fixes #530

now it checks if all stacks can be inserted together and not just inserted

src/main/java/com/raoulvdberge/refinedstorage/apiimpl/autocrafting/task/CraftingStepProcess.java

@@ -12,6 +12,10 @@ import net.minecraftforge.items.IItemHandler;
 import net.minecraftforge.items.ItemHandlerHelper;
 
 import java.util.Deque;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
 
 public class CraftingStepProcess extends CraftingStep {
     public static final String ID = "process";
@@ -28,17 +32,18 @@ public class CraftingStepProcess extends CraftingStep {
     public boolean canStartProcessing(IItemStackList items, IFluidStackList fluids) {
         IItemHandler inventory = getPattern().getContainer().getFacingInventory();
         if (inventory != null) {
+            Deque<ItemStack> toInsert = new LinkedList<>();
             for (ItemStack stack : getToInsert()) {
                 ItemStack actualStack = items.get(stack, IComparer.COMPARE_DAMAGE | IComparer.COMPARE_NBT | (pattern.isOredict() ? IComparer.COMPARE_OREDICT : 0));
-
+                ItemStack removeStack = ItemHandlerHelper.copyStackWithSize(actualStack, stack.stackSize);
-                boolean canInsert = ItemHandlerHelper.insertItem(inventory, ItemHandlerHelper.copyStackWithSize(actualStack, stack.stackSize), true) == null;
+                if (actualStack == null || actualStack.stackSize == 0 || !items.trackedRemove(removeStack, true) ) {
-                if (actualStack == null || actualStack.stackSize == 0 || !items.trackedRemove(actualStack, stack.stackSize, true) || !canInsert) {
                     items.undo();
                     return false;
                 }
+                toInsert.add(removeStack.copy());
             }
             items.undo();
-            return true;
+            return insertSimulation(inventory, toInsert);
         }
         return false;
     }
@@ -71,4 +76,34 @@ public class CraftingStepProcess extends CraftingStep {
 
         return super.writeToNBT(tag);
     }
+
+    /**
+     * Checks whether all stacks can be inserted or not
+     *
+     * @param dest target {@link IItemHandler}
+     * @param stacks a {@link Deque} of {@link ItemStack}s
+     * @return true when all can be inserted, false otherwise
+     */
+    private static boolean insertSimulation(IItemHandler dest, Deque<ItemStack> stacks) {
+        ItemStack current = stacks.poll();
+        List<Integer> availableSlots = IntStream.range(0, dest.getSlots()).boxed().collect(Collectors.toList());
+        while (current != null  && !availableSlots.isEmpty()) {
+            ItemStack remainder = null;
+            for (Integer slot : availableSlots) {
+                remainder = dest.insertItem(slot, current, true);
+                if (remainder == null || current.stackSize != remainder.stackSize) {
+                    availableSlots.remove(slot);
+                    break;
+                }
+            }
+            if (remainder == null || remainder.stackSize <= 0) {
+                current = stacks.poll();
+            } else if (current.stackSize == remainder.stackSize) {
+                break; // Can't be inserted
+            } else {
+                current = remainder;
+            }
+        }
+        return current == null && stacks.isEmpty();
+    }
 }