Add recursive item stack NBT walker

src/main/java/com/gtnewhorizons/postea/utility/NbtItemStacks.java

@@ -0,0 +1,43 @@
+package com.gtnewhorizons.postea.utility;
+
+import static net.minecraftforge.common.util.Constants.NBT.TAG_ANY_NUMERIC;
+import static net.minecraftforge.common.util.Constants.NBT.TAG_COMPOUND;
+import static net.minecraftforge.common.util.Constants.NBT.TAG_INT;
+import static net.minecraftforge.common.util.Constants.NBT.TAG_SHORT;
+
+import java.util.ArrayList;
+import java.util.function.Consumer;
+
+import net.minecraft.nbt.NBTBase;
+import net.minecraft.nbt.NBTTagCompound;
+import net.minecraft.nbt.NBTTagList;
+
+/**
+ * Visits every serialized item stack in an NBT tree. A compound is a stack when it has a numeric {@code id} or an
+ * EndlessIDs {@code idExt} together with a {@code Count}. The walk is pre-order and descends into every compound
+ * and every list of compounds, so stacks nested inside another stack's {@code tag} (backpacks, storage cells) are
+ * visited too. Lists of lists are not descended.
+ */
+public final class NbtItemStacks {
+
+    private NbtItemStacks() {}
+
+    public static void forEach(NBTBase root, Consumer<NBTTagCompound> visitor) {
+        if (root instanceof NBTTagCompound compound) {
+            if (isStack(compound)) visitor.accept(compound);
+            for (Object key : new ArrayList<>(compound.func_150296_c())) {
+                forEach(compound.getTag((String) key), visitor);
+            }
+        } else if (root instanceof NBTTagList list && list.func_150303_d() == TAG_COMPOUND) {
+            for (int i = 0; i < list.tagCount(); i++) {
+                forEach(list.getCompoundTagAt(i), visitor);
+            }
+        }
+    }
+
+    public static boolean isStack(NBTTagCompound compound) {
+        return compound.hasKey("Count", TAG_ANY_NUMERIC)
+            && (compound.hasKey("id", TAG_SHORT) || compound.hasKey("id", TAG_INT)
+                || compound.hasKey("idExt", TAG_INT));
+    }
+}

src/test/java/com/gtnewhorizons/postea/utility/NbtItemStacksTest.java

@@ -0,0 +1,98 @@
+package com.gtnewhorizons.postea.utility;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+import net.minecraft.nbt.NBTTagCompound;
+import net.minecraft.nbt.NBTTagList;
+
+import org.junit.jupiter.api.Test;
+
+class NbtItemStacksTest {
+
+    private static NBTTagCompound stack(int id, int damage) {
+        NBTTagCompound stack = new NBTTagCompound();
+        stack.setShort("id", (short) id);
+        stack.setByte("Count", (byte) 1);
+        stack.setShort("Damage", (short) damage);
+        return stack;
+    }
+
+    private static List<NBTTagCompound> visited(NBTTagCompound root) {
+        List<NBTTagCompound> stacks = new ArrayList<>();
+        NbtItemStacks.forEach(root, stacks::add);
+        return stacks;
+    }
+
+    @Test
+    void visitsStacksInInventoryListsAndStacksNestedInsideAStacksTag() {
+        NBTTagCompound nested = stack(2, 0);
+        NBTTagCompound backpack = stack(1, 0);
+        NBTTagCompound backpackTag = new NBTTagCompound();
+        NBTTagList contents = new NBTTagList();
+        contents.appendTag(nested);
+        backpackTag.setTag("Items", contents);
+        backpack.setTag("tag", backpackTag);
+        NBTTagList items = new NBTTagList();
+        items.appendTag(backpack);
+        NBTTagCompound tileEntity = new NBTTagCompound();
+        tileEntity.setString("id", "Chest");
+        tileEntity.setTag("Items", items);
+        NBTTagList tileEntities = new NBTTagList();
+        tileEntities.appendTag(tileEntity);
+        NBTTagCompound level = new NBTTagCompound();
+        level.setTag("TileEntities", tileEntities);
+
+        assertEquals(Arrays.asList(backpack, nested), visited(level));
+    }
+
+    @Test
+    void ignoresCompoundsThatAreNotStacks() {
+        NBTTagCompound enchantment = new NBTTagCompound();
+        enchantment.setShort("id", (short) 3);
+        enchantment.setShort("lvl", (short) 1);
+        NBTTagCompound tileEntity = new NBTTagCompound();
+        tileEntity.setString("id", "Chest");
+        tileEntity.setInteger("Count", 1);
+        NBTTagCompound root = new NBTTagCompound();
+        root.setTag("ench", enchantment);
+        root.setTag("te", tileEntity);
+
+        assertEquals(Collections.emptyList(), visited(root));
+    }
+
+    @Test
+    void recognisesExtendedIdStacksWithoutADamageKey() {
+        NBTTagCompound extended = new NBTTagCompound();
+        extended.setShort("id", (short) 0);
+        extended.setInteger("idExt", 40000);
+        extended.setByte("Count", (byte) 3);
+        NBTTagCompound root = new NBTTagCompound();
+        root.setTag("Item", extended);
+
+        assertEquals(Collections.singletonList(extended), visited(root));
+    }
+
+    @Test
+    void aVisitorMayInvalidateTheStackItIsGiven() {
+        NBTTagCompound first = stack(5, 1);
+        NBTTagCompound second = stack(5, 2);
+        NBTTagList items = new NBTTagList();
+        items.appendTag(first);
+        items.appendTag(second);
+        NBTTagCompound root = new NBTTagCompound();
+        root.setTag("Items", items);
+        List<NBTTagCompound> seen = new ArrayList<>();
+
+        NbtItemStacks.forEach(root, tag -> {
+            seen.add(tag);
+            tag.removeTag("id");
+        });
+
+        assertEquals(Arrays.asList(first, second), seen);
+    }
+}