implement cost formula for asteroid expansion

bin/app/data/config/world.toml

@@ -19,9 +19,7 @@ enemy_buffer_width_tiles = 20
 
 [expansion]
 columns_per_expansion_tiles = 10
-# Flat until the escalating cost formula lands (progression_design.md
+cost_building_blocks_formula = "300 + 50*x + 10*x*x"
-# action item 4).
-cost_building_blocks = 400
 
 [push]
 push_expand_columns_tiles = 10

bin/test/data/config/world.toml

@@ -19,7 +19,7 @@ enemy_buffer_width_tiles = 15
 
 [expansion]
 columns_per_expansion_tiles = 10
-cost_building_blocks = 200
+cost_building_blocks_formula = "400 * 2^x"
 
 [push]
 push_expand_columns_tiles = 20

docs/requirements.md

@@ -367,7 +367,7 @@ Modules in `modules.toml` define a `surface_mask` — a list of strings that des
 ## Asteroid Expansion
 
 - REQ-EXP-UNLOCK: The player can unlock additional asteroid tile columns to the left of the existing asteroid by spending building blocks from the global stock.
-- REQ-EXP-COST: Each expansion adds `world.toml [expansion].columns_per_expansion` columns and costs `[expansion].cost_building_blocks` building blocks.
+- REQ-EXP-COST: Each expansion adds `world.toml [expansion].columns_per_expansion` columns. The building block cost of an expansion is defined by the formula `world.toml [expansion].cost_building_blocks_formula`, where `x` is the number of expansions already purchased (0 for the first expansion, incrementing by 1 for each subsequent expansion). The formula is evaluated at purchase time and its result is floored to an integer number of building blocks.
 
 ## UI
 
@@ -392,9 +392,10 @@ The screen is divided into two columns: a main column (75% width) containing the
            (75% width)                   (25% width)
 ```
 
-- REQ-UI-HEADER: The header bar spans the width of the game world column (75% of the screen width) and always shows the elapsed survival time, the current global building blocks stock, and the artifact count (REQ-WIN-ARTIFACT-COUNT) displayed as `Artifacts: x/y` (where `x` is the current artifact count and `y` is `world.toml [world].artifact_win_count`) on the left, the boss wave counter and boss countdown (REQ-UI-BOSS-STATUS) to the left of the speed buttons, and game speed controls on the right.
+- REQ-UI-HEADER: The header bar spans the width of the game world column (75% of the screen width) and always shows the elapsed survival time, the current global building blocks stock, and the artifact count (REQ-WIN-ARTIFACT-COUNT) displayed as `Artifacts: x/y` (where `x` is the current artifact count and `y` is `world.toml [world].artifact_win_count`) on the left, the boss wave counter and boss countdown (REQ-UI-BOSS-STATUS) and an asteroid expansion button (REQ-UI-EXPAND-BUTTON) to the left of the speed buttons, and game speed controls on the right.
 - REQ-UI-BOSS-STATUS: The header bar displays, to the left of the speed buttons, the current boss wave counter (REQ-WAV-BOSS-COUNTER) and the time remaining on the boss countdown (REQ-WAV-BOSS-COUNTDOWN). The boss wave counter is shown as `Boss Wave #<x>` and the countdown as `Next boss: <M:SS>`, where `<M:SS>` is the remaining seconds formatted as whole minutes and two-digit seconds. Both values update continuously as the simulation runs.
 - REQ-UI-SPEED: The game speed controls in the header bar are buttons for 0×, 0.5×, 1×, 2×, and 4× speed. The currently active speed is shown as selected. All game simulation (production, movement, threat accumulation, wave timing) scales with the selected speed. 0× pauses the game.
+- REQ-UI-EXPAND-BUTTON: The header bar shows an asteroid expansion button captioned `Expand: <x> Blocks`, where `<x>` is the current expansion cost computed from `world.toml [expansion].cost_building_blocks_formula` at the current number of purchased expansions (REQ-EXP-COST). Clicking the button unlocks the next asteroid expansion (REQ-EXP-UNLOCK, REQ-GW-ASTEROID-EXPAND), spending that many building blocks from the global stock. The button is disabled when the player cannot currently afford the cost (consistent with REQ-UI-BUILD-DISABLED). The caption updates as the cost changes with each purchased expansion.
 - REQ-UI-WORLD-SIZE: The game world view occupies the full height below the header bar in the main column (75% of the screen width).
 - REQ-UI-PANEL-COLUMN: The side panel column occupies 25% of the screen width and the full screen height. It is divided into three equal-height panels stacked top to bottom: selected building panel (top), build button grid (middle), and blueprint panel (bottom).
 

src/lib/config/ConfigLoader.cpp

@@ -279,7 +279,7 @@ WorldConfig ConfigLoader::loadWorld(const std::string& path)
     cfg.regions.enemyBufferWidth_tiles  = static_cast<int>(requireInt(tbl["regions"]["enemy_buffer_width_tiles"],  file, "regions.enemy_buffer_width_tiles"));
 
     cfg.expansion.columnsPerExpansion_tiles   = static_cast<int>(requireInt(tbl["expansion"]["columns_per_expansion_tiles"], file, "expansion.columns_per_expansion_tiles"));
-    cfg.expansion.costBuildingBlocks        = static_cast<int>(requireInt(tbl["expansion"]["cost_building_blocks"],        file, "expansion.cost_building_blocks"));
+    cfg.expansion.costBuildingBlocksFormula   = requireFormula(tbl["expansion"]["cost_building_blocks_formula"],            file, "expansion.cost_building_blocks_formula");
 
     cfg.push.pushExpandColumns_tiles = static_cast<int>(requireInt(tbl["push"]["push_expand_columns_tiles"], file, "push.push_expand_columns_tiles"));
     cfg.push.bossAdvanceSeconds = requireDouble(tbl["push"]["boss_advance_seconds"], file, "push.boss_advance_seconds");

src/lib/config/WorldConfig.h

@@ -15,7 +15,7 @@ struct WorldRegions
 struct WorldExpansion
 {
     int     columnsPerExpansion_tiles;
-    int costBuildingBlocks;
+    Formula costBuildingBlocksFormula;  // cost in building blocks; x = expansions already purchased
 };
 
 // Push effects (REQ-PSH-*, REQ-WAV-BOSS-ADVANCE).

src/lib/eventsystem/event/CMakeLists.txt

@@ -3,6 +3,7 @@ SET(HDRS
 	${CMAKE_CURRENT_SOURCE_DIR}/TracePrintRequestedEvent.h
 	${CMAKE_CURRENT_SOURCE_DIR}/TickAdvancedEvent.h
 	${CMAKE_CURRENT_SOURCE_DIR}/BuildingBlocksChangedEvent.h
+	${CMAKE_CURRENT_SOURCE_DIR}/ExpansionCostChangedEvent.h
 	${CMAKE_CURRENT_SOURCE_DIR}/EntitySelectedEvent.h
 	${CMAKE_CURRENT_SOURCE_DIR}/GameSpeedChangedEvent.h
 	${CMAKE_CURRENT_SOURCE_DIR}/BossWaveUpdatedEvent.h

src/lib/eventsystem/event/ExpansionCostChangedEvent.h

@@ -0,0 +1,17 @@
+#ifndef EXPANSION_COST_CHANGED_EVENT_H
+#define EXPANSION_COST_CHANGED_EVENT_H
+
+#include "Event.h"
+
+// Fired when the current asteroid-expansion cost changes (REQ-EXP-COST): once at
+// startup and again after each expansion is purchased. Carries the cost in
+// building blocks so the header Expand button can update its caption/enabled
+// state (REQ-UI-EXPAND-BUTTON).
+class ExpansionCostChangedEvent : public Event
+{
+public:
+	explicit ExpansionCostChangedEvent(int cost) : cost(cost) {}
+	const int cost;
+};
+
+#endif   // EXPANSION_COST_CHANGED_EVENT_H

src/lib/sim/BuildingSystem.cpp

@@ -24,6 +24,7 @@ BuildingSystem::BuildingSystem(const GameConfig& config,
     , m_spawnShip(std::move(spawnShip))
     , m_isItemUnlocked(std::move(isItemUnlocked))
     , m_rng(rng)
+    , m_asteroidWidth_tiles(config.world.regions.asteroidWidth_tiles)
 {
 }
 
@@ -281,7 +282,7 @@ bool BuildingSystem::bodyCellsWithinWorldBounds(const std::vector<QPoint>& bodyC
                                                 QPoint anchor) const
 {
     const int heightTiles = m_config.world.heightTiles;
-    const int leftEdgeX   = -m_config.world.regions.asteroidWidth_tiles;
+    const int leftEdgeX   = -m_asteroidWidth_tiles;
     for (const QPoint& cell : bodyCells)
     {
         const QPoint worldCell = anchor + cell;

src/lib/sim/BuildingSystem.h

@@ -59,6 +59,11 @@ public:
     bool isPlacementValid(BuildingType type, QPoint anchor,
                           Rotation rotation) const;
 
+    // Sets the current buildable asteroid width in tiles. Grows the left
+    // placement bound as the player unlocks asteroid expansions (REQ-EXP-UNLOCK).
+    // Defaults to world.regions.asteroid_width_tiles at construction.
+    void setAsteroidWidth_tiles(int widthTiles) { m_asteroidWidth_tiles = widthTiles; }
+
     // Remove a building or construction site by id.  Returns the refund in
     // building blocks (floor(cost * refundPercentage / 100)).  Returns 0 for
     // unknown ids.
@@ -179,6 +184,7 @@ private:
                        const std::optional<ShipLayoutConfig>&)> m_spawnShip;
     std::function<bool(const std::string&)>        m_isItemUnlocked;
     std::mt19937&                                  m_rng;
+    int                                            m_asteroidWidth_tiles;
 
     std::vector<Building>           m_buildings;
     std::deque<ConstructionSite>    m_constructionQueue;

src/lib/sim/Command.h

@@ -35,6 +35,7 @@ enum class CommandKind
     SetSplitterFilters,
     ClearBeltTiles,
     ApplySchematicChoice,
+    ExpandAsteroid,
     Reset
 };
 
@@ -129,6 +130,14 @@ struct ApplySchematicChoiceCommand : Command
     int choiceIndex = 0;
 };
 
+// Unlocks the next asteroid expansion (REQ-EXP-UNLOCK). Carries no payload: the
+// simulation derives the cost and column count from its own expansion counter
+// and config, so a recorded command replays identically.
+struct ExpandAsteroidCommand : Command
+{
+    ExpandAsteroidCommand() : Command(CommandKind::ExpandAsteroid) {}
+};
+
 // Restart boundary: reinitializes the simulation with a fresh seed and, if
 // config is set, a reloaded config (GameConfig is move-only, so it is carried by
 // shared_ptr and moved into the sim on apply). A null config keeps the current

src/lib/sim/Simulation.cpp

@@ -2,6 +2,7 @@
 
 #include <algorithm>
 #include <cassert>
+#include <cmath>
 
 #include "AiSystem.h"
 #include "Command.h"
@@ -132,6 +133,7 @@ void Simulation::reset(unsigned int seed)
     m_nextDepartureTick        = secondsToTicks(m_config.world.departureIntervalSeconds);
     m_nextBuildingId                   = 1;
     m_buildingBlocksStock      = m_config.world.startingBuildingBlocks;
+    m_expansionsPurchased      = 0;
     m_gameOver                      = false;
     m_isWon                         = false;
     m_artifactCount                 = 0;
@@ -275,6 +277,9 @@ void Simulation::apply(const Command& command)
     case CommandKind::ApplySchematicChoice:
         applySchematicChoice(static_cast<const ApplySchematicChoiceCommand&>(command).choiceIndex);
         break;
+    case CommandKind::ExpandAsteroid:
+        tryExpandAsteroid();
+        break;
     case CommandKind::Reset:
     {
         const ResetCommand& c = static_cast<const ResetCommand&>(command);
@@ -993,6 +998,7 @@ unsigned long long Simulation::computeStateChecksum() const
     hasher.append(m_gameOver);
     hasher.append(m_isWon);
     hasher.append(m_artifactCount);
+    hasher.append(m_expansionsPurchased);
 
     // WaveSystem scalar state, reached through existing accessors.
     hasher.append(threatLevel());
@@ -1100,6 +1106,31 @@ int Simulation::buildingBlocksStock() const
     return m_buildingBlocksStock;
 }
 
+int Simulation::currentAsteroidWidth_tiles() const
+{
+    return m_config.world.regions.asteroidWidth_tiles
+        + m_expansionsPurchased * m_config.world.expansion.columnsPerExpansion_tiles;
+}
+
+int Simulation::currentExpansionCost() const
+{
+    const double cost = m_config.world.expansion.costBuildingBlocksFormula.evaluate(
+        static_cast<double>(m_expansionsPurchased));
+    return static_cast<int>(std::floor(cost));
+}
+
+void Simulation::tryExpandAsteroid()
+{
+    const int cost = currentExpansionCost();
+    if (m_buildingBlocksStock < cost)
+    {
+        return;
+    }
+    m_buildingBlocksStock -= cost;
+    ++m_expansionsPurchased;
+    m_buildingSystem->setAsteroidWidth_tiles(currentAsteroidWidth_tiles());
+}
+
 bool Simulation::isGameOver() const
 {
     return m_gameOver;

src/lib/sim/Simulation.h

@@ -72,6 +72,12 @@ public:
     // The seed this run was (re)initialized with; written to the replay header.
     unsigned int getSeed()        const;
     int    buildingBlocksStock()  const;
+    // Current asteroid width in tiles = base width + purchased expansions
+    // (REQ-EXP-UNLOCK, REQ-GW-ASTEROID-EXPAND).
+    int    currentAsteroidWidth_tiles() const;
+    // Building block cost of the next expansion, floored to an integer
+    // (REQ-EXP-COST); x = number of expansions already purchased.
+    int    currentExpansionCost()  const;
     bool   isGameOver()           const;
     bool   isWon()                const;
     int    artifactCount()        const;
@@ -136,6 +142,11 @@ private:
     // Clears the pending choices after application.
     void applySchematicChoice(int choiceIndex);
 
+    // Unlocks one asteroid expansion if affordable (REQ-EXP-UNLOCK): checks the
+    // current cost against the stock, deducts it, increments the expansion
+    // counter, and widens the buildable asteroid. No-op if blocks are short.
+    void tryExpandAsteroid();
+
     // Mutable subsystem accessors; same chokepoint rule as the mutators above.
     BuildingSystem&       buildingsMutable();
     BeltSystem&           beltsMutable();
@@ -165,6 +176,7 @@ private:
     Tick     m_nextDepartureTick;
     BuildingId m_nextBuildingId;
     int      m_buildingBlocksStock;
+    int      m_expansionsPurchased = 0;  // REQ-EXP-COST formula variable x
     bool     m_gameOver    = false;
     bool     m_isWon       = false;
     int      m_artifactCount = 0;

src/test/ConfigLoaderTest.cpp

@@ -76,6 +76,8 @@ TEST_CASE("ConfigLoader loads the committed bin/config/ configs end-to-end", "[c
     REQUIRE(cfg.world.regions.playerBufferWidth_tiles == 10);
     REQUIRE(cfg.world.regions.enemyBufferWidth_tiles == 15);
     REQUIRE(cfg.world.expansion.columnsPerExpansion_tiles == 10);
+    REQUIRE(cfg.world.expansion.costBuildingBlocksFormula.evaluate(0) == Approx(400.0));
+    REQUIRE(cfg.world.expansion.costBuildingBlocksFormula.evaluate(1) == Approx(800.0));
     REQUIRE(cfg.world.push.bossAdvanceSeconds == Approx(60.0));
     REQUIRE(cfg.world.orbitFactor == Approx(0.8));
     REQUIRE(cfg.world.rallyOrbitRadius_tiles == Approx(5.0));
@@ -186,7 +188,7 @@ contest_zone_width_tiles = 30
 
 [expansion]
 columns_per_expansion_tiles = 10
-cost_building_blocks = 200
+cost_building_blocks_formula = "400 * 2^x"
 
 [push]
 push_expand_columns_tiles = 20
@@ -237,7 +239,7 @@ enemy_buffer_width_tiles = 15
 
 [expansion]
 columns_per_expansion_tiles = 10
-cost_building_blocks = 200
+cost_building_blocks_formula = "400 * 2^x"
 
 [push]
 push_expand_columns_tiles = 20
@@ -284,7 +286,7 @@ enemy_buffer_width_tiles = 15
 
 [expansion]
 columns_per_expansion_tiles = 10
-cost_building_blocks = 200
+cost_building_blocks_formula = "400 * 2^x"
 
 [push]
 push_expand_columns_tiles = 20

src/ui/GameWorldView.cpp

@@ -59,6 +59,7 @@
 #include "BuilderModeExitedEvent.h"
 #include "BlueprintModeExitedEvent.h"
 #include "BuildingBlocksChangedEvent.h"
+#include "ExpansionCostChangedEvent.h"
 #include "GameSpeedChangedEvent.h"
 #include "SchematicChoicesAvailableEvent.h"
 #include "TickAdvancedEvent.h"
@@ -276,6 +277,7 @@ void GameWorldView::onFrame()
     {
         const Tick newTick      = m_sim->currentTick();
         const int  newBlocks    = m_sim->buildingBlocksStock();
+        const int  newExpCost   = m_sim->currentExpansionCost();
         const int  newBoss      = m_sim->bossWaveCounter();
         const Tick newCountdown = m_sim->bossCountdownTicks();
 
@@ -291,6 +293,12 @@ void GameWorldView::onFrame()
             EventManager::getInstance()->sendEventImmediately(
                 std::make_shared<BuildingBlocksChangedEvent>(newBlocks));
         }
+        if (newExpCost != m_lastExpansionCost)
+        {
+            m_lastExpansionCost = newExpCost;
+            EventManager::getInstance()->sendEventImmediately(
+                std::make_shared<ExpansionCostChangedEvent>(newExpCost));
+        }
         if (newBoss != m_lastBossCounter || newCountdown != m_lastBossCountdown)
         {
             m_lastBossCounter   = newBoss;
@@ -435,7 +443,7 @@ QRect GameWorldView::viewportRect() const
 
 float GameWorldView::asteroidLeftEdge() const
 {
-    float leftX = -static_cast<float>(m_config->world.regions.asteroidWidth_tiles);
+    float leftX = -static_cast<float>(m_sim->currentAsteroidWidth_tiles());
     for (const Building& b : m_sim->buildings().allBuildings())
     {
         for (const QPoint& cell : b.bodyCells)
@@ -1827,6 +1835,7 @@ void GameWorldView::resetForNewGame()
     m_prevNonZeroSpeed  = 1.0;
     m_lastTick          = Tick(-1);
     m_lastBlocks        = -1;
+    m_lastExpansionCost = -1;
     m_lastBossCounter   = -1;
     m_lastBossCountdown = Tick(-1);
     m_lastArtifactCount = -1;

src/ui/GameWorldView.h

@@ -226,6 +226,7 @@ private:
 
     Tick m_lastTick          = Tick(-1);
     int  m_lastBlocks        = -1;
+    int  m_lastExpansionCost = -1;
     int  m_lastBossCounter   = -1;
     Tick m_lastBossCountdown = Tick(-1);
     int  m_lastArtifactCount = -1;

src/ui/HeaderBar.cpp

@@ -8,6 +8,8 @@
 #include <QPushButton>
 #include <QSignalMapper>
 
+#include "Command.h"
+#include "CommandRequestedEvent.h"
 #include "EventManager.h"
 #include "SpeedChangeRequestedEvent.h"
 #include "Tick.h"
@@ -32,6 +34,17 @@ HeaderBar::HeaderBar(QWidget* parent)
     layout->addStretch();
     layout->addWidget(m_bossLabel);
 
+    // Asteroid expansion button, to the left of the speed buttons (REQ-UI-HEADER,
+    // REQ-UI-EXPAND-BUTTON). Caption/enabled state are set on the first
+    // ExpansionCostChangedEvent; clicking requests an ExpandAsteroidCommand.
+    m_expandButton = new QPushButton(tr("Expand"), this);
+    layout->addWidget(m_expandButton);
+    connect(m_expandButton, &QPushButton::clicked, this, []() {
+        EventManager::getInstance()->sendEventImmediately(
+            std::make_shared<CommandRequestedEvent>(
+                std::make_shared<ExpandAsteroidCommand>()));
+    });
+
     const char* labels[] = { "0x", "0.5x", "1x", "2x", "10x" };
     QSignalMapper* mapper = new QSignalMapper(this);
     for (int i = 0; i < kSpeedCount; ++i)
@@ -67,7 +80,21 @@ void HeaderBar::handleEvent(std::shared_ptr<const TickAdvancedEvent> event)
 
 void HeaderBar::handleEvent(std::shared_ptr<const BuildingBlocksChangedEvent> event)
 {
+    m_blocks = event->blocks;
     m_blocksLabel->setText(tr("Blocks: %1").arg(event->blocks));
+    updateExpandButton();
+}
+
+void HeaderBar::handleEvent(std::shared_ptr<const ExpansionCostChangedEvent> event)
+{
+    m_expansionCost = event->cost;
+    updateExpandButton();
+}
+
+void HeaderBar::updateExpandButton()
+{
+    m_expandButton->setText(tr("Expand: %1 Blocks").arg(m_expansionCost));
+    m_expandButton->setEnabled(m_blocks >= m_expansionCost);
 }
 
 void HeaderBar::handleEvent(std::shared_ptr<const GameSpeedChangedEvent> event)

src/ui/HeaderBar.h

@@ -8,6 +8,7 @@
 #include "BossWaveUpdatedEvent.h"
 #include "BuildingBlocksChangedEvent.h"
 #include "EventHandler.h"
+#include "ExpansionCostChangedEvent.h"
 #include "GameSpeedChangedEvent.h"
 #include "Tick.h"
 #include "TickAdvancedEvent.h"
@@ -18,6 +19,7 @@ class QPushButton;
 class HeaderBar : public QWidget,
                   public CombinedEventHandler<TickAdvancedEvent,
                                               BuildingBlocksChangedEvent,
+                                              ExpansionCostChangedEvent,
                                               GameSpeedChangedEvent,
                                               BossWaveUpdatedEvent,
                                               ArtifactCountChangedEvent>
@@ -34,16 +36,25 @@ private slots:
 private:
     void handleEvent(std::shared_ptr<const TickAdvancedEvent> event) override;
     void handleEvent(std::shared_ptr<const BuildingBlocksChangedEvent> event) override;
+    void handleEvent(std::shared_ptr<const ExpansionCostChangedEvent> event) override;
     void handleEvent(std::shared_ptr<const GameSpeedChangedEvent> event) override;
     void handleEvent(std::shared_ptr<const BossWaveUpdatedEvent> event) override;
     void handleEvent(std::shared_ptr<const ArtifactCountChangedEvent> event) override;
 
+    // Refreshes the Expand button caption and enabled state from the current
+    // expansion cost and building block stock (REQ-UI-EXPAND-BUTTON).
+    void updateExpandButton();
+
     QLabel*                  m_timeLabel;
     QLabel*                  m_blocksLabel;
     QLabel*                  m_artifactsLabel;
     QLabel*                  m_bossLabel;
+    QPushButton*             m_expandButton;
     std::vector<QPushButton*> m_speedButtons;
 
+    int                      m_blocks        = 0;
+    int                      m_expansionCost = 0;
+
     static const double kSpeeds[];
     static const int    kSpeedCount;
 };