Add ability for minecarts to specify their detector rail comparator value (#1321)

* Add ability for minecarts to specify their detector rail comparator value

Address comments

* Apply suggestions from code review

Co-authored-by: Juuxel <6596629+Juuxel@users.noreply.github.com>

* Warn instead of debug

Co-authored-by: Juuxel <6596629+Juuxel@users.noreply.github.com>

fabric-object-builder-api-v1/src/main/java/net/fabricmc/fabric/api/object/builder/v1/entity/MinecartComparatorLogic.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2016, 2017, 2018, 2019 FabricMC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.fabricmc.fabric.api.object.builder.v1.entity;
+
+import net.minecraft.block.BlockState;
+import net.minecraft.entity.vehicle.AbstractMinecartEntity;
+import net.minecraft.util.math.BlockPos;
+
+/**
+ * Provides custom comparator output for minecarts resting on detector rails.
+ * @param <T> the handled minecart type
+ */
+@FunctionalInterface
+public interface MinecartComparatorLogic<T extends AbstractMinecartEntity> {
+	/**
+	 * Compute the comparator output of a detector rail when a minecart is resting
+	 * on top of it. Called from {@link net.minecraft.block.DetectorRailBlock#getComparatorOutput}.
+	 * @param minecart The minecart on the rail
+	 * @param state Block state of the rail
+	 * @param pos Position of the rail
+	 * @return A redstone power value {@literal >=} 0 to use, else a value {@literal <} 0 to try the next minecart with
+	 * 	a registered logic. If no logic chooses to provide a value, vanilla's logic is invoked.
+	 */
+	int getComparatorValue(T minecart, BlockState state, BlockPos pos);
+}

fabric-object-builder-api-v1/src/main/java/net/fabricmc/fabric/api/object/builder/v1/entity/MinecartComparatorLogicRegistry.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright (c) 2016, 2017, 2018, 2019 FabricMC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.fabricmc.fabric.api.object.builder.v1.entity;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.jetbrains.annotations.Nullable;
+
+import net.minecraft.entity.EntityType;
+import net.minecraft.entity.vehicle.AbstractMinecartEntity;
+import net.minecraft.util.registry.Registry;
+
+/**
+ * A registry for {@linkplain MinecartComparatorLogic custom minecart compator logic}.
+ */
+public final class MinecartComparatorLogicRegistry {
+	private static final Logger LOGGER = LogManager.getLogger();
+	private static final Map<EntityType<?>, MinecartComparatorLogic<?>> logics = new HashMap<>();
+
+	/**
+	 * Gets the registered custom comparator logic for the specified minecart entity type.
+	 *
+	 * @param type the entity type
+	 * @return the comparator logic, or {@code null} if not registered
+	 */
+	@Nullable
+	@SuppressWarnings("unchecked")
+	public static MinecartComparatorLogic<AbstractMinecartEntity> getCustomComparatorLogic(EntityType<?> type) {
+		return (MinecartComparatorLogic<AbstractMinecartEntity>) logics.get(type);
+	}
+
+	/**
+	 * Registers a comparator logic for a minecart entity type.
+	 *
+	 * <p>Registering a second value for an entity type will replace the old logic.
+	 *
+	 * @param <T>   the handled minecart type
+	 * @param type  the minecart entity type
+	 * @param logic the logic to register
+	 */
+	public static <T extends AbstractMinecartEntity> void register(EntityType<T> type, MinecartComparatorLogic<? super T> logic) {
+		if (logics.put(type, logic) != null) {
+			LOGGER.warn("Overriding existing minecart comparator logic for entity type {}", Registry.ENTITY_TYPE.getId(type));
+		}
+	}
+}

fabric-object-builder-api-v1/src/main/java/net/fabricmc/fabric/mixin/object/builder/DetectorRailBlockMixin.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2016, 2017, 2018, 2019 FabricMC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.fabricmc.fabric.mixin.object.builder;
+
+import java.util.List;
+import java.util.function.Predicate;
+
+import org.jetbrains.annotations.Nullable;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+import net.minecraft.block.BlockState;
+import net.minecraft.block.DetectorRailBlock;
+import net.minecraft.entity.Entity;
+import net.minecraft.entity.vehicle.AbstractMinecartEntity;
+import net.minecraft.util.math.BlockPos;
+import net.minecraft.world.World;
+
+import net.fabricmc.fabric.api.object.builder.v1.entity.MinecartComparatorLogicRegistry;
+
+@Mixin(DetectorRailBlock.class)
+public abstract class DetectorRailBlockMixin {
+	@Shadow protected abstract <T extends AbstractMinecartEntity> List<T> getCarts(World world, BlockPos pos, Class<T> entityClass, @Nullable Predicate<Entity> entityPredicate);
+
+	@Inject(at = @At("HEAD"), method = "getComparatorOutput", cancellable = true)
+	private void getCustomComparatorOutput(BlockState state, World world, BlockPos pos, CallbackInfoReturnable<Integer> cir) {
+		if (state.get(DetectorRailBlock.POWERED)) {
+			List<AbstractMinecartEntity> carts = getCarts(world, pos, AbstractMinecartEntity.class,
+					cart -> MinecartComparatorLogicRegistry.getCustomComparatorLogic(cart.getType()) != null);
+			for (AbstractMinecartEntity cart : carts) {
+				int comparatorValue = MinecartComparatorLogicRegistry.getCustomComparatorLogic(cart.getType())
+						.getComparatorValue(cart, state, pos);
+				if (comparatorValue >= 0) {
+					cir.setReturnValue(comparatorValue);
+					break;
+				}
+			}
+		}
+	}
+}

fabric-object-builder-api-v1/src/main/resources/fabric-object-builder-v1.mixins.json

@@ -9,6 +9,7 @@
     "CriteriaAccessor",
     "DefaultAttributeRegistryAccessor",
     "DefaultAttributeRegistryMixin",
+    "DetectorRailBlockMixin",
     "MaterialBuilderAccessor",
     "MixinBlock",
     "PointOfInterestTypeAccessor",