Include data packs from mod in in-world selector

src/main/java/ml/unbreakinggold/datapackinstaller/mixin/GameMenuScreenMixin.java

@@ -7,6 +7,10 @@
 import net.minecraft.client.gui.widget.ButtonWidget;
 import net.minecraft.client.gui.widget.GridWidget;
 import net.minecraft.text.Text;
+import net.minecraft.util.WorldSavePath;
+import org.apache.commons.io.FileUtils;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
 import org.spongepowered.asm.mixin.Mixin;
 import org.spongepowered.asm.mixin.Shadow;
 import org.spongepowered.asm.mixin.Unique;
@@ -15,14 +19,19 @@
 import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
 import org.spongepowered.asm.mixin.injection.callback.LocalCapture;
 
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Path;
 import java.util.Collection;
 import java.util.function.Supplier;
 
 @Mixin(GameMenuScreen.class)
 public abstract class GameMenuScreenMixin extends Screen {
-    @Shadow private ButtonWidget createButton(Text text, Supplier<Screen> screenSupplier) { return null; };
+    @Unique private final Logger LOGGER = LogManager.getLogger(GameMenuScreenMixin.class);
     @Unique private static final Text DATA_PACK_TEXT = Text.translatable("dataPack.title");
 
+    @Shadow private ButtonWidget createButton(Text text, Supplier<Screen> screenSupplier) { return null; };
+
     private GameMenuScreenMixin(Text title) {
         super(title);
     }
@@ -32,6 +41,15 @@ private void onInitWidgets(CallbackInfo ci, GridWidget gridWidget, GridWidget.Ad
         if (!this.client.isIntegratedServerRunning() || this.client.getServer().isRemote()) return;
 
         adder.add(this.createButton(DATA_PACK_TEXT, () -> {
+            Path worldDataPackPath = ((MinecraftServerAccessor)this.client.getServer()).getSession().getDirectory(WorldSavePath.DATAPACKS);
+            File modDatapackDir = DatapackInstallerClient.MAIN_PATH.toFile();
+            File worldDataPackDir = worldDataPackPath.toFile();
+            try {
+                FileUtils.copyDirectory(modDatapackDir, worldDataPackDir);
+            } catch(IOException exception) {
+                LOGGER.error("Unable to install new data packs to world. Data packs not yet seen by this world may be missing.", exception);
+            }
+
             return new PackScreen(this.client.getServer().getDataPackManager(), (dataPackManager) -> {
                 Collection<String> enabledProfiles = dataPackManager.getEnabledIds();
 

src/main/java/ml/unbreakinggold/datapackinstaller/mixin/MinecraftServerAccessor.java

@@ -0,0 +1,12 @@
+package ml.unbreakinggold.datapackinstaller.mixin;
+
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.world.level.storage.LevelStorage;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.gen.Accessor;
+
+@Mixin(MinecraftServer.class)
+public interface MinecraftServerAccessor {
+    @Accessor
+    LevelStorage.Session getSession();
+}

src/main/resources/DatapackInstaller.mixins.json

@@ -4,6 +4,7 @@
   "package": "ml.unbreakinggold.datapackinstaller.mixin",
   "compatibilityLevel": "JAVA_17",
   "mixins": [
+    "MinecraftServerAccessor"
   ],
   "client": [
     "CreateWorldScreenMixin",