Add descriptive book age references

docs/PORTING.md

@@ -44,7 +44,7 @@ the symbol grammar is introduced.
 - [x] Server-authoritative cross-dimension travel with world-border, collision,
   fluid, and floor checks.
 - [x] Nearby landing search and clear failure messages.
-- [ ] Descriptive Book identity and Age reference components.
+- [x] Descriptive Book identity and Age reference components.
 - [ ] Return-link creation as part of Descriptive Book travel.
 - [ ] Lectern/book-stand interaction.
 - [ ] Automated in-game tests for binding, persistence, and travel.
@@ -53,6 +53,10 @@ The temporary shapeless Linking Book recipe makes the linking subsystem easy
 to test. It can move into the writing/bookbinder progression when that system
 is implemented.
 
+Age references use UUIDs rather than dimension keys. Milestone 3 will own the
+mapping from that stable identity to server data and a runtime dimension. This
+keeps saved books valid if an Age is migrated or regenerated.
+
 ## Version policy
 
 Versions follow `x.y.z`:

gradle.properties

@@ -32,7 +32,7 @@ mod_name=Rivencraft
 # The license of the mod. Review your options at https://choosealicense.com/. All Rights Reserved is the default.
 mod_license=LGPL-3.0-or-later
 # The mod version. See https://semver.org/
-mod_version=0.1.1
+mod_version=0.1.2
 # The group ID for the mod. It is only important when publishing as an artifact to a Maven repository.
 # This should match the base package used for the mod sources.
 # See https://maven.apache.org/guides/mini/guide-naming-conventions.html

src/main/java/net/dnorberg/rivencraft/book/AgeReference.java

@@ -0,0 +1,27 @@
+package net.dnorberg.rivencraft.book;
+
+import com.mojang.serialization.Codec;
+import io.netty.buffer.ByteBuf;
+import java.util.UUID;
+import net.minecraft.core.UUIDUtil;
+import net.minecraft.network.codec.StreamCodec;
+
+/**
+ * Stable identity for an Age, independent of its eventual dimension key.
+ *
+ * <p>Milestone 3 will resolve this identifier through server-owned Age data.
+ * Books only retain the identifier so dimension regeneration or migration does
+ * not invalidate every existing book.</p>
+ */
+public record AgeReference(UUID id) {
+    public static final Codec<AgeReference> CODEC = UUIDUtil.STRING_CODEC.xmap(AgeReference::new, AgeReference::id);
+    public static final StreamCodec<ByteBuf, AgeReference> STREAM_CODEC = StreamCodec.composite(
+            UUIDUtil.STREAM_CODEC,
+            AgeReference::id,
+            AgeReference::new
+    );
+
+    public String shortId() {
+        return id.toString().substring(0, 8);
+    }
+}

src/main/java/net/dnorberg/rivencraft/item/DescriptiveBookItem.java

@@ -1,8 +1,11 @@
 package net.dnorberg.rivencraft.item;
 
 import java.util.List;
+import net.dnorberg.rivencraft.book.AgeReference;
+import net.dnorberg.rivencraft.registry.ModDataComponents;
 import net.minecraft.ChatFormatting;
 import net.minecraft.network.chat.Component;
+import net.minecraft.network.chat.MutableComponent;
 import net.minecraft.world.item.Item;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.TooltipFlag;
@@ -19,6 +22,11 @@ public final class DescriptiveBookItem extends Item {
         super(properties);
     }
 
+    @Override
+    public boolean isFoil(ItemStack stack) {
+        return stack.has(ModDataComponents.AGE_REFERENCE.get()) || super.isFoil(stack);
+    }
+
     @Override
     public void appendHoverText(
             ItemStack stack,
@@ -26,7 +34,10 @@ public final class DescriptiveBookItem extends Item {
             List<Component> tooltipComponents,
             TooltipFlag tooltipFlag
     ) {
-        tooltipComponents.add(Component.translatable("item.rivencraft.descriptive_book.unwritten")
+        AgeReference age = stack.get(ModDataComponents.AGE_REFERENCE.get());
-                .withStyle(ChatFormatting.GRAY));
+        MutableComponent status = age == null
+                ? Component.translatable("item.rivencraft.descriptive_book.unwritten")
+                : Component.translatable("item.rivencraft.descriptive_book.age", age.shortId());
+        tooltipComponents.add(status.withStyle(ChatFormatting.GRAY));
     }
 }

src/main/java/net/dnorberg/rivencraft/registry/ModDataComponents.java

@@ -2,6 +2,7 @@ package net.dnorberg.rivencraft.registry;
 
 import net.dnorberg.rivencraft.Rivencraft;
 import net.dnorberg.rivencraft.book.LinkTarget;
+import net.dnorberg.rivencraft.book.AgeReference;
 import net.minecraft.core.component.DataComponentType;
 import net.minecraft.core.registries.Registries;
 import net.neoforged.bus.api.IEventBus;
@@ -18,6 +19,12 @@ public final class ModDataComponents {
                     .networkSynchronized(LinkTarget.STREAM_CODEC)
                     .cacheEncoding()
                     .build());
+    public static final DeferredHolder<DataComponentType<?>, DataComponentType<AgeReference>> AGE_REFERENCE =
+            DATA_COMPONENTS.register("age_reference", () -> DataComponentType.<AgeReference>builder()
+                    .persistent(AgeReference.CODEC)
+                    .networkSynchronized(AgeReference.STREAM_CODEC)
+                    .cacheEncoding()
+                    .build());
 
     private ModDataComponents() {
     }

src/main/resources/assets/rivencraft/lang/en_us.json

@@ -1,6 +1,7 @@
 {
   "item.rivencraft.descriptive_book": "Descriptive Book",
   "item.rivencraft.descriptive_book.unwritten": "Unwritten",
+  "item.rivencraft.descriptive_book.age": "Age %s",
   "item.rivencraft.linking_book": "Linking Book",
   "item.rivencraft.linking_book.unbound": "Unbound — sneak-use to bind",
   "item.rivencraft.linking_book.destination": "%s (%s, %s, %s)",