SPIGOT-6078: Add SmithItemEvent and expand SmithingInventory API

By: Julian van den Berkmortel <julianvdberkmortel@outlook.com>

paper-api/src/main/java/org/bukkit/event/inventory/SmithItemEvent.java

@@ -0,0 +1,25 @@
+package org.bukkit.event.inventory;
+
+import org.bukkit.inventory.InventoryView;
+import org.bukkit.inventory.SmithingInventory;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Called when the recipe of an Item is completed inside a smithing table.
+ */
+public class SmithItemEvent extends InventoryClickEvent {
+
+    public SmithItemEvent(@NotNull InventoryView view, @NotNull InventoryType.SlotType type, int slot, @NotNull ClickType click, @NotNull InventoryAction action) {
+        super(view, type, slot, click, action);
+    }
+
+    public SmithItemEvent(@NotNull InventoryView view, @NotNull InventoryType.SlotType type, int slot, @NotNull ClickType click, @NotNull InventoryAction action, int key) {
+        super(view, type, slot, click, action, key);
+    }
+
+    @NotNull
+    @Override
+    public SmithingInventory getInventory() {
+        return (SmithingInventory) super.getInventory();
+    }
+}

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

@@ -1,6 +1,33 @@
 package org.bukkit.inventory;
 
+import org.jetbrains.annotations.Nullable;
+
 /**
  * Interface to the inventory of a Smithing table.
  */
-public interface SmithingInventory extends Inventory { }
+public interface SmithingInventory extends Inventory {
+
+    /**
+     * Check what item is in the result slot of this smithing table.
+     *
+     * @return the result item
+     */
+    @Nullable
+    ItemStack getResult();
+
+    /**
+     * Set the item in the result slot of the smithing table
+     *
+     * @param newResult the new result item
+     */
+    void setResult(@Nullable ItemStack newResult);
+
+    /**
+     * Get the current recipe formed on the smithing table, if any.
+     *
+     * @return the recipe, or null if the current contents don't match any
+     * recipe
+     */
+    @Nullable
+    Recipe getRecipe();
+}