path: root/internal/casino/pachinko.go

package casino

import (
	"fmt"
	"math"
	"math/rand"
	"strconv"
	"strings"
	"sync"
)

// Pachinko is Plinko's rectangular cousin: the player picks one of eight top
// slots, a single ball makes pachinkoRows fair 50:50 bounces inside a fixed
// rectangle (the walls reflect), and it lands on one of eight prize pockets.
// The board is populated with fractional prizes and revealed before the player
// chooses, so the best slot changes from board to board. A rare DOUBLE pocket
// doubles every prize and grants a free re-drop, staying on the board so the
// doubling can chain.
const (
	pachinkoLanes = 8
	pachinkoRows  = 20
)

// Board composition. Seven pockets are i.i.d. "filler" prizes (0.1-1.5x in 0.1
// steps, heavily weighted toward small returns) and one pocket is a guaranteed
// "premium" above 1.5x. So every board is populated and every board has at
// least one reason to aim. Best-slot play returns 100%; the house edge comes
// only from landing on a worse slot. Premium values at or above 2x are whole
// numbers.
var (
	pachinkoFillers       = [4]float64{0.1, 0.5, 1.0, 1.5}
	pachinkoFillerWeights = [4]float64{0.30, 0.38, 0.22, 0.10}
	pachinkoPremiums      = [5]float64{1.7, 2, 5, 10, 100}
	// Premium tickets per 10,000 boards. Tuned against the eight-lane
	// half-lane ball walk so the best-slot return is exactly 100%; the rare
	// tails keep their shape and the 1.7x/2x bulk absorbs the tuning.
	pachinkoPremiumWeights = [5]float64{0.41312, 0.53726, 0.03730, 0.01120, 0.00112}
)

const (
	pachinkoPremiumRoll = 10000
	pachinkoDoubleRoll  = 100
	pachinkoDoubleBelow = 5 // 5% of boards carry a DOUBLE pocket
	pachinkoMaxDoubling = 40
)

// Pachinko phases.
const (
	pachinkoIdle     = "idle"
	pachinkoChoosing = "choosing"
	pachinkoDropping = "dropping"
	// pachinkoResult is a transient phase so the settled prize row renders once.
	pachinkoResult = "result"
)

// PachinkoPocket is one prize slot. Value is the total-return multiplier
// (including stake) when Double is false; Double marks the chaining DOUBLE
// space, whose Value is ignored.
type PachinkoPocket struct {
	Value  float64 `json:"value" yaml:"value"`
	Double bool    `json:"double" yaml:"double"`
}

// pachinkoMultiplier scales a pocket value by `doubling` doublings, clamped so
// the displayed and paid value never overflows.
func pachinkoMultiplier(value float64, doubling int) float64 {
	if doubling > pachinkoMaxDoubling {
		return float64(MaxCredits)
	}
	for i := 0; i < doubling; i++ {
		value *= 2
		if value >= float64(MaxCredits) {
			return float64(MaxCredits)
		}
	}
	return value
}

// pachinkoPocketText renders a pocket after `doubling` doublings.
func pachinkoPocketText(p PachinkoPocket, doubling int) string {
	if p.Double {
		return "DOUBLE"
	}
	value := pachinkoMultiplier(p.Value, doubling)
	if value >= float64(MaxCredits) {
		return "MAX"
	}
	return strconv.FormatFloat(value, 'f', -1, 64) + "x"
}

func validatePachinko(c TableConfig) error {
	if c.MaxPlayers > 1 {
		return fmt.Errorf("pachinko has one seat")
	}
	return nil
}

// pachinkoReach returns P[start][pocket], the probability a ball dropped from
// each top slot lands in each pocket after pachinkoRows reflected bounces.
func pachinkoReach() [pachinkoLanes][pachinkoLanes]float64 {
	var reach [pachinkoLanes][pachinkoLanes]float64
	positions := 2*pachinkoLanes - 1 // one position per lane plus the gaps
	for start := 0; start < pachinkoLanes; start++ {
		v := make([]float64, positions)
		v[2*start] = 1
		for row := 0; row < pachinkoRows; row++ {
			next := make([]float64, positions)
			for p, prob := range v {
				if prob == 0 {
					continue
				}
				switch p {
				case 0:
					next[1] += prob
				case positions - 1:
					next[p-1] += prob
				default:
					next[p-1] += prob * 0.5
					next[p+1] += prob * 0.5
				}
			}
			v = next
		}
		for pocket := 0; pocket < pachinkoLanes; pocket++ {
			reach[start][pocket] = v[2*pocket]
		}
	}
	return reach
}

// pachinkoBoardValue is the expected return of a board when the player always
// drops from the best top slot. If the ball lands on DOUBLE it doubles the
// board and drops again; the value V therefore satisfies
// V = max_s (A_s + 2*q_s*V), where A_s is the numeric prize from slot s and
// q_s its DOUBLE chance. Rearranged, V = max_s A_s/(1-2*q_s).
func pachinkoBoardValue(reach *[pachinkoLanes][pachinkoLanes]float64, pockets *[pachinkoLanes]PachinkoPocket) float64 {
	best := 0.0
	for start := 0; start < pachinkoLanes; start++ {
		numeric, double := 0.0, 0.0
		for lane := 0; lane < pachinkoLanes; lane++ {
			prob := reach[start][lane]
			if pockets[lane].Double {
				double += prob
			} else {
				numeric += prob * pockets[lane].Value
			}
		}
		denom := 1 - 2*double
		if denom <= 1e-9 {
			return math.Inf(1)
		}
		if value := numeric / denom; value > best {
			best = value
		}
	}
	return best
}

// pachinkoOptimalRTP computes, once, the exact expected return when the player
// always chooses the best top slot. Seven filler pockets are i.i.d. and the
// eighth is the guaranteed premium; DOUBLE replaces a filler pocket. The
// enumeration is over 4^(lanes-1) filler rows and every premium position and
// value.
var pachinkoOptimalRTP = sync.OnceValue(func() float64 {
	return pachinkoRTPwith(pachinkoPremiumWeights)
})

// pachinkoRTPwith computes the exact expected best-slot return for a given
// distribution over the five premium tiers. It is separated from the cached
// pachinkoOptimalRTP so the premium weights can be solved for numerically and
// the result verified during tuning.
func pachinkoRTPwith(premiumWeights [5]float64) float64 {
	reach := pachinkoReach()
	const fillers = len(pachinkoFillers)
	total := 1
	for i := 0; i < pachinkoLanes-1; i++ {
		total *= fillers
	}
	pDouble := float64(pachinkoDoubleBelow) / pachinkoDoubleRoll
	// invDouble precomputes 1/(1-2q) for every slot/pocket pair so the doubling
	// term is a multiply in the hot loop rather than a division.
	var invDouble [pachinkoLanes][pachinkoLanes]float64
	for s := 0; s < pachinkoLanes; s++ {
		for d := 0; d < pachinkoLanes; d++ {
			invDouble[s][d] = 1 / (1 - 2*reach[s][d])
		}
	}
	var f [pachinkoLanes - 1]float64
	var baseA, premContrib [pachinkoLanes]float64
	var rtp float64
	for code := 0; code < total; code++ {
		x := code
		prob := 1.0
		for i := 0; i < pachinkoLanes-1; i++ {
			kind := x % fillers
			x /= fillers
			f[i] = pachinkoFillers[kind]
			prob *= pachinkoFillerWeights[kind]
		}
		if prob == 0 {
			continue
		}
		// Base contributions with the premium pocket counting zero. The first
		// position is built directly; each step moves the premium one lane and
		// swaps one filler in and one out.
		for s := 0; s < pachinkoLanes; s++ {
			sum := 0.0
			for j := 1; j < pachinkoLanes; j++ {
				sum += reach[s][j] * f[j-1]
			}
			baseA[s] = sum
		}
		for p := 0; p < pachinkoLanes; p++ {
			if p > 0 {
				fp := f[p-1]
				for s := 0; s < pachinkoLanes; s++ {
					baseA[s] += reach[s][p-1]*fp - reach[s][p]*fp
				}
			}
			for pi, prem := range pachinkoPremiums {
				w := prob * premiumWeights[pi] / pachinkoLanes
				if w == 0 {
					continue
				}
				for s := 0; s < pachinkoLanes; s++ {
					premContrib[s] = reach[s][p] * prem
				}
				best := 0.0
				for s := 0; s < pachinkoLanes; s++ {
					if value := baseA[s] + premContrib[s]; value > best {
						best = value
					}
				}
				rtp += w * (1 - pDouble) * best
				if pDouble == 0 {
					continue
				}
				var doubles float64
				for d := 0; d < pachinkoLanes; d++ {
					if d == p {
						continue
					}
					fd := 0.0
					if d < p {
						fd = f[d]
					} else {
						fd = f[d-1]
					}
					best := 0.0
					for s := 0; s < pachinkoLanes; s++ {
						q := reach[s][d]
						if value := (baseA[s] + premContrib[s] - q*fd) * invDouble[s][d]; value > best {
							best = value
						}
					}
					doubles += best
				}
				rtp += w * pDouble * doubles / float64(pachinkoLanes-1)
			}
		}
	}
	return rtp
}

// pachinkoUniformRTP is the return for a player who ignores the board and
// drops from a uniformly random slot. It averages the pocket mean over the
// composition, removes the value a DOUBLE replaces, then divides by the
// average double-free probability so the DOUBLE chain is priced in. The exact
// best-slot return is far higher; the gap is the skill of reading the board.
var pachinkoUniformRTP = (func() float64 {
	meanFiller := 0.0
	for i, value := range pachinkoFillers {
		meanFiller += pachinkoFillerWeights[i] * value
	}
	meanPremium := 0.0
	for i, value := range pachinkoPremiums {
		meanPremium += pachinkoPremiumWeights[i] * value
	}
	pDouble := float64(pachinkoDoubleBelow) / pachinkoDoubleRoll
	sum := float64(pachinkoLanes-1)*meanFiller + meanPremium - pDouble*meanFiller
	return (sum / pachinkoLanes) / (1 - 2*pDouble/pachinkoLanes)
})()

// pachinkoHouseEdge: best-slot play is exactly fair, so the theoretical edge is
// zero. The real edge comes from dropping on a worse slot, which the paytable's
// uniform-slot figure quantifies.
func pachinkoHouseEdge(TableConfig, string) HouseEdge {
	return HouseEdge{
		Parts: []EdgePart{{Loss: max(0, 1-pachinkoOptimalRTP())}},
		Note:  "best-slot play returns 100%; the edge depends on slot choice",
	}
}

func pachinkoRules(TableConfig) string {
	return fmt.Sprintf("Pachinko: a %d-slot rectangle; one ball per drop makes %d fair 50:50 bounces off the walls.\n"+
		"bet N sets and reveals the board; then drop SLOT (a bare slot number also works) chooses any top slot 1-%d. The board is always revealed before you pick.\n"+
		"Seven pockets are filler prizes (0.1x to 1.5x, mostly 0.5x and below); the eighth is a guaranteed premium above 1.5x: usually 1.7x or 2x, occasionally 5x or 10x, and about 1 board in 900 carries the 100x.\n"+
		"Multipliers INCLUDE your stake. DOUBLE doubles every prize on the board and re-drops the ball for free, staying in place so it can double again and again.\n"+
		"The best slot changes with every board. Return assumes you always choose it: about %.2f%%; dropping from a random slot returns about %.2f%%.\n"+
		"You cannot leave or change a committed board. Shutdown refunds it, disconnect forfeits an unfinished drop, and a failed payout keeps its stake pending.",
		pachinkoLanes, pachinkoRows, pachinkoLanes, 100*pachinkoOptimalRTP(), 100*pachinkoUniformRTP)
}

type PachinkoPrizeOdds struct {
	Label  string
	Odds   string  // qualitative wording shown to every player
	Chance float64 // probability per board; 0 when no single chance applies
}

type PachinkoSnapshot struct {
	Phase    string
	Pockets  [pachinkoLanes]PachinkoPocket
	Doubling int
	Row      int // 0 at the chosen slot, pachinkoRows at the pockets
	Lane     int // 0-based lane of the ball
	Slot     int // 1-based chosen slot; 0 when unchosen
	Landing  int // 0-based landed pocket; -1 when not landed
	RTP      float64
	Uniform  float64
	Odds     []PachinkoPrizeOdds // populated for the idle/paytable views
}

func (*PachinkoSnapshot) snapshot() {}

// PachinkoOdds summarises the board composition in probability order. Chance
// is a fraction of boards; the presentation layer shows it only to players
// carrying a House Edge instrument.
func PachinkoOdds() []PachinkoPrizeOdds {
	double := float64(pachinkoDoubleBelow) / pachinkoDoubleRoll
	return []PachinkoPrizeOdds{
		{Label: "0.1-1.5x", Odds: "7 filler pockets"},
		{Label: "1.7x", Odds: "floors", Chance: pachinkoPremiumWeights[0]},
		{Label: "2x", Odds: "floors", Chance: pachinkoPremiumWeights[1]},
		{Label: "5x", Odds: "floors", Chance: pachinkoPremiumWeights[2]},
		{Label: "10x", Odds: "floors", Chance: pachinkoPremiumWeights[3]},
		{Label: "100x", Odds: "floors", Chance: pachinkoPremiumWeights[4]},
		{Label: "DOUBLE", Odds: "per board", Chance: double},
	}
}

type pachinkoTable struct {
	*tableBase
	mu       sync.Mutex
	rng      *rand.Rand
	name     string
	betSize  int
	wallet   Wallet
	stake    Wager
	phase    string
	pockets  [pachinkoLanes]PachinkoPocket
	doubling int
	row      int
	pos      int // half-lane position 0..2*pachinkoLanes-2; even on a pocket
	lane     int // display lane, pos/2
	slot     int
	landing  int
}

func newPachinkoTable(room int, c TableConfig, rng *rand.Rand) tableGame {
	return &pachinkoTable{tableBase: &tableBase{RoomID: room, Config: c}, rng: rng, phase: pachinkoIdle, landing: -1}
}
func (t *pachinkoTable) base() *tableBase { return t.tableBase }
func (t *pachinkoTable) idle() bool {
	t.mu.Lock()
	defer t.mu.Unlock()
	return t.name == ""
}
func (t *pachinkoTable) hasParticipant(n string) bool {
	t.mu.Lock()
	defer t.mu.Unlock()
	return t.name != "" && t.name == n
}
func (t *pachinkoTable) busy(n string) bool {
	t.mu.Lock()
	defer t.mu.Unlock()
	return t.name == n && t.phase == pachinkoDropping
}
func (t *pachinkoTable) overview() string { return "Pachinko / 8-slot rectangle" }
func (t *pachinkoTable) seats() []string {
	t.mu.Lock()
	defer t.mu.Unlock()
	if t.name == "" {
		return nil
	}
	return []string{t.name}
}
func (t *pachinkoTable) state() string {
	t.mu.Lock()
	defer t.mu.Unlock()
	switch t.phase {
	case pachinkoDropping:
		return "dropping"
	case pachinkoChoosing:
		return "choosing a slot"
	default:
		return "waiting"
	}
}
func (t *pachinkoTable) wagers(string) []WagerRow { return nil }

func (t *pachinkoTable) hintsLocked() []MenuCommand {
	switch t.phase {
	case pachinkoDropping:
		return nil
	case pachinkoChoosing:
		return []MenuCommand{
			{Command: "drop N", Desc: "Drop from top slot 1-9; a bare number also works"},
			{Command: "table", Desc: "Show the blank board and pay table"},
			{Command: "rules", Desc: "Pachinko rules"},
		}
	default:
		return []MenuCommand{
			{Command: "bet N", Desc: "Set and reveal the board"},
			{Command: "table", Desc: "Show the blank board and pay table"},
			{Command: "rules", Desc: "Pachinko rules"},
			{Command: "stop", Desc: "Leave Pachinko"},
		}
	}
}
func (t *pachinkoTable) hints(n string) []MenuCommand {
	t.mu.Lock()
	defer t.mu.Unlock()
	if n != t.name {
		return nil
	}
	return t.hintsLocked()
}
func (t *pachinkoTable) snapLocked(phase string) *PachinkoSnapshot {
	s := &PachinkoSnapshot{
		Phase:    phase,
		Pockets:  t.pockets,
		Doubling: t.doubling,
		Row:      t.row,
		Lane:     t.lane,
		Slot:     t.slot,
		Landing:  t.landing,
		RTP:      100 * pachinkoOptimalRTP(),
		Uniform:  100 * pachinkoUniformRTP,
	}
	if phase == pachinkoIdle || phase == "paytable" {
		s.Odds = PachinkoOdds()
	}
	return s
}
func (t *pachinkoTable) phaseLocked() string {
	if t.phase == "" {
		return pachinkoIdle
	}
	return t.phase
}

// board is the table command's view: the reference blank board and pay table,
// never the live drop, so the command always answers "what can I win and how".
func (t *pachinkoTable) board(string) Snapshot {
	t.mu.Lock()
	defer t.mu.Unlock()
	return t.snapLocked("paytable")
}
func (t *pachinkoTable) statusLocked(n string) []Event {
	e := t.private(n, "")
	e.Color = "casino_menu"
	e.Snapshot = t.snapLocked(t.phaseLocked())
	if n == t.name {
		e.Menu = &MenuView{ShowBalance: true, Commands: t.hintsLocked()}
	}
	return []Event{e}
}
func (t *pachinkoTable) status(n string) []Event {
	t.mu.Lock()
	defer t.mu.Unlock()
	return t.statusLocked(n)
}
func (t *pachinkoTable) join(n string) []Event {
	t.mu.Lock()
	defer t.mu.Unlock()
	if t.name != "" {
		return []Event{t.private(n, "Pachinko is occupied.")}
	}
	t.clearLocked()
	t.name = n
	e := t.private(n, "")
	e.Type = EventJoined
	e.Player = n
	return append([]Event{e}, t.statusLocked(n)...)
}
func (t *pachinkoTable) clearLocked() {
	t.name = ""
	t.phase = pachinkoIdle
	t.betSize = 0
	t.wallet = nil
	t.stake = Wager{}
	t.pockets = [pachinkoLanes]PachinkoPocket{}
	t.doubling = 0
	t.row = 0
	t.pos = 0
	t.lane = 0
	t.slot = 0
	t.landing = -1
}
func (t *pachinkoTable) leave(n string) []Event {
	t.mu.Lock()
	defer t.mu.Unlock()
	if n != t.name {
		return nil
	}
	if t.phase != pachinkoIdle {
		return []Event{t.private(n, "Finish this board before leaving.")}
	}
	t.clearLocked()
	e := t.playerAction(n, n+" leaves Pachinko.", "You leave Pachinko.")
	e.Type = EventLeft
	e.Player = n
	return []Event{e}
}
func (t *pachinkoTable) rebet(n string) (string, int) {
	t.mu.Lock()
	defer t.mu.Unlock()
	if n == t.name && t.phase == pachinkoIdle {
		return "", t.betSize
	}
	return "", 0
}

// dealLocked generates a fresh board. It chooses the eight filler pockets and
// the guaranteed premium first, optionally turns one filler into DOUBLE,
// then shuffles all eight prizes into the slots, so the premium and the DOUBLE
// can appear anywhere on the board.
func (t *pachinkoTable) dealLocked() {
	var board [pachinkoLanes]PachinkoPocket
	for i := 0; i < pachinkoLanes-1; i++ {
		ticket := t.rng.Intn(100)
		switch {
		case ticket < 30:
			board[i] = PachinkoPocket{Value: 0.1}
		case ticket < 68:
			board[i] = PachinkoPocket{Value: 0.5}
		case ticket < 90:
			board[i] = PachinkoPocket{Value: 1.0}
		default:
			board[i] = PachinkoPocket{Value: 1.5}
		}
	}
	ticket := t.rng.Intn(pachinkoPremiumRoll)
	switch {
	case ticket < 2818:
		board[pachinkoLanes-1] = PachinkoPocket{Value: 1.7}
	case ticket < 9504:
		board[pachinkoLanes-1] = PachinkoPocket{Value: 2}
	case ticket < 9877:
		board[pachinkoLanes-1] = PachinkoPocket{Value: 5}
	case ticket < 9989:
		board[pachinkoLanes-1] = PachinkoPocket{Value: 10}
	default:
		board[pachinkoLanes-1] = PachinkoPocket{Value: 100}
	}
	if t.rng.Intn(pachinkoDoubleRoll) < pachinkoDoubleBelow {
		// DOUBLE replaces one of the eight filler prizes, never the premium.
		board[t.rng.Intn(pachinkoLanes-1)] = PachinkoPocket{Double: true}
	}
	t.rng.Shuffle(pachinkoLanes, func(i, j int) { board[i], board[j] = board[j], board[i] })
	t.pockets = board
}

// startDropLocked validates a chosen top slot and begins the animation.
func (t *pachinkoTable) startDropLocked(slot int) []Event {
	if slot < 1 || slot > pachinkoLanes {
		return []Event{t.private(t.name, fmt.Sprintf("Choose a top slot from 1 to %d.", pachinkoLanes))}
	}
	t.slot = slot
	t.row = 0
	t.pos = 2 * (slot - 1)
	t.lane = slot - 1
	t.landing = -1
	t.phase = pachinkoDropping
	e := t.private(t.name, fmt.Sprintf("Dropping from slot %d...", slot))
	e.Snapshot = t.snapLocked(pachinkoDropping)
	return []Event{e}
}

func (t *pachinkoTable) bet(n, spot string, amount int, w Wallet) []Event {
	t.mu.Lock()
	defer t.mu.Unlock()
	if n != t.name {
		return nil
	}
	if t.phase != pachinkoIdle {
		return []Event{t.private(n, "Finish this board before betting again.")}
	}
	if spot != "" && spot != "main" {
		return []Event{t.private(n, "Use bet N; the board is revealed before you choose a slot.")}
	}
	if amount < t.Config.MinBet || amount > t.Config.MaxBet {
		return []Event{t.private(n, "Bets must be "+betRangeText(t.Config.MinBet, t.Config.MaxBet)+".")}
	}
	if w == nil {
		return []Event{t.private(n, "No wallet is available.")}
	}
	stake, err := w.Wager(amount)
	if err != nil {
		return []Event{t.private(n, walletErrorMessage(err, "Not enough chips and credits."))}
	}
	t.wallet = w
	t.stake = stake
	t.betSize = amount
	t.doubling = 0
	t.row = 0
	t.pos = 0
	t.lane = 0
	t.landing = -1
	t.slot = 0
	t.dealLocked()
	t.phase = pachinkoChoosing
	board := t.private(n, fmt.Sprintf("Stake: %d credits. Choose a top slot 1-%d.", amount, pachinkoLanes))
	board.Snapshot = t.snapLocked(pachinkoChoosing)
	board.Color = "casino_menu"
	board.Menu = &MenuView{Commands: t.hintsLocked()}
	return []Event{board}
}

func (t *pachinkoTable) action(n, action string) []Event {
	t.mu.Lock()
	defer t.mu.Unlock()
	if n != t.name {
		return nil
	}
	f := strings.Fields(strings.ToLower(action))
	if len(f) == 1 && f[0] == "paytable" {
		return []Event{t.private(n, "Use table to see the blank board and pay table.")}
	}
	if t.phase == pachinkoDropping {
		return []Event{t.private(n, "Wait for the ball to land.")}
	}
	if t.phase != pachinkoChoosing {
		return []Event{t.private(n, "Use bet N to set a board first.")}
	}
	if len(f) == 2 && f[0] == "drop" {
		f = f[1:]
	}
	if len(f) != 1 {
		return []Event{t.private(n, fmt.Sprintf("Choose a top slot with drop N or a number from 1 to %d.", pachinkoLanes))}
	}
	slot, err := strconv.Atoi(f[0])
	if err != nil {
		return []Event{t.private(n, fmt.Sprintf("Choose a top slot from 1 to %d.", pachinkoLanes))}
	}
	return t.startDropLocked(slot)
}

func (t *pachinkoTable) tick() []Event {
	t.mu.Lock()
	defer t.mu.Unlock()
	if t.phase != pachinkoDropping {
		return nil
	}
	t.row++
	t.advanceBallLocked()
	events := []Event{t.dropSnapshotLocked()}
	if t.row < pachinkoRows {
		return events
	}
	return append(events, t.resolveLocked()...)
}

func (t *pachinkoTable) dropSnapshotLocked() Event {
	e := t.private(t.name, "")
	e.Snapshot = t.snapLocked(pachinkoDropping)
	return e
}

// advanceBallLocked takes one 50:50 bounce in half-lane units, reflecting off
// either wall. Half-lane positions keep the walk from locking onto one parity,
// so every pocket is reachable from every top slot, and the display always
// slides the ball one half-lane rather than skipping a column.
func (t *pachinkoTable) advanceBallLocked() {
	last := 2*pachinkoLanes - 2
	switch {
	case t.pos <= 0:
		t.pos = 1
	case t.pos >= last:
		t.pos = last - 1
	case t.rng.Intn(2) == 0:
		t.pos--
	default:
		t.pos++
	}
	t.lane = t.pos / 2
}

// payoutLocked converts a multiplier into whole credits with unbiased
// rounding: the fractional part becomes a chance of one extra credit. That
// keeps a 0.1x return on a one-credit bet worth exactly its expected value.
func (t *pachinkoTable) payoutLocked(multiplier float64) int {
	total := float64(t.betSize) * multiplier
	if total >= float64(MaxCredits) {
		return MaxCredits
	}
	paid := int(math.Floor(total))
	if t.rng.Float64() < total-float64(paid) {
		paid++
	}
	if paid > MaxCredits {
		return MaxCredits
	}
	return paid
}

// resolveLocked settles the landed pocket. A DOUBLE doubles the board and asks
// for another free drop; any other pocket pays and ends the round.
func (t *pachinkoTable) resolveLocked() []Event {
	t.landing = t.pos / 2
	pocket := t.pockets[t.landing]
	if pocket.Double {
		t.doubling++
		t.phase = pachinkoChoosing
		t.slot = 0
		label := "DOUBLE!"
		if t.doubling > 1 {
			label = fmt.Sprintf("DOUBLE x%d!", t.doubling)
		}
		announce := t.private(t.name, label+" Every prize doubles. Drop again from any slot, free.")
		announce.Color = "casino_big_win"
		board := t.private(t.name, "")
		board.Color = "casino_menu"
		board.Snapshot = t.snapLocked(pachinkoChoosing)
		board.Menu = &MenuView{ShowBalance: true, Commands: t.hintsLocked()}
		return []Event{announce, board}
	}
	multiplier := pachinkoMultiplier(pocket.Value, t.doubling)
	paid := t.payoutLocked(multiplier)
	result := t.private(t.name, "")
	result.Snapshot = t.snapLocked(pachinkoResult)
	if err := t.wallet.PayCredits(paid, t.stake.ID); err != nil {
		t.phase = pachinkoIdle
		return []Event{result, t.private(t.name, payoutFailedMessage())}
	}
	t.stake = Wager{}
	t.phase = pachinkoIdle
	label := fmt.Sprintf("Slot %d [%s]", t.slot, pachinkoPocketText(pocket, t.doubling))
	if t.doubling > 0 {
		label = fmt.Sprintf("Slot %d [%s after %d DOUBLE]", t.slot, pachinkoPocketText(pocket, t.doubling), t.doubling)
	}
	result.Settlement = []SettlementLine{{
		Label:    label,
		Odds:     "Varies",
		Stake:    t.betSize,
		Returned: paid,
		Result:   returnResult(t.betSize, paid),
	}}
	result.Color = "casino_payout"
	if multiplier >= 2 {
		result.Color = "casino_big_win"
	}
	return []Event{result, t.betMenuEvent(t.name, t.hintsLocked())}
}

func (t *pachinkoTable) markDisconnected(n string) []Event {
	t.mu.Lock()
	defer t.mu.Unlock()
	if n != t.name {
		return nil
	}
	if t.phase != pachinkoIdle && t.wallet != nil {
		t.wallet.ResolveStake(t.stake.ID)
	}
	t.clearLocked()
	e := t.event(n+" leaves Pachinko.", true)
	e.Type = EventLeft
	e.Player = n
	return []Event{e}
}
func (t *pachinkoTable) refundAll() []Event {
	t.mu.Lock()
	defer t.mu.Unlock()
	var events []Event
	if t.phase != pachinkoIdle && t.wallet != nil {
		chips, credits, err := t.wallet.RefundOutstanding()
		message := fmt.Sprintf("Pachinko closes; %d credits/chips refunded.", chips+credits)
		if err != nil {
			message = "Pachinko refund could not be persisted; your stake remains pending for recovery."
		}
		events = append(events, t.private(t.name, message))
	}
	t.clearLocked()
	return events
}