Proxy the current turtle's inventory

Previously we were just returning the current tile. However, if someone
was holding a reference to this inventory (such as a GUI), then it'd be
outdated and invalid once the turtle had moved.

This caused a couple of issues:
 - turtle_inventory events would not be fired when moving items in the
   turtle GUI.
 - As of 75e2845c01, turtles would no
   longer share their inventory state after moving. Thus, removing items
   from a GUI using an invalid inventory would move them from an old
   tile, duplicating the items.

Fixes #298, fixes #300

src/main/java/dan200/computercraft/shared/media/inventory/ContainerHeldItem.java

@@ -6,7 +6,6 @@
 
 package dan200.computercraft.shared.media.inventory;
 
-import dan200.computercraft.shared.util.InventoryUtil;
 import net.minecraft.entity.player.EntityPlayer;
 import net.minecraft.inventory.Container;
 import net.minecraft.item.ItemStack;
@@ -22,7 +21,7 @@ public class ContainerHeldItem extends Container
     public ContainerHeldItem( EntityPlayer player, EnumHand hand )
     {
         m_hand = hand;
-        m_stack = InventoryUtil.copyItem( player.getHeldItem( hand ) );
+        m_stack = player.getHeldItem( hand ).copy();
     }
 
     @Nonnull

src/main/java/dan200/computercraft/shared/turtle/blocks/TileTurtle.java

@@ -224,7 +224,7 @@ public void update()
             m_inventoryChanged = false;
             for( int n = 0; n < getSizeInventory(); n++ )
             {
-                m_previousInventory.set( n, InventoryUtil.copyItem( getStackInSlot( n ) ) );
+                m_previousInventory.set( n, getStackInSlot( n ).copy() );
             }
         }
     }
@@ -268,7 +268,7 @@ public void readFromNBT( NBTTagCompound nbt )
             if( slot < getSizeInventory() )
             {
                 m_inventory.set( slot, new ItemStack( tag ) );
-                m_previousInventory.set( slot, InventoryUtil.copyItem( m_inventory.get( slot ) ) );
+                m_previousInventory.set( slot, m_inventory.get( slot ).copy() );
             }
         }
 

src/main/java/dan200/computercraft/shared/turtle/core/TurtleBrain.java

@@ -20,10 +20,7 @@
 import dan200.computercraft.shared.computer.core.ComputerFamily;
 import dan200.computercraft.shared.computer.core.ServerComputer;
 import dan200.computercraft.shared.turtle.blocks.TileTurtle;
-import dan200.computercraft.shared.util.Colour;
-import dan200.computercraft.shared.util.ColourUtils;
-import dan200.computercraft.shared.util.Holiday;
-import dan200.computercraft.shared.util.HolidayUtil;
+import dan200.computercraft.shared.util.*;
 import net.minecraft.block.Block;
 import net.minecraft.entity.Entity;
 import net.minecraft.entity.MoverType;
@@ -40,6 +37,7 @@
 import net.minecraft.world.World;
 import net.minecraftforge.common.util.Constants;
 import net.minecraftforge.items.IItemHandlerModifiable;
+import net.minecraftforge.items.wrapper.InvWrapper;
 
 import javax.annotation.Nonnull;
 import java.util.*;
@@ -53,6 +51,9 @@ public class TurtleBrain implements ITurtleAccess
     private ComputerProxy m_proxy;
     private GameProfile m_owningPlayer;
 
+    private final IInventory m_inventory = (InventoryDelegate) () -> m_owner;
+    private final IItemHandlerModifiable m_inventoryWrapper = new InvWrapper( m_inventory );
+
     private Queue<TurtleCommandQueueEntry> m_commandQueue = new ArrayDeque<>();
     private int m_commandsIssued = 0;
 
@@ -531,14 +532,14 @@ public void setSelectedSlot( int slot )
     @Override
     public IInventory getInventory()
     {
-        return m_owner;
+        return m_inventory;
     }
 
     @Nonnull
     @Override
     public IItemHandlerModifiable getItemHandler()
     {
-        return m_owner.getItemHandler();
+        return m_inventoryWrapper;
     }
 
     @Override

src/main/java/dan200/computercraft/shared/util/InventoryDelegate.java

@@ -0,0 +1,146 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2019. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+
+package dan200.computercraft.shared.util;
+
+import net.minecraft.entity.player.EntityPlayer;
+import net.minecraft.inventory.IInventory;
+import net.minecraft.item.ItemStack;
+import net.minecraft.util.text.ITextComponent;
+
+import javax.annotation.Nonnull;
+
+/**
+ * Provides a delegate over inventories.
+ *
+ * This may be used both on {@link net.minecraft.tileentity.TileEntity}s to redirect the inventory to another tile,
+ * and by other interfaces to have inventories which change their backing store.
+ */
+@FunctionalInterface
+public interface InventoryDelegate extends IInventory
+{
+    IInventory getInventory();
+
+    @Override
+    default int getSizeInventory()
+    {
+        return getInventory().getSizeInventory();
+    }
+
+    @Override
+    default boolean isEmpty()
+    {
+        return getInventory().isEmpty();
+    }
+
+    @Nonnull
+    @Override
+    default ItemStack getStackInSlot( int slot )
+    {
+        return getInventory().getStackInSlot( slot );
+    }
+
+    @Nonnull
+    @Override
+    default ItemStack decrStackSize( int slot, int count )
+    {
+        return getInventory().decrStackSize( slot, count );
+    }
+
+    @Nonnull
+    @Override
+    default ItemStack removeStackFromSlot( int slot )
+    {
+        return getInventory().removeStackFromSlot( slot );
+    }
+
+    @Override
+    default void setInventorySlotContents( int slot, ItemStack stack )
+    {
+        getInventory().setInventorySlotContents( slot, stack );
+    }
+
+    @Override
+    default int getInventoryStackLimit()
+    {
+        return getInventory().getInventoryStackLimit();
+    }
+
+    @Override
+    default void markDirty()
+    {
+        getInventory().markDirty();
+    }
+
+    @Override
+    default boolean isUsableByPlayer( @Nonnull EntityPlayer player )
+    {
+        return getInventory().isUsableByPlayer( player );
+    }
+
+    @Override
+    default void openInventory( @Nonnull EntityPlayer player )
+    {
+        getInventory().openInventory( player );
+    }
+
+    @Override
+    default void closeInventory( @Nonnull EntityPlayer player )
+    {
+        getInventory().closeInventory( player );
+    }
+
+    @Override
+    default boolean isItemValidForSlot( int slot, @Nonnull ItemStack stack )
+    {
+        return getInventory().isItemValidForSlot( slot, stack );
+    }
+
+    @Override
+    default int getField( int id )
+    {
+        return getInventory().getField( id );
+    }
+
+    @Override
+    default void setField( int id, int val )
+    {
+        getInventory().setField( id, val );
+
+    }
+
+    @Override
+    default int getFieldCount()
+    {
+        return getInventory().getFieldCount();
+    }
+
+    @Override
+    default void clear()
+    {
+        getInventory().clear();
+    }
+
+    @Nonnull
+    @Override
+    default String getName()
+    {
+        return getInventory().getName();
+    }
+
+    @Override
+    default boolean hasCustomName()
+    {
+        return getInventory().hasCustomName();
+    }
+
+    @Nonnull
+    @Override
+    default ITextComponent getDisplayName()
+    {
+        return getInventory().getDisplayName();
+    }
+}

src/main/java/dan200/computercraft/shared/util/InventoryUtil.java

@@ -69,12 +69,6 @@ public static boolean areItemsSimilar( @Nonnull ItemStack a, @Nonnull ItemStack
         return shareTagA.equals( shareTagB );
     }
 
-    @Nonnull
-    public static ItemStack copyItem( @Nonnull ItemStack a )
-    {
-        return a.copy();
-    }
-
     // Methods for finding inventories:
 
     public static IItemHandler getInventory( World world, BlockPos pos, EnumFacing side )