Add Merchant API

By: Xor Boole <mcyoung@mit.edu>

paper-api/src/main/java/org/bukkit/inventory/MerchantInventory.java

@@ -1,4 +1,23 @@
 package org.bukkit.inventory;
 
+/**
+ * Represents a trading inventory between a player and a villager.
+ * <br>
+ * The holder of this Inventory is the owning Villager.
+ */
 public interface MerchantInventory extends Inventory {
+
+    /**
+     * Get the index of the currently selected recipe.
+     *
+     * @return the index of the currently selected recipe
+     */
+    int getSelectedRecipeIndex();
+
+    /**
+     * Get the currently selected recipe.
+     *
+     * @return the currently selected recipe
+     */
+    MerchantRecipe getSelectedRecipe();
 }

paper-api/src/main/java/org/bukkit/inventory/MerchantRecipe.java

@@ -0,0 +1,125 @@
+package org.bukkit.inventory;
+
+import com.google.common.base.Preconditions;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Represents a Villager's trade.
+ *
+ * Trades can take one or two ingredients, and provide one result. The
+ * ingredients' Itemstack amounts are respected in the trade.
+ * <br>
+ * A trade has a limited number of uses, after which the trade can no longer be
+ * used, unless the player uses a different trade, which will cause its maximum
+ * uses to increase.
+ * <br>
+ * A trade may or may not reward experience for being completed.
+ *
+ * @see org.bukkit.event.entity.VillagerReplenishTradeEvent
+ */
+public class MerchantRecipe implements Recipe {
+
+    private ItemStack result;
+    private List<ItemStack> ingredients = new ArrayList<ItemStack>();
+    private int uses;
+    private int maxUses;
+    private boolean experienceReward;
+
+    public MerchantRecipe(ItemStack result, int maxUses) {
+        this(result, 0, maxUses, false);
+    }
+
+    public MerchantRecipe(ItemStack result, int uses, int maxUses, boolean experienceReward) {
+        this.result = result;
+        this.uses = uses;
+        this.maxUses = maxUses;
+        this.experienceReward = experienceReward;
+    }
+
+    @Override
+    public ItemStack getResult() {
+        return result;
+    }
+
+    public void addIngredient(ItemStack item) {
+        Preconditions.checkState(ingredients.size() < 2, "Merchant can only have 2 ingredients");
+        ingredients.add(item.clone());
+    }
+
+    public void removeIngredient(int index) {
+        ingredients.remove(index);
+    }
+
+    public void setIngredients(List<ItemStack> ingredients) {
+        this.ingredients = new ArrayList<ItemStack>();
+        for (ItemStack item : ingredients) {
+            this.ingredients.add(item.clone());
+        }
+    }
+
+    public List<ItemStack> getIngredients() {
+        List<ItemStack> copy = new ArrayList<ItemStack>();
+        for (ItemStack item : ingredients) {
+            copy.add(item.clone());
+        }
+        return copy;
+    }
+
+    /**
+     * Get the number of times this trade has been used.
+     *
+     * @return the number of uses
+     */
+    public int getUses() {
+        return uses;
+    }
+
+    /**
+     * Set the number of times this trade has been used.
+     *
+     * @param uses the number of uses
+     */
+    public void setUses(int uses) {
+        this.uses = uses;
+    }
+
+    /**
+     * Get the maximum number of uses this trade has.
+     * <br>
+     * The maximum uses of this trade may increase when a player trades with the
+     * owning villager.
+     *
+     * @return the maximum number of uses
+     */
+    public int getMaxUses() {
+        return maxUses;
+    }
+
+    /**
+     * Set the maximum number of uses this trade has.
+     *
+     * @param maxUses the maximum number of time this trade can be used
+     */
+    public void setMaxUses(int maxUses) {
+        this.maxUses = maxUses;
+    }
+
+    /**
+     * Whether to reward experience for the trade.
+     *
+     * @return whether to reward experience for completing this trade
+     */
+    public boolean hasExperienceReward() {
+        return experienceReward;
+    }
+
+    /**
+     * Set whether to reward experience for the trade.
+     *
+     * @param flag whether to reward experience for completing this trade
+     */
+    public void setExperienceReward(boolean flag) {
+        this.experienceReward = flag;
+    }
+}