Pete/internal/games/uno/nomercy_test.go

package uno

import (
	"math/rand/v2"
	"testing"
)

func nmDuel() Tier  { t, _ := TierBySlug("nm-duel"); return t }
func nmTable() Tier { t, _ := TierBySlug("nm-table"); return t }
func nmFull() Tier  { t, _ := TierBySlug("nm-full"); return t }

func TestNoMercyDeckIsADeck(t *testing.T) {
	m := census(State{Deck: NewNoMercyDeck()})
	if got := total(m); got != 168 {
		t.Fatalf("deck has %d cards, want 168", got)
	}
	want := map[Card]int{
		{Red, Zero}:          2, // two of every number, unlike the normal deck's single zero
		{Blue, Seven}:        2,
		{Green, Skip}:        3,
		{Yellow, SkipAll}:    2,
		{Red, Reverse}:       4,
		{Blue, DrawTwo}:      2,
		{Green, DrawFour}:    2, // the *coloured* +4
		{Yellow, DiscardAll}: 3,
		{Wild, WildRevFour}:  8,
		{Wild, WildDrawSix}:  4,
		{Wild, WildDrawTen}:  4,
		{Wild, WildRoulette}: 8,
	}
	for c, n := range want {
		if m[c] != n {
			t.Errorf("%v %v: got %d, want %d", c.Color, c.Value, m[c], n)
		}
	}
	// The normal deck's wilds are not in this one, and its coloured +4 is not in
	// the normal one. They are different cards that print the same thing.
	if m[Card{Wild, WildCard}] != 0 || m[Card{Wild, WildDrawFour}] != 0 {
		t.Error("the No Mercy deck should print none of the normal wilds")
	}
}

// TestNoMercyCensus is the load-bearing one, and the same one the normal game
// has: 168 cards, each in exactly one place, checked after every move of a
// hundred games played to the end.
//
// It is what would catch the two new ways this deck can lose a card. Discard All
// buries a whole colour under the pile, and a mercy kill shovels a
// twenty-five-card hand back into the deck — either of those dropping a card on
// the floor is a deck that quietly shrinks until the table can't be dealt.
func TestNoMercyCensus(t *testing.T) {
	for _, tier := range []Tier{nmDuel(), nmTable(), nmFull()} {
		for seed := uint64(0); seed < 100; seed++ {
			s := deal(t, tier, 100, seed)
			start := census(s)
			if got := total(start); got != 168 {
				t.Fatalf("%s seed %d: dealt %d cards, want 168", tier.Slug, seed, got)
			}
			rng := rand.New(rand.NewPCG(seed, 99))
			for moves := 0; s.Phase != PhaseDone && moves < 800; moves++ {
				next, _, err := ApplyMove(s, naive(s, rng))
				if err != nil {
					t.Fatalf("%s seed %d: %v (phase %s)", tier.Slug, seed, err, s.Phase)
				}
				s = next
				if got := census(s); total(got) != 168 {
					t.Fatalf("%s seed %d: %d cards after a move, want 168",
						tier.Slug, seed, total(got))
				}
			}
			if s.Phase != PhaseDone {
				t.Fatalf("%s seed %d: game never ended", tier.Slug, seed)
			}
		}
	}
}

// naive is the strategy the multiples are priced against: play the first legal
// card you hold, take a stack you can't answer, and draw when you have nothing.
// It is a real way to play and a bad one, which is exactly what a house edge is
// measured against.
func naive(s State, rng *rand.Rand) Move {
	if s.Phase == PhaseStack {
		if p := s.Playable(); len(p) > 0 {
			return playMove(s, p[0], rng)
		}
		return Move{Kind: MoveTake}
	}
	if p := s.Playable(); len(p) > 0 {
		return playMove(s, p[0], rng)
	}
	return Move{Kind: MoveDraw}
}

// stack loads a seat's hand up to n cards by taking them off the deck, so the
// table still holds 168 of them. Every card it moves is one that can't be played
// on the pile, which is what a hand on its way to the mercy limit looks like.
func stack(s *State, seat, n int) {
	// Every card the seat was holding goes back in the deck first, so the table is
	// whole before we take n out of it again. The pile keeps whatever the deal
	// turned over — replacing it with a card of our choosing would quietly destroy
	// one, and the census below would blame the engine for it.
	s.Deck = append(s.Deck, s.Hands[seat]...)
	s.Hands[seat] = nil
	s.Color = s.top().Color

	kept := make([]Card, 0, len(s.Deck))
	for _, c := range s.Deck {
		if len(s.Hands[seat]) < n {
			s.Hands[seat] = append(s.Hands[seat], c)
			continue
		}
		kept = append(kept, c)
	}
	s.Deck = kept
}

func playMove(s State, idx int, rng *rand.Rand) Move {
	m := Move{Kind: MovePlay, Index: idx}
	if s.Hands[You][idx].IsWild() {
		m.Color = Red + Color(rng.IntN(4))
	}
	return m
}

// TestAStackIsPassedOnAndPaidOnce walks the one rule the whole mode turns on: a
// draw card doesn't land on you, it *opens a bill*, and the seat that can't
// answer pays the whole thing.
func TestAStackIsPassedOnAndPaid(t *testing.T) {
	s := deal(t, nmDuel(), 100, 7)
	// Rig it: you hold a +2 on a red pile, the bot holds one card that can answer
	// and one that can't.
	s.Color = Red
	s.Discard = []Card{{Red, Five}}
	s.Hands[You] = []Card{{Red, DrawTwo}, {Blue, One}}
	s.Hands[1] = []Card{{Red, DrawTwo}, {Blue, Nine}}
	s.Turn = You
	s.Phase = PhasePlay

	// You play the +2. The bot answers with its own, so the bill comes back to you
	// at four — and you have nothing to answer with, so you pay it.
	next, evs, err := ApplyMove(s, Move{Kind: MovePlay, Index: 0})
	if err != nil {
		t.Fatalf("play +2: %v", err)
	}
	if next.Phase != PhaseStack {
		t.Fatalf("phase is %s, want stack: a +2 in No Mercy opens a stack", next.Phase)
	}
	if next.Turn != You {
		t.Fatalf("the stack came back to seat %d, want you", next.Turn)
	}
	if next.Pending != 4 {
		t.Fatalf("the bill is %d, want 4 (your two, plus the bot's two)", next.Pending)
	}
	if !hasKind(evs, EvStack) {
		t.Error("no stack event: the felt has nothing to show the player")
	}
	// You cannot draw your way out of it, and you cannot play a card that isn't a
	// draw card.
	if _, _, err := ApplyMove(next, Move{Kind: MoveDraw}); err != ErrMustStack {
		t.Errorf("drawing out of a stack: %v, want ErrMustStack", err)
	}
	if _, _, err := ApplyMove(next, Move{Kind: MovePlay, Index: 0}); err != ErrMustStack {
		t.Errorf("playing a plain card under a stack: %v, want ErrMustStack", err)
	}

	// Pay it. The bot is left holding one card it cannot play, and — because No
	// Mercy makes it draw until it can — it will draw into a fresh hand and may
	// well open a *new* stack on the way. That's the game working, not a leak, so
	// what's asserted here is the bill this seat paid, not the state of the table
	// afterwards: four cards into the hand, and the bill discharged.
	before := len(next.Hands[You])
	paid, evs, err := ApplyMove(next, Move{Kind: MoveTake})
	if err != nil {
		t.Fatalf("take: %v", err)
	}
	var forced int
	for _, e := range evs {
		if e.Kind == EvForced && e.Seat == You {
			forced = e.N
		}
	}
	if forced != 4 {
		t.Errorf("the stack made you take %d cards, want 4", forced)
	}
	if len(paid.Hands[You]) < before+4 {
		t.Errorf("hand went %d → %d, want at least four more", before, len(paid.Hands[You]))
	}
	// The bill you paid is gone. Anything pending now is a new stack the bot
	// opened after yours was settled, and it is never the one you just paid.
	if paid.Pending == 4 && paid.Phase == PhaseStack {
		t.Error("the bill you just paid is still standing")
	}
}

// TestTwentyFiveCardsKillsYou is the mercy rule, from the player's side: the
// stake is gone the moment the hand hits the limit, whoever else is still playing.
func TestTwentyFiveCardsKillsYou(t *testing.T) {
	s := deal(t, nmFull(), 100, 3)
	// Twenty-four cards in your hand, and a stack of ten pointed at you.
	//
	// The cards are *moved* from the deck, not invented: a fixture that conjures
	// a hand out of nothing breaks the census before the engine gets a chance to,
	// and then the census assertion below is testing the fixture instead of the
	// mercy rule.
	stack(&s, You, 24)
	s.Turn = You
	s.Phase = PhaseStack
	s.Pending = 10

	next, evs, err := ApplyMove(s, Move{Kind: MoveTake})
	if err != nil {
		t.Fatalf("take: %v", err)
	}
	if !hasKind(evs, EvMercy) {
		t.Fatal("no mercy event: twenty-five cards should have killed the seat")
	}
	if next.Phase != PhaseDone || next.Outcome != OutcomeLost {
		t.Fatalf("phase %s outcome %q, want done/lost", next.Phase, next.Outcome)
	}
	if next.Payout != 0 {
		t.Errorf("a mercy kill paid out %d, want nothing", next.Payout)
	}
	if len(next.Hands[You]) != 0 || next.live(You) {
		t.Error("a dead seat should hold no cards and be out of the game")
	}
	if got := total(census(next)); got != 168 {
		t.Errorf("%d cards after a mercy kill, want 168 — the hand goes back in the deck", got)
	}
}

// TestOutlivingTheTableWins is the other side of the mercy rule, and the one
// that makes No Mercy pay less than it looks like it should: the deck buries bots
// too, and a table with every bot dead is a table you have won.
func TestOutlivingTheTableWins(t *testing.T) {
	s := deal(t, nmDuel(), 100, 11)
	s.Color = Red
	s.Discard = []Card{{Red, Five}}
	s.Hands[You] = []Card{{Red, DrawTwo}, {Blue, One}}
	s.Hands[1] = make([]Card, 0, 24)
	for i := 0; i < 24; i++ {
		s.Hands[1] = append(s.Hands[1], Card{Blue, Nine}) // nothing it can answer with
	}
	s.Turn = You
	s.Phase = PhasePlay

	next, evs, err := ApplyMove(s, Move{Kind: MovePlay, Index: 0})
	if err != nil {
		t.Fatalf("play +2: %v", err)
	}
	if !hasKind(evs, EvMercy) {
		t.Fatal("the bot should have died taking the stack")
	}
	if next.Phase != PhaseDone || next.Outcome != OutcomeWon {
		t.Fatalf("phase %s outcome %q, want done/won: the last seat standing wins",
			next.Phase, next.Outcome)
	}
	if next.Payout != next.Pays() {
		t.Errorf("paid %d, quoted %d — settle and the felt must agree", next.Payout, next.Pays())
	}
}

// TestYouDrawUntilYouCanPlay: no drawing one card and shrugging. The turn only
// moves on when the deck itself has nothing left.
func TestYouDrawUntilYouCanPlay(t *testing.T) {
	s := deal(t, nmDuel(), 100, 5)
	s.Color = Red
	s.Discard = []Card{{Red, Five}}
	s.Hands[You] = []Card{{Blue, One}} // nothing playable
	// A deck whose first two cards are dead and whose third plays.
	s.Deck = []Card{{Green, Two}, {Yellow, Three}, {Red, Nine}, {Blue, Four}}
	s.Turn = You
	s.Phase = PhasePlay

	next, _, err := ApplyMove(s, Move{Kind: MoveDraw})
	if err != nil {
		t.Fatalf("draw: %v", err)
	}
	if len(next.Hands[You]) != 4 {
		t.Fatalf("hand is %d, want 4: you draw until something plays",
			len(next.Hands[You]))
	}
	if next.Phase != PhaseDrawn {
		t.Fatalf("phase %s, want drawn: the card you stopped on is one you must play",
			next.Phase)
	}
	// And you may not pass on it: you drew for it, you play it.
	if _, _, err := ApplyMove(next, Move{Kind: MovePass}); err != ErrMustPlayNow {
		t.Errorf("passing in No Mercy: %v, want ErrMustPlayNow", err)
	}
}

// TestSkipAllComesBackToYou — everyone else loses their turn, so the turn never
// actually leaves the seat that played it.
func TestSkipAllComesBackToYou(t *testing.T) {
	s := deal(t, nmFull(), 100, 13)
	s.Color = Red
	s.Discard = []Card{{Red, Five}}
	s.Hands[You] = []Card{{Red, SkipAll}, {Blue, One}}
	s.Turn = You
	s.Phase = PhasePlay

	next, evs, err := ApplyMove(s, Move{Kind: MovePlay, Index: 0})
	if err != nil {
		t.Fatalf("play skip-all: %v", err)
	}
	if next.Turn != You {
		t.Errorf("turn went to seat %d, want you: skip-all skips everyone else", next.Turn)
	}
	if !hasKind(evs, EvSkipAll) {
		t.Error("no skipall event")
	}
}

// TestDiscardAllTakesTheColourWithIt, and the cards it takes are still in the
// game — buried under the pile, not deleted.
func TestDiscardAllTakesTheColourWithIt(t *testing.T) {
	s := deal(t, nmDuel(), 100, 17)
	s.Color = Red
	s.Discard = []Card{{Red, Five}}
	s.Hands[You] = []Card{{Red, DiscardAll}, {Red, One}, {Red, Nine}, {Blue, Two}}
	s.Turn = You
	s.Phase = PhasePlay
	before := total(census(s))

	next, evs, err := ApplyMove(s, Move{Kind: MovePlay, Index: 0})
	if err != nil {
		t.Fatalf("play discard-all: %v", err)
	}
	if len(next.Hands[You]) != 1 {
		t.Fatalf("hand is %d, want 1: every red should have gone with it",
			len(next.Hands[You]))
	}
	if next.Hands[You][0] != (Card{Blue, Two}) {
		t.Errorf("kept %v, want the blue two", next.Hands[You][0])
	}
	if top := next.Top(); top.Value != DiscardAll {
		t.Errorf("the card in play is %v, want the discard-all that was played", top.Value)
	}
	if !hasKind(evs, EvDiscardAll) {
		t.Error("no discard event")
	}
	if got := total(census(next)); got != before {
		t.Errorf("%d cards, want %d: a dumped colour is buried, not destroyed", got, before)
	}
}

// TestRouletteFlipsUntilTheColour — and the victim keeps every card it turned.
func TestRouletteFlipsUntilTheColour(t *testing.T) {
	s := deal(t, nmDuel(), 100, 19)
	s.Color = Blue
	s.Discard = []Card{{Blue, Five}}
	s.Hands[You] = []Card{{Wild, WildRoulette}, {Blue, One}}
	s.Hands[1] = []Card{{Green, Three}}
	s.Deck = []Card{{Blue, Two}, {Green, Four}, {Yellow, Six}, {Red, Seven}, {Blue, Eight}}
	s.Turn = You
	s.Phase = PhasePlay

	// Name red: the bot flips blue, green, yellow, red — four cards — and keeps them.
	next, evs, err := ApplyMove(s, Move{Kind: MovePlay, Index: 0, Color: Red})
	if err != nil {
		t.Fatalf("play roulette: %v", err)
	}
	var got int
	for _, e := range evs {
		if e.Kind == EvRoulette {
			got = e.N
		}
	}
	if got != 4 {
		t.Errorf("flipped %d, want 4 — up to and including the first red", got)
	}
	// One card it started with, plus the four it turned. (The bot is then skipped,
	// so the turn is back with you and it never played any of them.)
	if n := len(next.Hands[1]); n != 5 {
		t.Errorf("the bot holds %d, want 5", n)
	}
	if total(census(next)) != total(census(s)) {
		t.Error("the roulette lost a card")
	}
}

// TestTheMultiplesAreStillPriced measures the naive strategy against the bots and
// checks each tier still charges roughly the house's edge for it.
//
// This is the test that fails when somebody changes the bots, the deck, or a
// rule, and it is *supposed* to: the tier and the game it prices are a pair. If
// this goes red, re-measure and move the number, don't loosen the bound.
func TestTheMultiplesAreStillPriced(t *testing.T) {
	if testing.Short() {
		t.Skip("slow: plays thousands of games")
	}
	for _, tier := range AllTiers() {
		wins, games := 0, 3000
		for seed := 0; seed < games; seed++ {
			s := deal(t, tier, 100, uint64(seed)+7777)
			rng := rand.New(rand.NewPCG(uint64(seed), 4242))
			for moves := 0; s.Phase != PhaseDone && moves < 800; moves++ {
				next, _, err := ApplyMove(s, naive(s, rng))
				if err != nil {
					t.Fatalf("%s: %v", tier.Slug, err)
				}
				s = next
			}
			if s.Outcome.Won() {
				wins++
			}
		}
		p := float64(wins) / float64(games)
		// What a staked chip comes back as, playing badly: you win p of the time and
		// keep the multiple less the rake on the profit, and lose the stake the rest.
		ev := p*(1+(tier.Base-1)*(1-rake)) - 1
		t.Logf("%-8s bots=%d base=%.2f  naive win rate %.1f%%  house edge %.1f%%",
			tier.Slug, tier.Bots, tier.Base, p*100, -ev*100)
		if ev < -0.14 || ev > -0.02 {
			t.Errorf("%s: the house edge on naive play is %.1f%%, which is outside the 2–14%% "+
				"band the tiers are priced to. Re-measure Base: %.2f would put it near 8%%.",
				tier.Slug, -ev*100, (0.92/p-1)/(1-rake)+1)
		}
	}
}