EnergonRelics/src/main/java/com/thebrokenrail/energonrelics/block/entity/battery/BatteryCoreBlockEntity.java

package com.thebrokenrail.energonrelics.block.entity.battery;

import net.minecraft.block.BlockState;
import net.minecraft.block.entity.BlockEntity;
import net.minecraft.block.entity.BlockEntityType;
import net.minecraft.nbt.CompoundTag;

public class BatteryCoreBlockEntity extends BlockEntity {
    private long energy = 0;

    public BatteryCoreBlockEntity(BlockEntityType<?> type) {
        super(type);
    }

    @Override
    public CompoundTag toTag(CompoundTag tag) {
        super.toTag(tag);
        tag.putLong("Energy", energy);
        return tag;
    }

    @Override
    public void fromTag(BlockState state, CompoundTag tag) {
        super.fromTag(state, tag);
        energy = Math.max(0, tag.getLong("Energy"));
    }

    long getEnergy() {
        return energy;
    }

    void setEnergy(long value) {
        if (value < 0) {
            throw new UnsupportedOperationException();
        }
        energy = value;
        markDirty();
    }
}