nbt tag issues (line 189)

package net.dyeo.teleporter;

import java.util.ArrayList;

import com.sun.org.apache.bcel.internal.Constants;

import net.minecraft.block.Block;
import net.minecraft.client.gui.GuiScreenBook;
import net.minecraft.entity.Entity;
import net.minecraft.entity.player.EntityPlayer;
import net.minecraft.init.Blocks;
import net.minecraft.init.Items;
import net.minecraft.item.Item;
import net.minecraft.item.ItemStack;
import net.minecraft.nbt.NBTBase;
import net.minecraft.nbt.NBTTagCompound;
import net.minecraft.nbt.NBTTagList;
import net.minecraft.util.BlockPos;
import net.minecraft.util.ChatComponentTranslation;
import net.minecraft.world.World;
import net.minecraft.world.WorldSavedData;

/*
 * TeleporterNetwork is the singleton responsible for saving the teleporter data onto the world file, and is
 * responsible for retrieving destination and source nodes during teleportation.
 */
public class TeleporterNetwork extends WorldSavedData
{

    //

    private ArrayList<TeleporterNode> network = new ArrayList<TeleporterNode>();

    //

    private static final String IDENTIFIER = Reference.MODID.toLowerCase();

    public TeleporterNetwork()
    {
        super(IDENTIFIER);
    }

    public TeleporterNetwork(String identifier)
    {
        super(identifier);
    }

    //

    @Override
    public void readFromNBT(NBTTagCompound nbt)
    {
        final int NBT_TYPE = 10; // compound
        NBTTagList netNBT = nbt.getTagList("Network", NBT_TYPE);

        if(network.size() != 0)
        {
            network.clear();
        }

        for(int i = 0; i < netNBT.tagCount(); ++i)
        {
            TeleporterNode tempNode = new TeleporterNode();
            NBTTagCompound nodeNBT = netNBT.getCompoundTagAt(i);
            tempNode.readFromNBT(nodeNBT);
            network.add(tempNode);

            System.out.println("[Teleporter][readFromNBT] Read worldData node " + i);
        }

    }

    @Override
    public void writeToNBT(NBTTagCompound nbt)
    {
        NBTTagList netNBT = new NBTTagList();

        for(int i = 0; i < network.size(); ++i)
        {
            TeleporterNode tempNode = network.get(i);
            NBTTagCompound nodeNBT = new NBTTagCompound();
            tempNode.writeToNBT(nodeNBT);
            netNBT.appendTag(nodeNBT);

            System.out.println("[Teleporter][writeToNBT] Saved worldData node " + i);
        }

        nbt.setTag("Network", netNBT);
    }

    private boolean isObstructed(World world, TeleporterNode node)
    {
        BlockPos bl1p = new BlockPos(node.pos.getX(),node.pos.getY()+1,node.pos.getZ());
        BlockPos bl2p = new BlockPos(node.pos.getX(),node.pos.getY()+2,node.pos.getZ());
        Block bl1 = world.getBlockState(bl1p).getBlock();
        Block bl2 = world.getBlockState(bl2p).getBlock();

        if ((/*bl1 == Blocks.wall_sign || bl1 == Blocks.standing_sign || bl1 == Blocks.lever || bl1 == Blocks.vine || bl1 == Blocks.torch || bl1 == Blocks.air || bl1 == Blocks.redstone_torch || bl1 == Blocks.ladder || */bl1.isPassable(world, bl1p))
                &&
            (/*bl2 == Blocks.wall_sign || bl2 == Blocks.standing_sign || bl2 == Blocks.lever || bl2 == Blocks.vine || bl2 == Blocks.torch || bl2 == Blocks.air || bl2 == Blocks.redstone_torch || bl2 == Blocks.ladder || */bl2.isPassable(world, bl2p)))
        {
            return false;
        }

        return true;
    }

    public TeleporterNode getNextNode(Entity entityIn, World world, ItemStack stack, TeleporterNode source)
    {
        TileEntityTeleporter sourceEnt = TileEntityTeleporter.getTileEntityAt(world, source.pos);

        boolean playerEnt = false;
        if(entityIn instanceof EntityPlayer)
        {
            playerEnt = true;
        }
        int index = network.indexOf(source);
        for(int i = index+1; i < network.size()+index; ++i)
        {
            TeleporterNode node =  network.get(i % network.size());
            TileEntityTeleporter nodeEnt = TileEntityTeleporter.getTileEntityAt(world, node.pos);

            boolean isUnique = false;
            boolean matches = false;
            boolean diffDimension = false;

            // check if dimensions are different
            if(node == source)
            {
                matches = false;
            }
            if(source.dimension != node.dimension)
            {
                matches = false;
                diffDimension = true;
            }
            // check if keys are completely different
            else if(stack == null && nodeEnt.itemStacks[0] != null)
            {
                matches = false;
            }
            else if(stack != null && nodeEnt.itemStacks[0] == null)
            {
                matches = false;
            }
            // check if keys are both empty
            else if(stack == null && nodeEnt.itemStacks[0] == null)
            {
                matches = true;
            }
            // check if keys are the same
            else if(stack.getItem().getUnlocalizedName().equals(nodeEnt.itemStacks[0].getItem().getUnlocalizedName()))
            {
                matches = true;
            }

            if (matches == true)
            {
                Item thisItem = stack.getItem(), nextItem = nodeEnt.itemStacks[0].getItem();
                if (thisItem == Items.written_book && nextItem == Items.written_book)
                {
                    String author = stack.getTagCompound().getString("author");
                    author += ":" + stack.getTagCompound().getString("title");

                    String nodeAuthor = nodeEnt.itemStacks[0].getTagCompound().getString("author");
                    nodeAuthor += ":" + nodeEnt.itemStacks[0].getTagCompound().getString("title");
                    if (author.equals(nodeAuthor))
                    {
                        matches = true;
                    }
                    else
                    {
                        matches = false;
                    }
                }
                else if (thisItem == Items.filled_map && nextItem == Items.filled_map)
                {
                    if (stack.getItemDamage() == nodeEnt.itemStacks[0].getItemDamage())
                    {
                        matches = true;
                    }
                    else
                    {
                        matches = false;
                    }
                }
                else
                {
                    // this is where i'm having the issue
                    NBTTagCompound tag = (NBTTagCompound)stack.getTagCompound().getTag("display");
                    NBTTagCompound nextTag = (NBTTagCompound)nodeEnt.itemStacks[0].getTagCompound().getTag("display");

                    String name = tag.getString("name");
                    String nodeName = nextTag.getString("name");
                    if (name.equals(nodeName))
                    {
                        matches = true;
                    }
                    else
                    {
                        matches = false;
                    }
                }
            }

            boolean obstructed = isObstructed(world,node);

            if(matches == true && obstructed == false && diffDimension == false && nodeEnt.isPowered == false)
            {
                return node;
            }
            else if(matches == true && obstructed == true && diffDimension == false)
            {
                EntityPlayer entp = (EntityPlayer)entityIn;
                if(playerEnt == true) entp.addChatMessage(new ChatComponentTranslation("Teleporter is blocked; skipping..."));
            }
            else if(matches == true && obstructed == false && diffDimension == false && nodeEnt.isPowered == true)
            {
                EntityPlayer entp = (EntityPlayer)entityIn;
                if(playerEnt == true) entp.addChatMessage(new ChatComponentTranslation("Teleporter is disabled; skipping..."));
            }
        }

        if(playerEnt == true)
        {
            EntityPlayer entp = (EntityPlayer)entityIn;
            entp.addChatMessage(new ChatComponentTranslation("No teleporters found that match your key."));
        }

        System.out.println("[Teleporter] Destination not found");
        return null;
    }

    public TeleporterNode getNode(BlockPos pos, int dimension, boolean debug)
    {
        for(int i = 0; i < network.size(); ++i)
        {
            TeleporterNode node = network.get(i);
            if(pos.getX() == node.pos.getX() && pos.getY() == node.pos.getY() && pos.getZ() == node.pos.getZ() && dimension == node.dimension)
            {
                if(debug) System.out.println("[Teleporter][getNode] Getting node " + pos.getX() + "," + pos.getY() + "," + pos.getZ() + " from network");
                return node;
            }
        }

        if(debug) System.out.println("[Teleporter][getNode] No node " + pos.getX() + "," + pos.getY() + "," + pos.getZ() + " found in network");
        return null;
    }

    public void addNode(TeleporterNode node)
    {
        int index = network.size();
        network.add(node);
        markDirty();
        System.out.println("[Teleporter][addNode] Appending node " + node.pos.getX() + "," + node.pos.getY() + "," + node.pos.getZ() + " to network " + "[" + index + "]");
    }

    public boolean removeNode(BlockPos pos, int dimension)
    {
        for(int i = 0; i < network.size(); ++i)
        {
            TeleporterNode node = network.get(i);
            if(pos.getX() == node.pos.getX() && pos.getY() == node.pos.getY() && pos.getZ() == node.pos.getZ() && dimension == node.dimension)
            {
                network.remove(node);
                System.out.println("[Teleporter][removeNode] Removing node " + pos.getX() + "," + pos.getY() + "," + pos.getZ() + " from network");
                return true;
            }
        }

        System.out.println("[Teleporter][removeNode] No node " + pos.getX() + "," + pos.getY() + "," + pos.getZ() + " found in network");
        return false;
    }

    public static TeleporterNetwork get(World world, boolean debug)
    {
        TeleporterNetwork data = (TeleporterNetwork)world.loadItemData(TeleporterNetwork.class, IDENTIFIER);

        if(data == null)
        {
            if(debug) System.out.println("[Teleporter][get] New network created!");
            data = new TeleporterNetwork();
            world.setItemData(IDENTIFIER, data);
        }
        else
        {
            if(debug) System.out.println("[Teleporter][get] Network loaded!");
        }

        data.markDirty();
        return data;
    }

}