InventoryExpansion.java

package gigaherz.packingtape.cap;

import net.minecraft.entity.player.EntityPlayer;
import net.minecraft.item.ItemStack;
import net.minecraftforge.items.ItemStackHandler;

/**
 * Created by gigaherz on 06/08/2016.
 *
 * This class is the feature we want to attach to the player.
 */
public class InventoryExpansion
{
    public static final int INVENTORY_SLOTS = 5;
    final ItemStackHandler slots = new ItemStackHandler(INVENTORY_SLOTS);

    EntityPlayer player;

    public InventoryExpansion()
    {
    }

    public EntityPlayer getPlayer() { return player; }
    public void setPlayer(EntityPlayer newPlayer)
    {
        this.player = newPlayer;
    }

    /*
     * Internal method used by IStorage in the capability
     */
    protected ItemStackHandler getSlots()
    {
        return slots;
    }

    /*
     * API method for getting a slot by name
     */
    public ItemStack getStackInSlot(ExpansionSlots slot)
    {
        return slots.getStackInSlot(slot.ordinal());
    }

    /*
     * API method for setting a slot by name
     */
    public void setStackInSlot(ExpansionSlots slot, ItemStack stack)
    {
        // TODO: Remove old attribute modifiers from player
        slots.setStackInSlot(slot.ordinal(), stack);
        // TODO: Add new attribute modifiers to player
    }

    /*
     * An arbitrary set of slots, for example purposes
     */
    public enum ExpansionSlots
    {
        NECK,
        WRISTS,
        ANKLES,
        EARS,
        FINGERS
    }
}

InventoryExpansionCapability.java

package gigaherz.packingtape.cap;

import net.minecraft.nbt.NBTBase;
import net.minecraft.nbt.NBTTagCompound;
import net.minecraft.util.EnumFacing;
import net.minecraftforge.common.capabilities.Capability;
import net.minecraftforge.common.capabilities.CapabilityInject;
import net.minecraftforge.common.capabilities.CapabilityManager;

import java.util.concurrent.Callable;

/**
 * Created by gigaherz on 06/08/2016.
 *
 * This class is only for structure only, everything important is a nested/anonymous class.
 */
public class InventoryExpansionCapability
{
    /*
     * This field will contain the forge-allocated Capability class.
     * This instance will be initialized internally by Forge, upon calling register.
     */
    @CapabilityInject(InventoryExpansion.class)
    public static Capability<InventoryExpansion> INSTANCE;

    /*
     * This
     */
    public void register()
    {
        CapabilityManager.INSTANCE.register(

                // This is theclass the capability works with
                InventoryExpansion.class,

                // This is a helper for users to save and load
                new StorageHelper(),

                // This is a factory for default instances
                new DefaultInstanceFactory()
        );
    }

    /*
     * This class handles saving and loading the data.
     */
    public static class StorageHelper implements Capability.IStorage<InventoryExpansion>
    {

        @Override
        public NBTBase writeNBT(Capability<InventoryExpansion> capability, InventoryExpansion instance, EnumFacing side)
        {
            return instance.getSlots().serializeNBT();
        }

        @Override
        public void readNBT(Capability<InventoryExpansion> capability, InventoryExpansion instance, EnumFacing side, NBTBase nbt)
        {
            instance.getSlots().deserializeNBT((NBTTagCompound)nbt);
        }
    }

    /*
     * This class handles constructing new instances for this capability
     */
    public static class DefaultInstanceFactory implements Callable<InventoryExpansion>
    {
        @Override
        public InventoryExpansion call() throws Exception
        {
            return new InventoryExpansion();
        }
    }
}

InventoryExpansionEventHandlers.java

package gigaherz.packingtape.cap;

import gigaherz.packingtape.ModPackingTape;
import net.minecraft.entity.player.EntityPlayer;
import net.minecraft.nbt.NBTTagCompound;
import net.minecraft.util.EnumFacing;
import net.minecraft.util.ResourceLocation;
import net.minecraftforge.common.MinecraftForge;
import net.minecraftforge.common.capabilities.Capability;
import net.minecraftforge.common.capabilities.ICapabilitySerializable;
import net.minecraftforge.event.AttachCapabilitiesEvent;
import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;

import javax.annotation.Nullable;

/**
 * Created by gigaherz on 06/08/2016.
 *
 * This class handles events for the inventory expansion capability
 */
public class InventoryExpansionEventHandlers
{
    public static void register()
    {
        MinecraftForge.EVENT_BUS.register(new InventoryExpansionEventHandlers());
    }

    @SubscribeEvent
    public void onAttach(AttachCapabilitiesEvent.Entity ev)
    {
        if (!(ev.getEntity() instanceof EntityPlayer))
            return;

        ev.addCapability(ExpansionProvider.KEY, new ExpansionProvider((EntityPlayer)ev.getEntity()));
    }
    
    /*
     * TODO: Add event handlers for synchronizing data with clients,
     * dropping/transferring items upon death, etc.
     */

    /*
     * This class handles the capability requests on behalf of the player
     */
    public static class ExpansionProvider implements ICapabilitySerializable<NBTTagCompound>
    {
        /*
         * Unique key to identify the attached provider from others
         */
        static final ResourceLocation KEY = new ResourceLocation(ModPackingTape.MODID, "inventoryExpansion");

        /*
         * The instance that we are providing
         */
        final InventoryExpansion slots = new InventoryExpansion();

        public ExpansionProvider(EntityPlayer player)
        {
            slots.setPlayer(player);
        }

        @Override
        public boolean hasCapability(Capability<?> capability, @Nullable EnumFacing facing)
        {
            if (capability == InventoryExpansionCapability.INSTANCE)
                return true;
            return false;
        }

        @SuppressWarnings("unchecked")
        @Override
        public <T> T getCapability(Capability<T> capability, @Nullable EnumFacing facing)
        {
            if (capability == InventoryExpansionCapability.INSTANCE)
                return (T)slots;
            return null;
        }

        @Override
        public NBTTagCompound serializeNBT()
        {
            return (NBTTagCompound) InventoryExpansionCapability.INSTANCE.writeNBT(slots, null);
        }

        @Override
        public void deserializeNBT(NBTTagCompound nbt)
        {
            InventoryExpansionCapability.INSTANCE.readNBT(slots, null, nbt);
        }
    }
}