrs \\ %{}) do
+    %Payout{}
+    |> Payout.changeset(attrs)
+    |> Repo.insert()
+  end
+
+  def spin(attendee, bet) do
+    spin_transaction(attendee, bet)
+    |> case do
+      {:error, :attendee_state, changeset, data} ->
+        if Map.get(get_errors(changeset), :token_balance) != nil do
+          {:error, :not_enough_tokens}
+        else
+          {:error, :attendee, changeset, data}
+        end
+
+      result ->
+        result
+    end
+  end
+
+  @doc """
+  Transaction that takes a number of tokens bet by an attendee,
+  and applies a probability-based function for "spinning the reels on a slot machine"
+  that calculates a payout and then updates the attendee's token balance.
+  """
+  def spin_transaction(attendee, bet) do
+    Multi.new()
+    # remove the bet from the attendee's token balance
+    |> Multi.update(
+      :attendee_state,
+      Attendee.update_token_balance_changeset(attendee, %{
+        token_balance: attendee.token_balance - bet
+      })
+    )
+    # generate a random payout
+    |> Multi.run(:payout, fn _repo, _changes -> {:ok, generate_spin()} end)
+    # calculate the tokens (if any)
+    |> Multi.run(:tokens, fn _repo, %{payout: payout} ->
+      {:ok, (bet * payout.multiplier) |> round}
+    end)
+    # log slots result for statistical purposes
+    |> Multi.insert(:attendee_payout, fn %{payout: payout, tokens: tokens} ->
+      %AttendeePayout{}
+      |> AttendeePayout.changeset(%{
+        attendee_id: attendee.id,
+        payout_id: payout.id,
+        bet: bet,
+        tokens: tokens
+      })
+    end)
+    # update user tokens based on the payout
+    |> Multi.update(:attendee, fn %{attendee_state: attendee, tokens: tokens} ->
+      Attendee.update_token_balance_changeset(attendee, %{
+        token_balance: attendee.token_balance + tokens
+      })
+    end)
+    # update the daily token count for leaderboard purposes
+    |> Multi.insert_or_update(:daily_token, fn %{attendee: attendee} ->
+      {:ok, date, _} = DateTime.from_iso8601("#{Date.utc_today()}T00:00:00Z")
+      changeset_daily = Contest.get_keys_daily_token(attendee.id, date) || %DailyToken{}
+
+      DailyToken.changeset(changeset_daily, %{
+        quantity: attendee.token_balance,
+        attendee_id: attendee.id,
+        day: date
+      })
+    end)
+    |> Repo.transaction()
+  end
+
+  # Generates a random payout, based on the probability of each multiplier
+  defp generate_spin do
+    random = strong_randomizer() |> Float.round(12)
+
+    payouts =
+      Repo.all(Payout)
+      |> Enum.filter(fn x -> x.probability > 0 end)
+
+    cumulative_prob =
+      payouts
+      |> Enum.sort_by(& &1.probability)
+      |> Enum.map_reduce(0, fn payout, acc ->
+        {Float.round(acc + payout.probability, 12), acc + payout.probability}
+      end)
+
+    cumulatives =
+      cumulative_prob
+      |> elem(0)
+      |> Enum.concat([1])
+
+    sum =
+      cumulative_prob
+      |> elem(1)
+
+    remaining_prob = 1 - sum
+
+    real_payouts = payouts ++ [%{multiplier: 0, probability: remaining_prob, id: nil}]
+
+    prob =
+      cumulatives
+      |> Enum.filter(fn x -> x >= random end)
+      |> Enum.at(0)
+
+    real_payouts
+    |> Enum.sort_by(& &1.probability)
+    |> Enum.at(
+      cumulatives
+      |> Enum.find_index(fn x -> x == prob end)
+    )
+  end
+
+  # Generates a random number using the Erlang crypto module
+  defp strong_randomizer do
+    <<i1::unsigned-integer-32, i2::unsigned-integer-32, i3::unsigned-integer-32>> =
+      :crypto.strong_rand_bytes(12)
+
+    :rand.seed(:exsplus, {i1, i2, i3})
+    :rand.uniform()
+  end
+
+  defp get_errors(changeset) do
+    Ecto.Changeset.traverse_errors(changeset, fn {msg, opts} ->
+      Enum.reduce(opts, msg, fn {key, value}, acc ->
+        String.replace(acc, "%{#{key}}", to_string(value))
+      end)
+    end)
+  end
+end

lib/safira_web/controllers/slots/slots_controller.ex

@@ -0,0 +1,42 @@
+defmodule SafiraWeb.SlotsController do
+  use SafiraWeb, :controller
+
+  alias Safira.Accounts
+  alias Safira.Slots
+
+  action_fallback SafiraWeb.FallbackController
+
+  def spin(conn, %{"bet" => bet}) do
+    attendee = Accounts.get_user(conn) |> Map.fetch!(:attendee)
+
+    if is_nil(attendee) do
+      conn
+      |> put_status(:unauthorized)
+      |> json(%{error: "Only attendees can play the slots"})
+    else
+      case Integer.parse(bet) do
+        {bet, ""} ->
+          if bet > 0 do
+            case Slots.spin(attendee, bet) do
+              {:ok, outcome} ->
+                render(conn, :spin_result, outcome)
+
+              {:error, :not_enough_tokens} ->
+                conn
+                |> put_status(:unauthorized)
+                |> json(%{error: "Insufficient token balance"})
+            end
+          else
+            conn
+            |> put_status(:bad_request)
+            |> json(%{error: "Bet should be a positive integer"})
+          end
+
+        _ ->
+          conn
+          |> put_status(:bad_request)
+          |> json(%{error: "Bet should be an integer"})
+      end
+    end
+  end
+end

lib/safira_web/controllers/slots/slots_json.ex

@@ -0,0 +1,13 @@
+defmodule SafiraWeb.SlotsJSON do
+  @moduledoc false
+
+  def spin_result(data) do
+    payout = Map.get(data, :payout)
+    tokens = Map.get(data, :tokens)
+
+    %{
+      multiplier: payout.multiplier,
+      tokens: tokens
+    }
+  end
+end

lib/safira_web/router.ex

@@ -63,6 +63,7 @@ defmodule SafiraWeb.Router do
     post "/spotlight", SpotlightController, :create
     post "/store/redeem", DeliverRedeemableController, :create
     post "/roulette/redeem", DeliverPrizeController, :create
+    post "/slots", SlotsController, :spin
 
     delete "/roulette/redeem/:badge_id/:user_id", DeliverPrizeController, :delete
 

priv/repo/migrations/20240120000345_create_payouts.exs

@@ -0,0 +1,14 @@
+defmodule Safira.Repo.Migrations.CreatePayouts do
+  use Ecto.Migration
+
+  def change do
+    create table(:payouts) do
+      add :probability, :float
+      add :multiplier, :float
+
+      timestamps()
+    end
+
+    create unique_index(:payouts, [:multiplier])
+  end
+end

priv/repo/migrations/20240120001336_create_attendees_payouts.exs

@@ -0,0 +1,17 @@
+defmodule Safira.Repo.Migrations.CreateAttendeesPayouts do
+  use Ecto.Migration
+
+  def change do
+    create table(:attendees_payouts) do
+      add :attendee_id, references(:attendees, on_delete: :delete_all, type: :uuid)
+      add :payout_id, references(:payouts, on_delete: :delete_all)
+      add :bet, :integer
+      add :tokens, :integer
+
+      timestamps()
+    end
+
+    create index(:attendees_payouts, [:attendee_id])
+    create index(:attendees_payouts, [:payout_id])
+  end
+end