#522: Add piglin bartering API

By: Lars Dormans <lars.dormans@live.nl>

paper-api/src/main/java/org/bukkit/entity/Piglin.java

@@ -1,9 +1,14 @@
 package org.bukkit.entity;
 
+import java.util.Set;
+import org.bukkit.Material;
+import org.bukkit.inventory.InventoryHolder;
+import org.jetbrains.annotations.NotNull;
+
 /**
  * Represents a Piglin.
  */
-public interface Piglin extends PiglinAbstract {
+public interface Piglin extends PiglinAbstract, InventoryHolder {
 
     /**
      * Get whether the piglin is able to hunt hoglins.
@@ -18,4 +23,71 @@ public interface Piglin extends PiglinAbstract {
      * @param flag Whether the piglin is able to hunt hoglins.
      */
     public void setIsAbleToHunt(boolean flag);
+
+    /**
+     * Adds a material to the allowed list of materials to barter with.
+     *
+     * @param material The material to add
+     *
+     * @return true if the item has been added successfully, false otherwise
+     */
+    public boolean addBarterMaterial(@NotNull Material material);
+
+    /**
+     * Removes a material from the allowed list of materials to barter with.
+     *
+     * <strong>Note:</strong> It's not possible to override the default
+     * bartering item gold_ingots as payment. To block gold_ingots see
+     * {@link org.bukkit.event.entity.PiglinBarterEvent}.
+     *
+     * @param material The material to remove
+     *
+     * @return true if the item has been removed successfully, false otherwise
+     */
+    public boolean removeBarterMaterial(@NotNull Material material);
+
+    /**
+     * Adds a material the piglin will pickup and store in his inventory.
+     *
+     * @param material The material you want the piglin to be interested in
+     *
+     * @return true if the item has been added successfully, false otherwise
+     */
+    public boolean addMaterialOfInterest(@NotNull Material material);
+
+    /**
+     * Removes a material from the list of materials the piglin will pickup.
+     *
+     * <strong>Note:</strong> It's not possible to override the default list of
+     * item the piglin will pickup. To cancel pickup see
+     * {@link org.bukkit.event.entity.EntityPickupItemEvent}.
+     *
+     * @param material The material you want removed from the interest list
+     * @return true if the item has been removed successfully, false otherwise
+     */
+    public boolean removeMaterialOfInterest(@NotNull Material material);
+
+    /**
+     * Returns a immutable set of materials the piglins will pickup.
+     * <br>
+     * <strong>Note:</strong> This set will not include the items that are set
+     * by default. To interact with those items see
+     * {@link org.bukkit.event.entity.EntityPickupItemEvent}.
+     *
+     * @return An immutable materials set
+     */
+    @NotNull
+    public Set<Material> getInterestList();
+
+    /**
+     * Returns a immutable set of materials the piglins will barter with.
+     *
+     * <strong>Note:</strong> This set will not include the items that are set
+     * by default. To interact with those items see
+     * {@link org.bukkit.event.entity.PiglinBarterEvent}.
+     *
+     * @return An immutable materials set
+     */
+    @NotNull
+    public Set<Material> getBarterList();
 }

paper-api/src/main/java/org/bukkit/event/entity/PiglinBarterEvent.java

@@ -0,0 +1,76 @@
+package org.bukkit.event.entity;
+
+import java.util.List;
+import org.bukkit.entity.Piglin;
+import org.bukkit.event.Cancellable;
+import org.bukkit.event.HandlerList;
+import org.bukkit.inventory.ItemStack;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Stores all data related to the bartering interaction with a piglin.
+ *
+ * This event can be triggered by a piglin picking up an item that's on its
+ * bartering list.
+ */
+public class PiglinBarterEvent extends EntityEvent implements Cancellable {
+
+    private static final HandlerList handlers = new HandlerList();
+    private boolean cancelled;
+    private final List<ItemStack> outcome;
+    private final ItemStack input;
+
+    public PiglinBarterEvent(@NotNull Piglin what, @NotNull ItemStack input, @NotNull List<ItemStack> outcome) {
+        super(what);
+
+        this.input = input;
+        this.outcome = outcome;
+    }
+
+    @NotNull
+    @Override
+    public Piglin getEntity() {
+        return (Piglin) super.getEntity();
+    }
+
+    /**
+     * Gets the input of the barter.
+     *
+     * @return The item that was used to barter with
+     */
+    @NotNull
+    public ItemStack getInput() {
+        return input.clone();
+    }
+
+    /**
+     * Returns a mutable list representing the outcome of the barter.
+     *
+     * @return A mutable list of the item the player will receive
+     */
+    @NotNull
+    public List<ItemStack> getOutcome() {
+        return outcome;
+    }
+
+    @Override
+    public boolean isCancelled() {
+        return cancelled;
+    }
+
+    @Override
+    public void setCancelled(boolean cancel) {
+        cancelled = cancel;
+    }
+
+    @NotNull
+    @Override
+    public HandlerList getHandlers() {
+        return handlers;
+    }
+
+    @NotNull
+    public static HandlerList getHandlerList() {
+        return handlers;
+    }
+}