Merge pull request 'Katan: open trade offers and counter-offers' (#6) from feature/catan-open-trades-counter into dev

- Offers can go to the whole table (asked in seat order, empty hands skipped) or one seat.
- The asked seat may accept (trade happens at once), decline, or counter with new terms.
- If nobody accepts and there are counters, the offerer takes one or turns them all down (new TRADE_COUNTERS phase).
- AI: fixes an inverted accept test (it weighed what it gives against what it gets backwards), picks the best counter.
- UI: Everyone option in the offer dialog, Counter… in the reply dialog, a counter-choice dialog.
- Tests and docs updated.

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_018njn2eMPAYqAoE49hGRg2X

app/src/main/java/org/prolibertate/games/game/catan/CatanAi.kt

@@ -38,6 +38,8 @@ class CatanAi : GameAi<CatanState, CatanMove> {
 
             CatanPhase.TRADE_PENDING -> chooseResponse(state, seat, legal)
 
+            CatanPhase.TRADE_COUNTERS -> chooseCounter(state, legal)
+
             CatanPhase.PLAYING -> choosePlaying(state, seat, legal)
 
             CatanPhase.GAME_OVER -> legal.firstOrNull()
@@ -260,17 +262,32 @@ class CatanAi : GameAi<CatanState, CatanMove> {
     }
 
     private fun chooseResponse(state: CatanState, seat: Int, legal: List<CatanMove>): CatanMove {
-        val accept = legal.filterIsInstance<AcceptTrade>().firstOrNull() ?: run {
-            return legal.first { it is DeclineTrade }
-        }
-        val offer = state.pendingTrade ?: return legal.first()
-        // Accept when what arrives is worth more than what leaves: a mild
-        // table, not a shark.
-        val incoming = offer.get.sumOf { want(it) }
-        val outgoing = offer.give.sumOf { want(it) }
+        val accept = legal.filterIsInstance<AcceptTrade>().firstOrNull()
+        val offer = state.pendingTrade
+        if (accept == null || offer == null) return legal.first { it is DeclineTrade }
+        // Accept when what arrives (the offerer's give) is worth more than what
+        // leaves (the offerer's get): a mild table, not a shark.
+        val incoming = offer.give.sumOf { want(it) }
+        val outgoing = offer.get.sumOf { want(it) }
         return if (incoming > outgoing) accept else legal.first { it is DeclineTrade }
     }
 
+    /**
+     * Picks the counter-offer that gains the most by the same valuation, or
+     * turns them all down. The AI never counters itself: it only answers.
+     */
+    private fun chooseCounter(state: CatanState, legal: List<CatanMove>): CatanMove {
+        val offer = state.pendingTrade ?: return legal.first()
+        val best = legal.filterIsInstance<AcceptCounter>()
+            .map { choice -> choice to offer.counters.first { it.by == choice.seat } }
+            .maxByOrNull { (_, c) -> c.give.sumOf { want(it) } - c.get.sumOf { want(it) } }
+        if (best != null) {
+            val (choice, c) = best
+            if (c.give.sumOf { want(it) } > c.get.sumOf { want(it) }) return choice
+        }
+        return legal.first { it is DismissCounters }
+    }
+
     // -----------------------------------------------------------------------
     // Valuations
     // -----------------------------------------------------------------------

app/src/main/java/org/prolibertate/games/game/catan/CatanModel.kt

@@ -74,17 +74,34 @@ enum class DevCardType { KNIGHT, ROAD_BUILDING, MONOPOLY, YEAR_OF_PLENTY, VICTOR
 data class DevCard(val id: Int, val type: DevCardType, val boughtTurn: Int = 0)
 
 /**
- * A domestic trade offer on the table. [by] is the offering seat and [to]
- * the only seat that may respond — v1 has no counter-offers and no open
- * auctions, so an offer is always addressed to one player.
+ * A counter-proposal to a [TradeOffer]: seat [by] would [give] these cards to
+ * the offerer if the offerer would hand over [get].
  */
 @Serializable
-data class TradeOffer(val by: Int, val to: Int, val give: List<Resource>, val get: List<Resource>)
+data class TradeCounter(val by: Int, val give: List<Resource>, val get: List<Resource>)
+
+/**
+ * A domestic trade offer on the table. [by] is the offering seat. [to] is the
+ * one seat it is addressed to, or null for an open offer to the whole table.
+ * Seats are asked one at a time, in seat order after the offerer; [asking] is
+ * the seat that may answer now. Each may accept (the trade happens at once),
+ * decline, or counter; counters are kept in [counters] and, if nobody accepts,
+ * the offerer chooses among them in [CatanPhase.TRADE_COUNTERS].
+ */
+@Serializable
+data class TradeOffer(
+    val by: Int,
+    val to: Int?,
+    val give: List<Resource>,
+    val get: List<Resource>,
+    val asking: Int = to ?: -1,
+    val counters: List<TradeCounter> = emptyList(),
+)
 
 /**
  * Where the game stands. The phases that involve more than the player
  * whose turn it is carry their own bookkeeping: [discardSeat] during
- * [CatanPhase.DISCARDING], [pendingTrade] during [CatanPhase.TRADE_PENDING].
+ * [CatanPhase.DISCARDING], [pendingTrade] during [CatanPhase.TRADE_PENDING] and [CatanPhase.TRADE_COUNTERS].
  */
 @Serializable
 enum class CatanPhase {
@@ -109,9 +126,12 @@ enum class CatanPhase {
     /** A played Road Building card: up to two roads remain to be placed. */
     FREE_ROADS,
 
-    /** The offered seat must accept or decline. */
+    /** The [TradeOffer.asking] seat must accept, decline or counter. */
     TRADE_PENDING,
 
+    /** Nobody accepted but some seats countered: the offerer picks one or none. */
+    TRADE_COUNTERS,
+
     GAME_OVER,
 }
 
@@ -278,7 +298,8 @@ data class PlayMonopoly(val card: Int, val resource: Resource) : CatanMove
 data class PlayYearOfPlenty(val card: Int, val take: List<Resource>) : CatanMove
 
 /**
- * Offer a domestic trade to [to]: [give] of ours for [get] of theirs.
+ * Offer a domestic trade to [to] (null: everyone, asked in turn): [give] of
+ * ours for [get] of theirs.
  *
  * Like a forced dice roll this is a free-form intent rather than an
  * enumerated move — the space of two card multisets is combinatorial — so
@@ -287,7 +308,7 @@ data class PlayYearOfPlenty(val card: Int, val take: List<Resource>) : CatanMove
  */
 @Serializable
 @SerialName("offer")
-data class OfferTrade(val to: Int, val give: List<Resource>, val get: List<Resource>) : CatanMove
+data class OfferTrade(val to: Int?, val give: List<Resource>, val get: List<Resource>) : CatanMove
 
 @Serializable
 @SerialName("accept")
@@ -297,6 +318,25 @@ data object AcceptTrade : CatanMove
 @SerialName("decline")
 data object DeclineTrade : CatanMove
 
+/**
+ * Answer the offer on the table with different terms: we would [give] these
+ * cards if the offerer handed over [get]. Free-form like [OfferTrade], so
+ * validated by [CatanRules.isLegalMove] rather than listed.
+ */
+@Serializable
+@SerialName("counter")
+data class CounterTrade(val give: List<Resource>, val get: List<Resource>) : CatanMove
+
+/** The offerer takes the counter-proposal made by [seat]. */
+@Serializable
+@SerialName("acceptCounter")
+data class AcceptCounter(val seat: Int) : CatanMove
+
+/** The offerer takes none of the counter-proposals. */
+@Serializable
+@SerialName("dismissCounters")
+data object DismissCounters : CatanMove
+
 /** Bank trade: [give] at the best ratio this seat can trade at for [get]. */
 @Serializable
 @SerialName("bank")

app/src/main/java/org/prolibertate/games/game/catan/CatanRules.kt

@@ -101,7 +101,8 @@ object CatanRules : GameRules<CatanState, CatanMove> {
         CatanPhase.SETUP_FIRST -> state.setupIndex
         CatanPhase.SETUP_SECOND -> 2 * state.playerCount - 1 - state.setupIndex
         CatanPhase.DISCARDING -> state.discardSeat
-        CatanPhase.TRADE_PENDING -> state.pendingTrade?.to
+        CatanPhase.TRADE_PENDING -> state.pendingTrade?.asking?.takeIf { it >= 0 }
+        CatanPhase.TRADE_COUNTERS -> state.turn
         CatanPhase.AWAIT_ROLL, CatanPhase.ROBBER,
         CatanPhase.PLAYING, CatanPhase.FREE_ROADS,
         -> state.turn
@@ -130,6 +131,8 @@ object CatanRules : GameRules<CatanState, CatanMove> {
 
             is OfferTrade -> offerLegal(state, seat, move)
 
+            is CounterTrade -> counterLegal(state, seat, move)
+
             else -> move in legalMoves(state, seat)
         }
     }
@@ -152,6 +155,8 @@ object CatanRules : GameRules<CatanState, CatanMove> {
 
             CatanPhase.TRADE_PENDING -> tradeResponses(state, seat)
 
+            CatanPhase.TRADE_COUNTERS -> counterChoices(state)
+
             CatanPhase.GAME_OVER -> emptyList()
         }
     }
@@ -324,6 +329,29 @@ object CatanRules : GameRules<CatanState, CatanMove> {
         return responses
     }
 
+    /** What the offerer may do with the counters: take one that is still affordable, or none. */
+    private fun counterChoices(state: CatanState): List<CatanMove> {
+        val offer = state.pendingTrade ?: return emptyList()
+        val moves = mutableListOf<CatanMove>()
+        for (counter in offer.counters) {
+            if (state.holdsAll(counter.by, counter.give) && state.holdsAll(offer.by, counter.get)) {
+                moves += AcceptCounter(counter.by)
+            }
+        }
+        moves += DismissCounters
+        return moves
+    }
+
+    private fun counterLegal(state: CatanState, seat: Int, move: CounterTrade): Boolean {
+        val offer = state.pendingTrade ?: return false
+        if (state.phase != CatanPhase.TRADE_PENDING || offer.asking != seat) return false
+        if (move.give.isEmpty() || move.get.isEmpty()) return false
+        if (countOf(move.give) == countOf(move.get)) return false
+        // Taking the offer as made is Accept, not a counter.
+        if (countOf(move.give) == countOf(offer.get) && countOf(move.get) == countOf(offer.give)) return false
+        return state.holdsAll(seat, move.give) && state.holdsAll(offer.by, move.get)
+    }
+
     /** An empty vertex with no building on it or one edge away. */
     private fun vertexOpenForSettlement(state: CatanState, v: Int): Boolean =
         state.buildings[v] == null &&
@@ -352,7 +380,7 @@ object CatanRules : GameRules<CatanState, CatanMove> {
 
     private fun offerLegal(state: CatanState, seat: Int, move: OfferTrade): Boolean {
         if (state.phase != CatanPhase.PLAYING || state.turn != seat) return false
-        if (move.to !in 0 until state.playerCount || move.to == seat) return false
+        if (move.to != null && (move.to !in 0 until state.playerCount || move.to == seat)) return false
         if (move.give.isEmpty() || move.get.isEmpty()) return false
         // Like-for-like is not a trade; the published game rejects it too.
         if (countOf(move.give) == countOf(move.get)) return false
@@ -384,6 +412,9 @@ object CatanRules : GameRules<CatanState, CatanMove> {
             is OfferTrade -> applyOfferTrade(state, seat, move)
             AcceptTrade -> applyAcceptTrade(state, seat)
             DeclineTrade -> applyDeclineTrade(state, seat)
+            is CounterTrade -> applyCounterTrade(state, seat, move)
+            is AcceptCounter -> applyAcceptCounter(state, move)
+            DismissCounters -> applyDismissCounters(state)
             is MaritimeTrade -> applyMaritimeTrade(state, seat, move)
             EndTurn -> applyEndTurn(state, seat)
             EndFreeRoads -> applyEndFreeRoads(state, seat)
@@ -633,33 +664,111 @@ object CatanRules : GameRules<CatanState, CatanMove> {
         )
     }
 
-    private fun applyOfferTrade(state: CatanState, seat: Int, move: OfferTrade): CatanState =
-        state.copy(
-            phase = CatanPhase.TRADE_PENDING,
-            pendingTrade = TradeOffer(by = seat, to = move.to, give = move.give, get = move.get),
+    private fun applyOfferTrade(state: CatanState, seat: Int, move: OfferTrade): CatanState {
+        val audience = if (move.to == null) "the table" else "seat ${move.to}"
+        val offered = state.copy(
             log = state.log + "Seat $seat offers ${describe(countOf(move.give))} for " +
-                "${describe(countOf(move.get))} to seat ${move.to}.",
+                "${describe(countOf(move.get))} to $audience.",
         )
+        val offer = TradeOffer(by = seat, to = move.to, give = move.give, get = move.get)
+        val first = nextAsker(offered, offer, seat)
+            ?: return offered.copy(log = offered.log + "Nobody has any cards to trade.")
+        return offered.copy(
+            phase = CatanPhase.TRADE_PENDING,
+            pendingTrade = offer.copy(asking = first),
+        )
+    }
 
-    private fun applyAcceptTrade(state: CatanState, seat: Int): CatanState {
-        val offer = state.pendingTrade!!
-        var resources = withCards(state.resources, offer.to, offer.get, -1)
-        resources = withCards(resources, offer.by, offer.give, -1)
-        resources = withCards(resources, offer.by, offer.get, 1)
-        resources = withCards(resources, offer.to, offer.give, 1)
+    /**
+     * The next seat to ask after [after], or null when the round is over. An
+     * addressed offer asks only its addressee; an open one walks the table in
+     * seat order, skipping seats with no cards (they could neither pay nor counter).
+     */
+    private fun nextAsker(state: CatanState, offer: TradeOffer, after: Int): Int? {
+        if (offer.to != null) return if (after == offer.by) offer.to else null
+        var s = (after + 1) % state.playerCount
+        while (s != offer.by) {
+            if (state.resourceCount(s) > 0) return s
+            s = (s + 1) % state.playerCount
+        }
+        return null
+    }
+
+    /** Moves the offer on to the next seat, or closes the round when everyone has answered. */
+    private fun advanceTrade(state: CatanState, offer: TradeOffer, after: Int, said: String): CatanState {
+        val next = nextAsker(state, offer, after)
+        val log = state.log + said
+        if (next != null) {
+            return state.copy(pendingTrade = offer.copy(asking = next), log = log)
+        }
+        if (offer.counters.isNotEmpty()) {
+            return state.copy(
+                phase = CatanPhase.TRADE_COUNTERS,
+                pendingTrade = offer.copy(asking = -1),
+                log = log,
+            )
+        }
         return state.copy(
             phase = CatanPhase.PLAYING,
             pendingTrade = null,
-            resources = resources,
+            log = log + "Nobody takes the offer.",
+        )
+    }
+
+    /** Seat [a] hands [aGives] to seat [b] and gets [bGives] back. */
+    private fun swapCards(
+        resources: List<Map<Resource, Int>>,
+        a: Int,
+        aGives: List<Resource>,
+        b: Int,
+        bGives: List<Resource>,
+    ): List<Map<Resource, Int>> {
+        var r = withCards(resources, a, aGives, -1)
+        r = withCards(r, b, bGives, -1)
+        r = withCards(r, b, aGives, 1)
+        return withCards(r, a, bGives, 1)
+    }
+
+    private fun applyAcceptTrade(state: CatanState, seat: Int): CatanState {
+        val offer = state.pendingTrade!!
+        return state.copy(
+            phase = CatanPhase.PLAYING,
+            pendingTrade = null,
+            resources = swapCards(state.resources, offer.by, offer.give, seat, offer.get),
             log = state.log + "Seat $seat accepts — the cards cross the table.",
         )
     }
 
     private fun applyDeclineTrade(state: CatanState, seat: Int): CatanState =
+        advanceTrade(state, state.pendingTrade!!, seat, "Seat $seat declines the offer.")
+
+    private fun applyCounterTrade(state: CatanState, seat: Int, move: CounterTrade): CatanState {
+        val offer = state.pendingTrade!!
+        val counter = TradeCounter(by = seat, give = move.give, get = move.get)
+        return advanceTrade(
+            state,
+            offer.copy(counters = offer.counters + counter),
+            seat,
+            "Seat $seat counters: ${describe(countOf(move.give))} for ${describe(countOf(move.get))}.",
+        )
+    }
+
+    private fun applyAcceptCounter(state: CatanState, move: AcceptCounter): CatanState {
+        val offer = state.pendingTrade!!
+        val counter = offer.counters.first { it.by == move.seat }
+        return state.copy(
+            phase = CatanPhase.PLAYING,
+            pendingTrade = null,
+            resources = swapCards(state.resources, offer.by, counter.get, counter.by, counter.give),
+            log = state.log + "Seat ${offer.by} takes seat ${counter.by}'s counter — the cards cross the table.",
+        )
+    }
+
+    private fun applyDismissCounters(state: CatanState): CatanState =
         state.copy(
             phase = CatanPhase.PLAYING,
             pendingTrade = null,
-            log = state.log + "Seat $seat declines the offer.",
+            log = state.log + "Seat ${state.turn} turns the counter-offers down.",
         )
 
     private fun applyMaritimeTrade(state: CatanState, seat: Int, move: MaritimeTrade): CatanState {

app/src/main/java/org/prolibertate/games/ui/game/catan/CatanDialogs.kt

@@ -35,6 +35,9 @@ import org.prolibertate.games.game.catan.DevCardType
 import org.prolibertate.games.game.catan.Discard
 import org.prolibertate.games.game.catan.MaritimeTrade
 import org.prolibertate.games.game.catan.OfferTrade
+import org.prolibertate.games.game.catan.TradeCounter
+import org.prolibertate.games.game.catan.CounterTrade
+import org.prolibertate.games.game.catan.AcceptCounter
 import org.prolibertate.games.game.catan.PlayKnight
 import org.prolibertate.games.game.catan.PlayRoadBuilding
 import org.prolibertate.games.game.catan.Resource
@@ -312,6 +315,7 @@ fun CatanTradeDialog(
 ) {
     var tab by remember { mutableStateOf(TradeTab.BANK) }
     var bankGive by remember { mutableStateOf<Resource?>(null) }
+    var everyone by remember { mutableStateOf(true) }
     var partner by remember { mutableStateOf<Int?>(null) }
     var give by remember { mutableStateOf(emptyMap<Resource, Int>()) }
     var get by remember { mutableStateOf(emptyMap<Resource, Int>()) }
@@ -371,9 +375,16 @@ fun CatanTradeDialog(
                     }
                 } else {
                     Text("Offer to:", fontWeight = FontWeight.Bold)
-                    Row(horizontalArrangement = Arrangement.spacedBy(8.dp)) {
+                    FlowRow(
+                        horizontalArrangement = Arrangement.spacedBy(8.dp),
+                        verticalArrangement = Arrangement.spacedBy(8.dp),
+                    ) {
+                        TabButton(CatanText.EVERYONE, everyone) { everyone = true; partner = null }
                         (0 until state.playerCount).filter { it != seat }.forEach { other ->
-                            TabButton(seats.label(other), partner == other) { partner = other }
+                            TabButton(seats.label(other), !everyone && partner == other) {
+                                everyone = false
+                                partner = other
+                            }
                         }
                     }
                     Text(CatanText.YOU_GIVE, fontWeight = FontWeight.Bold)
@@ -389,13 +400,13 @@ fun CatanTradeDialog(
         },
         confirmButton = {
             if (tab == TradeTab.PLAYER) {
-                val to = partner
+                val to = if (everyone) null else partner
                 val giveCards = give.asCards()
                 val getCards = get.asCards()
-                val allowed = to != null &&
+                val allowed = (everyone || partner != null) &&
                     CatanInteraction.offerAllowed(state, seat, to, giveCards, getCards)
                 Button(
-                    onClick = { if (to != null) onOffer(OfferTrade(to, giveCards, getCards)) },
+                    onClick = { onOffer(OfferTrade(to, giveCards, getCards)) },
                     enabled = allowed,
                 ) { Text(CatanText.SEND_OFFER) }
             }
@@ -435,29 +446,57 @@ private fun TabButton(label: String, selected: Boolean, onClick: () -> Unit) {
     }
 }
 
-/** Another player has offered the local player a trade. */
+/**
+ * Another player has put an offer to the local player (alone, or as one of the
+ * table). Accept, decline, or — via a second step — answer with different terms.
+ */
+@OptIn(ExperimentalLayoutApi::class)
 @Composable
 fun CatanTradeResponseDialog(
+    state: CatanState,
+    seat: Int,
     offer: TradeOffer,
     seats: CatanSeats,
     canAccept: Boolean,
     onAccept: () -> Unit,
     onDecline: () -> Unit,
+    onCounter: (CounterTrade) -> Unit,
 ) {
+    var countering by remember(offer) { mutableStateOf(false) }
+    // What we would give the offerer, and what we would ask of them.
+    var give by remember(offer) { mutableStateOf(offer.get.groupingBy { it }.eachCount()) }
+    var get by remember(offer) { mutableStateOf(offer.give.groupingBy { it }.eachCount()) }
+
     AlertDialog(
         onDismissRequest = {},
-        title = { Text("Trade offer") },
+        title = { Text(if (countering) "Counter-offer" else "Trade offer") },
         text = {
-            Column(verticalArrangement = Arrangement.spacedBy(6.dp)) {
+            Column(
+                modifier = Modifier.heightIn(max = 460.dp).verticalScroll(rememberScrollState()),
+                verticalArrangement = Arrangement.spacedBy(8.dp),
+            ) {
                 Text(
                     CatanText.tradeSummary(
                         by = seats.label(offer.by),
-                        to = "you",
+                        to = if (offer.to == null) "the table" else "you",
                         give = offer.give,
                         get = offer.get,
                     ),
                 )
-                if (!canAccept) {
+                if (countering) {
+                    Text(CatanText.YOU_GIVE, fontWeight = FontWeight.Bold)
+                    CounterRow(
+                        counts = give,
+                        limit = { state.resources[seat][it] ?: 0 },
+                        onChange = { give = it },
+                    )
+                    Text(CatanText.YOU_GET, fontWeight = FontWeight.Bold)
+                    CounterRow(
+                        counts = get,
+                        limit = { state.resources[offer.by][it] ?: 0 },
+                        onChange = { get = it },
+                    )
+                } else if (!canAccept) {
                     Text(
                         "You cannot accept this: one side no longer holds the cards.",
                         style = MaterialTheme.typography.bodySmall,
@@ -465,8 +504,58 @@ fun CatanTradeResponseDialog(
                 }
             }
         },
-        confirmButton = { Button(onClick = onAccept, enabled = canAccept) { Text(CatanText.ACCEPT) } },
-        dismissButton = { TextButton(onClick = onDecline) { Text(CatanText.DECLINE) } },
+        confirmButton = {
+            if (countering) {
+                val move = CounterTrade(give.asCards(), get.asCards())
+                Button(
+                    onClick = { onCounter(move) },
+                    enabled = CatanInteraction.counterAllowed(state, seat, move.give, move.get),
+                ) { Text(CatanText.SEND_COUNTER) }
+            } else {
+                Button(onClick = onAccept, enabled = canAccept) { Text(CatanText.ACCEPT) }
+            }
+        },
+        dismissButton = {
+            Row(horizontalArrangement = Arrangement.spacedBy(4.dp)) {
+                if (countering) {
+                    TextButton(onClick = { countering = false }) { Text(CatanText.CANCEL) }
+                } else {
+                    TextButton(onClick = { countering = true }) { Text(CatanText.COUNTER) }
+                }
+                TextButton(onClick = onDecline) { Text(CatanText.DECLINE) }
+            }
+        },
+    )
+}
+
+/** The offerer's choice once nobody accepted: take a counter-offer, or none. */
+@Composable
+fun CatanCounterChoiceDialog(
+    counters: List<TradeCounter>,
+    seats: CatanSeats,
+    onTake: (AcceptCounter) -> Unit,
+    onNoDeal: () -> Unit,
+) {
+    AlertDialog(
+        onDismissRequest = {},
+        title = { Text("Counter-offers") },
+        text = {
+            Column(
+                modifier = Modifier.heightIn(max = 460.dp).verticalScroll(rememberScrollState()),
+                verticalArrangement = Arrangement.spacedBy(8.dp),
+            ) {
+                if (counters.isEmpty()) {
+                    Text("None of the counter-offers can be met any more.")
+                }
+                counters.forEach { counter ->
+                    Column(verticalArrangement = Arrangement.spacedBy(4.dp)) {
+                        Text(CatanText.counterSummary(seats.label(counter.by), counter.give, counter.get))
+                        Button(onClick = { onTake(AcceptCounter(counter.by)) }) { Text(CatanText.ACCEPT) }
+                    }
+                }
+            }
+        },
+        confirmButton = { TextButton(onClick = onNoDeal) { Text(CatanText.NO_DEAL) } },
     )
 }
 

app/src/main/java/org/prolibertate/games/ui/game/catan/CatanInteraction.kt

@@ -1,5 +1,6 @@
 package org.prolibertate.games.ui.game.catan
 
+import org.prolibertate.games.game.catan.AcceptCounter
 import org.prolibertate.games.game.catan.AcceptTrade
 import org.prolibertate.games.game.catan.BuildCity
 import org.prolibertate.games.game.catan.BuildRoad
@@ -10,6 +11,7 @@ import org.prolibertate.games.game.catan.CatanMove
 import org.prolibertate.games.game.catan.CatanPhase
 import org.prolibertate.games.game.catan.CatanRules
 import org.prolibertate.games.game.catan.CatanState
+import org.prolibertate.games.game.catan.CounterTrade
 import org.prolibertate.games.game.catan.DeclineTrade
 import org.prolibertate.games.game.catan.DevCard
 import org.prolibertate.games.game.catan.DevCardType
@@ -20,6 +22,7 @@ import org.prolibertate.games.game.catan.HexCoord
 import org.prolibertate.games.game.catan.MaritimeTrade
 import org.prolibertate.games.game.catan.MoveRobber
 import org.prolibertate.games.game.catan.OfferTrade
+import org.prolibertate.games.game.catan.TradeCounter
 import org.prolibertate.games.game.catan.PlayKnight
 import org.prolibertate.games.game.catan.PlayMonopoly
 import org.prolibertate.games.game.catan.PlayRoadBuilding
@@ -284,9 +287,20 @@ object CatanInteraction {
     fun offerAllowed(
         state: CatanState,
         seat: Int,
-        to: Int,
+        to: Int?,
         give: List<Resource>,
         get: List<Resource>,
     ): Boolean = give.isNotEmpty() && get.isNotEmpty() &&
         CatanRules.isLegalMove(state, seat, OfferTrade(to, give, get))
+
+    /** Whether [seat] may answer the offer on the table with [give] for [get]. */
+    fun counterAllowed(state: CatanState, seat: Int, give: List<Resource>, get: List<Resource>): Boolean =
+        give.isNotEmpty() && get.isNotEmpty() &&
+            CatanRules.isLegalMove(state, seat, CounterTrade(give, get))
+
+    /** The counter-offers the offerer may take right now, in the order they came in. */
+    fun counterChoices(state: CatanState, legal: List<CatanMove>): List<TradeCounter> {
+        val takeable = legal.filterIsInstance<AcceptCounter>().map { it.seat }.toSet()
+        return state.pendingTrade?.counters.orEmpty().filter { it.by in takeable }
+    }
 }

app/src/main/java/org/prolibertate/games/ui/game/catan/CatanScreen.kt

@@ -34,6 +34,7 @@ import org.prolibertate.games.game.catan.CatanPhase
 import org.prolibertate.games.game.catan.CatanRules
 import org.prolibertate.games.game.catan.CatanState
 import org.prolibertate.games.game.catan.DeclineTrade
+import org.prolibertate.games.game.catan.DismissCounters
 import org.prolibertate.games.game.catan.EndFreeRoads
 import org.prolibertate.games.game.catan.EndTurn
 import org.prolibertate.games.game.catan.MoveRobber
@@ -363,13 +364,24 @@ private fun CatanDialogHost(
                 onSubmit = onSubmit,
             )
 
-        state.phase == CatanPhase.TRADE_PENDING && offer != null && offer.to == localSeat ->
+        state.phase == CatanPhase.TRADE_PENDING && offer != null && offer.asking == localSeat ->
             CatanTradeResponseDialog(
+                state = state,
+                seat = localSeat,
                 offer = offer,
                 seats = seats,
                 canAccept = CatanInteraction.tradeResponses(legal).first,
                 onAccept = { onSubmit(AcceptTrade) },
                 onDecline = { onSubmit(DeclineTrade) },
+                onCounter = onSubmit,
+            )
+
+        state.phase == CatanPhase.TRADE_COUNTERS && state.turn == localSeat && legal.isNotEmpty() ->
+            CatanCounterChoiceDialog(
+                counters = CatanInteraction.counterChoices(state, legal),
+                seats = seats,
+                onTake = onSubmit,
+                onNoDeal = { onSubmit(DismissCounters) },
             )
 
         victimChoice != null ->

app/src/main/java/org/prolibertate/games/ui/game/catan/CatanText.kt

@@ -103,6 +103,10 @@ object CatanText {
     const val CONFIRM = "Confirm"
     const val STOP_ROADS = "Done with roads"
     const val BUILD = "Build"
+    const val COUNTER = "Counter…"
+    const val SEND_COUNTER = "Send counter"
+    const val EVERYONE = "Everyone"
+    const val NO_DEAL = "No deal"
 
     /**
      * The empty second line of a button that has no cost, so every button in the
@@ -194,11 +198,23 @@ object CatanText {
                 val offer = state.pendingTrade
                 when {
                     offer == null -> "Waiting for a reply…"
-                    offer.to == me -> "${seats.label(offer.by)} offers you a trade."
-                    offer.by == me -> "Waiting for ${seats.label(offer.to)} to answer your offer…"
-                    else -> "${seats.label(offer.by)} has offered ${seats.label(offer.to)} a trade."
+                    offer.asking == me -> if (offer.to == null) {
+                        "${seats.label(offer.by)} offers the table a trade. Accept, decline or counter."
+                    } else {
+                        "${seats.label(offer.by)} offers you a trade. Accept, decline or counter."
+                    }
+
+                    offer.by == me -> "Waiting for ${seats.label(offer.asking)} to answer your offer…"
+                    else -> "${seats.label(offer.by)}'s offer is with ${seats.label(offer.asking)}."
                 }
             }
+
+            CatanPhase.TRADE_COUNTERS ->
+                if (mine) {
+                    "Nobody accepted, but there are counter-offers. Take one or turn them down."
+                } else {
+                    "$turn is weighing counter-offers…"
+                }
         }
     }
 
@@ -212,6 +228,10 @@ object CatanText {
     fun tradeSummary(by: String, to: String, give: List<Resource>, get: List<Resource>): String =
         "$by offers ${cards(give)} to $to for ${cards(get)}"
 
+    /** One counter-offer as the offerer sees it: what that seat gives and wants. */
+    fun counterSummary(by: String, give: List<Resource>, get: List<Resource>): String =
+        "$by gives ${cards(give)} for your ${cards(get)}"
+
     fun winnerHeadline(state: CatanState, seats: CatanSeats): String {
         val winner = state.winner ?: return "Game over"
         return if (winner == seats.me) "You won!" else "${seats.label(winner)} won"

app/src/test/java/org/prolibertate/games/game/catan/CatanAiTest.kt

@@ -142,4 +142,50 @@ class CatanAiTest {
         assertEquals(CatanPhase.PLAYING, after.phase)
         assertNull(after.pendingTrade)
     }
+
+    private fun tradeTable(offer: TradeOffer, vararg hands: Map<Resource, Int>): CatanState =
+        CatanRules.initialState(config(CatanOptions(), seed = 7L)).copy(
+            phase = CatanPhase.TRADE_PENDING,
+            turn = 0,
+            turnNumber = 1,
+            pendingTrade = offer,
+            resources = hands.toList(),
+        )
+
+    @Test
+    fun `the AI accepts an offer that gives it more than it costs, and declines the reverse`() {
+        val generous = tradeTable(
+            TradeOffer(by = 0, to = null, give = listOf(Resource.ORE, Resource.ORE), get = listOf(Resource.WOOL), asking = 1),
+            hand(Resource.ORE to 2), hand(Resource.WOOL to 2), hand(),
+        )
+        assertEquals(AcceptTrade, CatanAi().chooseMove(generous, 1, CatanRules.legalMoves(generous, 1)))
+
+        val stingy = tradeTable(
+            TradeOffer(by = 0, to = null, give = listOf(Resource.WOOL), get = listOf(Resource.ORE), asking = 1),
+            hand(Resource.WOOL to 1), hand(Resource.ORE to 2), hand(),
+        )
+        assertEquals(DeclineTrade, CatanAi().chooseMove(stingy, 1, CatanRules.legalMoves(stingy, 1)))
+    }
+
+    @Test
+    fun `an AI offerer takes the best counter and refuses a losing one`() {
+        val counters = listOf(
+            TradeCounter(by = 1, give = listOf(Resource.ORE), get = listOf(Resource.LUMBER)),
+            TradeCounter(by = 2, give = listOf(Resource.ORE, Resource.GRAIN), get = listOf(Resource.WOOL)),
+        )
+        val state = tradeTable(
+            TradeOffer(by = 0, to = null, give = listOf(Resource.WOOL), get = listOf(Resource.ORE), asking = -1, counters = counters),
+            hand(Resource.LUMBER to 1, Resource.WOOL to 1), hand(Resource.ORE to 1), hand(Resource.ORE to 1, Resource.GRAIN to 1),
+        ).copy(phase = CatanPhase.TRADE_COUNTERS)
+        val legal = CatanRules.legalMoves(state, 0)
+        assertEquals(AcceptCounter(2), CatanAi().chooseMove(state, 0, legal))
+
+        val bad = state.copy(
+            pendingTrade = state.pendingTrade!!.copy(
+                counters = listOf(TradeCounter(by = 1, give = listOf(Resource.WOOL), get = listOf(Resource.LUMBER))),
+            ),
+            resources = listOf(hand(Resource.LUMBER to 1), hand(Resource.WOOL to 1), hand()),
+        )
+        assertEquals(DismissCounters, CatanAi().chooseMove(bad, 0, CatanRules.legalMoves(bad, 0)))
+    }
 }

app/src/test/java/org/prolibertate/games/game/catan/CatanRulesTest.kt

@@ -520,6 +520,113 @@ class CatanRulesTest {
         assertEquals(listOf<CatanMove>(DeclineTrade), CatanRules.legalMoves(offered, 1))
     }
 
+    private val twoLumberForBrick =
+        OfferTrade(to = null, give = listOf(Resource.LUMBER, Resource.LUMBER), get = listOf(Resource.BRICK))
+
+    private fun openTable() = craft().copy(
+        resources = hands(
+            hand(Resource.LUMBER to 3),
+            hand(Resource.BRICK to 2),
+            hand(Resource.BRICK to 1, Resource.WOOL to 1),
+        ),
+    )
+
+    @Test
+    fun `an open offer asks each other seat in turn until one accepts`() {
+        val state = openTable()
+        assertTrue(CatanRules.isLegalMove(state, 0, twoLumberForBrick))
+        val asked1 = CatanRules.applyMove(state, 0, twoLumberForBrick)
+        assertEquals(CatanPhase.TRADE_PENDING, asked1.phase)
+        assertEquals(1, CatanRules.currentSeat(asked1))
+
+        val asked2 = CatanRules.applyMove(asked1, 1, DeclineTrade)
+        assertEquals("a decline passes the offer on", 2, CatanRules.currentSeat(asked2))
+        assertEquals(CatanPhase.TRADE_PENDING, asked2.phase)
+
+        val done = CatanRules.applyMove(asked2, 2, AcceptTrade)
+        assertEquals(CatanPhase.PLAYING, done.phase)
+        assertNull(done.pendingTrade)
+        assertEquals(hand(Resource.LUMBER to 1, Resource.BRICK to 1), done.resources[0])
+        assertEquals(hand(Resource.LUMBER to 2, Resource.WOOL to 1), done.resources[2])
+        assertEquals("seat 1 never took part", state.resources[1], done.resources[1])
+    }
+
+    @Test
+    fun `an open offer nobody wants lapses back to the offerer`() {
+        var table = CatanRules.applyMove(openTable(), 0, twoLumberForBrick)
+        table = CatanRules.applyMove(table, 1, DeclineTrade)
+        table = CatanRules.applyMove(table, 2, DeclineTrade)
+        assertEquals(CatanPhase.PLAYING, table.phase)
+        assertNull(table.pendingTrade)
+        assertEquals(0, CatanRules.currentSeat(table))
+    }
+
+    @Test
+    fun `seats with no cards are not asked`() {
+        val state = openTable().copy(resources = hands(hand(Resource.LUMBER to 3), hand(), hand(Resource.BRICK to 1)))
+        val table = CatanRules.applyMove(state, 0, twoLumberForBrick)
+        assertEquals(2, CatanRules.currentSeat(table))
+    }
+
+    @Test
+    fun `a counter is kept and the offerer chooses once everyone has answered`() {
+        var table = CatanRules.applyMove(openTable(), 0, twoLumberForBrick)
+        // Seat 1 will not give a brick for two lumber but would for three.
+        val counter = CounterTrade(give = listOf(Resource.BRICK), get = listOf(Resource.LUMBER, Resource.LUMBER, Resource.LUMBER))
+        assertTrue(CatanRules.isLegalMove(table, 1, counter))
+        table = CatanRules.applyMove(table, 1, counter)
+        assertEquals(2, CatanRules.currentSeat(table))
+        table = CatanRules.applyMove(table, 2, DeclineTrade)
+
+        assertEquals(CatanPhase.TRADE_COUNTERS, table.phase)
+        assertEquals("the offerer chooses", 0, CatanRules.currentSeat(table))
+        assertEquals(
+            listOf<CatanMove>(AcceptCounter(1), DismissCounters),
+            CatanRules.legalMoves(table, 0),
+        )
+
+        val taken = CatanRules.applyMove(table, 0, AcceptCounter(1))
+        assertEquals(CatanPhase.PLAYING, taken.phase)
+        assertNull(taken.pendingTrade)
+        assertEquals(hand(Resource.BRICK to 1), taken.resources[0])
+        assertEquals(hand(Resource.LUMBER to 3, Resource.BRICK to 1), taken.resources[1])
+    }
+
+    @Test
+    fun `counters can all be turned down`() {
+        var table = CatanRules.applyMove(openTable(), 0, twoLumberForBrick)
+        table = CatanRules.applyMove(
+            table, 1,
+            CounterTrade(listOf(Resource.BRICK), listOf(Resource.LUMBER, Resource.LUMBER, Resource.LUMBER)),
+        )
+        table = CatanRules.applyMove(table, 2, DeclineTrade)
+        val after = CatanRules.applyMove(table, 0, DismissCounters)
+        assertEquals(CatanPhase.PLAYING, after.phase)
+        assertNull(after.pendingTrade)
+        assertEquals(openTable().resources, after.resources)
+    }
+
+    @Test
+    fun `a counter must differ from the offer and be affordable`() {
+        val table = CatanRules.applyMove(openTable(), 0, twoLumberForBrick)
+        assertFalse(
+            "the offer as made is an accept, not a counter",
+            CatanRules.isLegalMove(table, 1, CounterTrade(listOf(Resource.BRICK), listOf(Resource.LUMBER, Resource.LUMBER))),
+        )
+        assertFalse(
+            "cannot promise cards not held",
+            CatanRules.isLegalMove(table, 1, CounterTrade(listOf(Resource.ORE), listOf(Resource.LUMBER))),
+        )
+        assertFalse(
+            "cannot ask for cards the offerer lacks",
+            CatanRules.isLegalMove(table, 1, CounterTrade(listOf(Resource.BRICK), listOf(Resource.ORE))),
+        )
+        assertFalse(
+            "only the seat being asked may counter",
+            CatanRules.isLegalMove(table, 2, CounterTrade(listOf(Resource.WOOL), listOf(Resource.LUMBER))),
+        )
+    }
+
     @Test
     fun `the bank trades four for one and harbours do better`() {
         val base = craft()
@@ -912,6 +1019,10 @@ class CatanRulesTest {
             OfferTrade(1, listOf(Resource.LUMBER, Resource.LUMBER), listOf(Resource.ORE)),
             AcceptTrade,
             DeclineTrade,
+            OfferTrade(null, listOf(Resource.LUMBER), listOf(Resource.ORE)),
+            CounterTrade(listOf(Resource.WOOL), listOf(Resource.GRAIN, Resource.GRAIN)),
+            AcceptCounter(2),
+            DismissCounters,
             MaritimeTrade(Resource.WOOL, Resource.GRAIN),
             EndTurn,
             EndFreeRoads,

docs/RULES-catan.md

@@ -122,17 +122,32 @@ is the same code path.
 
 ### Domestic
 
-An offer names **one** addressee and two card multisets: what the offerer gives,
-what they want. There are no counter-offers and no open auctions in v1.
+An offer is addressed to **one** seat or, with `to = null`, to **everyone**, and
+names two card multisets: what the offerer gives, what they want.
+
+Seats are asked **one at a time**, in seat order after the offerer (seats holding
+no cards are skipped; an addressed offer asks only its addressee). The seat being
+asked may:
+
+- **accept** — the trade happens at once and the offer closes (first accept wins);
+- **decline** — the offer moves on to the next seat;
+- **counter** (`CounterTrade`) — propose different terms: what they would give and
+  what they want from the offerer. A counter must differ from the offer as made
+  (that is an accept), and both sides must hold the cards. The offer moves on.
+
+When every seat has answered and nobody accepted: with no counters the offer
+simply lapses; with counters the phase becomes `TRADE_COUNTERS` and the offerer
+either **takes one** (`AcceptCounter(seat)`, still checked for affordability) or
+**turns them all down** (`DismissCounters`).
 
 An offer is legal only when the offerer's turn is in PLAYING, the addressee is
 another seat, both legs are non-empty, the two legs are not the same multiset
 (`countOf(give) != countOf(get)` — like-for-like is not a trade), and the
 offerer actually holds the cards being offered.
 
-The addressee may **accept** only if they hold what was asked and the offerer
-still holds what was promised; otherwise only **decline** is offered. A decline
-clears the table and leaves every card where it was.
+A seat may **accept** only if it holds what was asked and the offerer still holds
+what was promised; otherwise only decline (or counter) is offered. A refusal
+leaves every card where it was.
 
 Offers are free-form intents rather than enumerated moves (the space of card
 multisets is combinatorial), so they are validated structurally by
@@ -292,15 +307,12 @@ timing rules; Longest Road and Largest Army worth five; victory at ten.
 - **Year of Plenty two-of-a-kind needs the bank to hold both cards**, not one.
 - **The robber must move.** Some printings allow staying put; this engine always
   requires a different hex.
-- **Offers are one-to-one, no auctions or counter-offers** in v1.
+- **Offers may be open to the whole table** and can be countered; the first accept wins (see Trading).
 
 ## Known gaps
 
-- **No domestic auction or counter-offer.** An offer is addressed to a single
-  seat. Open trading to the whole table, and counter-offers, are the obvious next
-  step and are not implemented.
-- **No player-to-player trade over the wire beyond accept/decline.** The engine
-  supports it; whether the UI surfaces it is the screen task's concern.
+- **No timer or cancel on offers.** An offer waits for each asked seat in turn; the offerer cannot withdraw it mid-round, and a player who never answers stalls the table.
+- **The AI never counters.** It accepts, declines, and picks among counters it is sent, but does not propose them.
 - **No trading away a development card.** Not part of the base game.
 - **The screen is built, not yet verified on two devices.** The Katan screen and
   setup options exist (see [UI-catan.md](UI-catan.md)); the catalogue entry is a

docs/UI-catan.md

@@ -89,7 +89,8 @@ screen's UI state. The legal-move list stays the gate.
 | Seven | **Discard** dialog (forced); then taps a hex to move the robber; a victim dialog appears only if more than one player can be robbed |
 | Main turn | arms **Road / Settlement / City** and taps a highlighted spot; **Buy card**; **Play card**; **Trade**; **End turn** |
 | Road Building | taps highlighted edges, or **Done with roads** |
-| Offered a trade | **Accept / Decline** dialog (forced) |
+| Offered a trade | **Accept / Decline / Counter…** dialog (forced); *Counter…* opens a picker pre-filled with the mirror of the offer |
+| Counter-offers received | **Counter-offers** dialog: *Accept* beside the one to take, or *No deal* |
 | Game over | result dialog |
 
 Trade offers are free-form (two card multisets), so they are validated with
@@ -137,6 +138,6 @@ Not done yet, in rough priority order:
    it does not say which hexes paid out, so that needs either a diff of two states
    or an engine addition.
 3. Art: terrain textures, resource and harbour icons, a real robber pawn.
-4. Open trade to the whole table and counter-offers (an engine limitation too).
+4. A timer or cancel button on offers (the engine has neither).
 5. A board that shows the *last* move (a faint highlight of what just changed).
 6. Landscape polish on large tablets; the right-hand panel scrolls but is plain.