Capability: Provider

package iitest.capability;

import net.minecraft.item.ItemStack;
import net.minecraft.nbt.NBTTagCompound;
import net.minecraft.nbt.NBTTagList;
import net.minecraft.util.EnumFacing;
import net.minecraftforge.common.capabilities.Capability;
import net.minecraftforge.common.capabilities.ICapabilitySerializable;
import net.minecraftforge.common.util.Constants;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;

public class ITestProvider implements ICapabilitySerializable<NBTTagCompound> {
    ITest instance = new ITestImpl();

    @Override
    public boolean hasCapability(@Nonnull Capability<?> capability, @Nullable EnumFacing facing) {
        return capability == ITest.instance;
    }

    @Nullable
    @Override
    public <T> T getCapability(@Nonnull Capability<T> capability, @Nullable EnumFacing facing) {
        if (capability == ITest.instance)
            return (T)instance;
        return null;
    }

    @Override
    public NBTTagCompound serializeNBT() {
        NBTTagCompound nbt = new NBTTagCompound();
        NBTTagList slot = new NBTTagList();

        if (instance.getStackInSlot(0) != ItemStack.EMPTY) {
            NBTTagCompound item = new NBTTagCompound();

            item.setByte("__slot__", (byte)0);
            item.setTag("__item__", instance.getStackInSlot(0).serializeNBT());
            slot.appendTag(item);

            nbt.setTag("__slot__", slot);
        }
        nbt.setInteger("__value__", instance.getValue());

        // nbt.setTag("__stack__", instance.getStackInSlot(0).serializeNBT());

        return nbt;
    }

    @Override
    public void deserializeNBT(NBTTagCompound nbt) {
        NBTTagList slot = nbt.getTagList("__slot__", Constants.NBT.TAG_COMPOUND);

        if (!slot.hasNoTags()) {
            NBTTagCompound item = slot.getCompoundTagAt(0);
            instance.setInventorySlotContents(0, new ItemStack(item));
        }
        instance.setValue(nbt.getInteger("__value__"));
    }
}