12 files changed, 63 insertions, 37 deletions
diff --git a/src/main/java/org/luxons/sevenwonders/game/api/Move.java b/src/main/java/org/luxons/sevenwonders/game/api/Move.java
index 223f6615..55af635e 100644
--- a/src/main/java/org/luxons/sevenwonders/game/api/Move.java
+++ b/src/main/java/org/luxons/sevenwonders/game/api/Move.java
@@ -3,6 +3,8 @@ package org.luxons.sevenwonders.game.api;
 import java.util.ArrayList;
 import java.util.List;
 
+import org.luxons.sevenwonders.game.resources.BoughtResources;
+
 public class Move {
 
     private int playerIndex;
diff --git a/src/main/java/org/luxons/sevenwonders/game/api/Table.java b/src/main/java/org/luxons/sevenwonders/game/api/Table.java
index 44c9076f..686b7ea5 100644
--- a/src/main/java/org/luxons/sevenwonders/game/api/Table.java
+++ b/src/main/java/org/luxons/sevenwonders/game/api/Table.java
@@ -6,6 +6,7 @@ import org.luxons.sevenwonders.game.boards.Board;
 import org.luxons.sevenwonders.game.boards.RelativeBoardPosition;
 import org.luxons.sevenwonders.game.cards.Card;
 import org.luxons.sevenwonders.game.cards.CardBack;
+import org.luxons.sevenwonders.game.resources.BoughtResources;
 
 /**
  * The table contains what is visible by all the players in the game: the boards and their played cards, and the
diff --git a/src/main/java/org/luxons/sevenwonders/game/boards/Board.java b/src/main/java/org/luxons/sevenwonders/game/boards/Board.java
index f2f39503..d0fc22b8 100644
--- a/src/main/java/org/luxons/sevenwonders/game/boards/Board.java
+++ b/src/main/java/org/luxons/sevenwonders/game/boards/Board.java
@@ -8,6 +8,7 @@ import org.luxons.sevenwonders.game.Settings;
 import org.luxons.sevenwonders.game.cards.Card;
 import org.luxons.sevenwonders.game.cards.Color;
 import org.luxons.sevenwonders.game.resources.Production;
+import org.luxons.sevenwonders.game.resources.TradingRules;
 import org.luxons.sevenwonders.game.wonders.Wonder;
 
 public class Board {
diff --git a/src/main/java/org/luxons/sevenwonders/game/boards/TradingRules.java b/src/main/java/org/luxons/sevenwonders/game/boards/TradingRules.java
deleted file mode 100644
index 97b60ea0..00000000
--- a/src/main/java/org/luxons/sevenwonders/game/boards/TradingRules.java
+++ /dev/null
@@ -1,25 +0,0 @@
-package org.luxons.sevenwonders.game.boards;
-
-import java.util.EnumMap;
-import java.util.Map;
-
-import org.luxons.sevenwonders.game.resources.ResourceType;
-
-public class TradingRules {
-
-    private final Map<ResourceType, Map<Provider, Integer>> costs = new EnumMap<>(ResourceType.class);
-
-    private final int defaultCost;
-
-    public TradingRules(int defaultCost) {
-        this.defaultCost = defaultCost;
-    }
-
-    public int getCost(ResourceType type, Provider provider) {
-        return costs.computeIfAbsent(type, t -> new EnumMap<>(Provider.class)).getOrDefault(provider, defaultCost);
-    }
-
-    public void setCost(ResourceType type, Provider provider, int cost) {
-        costs.computeIfAbsent(type, t -> new EnumMap<>(Provider.class)).put(provider, cost);
-    }
-}
diff --git a/src/main/java/org/luxons/sevenwonders/game/cards/Card.java b/src/main/java/org/luxons/sevenwonders/game/cards/Card.java
index 94c46839..76a3a82e 100644
--- a/src/main/java/org/luxons/sevenwonders/game/cards/Card.java
+++ b/src/main/java/org/luxons/sevenwonders/game/cards/Card.java
@@ -3,7 +3,7 @@ package org.luxons.sevenwonders.game.cards;
 import java.util.List;
 import java.util.Objects;
 
-import org.luxons.sevenwonders.game.api.BoughtResources;
+import org.luxons.sevenwonders.game.resources.BoughtResources;
 import org.luxons.sevenwonders.game.api.Table;
 import org.luxons.sevenwonders.game.boards.Board;
 import org.luxons.sevenwonders.game.effects.Effect;
diff --git a/src/main/java/org/luxons/sevenwonders/game/cards/Requirements.java b/src/main/java/org/luxons/sevenwonders/game/cards/Requirements.java
index 714f86a6..8fc6241a 100644
--- a/src/main/java/org/luxons/sevenwonders/game/cards/Requirements.java
+++ b/src/main/java/org/luxons/sevenwonders/game/cards/Requirements.java
@@ -2,7 +2,7 @@ package org.luxons.sevenwonders.game.cards;
 
 import java.util.List;
 
-import org.luxons.sevenwonders.game.api.BoughtResources;
+import org.luxons.sevenwonders.game.resources.BoughtResources;
 import org.luxons.sevenwonders.game.api.Table;
 import org.luxons.sevenwonders.game.boards.Board;
 import org.luxons.sevenwonders.game.resources.Resources;
@@ -52,6 +52,16 @@ public class Requirements {
     }
 
     void pay(Board board) {
-        board.setGold(board.getGold() - gold);
+        int newBalance = board.getGold() - gold;
+        if (newBalance < 0) {
+            throw new InsufficientFundsException(board.getGold(), gold);
+        }
+        board.setGold(newBalance);
+    }
+
+    private class InsufficientFundsException extends RuntimeException {
+        InsufficientFundsException(int current, int required) {
+            super(String.format("Current balance is %d gold, but %d are required", current, required));
+        }
     }
 }
diff --git a/src/main/java/org/luxons/sevenwonders/game/effects/Discount.java b/src/main/java/org/luxons/sevenwonders/game/effects/Discount.java
index a943b027..3a44574b 100644
--- a/src/main/java/org/luxons/sevenwonders/game/effects/Discount.java
+++ b/src/main/java/org/luxons/sevenwonders/game/effects/Discount.java
@@ -4,8 +4,8 @@ import java.util.ArrayList;
 import java.util.List;
 
 import org.luxons.sevenwonders.game.boards.Board;
-import org.luxons.sevenwonders.game.boards.Provider;
-import org.luxons.sevenwonders.game.boards.TradingRules;
+import org.luxons.sevenwonders.game.resources.Provider;
+import org.luxons.sevenwonders.game.resources.TradingRules;
 import org.luxons.sevenwonders.game.resources.ResourceType;
 
 public class Discount extends InstantOwnBoardEffect {
diff --git a/src/main/java/org/luxons/sevenwonders/game/api/BoughtResources.java b/src/main/java/org/luxons/sevenwonders/game/resources/BoughtResources.java
index 01277cab..ec261c8c 100644
--- a/src/main/java/org/luxons/sevenwonders/game/api/BoughtResources.java
+++ b/src/main/java/org/luxons/sevenwonders/game/resources/BoughtResources.java
@@ -1,7 +1,4 @@
-package org.luxons.sevenwonders.game.api;
-
-import org.luxons.sevenwonders.game.boards.Provider;
-import org.luxons.sevenwonders.game.resources.Resources;
+package org.luxons.sevenwonders.game.resources;
 
 public class BoughtResources {
 
diff --git a/src/main/java/org/luxons/sevenwonders/game/boards/Provider.java b/src/main/java/org/luxons/sevenwonders/game/resources/Provider.java
index bacd1e73..9a105725 100644
--- a/src/main/java/org/luxons/sevenwonders/game/boards/Provider.java
+++ b/src/main/java/org/luxons/sevenwonders/game/resources/Provider.java
@@ -1,4 +1,4 @@
-package org.luxons.sevenwonders.game.boards;
+package org.luxons.sevenwonders.game.resources;
 
 public enum Provider {
     LEFT_PLAYER, RIGHT_PLAYER
diff --git a/src/main/java/org/luxons/sevenwonders/game/resources/TradingRules.java b/src/main/java/org/luxons/sevenwonders/game/resources/TradingRules.java
new file mode 100644
index 00000000..4965c00e
--- /dev/null
+++ b/src/main/java/org/luxons/sevenwonders/game/resources/TradingRules.java
@@ -0,0 +1,40 @@
+package org.luxons.sevenwonders.game.resources;
+
+import java.util.EnumMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+
+public class TradingRules {
+
+    private final Map<ResourceType, Map<Provider, Integer>> costs = new EnumMap<>(ResourceType.class);
+
+    private final int defaultCost;
+
+    public TradingRules(int defaultCost) {
+        this.defaultCost = defaultCost;
+    }
+
+    private int getCost(ResourceType type, Provider provider) {
+        return costs.computeIfAbsent(type, t -> new EnumMap<>(Provider.class)).getOrDefault(provider, defaultCost);
+    }
+
+    public void setCost(ResourceType type, Provider provider, int cost) {
+        costs.computeIfAbsent(type, t -> new EnumMap<>(Provider.class)).put(provider, cost);
+    }
+
+    public int computeCost(List<BoughtResources> boughtResources) {
+        return boughtResources.stream().mapToInt(this::computeCost).sum();
+    }
+
+    private int computeCost(BoughtResources boughtResources) {
+        Resources resources = boughtResources.getResources();
+        int total = 0;
+        for (Entry<ResourceType, Integer> entry : resources.getQuantities().entrySet()) {
+            ResourceType type = entry.getKey();
+            int count = entry.getValue();
+            total += getCost(type, boughtResources.getProvider()) * count;
+        }
+        return total;
+    }
+}
diff --git a/src/main/java/org/luxons/sevenwonders/game/wonders/Wonder.java b/src/main/java/org/luxons/sevenwonders/game/wonders/Wonder.java
index d739354a..15b2b863 100644
--- a/src/main/java/org/luxons/sevenwonders/game/wonders/Wonder.java
+++ b/src/main/java/org/luxons/sevenwonders/game/wonders/Wonder.java
@@ -3,7 +3,7 @@ package org.luxons.sevenwonders.game.wonders;
 import java.util.Arrays;
 import java.util.List;
 
-import org.luxons.sevenwonders.game.api.BoughtResources;
+import org.luxons.sevenwonders.game.resources.BoughtResources;
 import org.luxons.sevenwonders.game.api.Table;
 import org.luxons.sevenwonders.game.cards.CardBack;
 import org.luxons.sevenwonders.game.resources.ResourceType;
diff --git a/src/main/java/org/luxons/sevenwonders/game/wonders/WonderStage.java b/src/main/java/org/luxons/sevenwonders/game/wonders/WonderStage.java
index 00a53fb1..64d506fc 100644
--- a/src/main/java/org/luxons/sevenwonders/game/wonders/WonderStage.java
+++ b/src/main/java/org/luxons/sevenwonders/game/wonders/WonderStage.java
@@ -2,7 +2,7 @@ package org.luxons.sevenwonders.game.wonders;
 
 import java.util.List;
 
-import org.luxons.sevenwonders.game.api.BoughtResources;
+import org.luxons.sevenwonders.game.resources.BoughtResources;
 import org.luxons.sevenwonders.game.api.Table;
 import org.luxons.sevenwonders.game.cards.CardBack;
 import org.luxons.sevenwonders.game.cards.Requirements;