simple components

BlockComponentFallback.java

package velvet.components;

import org.eclipse.jdt.annotation.Nullable;

import net.minecraft.block.BlockState;
import net.minecraft.util.math.BlockPos;
import net.minecraft.util.math.Direction;
import net.minecraft.world.BlockView;

public interface BlockComponentFallback<T> {
	@Nullable
	T getComponent(BlockState state, BlockView view, BlockPos pos, Direction direction);
}

BlockWithComponents.java

package velvet.components;

import org.eclipse.jdt.annotation.Nullable;

import net.minecraft.block.BlockState;
import net.minecraft.util.math.BlockPos;
import net.minecraft.util.math.Direction;
import net.minecraft.world.BlockView;

public interface BlockWithComponents {
	@Nullable
	<T> T getComponent(Component<T> component, BlockState state, BlockView view, BlockPos pos, Direction side);
}

Component.java

package velvet.components;

import java.util.ArrayList;
import java.util.List;

import org.apache.commons.lang3.Validate;

import net.minecraft.block.BlockState;
import net.minecraft.item.Item;
import net.minecraft.item.ItemStack;
import net.minecraft.util.math.BlockPos;
import net.minecraft.util.math.Direction;
import net.minecraft.world.BlockView;
import velvet.components.ItemWithComponents.ItemStackUpdater;

/**
 * Component provides a unified interface to work with features of game objects,
 * primarily storage and transport of items and fluids, by using different
 * overloads of {@linkplain Component#getComponent}, which return an object
 * representing and handling a requested feature.
 */
public class Component<T> {
	protected final T defaultValue;
	protected final List<BlockComponentFallback<T>> blockFallbacks = new ArrayList<>();

	public Component(T defaultValue) {
		this.defaultValue = defaultValue;
	}

	public T getDefault() {
		return this.defaultValue;
	}

	public T getComponent(ItemStack stack, ItemStackUpdater updater) {
		Item item = stack.getItem();
		if (item instanceof ItemWithComponents) {
			T component = ((ItemWithComponents) item).getComponent(this, stack, updater);
			if (component != null) {
				return component;
			}
		}
		return this.defaultValue;
	}

	public T getComponent(BlockView view, BlockPos pos, Direction direction) {
		BlockState state = view.getBlockState(pos);
		if (state.getBlock() instanceof BlockWithComponents) {
			T component = ((BlockWithComponents) state.getBlock()).getComponent(this, state, view, pos, direction);
			if (component != null) {
				return component;
			}
		}
		for (BlockComponentFallback<T> provider : this.blockFallbacks) {
			T component = provider.getComponent(state, view, pos, direction);
			if (component != null) {
				return component;
			}
		}
		return this.defaultValue;
	}

	public void addComponentFallback(BlockComponentFallback<T> provider) {
		this.blockFallbacks.add(Validate.notNull(provider));
	}

	@Override
	public final boolean equals(Object obj) {
		return this == obj;
	}

	@Override
	public final int hashCode() {
		return System.identityHashCode(this);
	}
}

ItemWithComponents.java

package velvet.components;

import org.eclipse.jdt.annotation.Nullable;

import net.minecraft.item.ItemStack;

public interface ItemWithComponents {
	@Nullable
	<T> T getComponent(Component<T> component, ItemStack stack, ItemStackUpdater updater);

	/**
	 * Functional interface for changing item stack/notifying of its mutation.
	 * <p>
	 * Components should **ALWAYS** call it when they mutate their item, otherwise
	 * changes might be not saved, leading to duplication bugs and other issues.
	 */
	@FunctionalInterface
	public interface ItemStackUpdater {
		void updateStack(ItemStack stack);
	}
}