InventoryWeightLimit

package com.happykiller.weightlimit.player.inventory;

import com.happykiller.weightlimit.items.ItemBackpack;

import net.minecraft.entity.player.EntityPlayer;
import net.minecraft.inventory.IInventory;
import net.minecraft.item.ItemStack;
import net.minecraft.nbt.NBTTagCompound;
import net.minecraft.nbt.NBTTagList;
import net.minecraft.util.ChatComponentText;
import net.minecraft.util.IChatComponent;

public class InventoryWeightLimit implements IInventory {

    private final String name = "Inventory";

    private final String tagName = "WLInvTag";

    public static final int INV_SIZE = 1;

    private final int SLOT_BACKPACK = 0;

    ItemStack[] inventory = new ItemStack[INV_SIZE];

    public InventoryWeightLimit() {}

    public String getName() {
        return name;
    }

    public boolean hasCustomName() {
        return name.length() > 0;
    }

    public IChatComponent getDisplayName() {
        return new ChatComponentText(name);
    }

    public int getSizeInventory() {
        return inventory.length;
    }

    public ItemStack getStackInSlot(int slot) {
        return inventory[slot];
    }

    public ItemStack decrStackSize(int slot, int amount) {
        ItemStack stack = getStackInSlot(slot);

        if(stack != null) {
            if(stack.stackSize > amount) {
                stack = stack.splitStack(amount);

                if(stack.stackSize == 0) {
                    setInventorySlotContents(slot, null);
                }
            }else {
                setInventorySlotContents(slot, null);
            }

            this.markDirty();
        }

        return stack;
    }

    public ItemStack getStackInSlotOnClosing(int slot) {

        ItemStack stack = getStackInSlot(slot);

        if(stack != null) {
            setInventorySlotContents(slot, null);
        }

        return stack;
    }

    public void setInventorySlotContents(int slot, ItemStack stack) {
        this.inventory[slot] = stack;

        if(stack != null && stack.stackSize > this.getInventoryStackLimit()) {
            stack.stackSize = this.getInventoryStackLimit();
        }

        this.markDirty();
    }

    public int getInventoryStackLimit() {
        return 1;
    }

    public void markDirty() {
        for(int i  = 0; i < this.getSizeInventory(); i++) {
            if(this.getStackInSlot(i) != null && this.getStackInSlot(i).stackSize == 0)
                this.setInventorySlotContents(i, null);
        }
    }

    public boolean isUseableByPlayer(EntityPlayer player) {
        return true;
    }

    public void openInventory(EntityPlayer player) {}

    public void closeInventory(EntityPlayer player) {}

    public boolean isItemValidForSlot(int slot, ItemStack stack) {
        if(slot == SLOT_BACKPACK && stack.getItem() instanceof ItemBackpack)
            return true;
        else
            return false;
    }

    public void writeToNBT(NBTTagCompound tag) {
        NBTTagList tagList = new NBTTagList();

        for(int i = 0; i < this.getSizeInventory(); i++) {
            if(this.getStackInSlot(i) != null) {
                NBTTagCompound tag1 = new NBTTagCompound();

                tag1.setByte("Slot", (byte)i);
                this.getStackInSlot(i).writeToNBT(tag1);

                tagList.appendTag(tag1);
            }
        }

        tag.setTag(tagName, tagList);
    }

    public void readFromNBT(NBTTagCompound tag) {
        NBTTagList items = tag.getTagList(tagName, tag.getId());

        for(int i = 0; i < items.tagCount(); i++) {
            NBTTagCompound item = items.getCompoundTagAt(i);

            byte slot = item.getByte("Slot");

            if(slot >= 0 && slot < this.getSizeInventory()) {
                this.setInventorySlotContents(slot, ItemStack.loadItemStackFromNBT(item));
            }
        }
    }

    public int getField(int id) {
        return 0;
    }

    public void setField(int id, int value) {

    }

    public int getFieldCount() {
        return 0;
    }

    public void clear() {
        for(int i = 0; i < inventory.length; i++) {
            inventory[i] = null;
        }
    }
}