Apply persisted Age weather traits

src/main/java/net/dnorberg/rivencraft/Rivencraft.java

@@ -12,6 +12,7 @@ import net.dnorberg.rivencraft.network.ModNetworking;
 import net.dnorberg.rivencraft.config.RivencraftConfig;
 import net.dnorberg.rivencraft.config.RivencraftClientConfig;
 import net.dnorberg.rivencraft.book.AgeDimensionService;
+import net.dnorberg.rivencraft.book.AgeWeatherService;
 import net.neoforged.bus.api.IEventBus;
 import net.neoforged.fml.ModContainer;
 import net.neoforged.fml.common.Mod;
@@ -36,6 +37,7 @@ public final class Rivencraft {
         ModSounds.register(modEventBus);
         ModCreativeTabs.register(modEventBus);
         NeoForge.EVENT_BUS.addListener(BookStandConversionHandler::onRightClickBlock);
+        NeoForge.EVENT_BUS.addListener(AgeWeatherService::onLevelTickPost);
         LOGGER.info("Initializing Rivencraft");
     }
 }

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

@@ -21,7 +21,7 @@ public record AgeDefinition(
     public static final ResourceLocation RANDOM_VANILLA_PROFILE = ResourceLocation.fromNamespaceAndPath(
             Rivencraft.MOD_ID, "random_vanilla"
     );
-    public static final int CURRENT_GENERATION_VERSION = 4;
+    public static final int CURRENT_GENERATION_VERSION = 5;
 
     public AgeDefinition {
         Objects.requireNonNull(id, "id");

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

@@ -0,0 +1,71 @@
+package net.dnorberg.rivencraft.book;
+
+import java.util.Map;
+import java.util.WeakHashMap;
+import net.dnorberg.rivencraft.Rivencraft;
+import net.minecraft.server.level.ServerLevel;
+import net.neoforged.neoforge.event.tick.LevelTickEvent;
+
+/** Applies persisted Legacy-inspired weather behavior to loaded Ages. */
+public final class AgeWeatherService {
+    private static final int FIXED_WEATHER_DURATION = 6000;
+    private static final Map<ServerLevel, WeatherState> STATES = new WeakHashMap<>();
+
+    private AgeWeatherService() {
+    }
+
+    public static void onLevelTickPost(LevelTickEvent.Post event) {
+        if (!(event.getLevel() instanceof ServerLevel level)
+                || !level.dimension().location().getNamespace().equals(Rivencraft.MOD_ID)) {
+            return;
+        }
+        AgeDefinition age = AgeRegistrySavedData.get(level)
+                .findByDimension(level.dimension().location())
+                .orElse(null);
+        if (age == null) {
+            return;
+        }
+
+        AgeTraits.Weather weather = age.traits().weather();
+        if (weather == AgeTraits.Weather.NORMAL) {
+            STATES.remove(level);
+            return;
+        }
+
+        if (weather == AgeTraits.Weather.FAST || weather == AgeTraits.Weather.SLOW) {
+            applyVariableWeather(level, weather);
+        } else {
+            STATES.remove(level);
+            applyFixedWeather(level, weather);
+        }
+    }
+
+    private static void applyVariableWeather(
+            ServerLevel level,
+            AgeTraits.Weather weather
+    ) {
+        WeatherState current = new WeatherState(level.isRaining(), level.isThundering());
+        WeatherState previous = STATES.put(level, current);
+        if (current.equals(previous)) {
+            return;
+        }
+
+        int scale = weather == AgeTraits.Weather.FAST ? 1 : 4;
+        int rainBase = 6000 * scale;
+        int rainRange = (current.raining() ? 6000 : 84000) * scale;
+        int duration = rainBase + level.getRandom().nextInt(rainRange);
+        level.setWeatherParameters(0, duration, current.raining(), current.thundering());
+    }
+
+    private static void applyFixedWeather(ServerLevel level, AgeTraits.Weather weather) {
+        boolean raining = weather != AgeTraits.Weather.OFF;
+        boolean thundering = weather == AgeTraits.Weather.STORM;
+        if (level.isRaining() != raining || level.isThundering() != thundering
+                || level.getGameTime() % 200L == 0L) {
+            level.setWeatherParameters(0, FIXED_WEATHER_DURATION, raining, thundering);
+        }
+    }
+
+    private record WeatherState(boolean raining, boolean thundering) {
+    }
+}