refactor: simplify wandering trader offers and add individual spawn chances

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/gameplay/wanderingTrader/TraderOffer.java

@@ -0,0 +1,32 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.gameplay.wanderingTrader;
+
+import org.bukkit.Material;
+import org.bukkit.inventory.ItemStack;
+import org.bukkit.inventory.MerchantRecipe;
+
+import java.util.Objects;
+import java.util.function.Supplier;
+
+record TraderOffer(Supplier<ItemStack> resultFactory, int emeraldPrice, int maxUses, double chance) {
+    TraderOffer {
+        Objects.requireNonNull(resultFactory, "resultFactory");
+        if(emeraldPrice < 1 || emeraldPrice > 64)
+            throw new IllegalArgumentException("emeraldPrice must be between 1 and 64");
+        if(maxUses < 1)
+            throw new IllegalArgumentException("maxUses must be positive");
+        if(!Double.isFinite(chance) || chance < 0 || chance > 1)
+            throw new IllegalArgumentException("chance must be finite and between 0 and 1");
+    }
+
+    static TraderOffer offer(Material material, int emeraldPrice, int maxUses, double chance) {
+        Objects.requireNonNull(material, "material");
+        return new TraderOffer(() -> new ItemStack(material), emeraldPrice, maxUses, chance);
+    }
+
+    MerchantRecipe createRecipe() {
+        ItemStack result = Objects.requireNonNull(this.resultFactory.get(), "resultFactory result").clone();
+        MerchantRecipe recipe = new MerchantRecipe(result, 0, this.maxUses, false, 0, 0f);
+        recipe.addIngredient(new ItemStack(Material.EMERALD, this.emeraldPrice));
+        return recipe;
+    }
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/gameplay/wanderingTrader/WanderingTraderSpawnListener.java

@@ -0,0 +1,19 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.gameplay.wanderingTrader;
+
+import eu.mhsl.craftattack.spawn.core.Main;
+import eu.mhsl.craftattack.spawn.core.appliance.ApplianceListener;
+import org.bukkit.Bukkit;
+import org.bukkit.entity.WanderingTrader;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.EventPriority;
+import org.bukkit.event.entity.CreatureSpawnEvent;
+
+class WanderingTraderSpawnListener extends ApplianceListener<WanderingTraderTrades> {
+    @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
+    public void onSpawn(CreatureSpawnEvent event) {
+        if(!(event.getEntity() instanceof WanderingTrader trader)) return;
+
+        // Add custom trades on the next tick, after the spawn has finished.
+        Bukkit.getScheduler().runTask(Main.instance(), () -> this.getAppliance().addTrades(trader));
+    }
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/gameplay/wanderingTrader/WanderingTraderTrades.java

@@ -0,0 +1,40 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.gameplay.wanderingTrader;
+
+import eu.mhsl.craftattack.spawn.core.Main;
+import eu.mhsl.craftattack.spawn.core.appliance.Appliance;
+import org.bukkit.Material;
+import org.bukkit.NamespacedKey;
+import org.bukkit.entity.WanderingTrader;
+import org.bukkit.event.Listener;
+import org.bukkit.inventory.MerchantRecipe;
+import org.bukkit.persistence.PersistentDataType;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.ThreadLocalRandom;
+
+public class WanderingTraderTrades extends Appliance {
+    private final NamespacedKey appliedKey = new NamespacedKey(Main.instance(), "wandering_trader_trades_applied");
+    private final List<TraderOffer> additionalTrades = List.of(
+        TraderOffer.offer(Material.HEART_OF_THE_SEA, 32, 1, 0.5)
+    );
+
+    void addTrades(WanderingTrader trader) {
+        if(!trader.isValid() || trader.isDead()) return;
+        if(trader.getPersistentDataContainer().has(this.appliedKey, PersistentDataType.BYTE)) return;
+
+        List<MerchantRecipe> recipes = new ArrayList<>(trader.getRecipes());
+        this.additionalTrades.forEach(offer -> {
+            if(ThreadLocalRandom.current().nextDouble() < offer.chance()) recipes.add(offer.createRecipe());
+        });
+        trader.setRecipes(recipes);
+        // Mark this trader as having had custom trades applied.
+        trader.getPersistentDataContainer().set(this.appliedKey, PersistentDataType.BYTE, (byte) 1);
+    }
+
+    @Override
+    protected @NotNull List<Listener> listeners() {
+        return List.of(new WanderingTraderSpawnListener());
+    }
+}