Convert turtle refuelling into an event

This should allow us (or other mods) to register custom refuel handlers
should they so wish.

src/main/java/dan200/computercraft/api/turtle/event/TurtleRefuelEvent.java

@@ -0,0 +1,90 @@
+/*
+ * 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.api.turtle.event;
+
+import dan200.computercraft.api.turtle.ITurtleAccess;
+import net.minecraft.item.ItemStack;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+import java.util.Objects;
+
+/**
+ * Fired when a turtle attempts to refuel from an item.
+ *
+ * One may use {@link #setCanceled(boolean, String)} to prevent refueling from this specific item. Additionally, you
+ * may use {@link #setHandler(Handler)} to register a custom fuel provider.
+ */
+public class TurtleRefuelEvent extends TurtleActionEvent
+{
+    private final ItemStack stack;
+    private Handler handler;
+
+    public TurtleRefuelEvent( @Nonnull ITurtleAccess turtle, @Nonnull ItemStack stack )
+    {
+        super( turtle, TurtleAction.REFUEL );
+
+        Objects.requireNonNull( turtle, "turtle cannot be null" );
+        this.stack = stack;
+    }
+
+    /**
+     * Get the stack we are attempting to refuel from.
+     *
+     * Do not modify the returned stack - all modifications should be done within the {@link Handler}.
+     *
+     * @return The stack to refuel from.
+     */
+    public ItemStack getStack()
+    {
+        return stack;
+    }
+
+    /**
+     * Get the refuel handler for this stack.
+     *
+     * @return The refuel handler, or {@code null} if none has currently been set.
+     * @see #setHandler(Handler)
+     */
+    @Nullable
+    public Handler getHandler()
+    {
+        return handler;
+    }
+
+    /**
+     * Set the refuel handler for this stack.
+     *
+     * You should call this if you can actually refuel from this item, and ideally only if there are no existing
+     * handlers.
+     *
+     * @param handler The new refuel handler.
+     * @see #getHandler()
+     */
+    public void setHandler( @Nullable Handler handler )
+    {
+        this.handler = handler;
+    }
+
+    /**
+     * Handles refuelling a turtle from a specific item.
+     */
+    public interface Handler
+    {
+        /**
+         * Refuel a turtle using an item.
+         *
+         * @param turtle The turtle to refuel.
+         * @param stack  The stack to refuel with.
+         * @param slot   The slot the stack resides within. This may be used to modify the inventory afterwards.
+         * @param limit  The maximum number of refuel operations to perform. This will often correspond to the number of
+         *               items to consume.
+         * @return The amount of fuel gained.
+         */
+        int refuel( @Nonnull ITurtleAccess turtle, @Nonnull ItemStack stack, int slot, int limit );
+    }
+}

src/main/java/dan200/computercraft/shared/turtle/FurnaceRefuelHandler.java

@@ -0,0 +1,61 @@
+/*
+ * 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.turtle;
+
+import dan200.computercraft.ComputerCraft;
+import dan200.computercraft.api.turtle.ITurtleAccess;
+import dan200.computercraft.api.turtle.event.TurtleRefuelEvent;
+import dan200.computercraft.shared.util.InventoryUtil;
+import dan200.computercraft.shared.util.WorldUtil;
+import net.minecraft.item.ItemStack;
+import net.minecraft.tileentity.TileEntityFurnace;
+import net.minecraftforge.fml.common.Mod;
+import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;
+
+import javax.annotation.Nonnull;
+
+@Mod.EventBusSubscriber( modid = ComputerCraft.MOD_ID )
+public final class FurnaceRefuelHandler implements TurtleRefuelEvent.Handler
+{
+    private static final FurnaceRefuelHandler INSTANCE = new FurnaceRefuelHandler();
+
+    private FurnaceRefuelHandler()
+    {
+    }
+
+    @Override
+    public int refuel( @Nonnull ITurtleAccess turtle, @Nonnull ItemStack currentStack, int slot, int limit )
+    {
+        ItemStack stack = turtle.getItemHandler().extractItem( slot, limit, false );
+        int fuelToGive = getFuelPerItem( stack ) * stack.getCount();
+
+        // Store the replacement item in the inventory
+        ItemStack replacementStack = stack.getItem().getContainerItem( stack );
+        if( !replacementStack.isEmpty() )
+        {
+            ItemStack remainder = InventoryUtil.storeItems( replacementStack, turtle.getItemHandler(), turtle.getSelectedSlot() );
+            if( !remainder.isEmpty() )
+            {
+                WorldUtil.dropItemStack( remainder, turtle.getWorld(), turtle.getPosition(), turtle.getDirection().getOpposite() );
+            }
+        }
+
+        return fuelToGive;
+    }
+
+
+    private static int getFuelPerItem( @Nonnull ItemStack stack )
+    {
+        return (TileEntityFurnace.getItemBurnTime( stack ) * 5) / 100;
+    }
+
+    @SubscribeEvent
+    public static void onTurtleRefuel( TurtleRefuelEvent event )
+    {
+        if( event.getHandler() == null && getFuelPerItem( event.getStack() ) > 0 ) event.setHandler( INSTANCE );
+    }
+}

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

@@ -10,92 +10,36 @@ import dan200.computercraft.api.turtle.ITurtleAccess;
 import dan200.computercraft.api.turtle.ITurtleCommand;
 import dan200.computercraft.api.turtle.TurtleAnimation;
 import dan200.computercraft.api.turtle.TurtleCommandResult;
-import dan200.computercraft.api.turtle.event.TurtleAction;
+import dan200.computercraft.api.turtle.event.TurtleRefuelEvent;
-import dan200.computercraft.api.turtle.event.TurtleActionEvent;
-import dan200.computercraft.shared.util.InventoryUtil;
 import net.minecraft.item.ItemStack;
-import net.minecraft.tileentity.TileEntityFurnace;
 import net.minecraftforge.common.MinecraftForge;
 
 import javax.annotation.Nonnull;
 
 public class TurtleRefuelCommand implements ITurtleCommand
 {
-    private final int m_limit;
+    private final int limit;
 
     public TurtleRefuelCommand( int limit )
     {
-        m_limit = limit;
+        this.limit = limit;
     }
 
     @Nonnull
     @Override
     public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
     {
-        if( m_limit == 0 )
+        int slot = turtle.getSelectedSlot();
+        ItemStack stack = turtle.getInventory().getStackInSlot( slot );
+        if( stack.isEmpty() ) return TurtleCommandResult.failure( "No items to combust" );
+
+        TurtleRefuelEvent event = new TurtleRefuelEvent( turtle, stack );
+        if( MinecraftForge.EVENT_BUS.post( event ) ) return TurtleCommandResult.failure( event.getFailureMessage() );
+        if( event.getHandler() == null ) return TurtleCommandResult.failure( "Items not combustible" );
+
+        if( limit != 0 )
         {
-            // If limit is zero, just check the item is combustible
+            turtle.addFuel( event.getHandler().refuel( turtle, stack, slot, limit ) );
-            ItemStack dummyStack = turtle.getInventory().getStackInSlot( turtle.getSelectedSlot() );
-            if( !dummyStack.isEmpty() )
-            {
-                return refuel( turtle, dummyStack, true );
-            }
-        }
-        else
-        {
-            // Otherwise, refuel for real
-            // Remove items from inventory
-            ItemStack stack = InventoryUtil.takeItems( m_limit, turtle.getItemHandler(), turtle.getSelectedSlot(), 1, turtle.getSelectedSlot() );
-            if( !stack.isEmpty() )
-            {
-                TurtleCommandResult result = refuel( turtle, stack, false );
-                if( !result.isSuccess() )
-                {
-                    // If the items weren't burnt, put them back
-                    InventoryUtil.storeItems( stack, turtle.getItemHandler(), turtle.getSelectedSlot() );
-                }
-                return result;
-            }
-        }
-        return TurtleCommandResult.failure( "No items to combust" );
-    }
-
-    private int getFuelPerItem( @Nonnull ItemStack stack )
-    {
-        return (TileEntityFurnace.getItemBurnTime( stack ) * 5) / 100;
-    }
-
-    private TurtleCommandResult refuel( ITurtleAccess turtle, @Nonnull ItemStack stack, boolean testOnly )
-    {
-        // Check if item is fuel
-        int fuelPerItem = getFuelPerItem( stack );
-        if( fuelPerItem <= 0 )
-        {
-            return TurtleCommandResult.failure( "Items not combustible" );
-        }
-
-        TurtleActionEvent event = new TurtleActionEvent( turtle, TurtleAction.REFUEL );
-        if( MinecraftForge.EVENT_BUS.post( event ) )
-        {
-            return TurtleCommandResult.failure( event.getFailureMessage() );
-        }
-
-        if( !testOnly )
-        {
-            // Determine fuel to give and replacement item to leave behind
-            int fuelToGive = fuelPerItem * stack.getCount();
-            ItemStack replacementStack = stack.getItem().getContainerItem( stack );
-
-            // Update fuel level
-            turtle.addFuel( fuelToGive );
-
-            // Store the replacement item in the inventory
-            if( !replacementStack.isEmpty() )
-            {
-                InventoryUtil.storeItems( replacementStack, turtle.getItemHandler(), turtle.getSelectedSlot() );
-            }
-
-            // Animate
             turtle.playAnimation( TurtleAnimation.Wait );
         }