Implement LMSR and order-book trading logic, wire MarketContext facade and new menu commands

Fill in the previously stubbed cost/pricing math for both trading
mechanisms, and give OrderBookTradingMechanism an actual matching engine
with resting bid/ask books. Fold EventRepository/UserRepository access
into a single MarketContext used by LocalGuessMarketContext, and move the
repository package under infrastructure. Add Buy/EventDetails/LoadState/
SaveState/SettleEvent console commands and wire them into App/Menu.

2 files changed, 88 insertions, 0 deletions

diff --git a/service/src/test/java/market/guess/service/mechanism/LmsrTradingMechanismTest.java b/service/src/test/java/market/guess/service/mechanism/LmsrTradingMechanismTest.java
new file mode 100644
index 0000000..f5c6af5
--- /dev/null
+++ b/service/src/test/java/market/guess/service/mechanism/LmsrTradingMechanismTest.java
@@ -0,0 +1,37 @@
+package market.guess.service.mechanism;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+
+import java.math.BigDecimal;
+import org.junit.Test;
+
+public class LmsrTradingMechanismTest {
+
+  @Test
+  public void openingCostMatchesLmsrFormula() {
+    var mechanism = new LmsrTradingMechanism(100, 2);
+
+    assertEquals(new BigDecimal("69.31"), mechanism.openingCost());
+  }
+
+  @Test
+  public void pricesStartEven() {
+    var mechanism = new LmsrTradingMechanism(100, 2);
+
+    assertArrayEquals(
+        new BigDecimal[] {new BigDecimal("0.50"), new BigDecimal("0.50")}, mechanism.prices());
+  }
+
+  @Test
+  public void buyingSharesShiftsCostAndPrice() {
+    var mechanism = new LmsrTradingMechanism(100, 2);
+
+    var execution = mechanism.buy(0, 100);
+
+    assertEquals(100, execution.filledQuantity());
+    assertEquals(new BigDecimal("62.01"), execution.cost());
+    assertArrayEquals(
+        new BigDecimal[] {new BigDecimal("0.73"), new BigDecimal("0.27")}, mechanism.prices());
+  }
+}
diff --git a/service/src/test/java/market/guess/service/mechanism/OrderBookTradingMechanismTest.java b/service/src/test/java/market/guess/service/mechanism/OrderBookTradingMechanismTest.java
new file mode 100644
index 0000000..b4b2da3
--- /dev/null
+++ b/service/src/test/java/market/guess/service/mechanism/OrderBookTradingMechanismTest.java
@@ -0,0 +1,51 @@
+package market.guess.service.mechanism;
+
+import static org.junit.Assert.assertEquals;
+
+import java.math.BigDecimal;
+import market.guess.service.mechanism.OrderBookTradingMechanism.Side;
+import org.junit.Test;
+
+public class OrderBookTradingMechanismTest {
+
+  @Test
+  public void limitBuyConsumesRestingAsksInFifoOrderAndLeavesRemainder() {
+    var mechanism = new OrderBookTradingMechanism(false, 100, 1, 2);
+    var price = new BigDecimal("0.60");
+
+    mechanism.placeOrder(0, Side.SELL, 20, price);
+    mechanism.placeOrder(0, Side.SELL, 40, price);
+
+    var execution = mechanism.placeOrder(0, Side.BUY, 50, price);
+
+    assertEquals(50, execution.filledQuantity());
+    assertEquals(new BigDecimal("30.00"), execution.cost());
+
+    var followUp = mechanism.buy(0, 100);
+    assertEquals(10, followUp.filledQuantity());
+  }
+
+  @Test
+  public void marketBuySweepsMultiplePriceLevelsAndPartiallyFillsWhenBookRunsOut() {
+    var mechanism = new OrderBookTradingMechanism(false, 100, 1, 2);
+    mechanism.placeOrder(0, Side.SELL, 10, new BigDecimal("0.50"));
+    mechanism.placeOrder(0, Side.SELL, 10, new BigDecimal("0.70"));
+
+    var execution = mechanism.buy(0, 15);
+
+    assertEquals(15, execution.filledQuantity());
+    assertEquals(new BigDecimal("8.50"), execution.cost());
+
+    var exhausted = mechanism.buy(0, 100);
+    assertEquals(5, exhausted.filledQuantity());
+  }
+
+  @Test
+  public void pricesReflectMidpointOfBestBidAndAsk() {
+    var mechanism = new OrderBookTradingMechanism(false, 100, 1, 2);
+    mechanism.placeOrder(0, Side.BUY, 10, new BigDecimal("0.40"));
+    mechanism.placeOrder(0, Side.SELL, 10, new BigDecimal("0.60"));
+
+    assertEquals(new BigDecimal("0.50"), mechanism.prices()[0]);
+  }
+}