fix: various backpack related issues

- client not opening backpack gui
- server crashing when client tries to open
- backpack slot blacklist not being enforced
- inventory not saving properly

src/exploration/java/mrtjp/projectred/exploration/gui/screen/inventory/BackpackScreen.java

@@ -16,11 +16,10 @@ public class BackpackScreen extends RedUIContainerScreen<BackpackContainer> {
     public static final ResourceLocation BACKGROUND = new ResourceLocation(MOD_ID, "textures/gui/backpack.png");
 
     public BackpackScreen(BackpackContainer container, PlayerInventory playerInventory, ITextComponent title) {
-        super(176, 68, container, playerInventory, title);
+        super(176, 168, container, playerInventory, title);
 
         inventoryLabelX = 8;
         inventoryLabelY = 75;
-
     }
 
     @Override

src/exploration/java/mrtjp/projectred/exploration/init/ExplorationClientInit.java

@@ -2,13 +2,23 @@
 
 import mrtjp.projectred.exploration.gui.screen.inventory.BackpackScreen;
 import net.minecraft.client.gui.ScreenManager;
+import net.minecraftforge.eventbus.api.IEventBus;
+import net.minecraftforge.fml.event.lifecycle.FMLClientSetupEvent;
+import net.minecraftforge.fml.javafmlmod.FMLJavaModLoadingContext;
 
 import static mrtjp.projectred.exploration.init.ExplorationReferences.BACKPACK_CONTAINER;
 
 public class ExplorationClientInit {
 
     public static void init() {
+        final IEventBus modEventBus = FMLJavaModLoadingContext.get().getModEventBus();
 
+        modEventBus.addListener(ExplorationClientInit::clientSetup);
+    }
+
+    private static void clientSetup(final FMLClientSetupEvent event) {
+
+        // Register screens
         ScreenManager.register(BACKPACK_CONTAINER, BackpackScreen::new);
     }
 }

src/exploration/java/mrtjp/projectred/exploration/inventory/BackpackInventory.java

@@ -31,4 +31,9 @@ public void saveInventoryToMainHand(PlayerInventory playerInventory) {
             BackpackItem.saveBackpackInventory(backpack, inventoryTag);
         }
     }
+
+    @Override
+    public boolean canPlaceItem(int slot, ItemStack stack) {
+        return BackpackItem.isItemAllowedInBackpack(stack);
+    }
 }

src/exploration/java/mrtjp/projectred/exploration/inventory/container/BackpackContainer.java

@@ -9,6 +9,7 @@
 import net.minecraft.inventory.IInventory;
 import net.minecraft.inventory.container.ClickType;
 import net.minecraft.inventory.container.Container;
+import net.minecraft.inventory.container.Slot;
 import net.minecraft.item.ItemStack;
 
 import static mrtjp.projectred.exploration.init.ExplorationReferences.BACKPACK_CONTAINER;
@@ -26,31 +27,41 @@ public BackpackContainer(int windowId, PlayerInventory playerInventory) {
 
         this.playerInventory = playerInventory;
 
-        InventoryLib.addPlayerInventory(playerInventory, 8, 86, this::addSlot);
-        InventoryLib.addInventory(inventory, 0, 8, 18, 9, 3, this::addSlot);
+        InventoryLib.addPlayerInventory(playerInventory, 8, 86, BackpackPlayerSlot::new, this::addSlot);
+        InventoryLib.addInventory(inventory, 0, 8, 18, 9, 3, BackpackSlot::new, this::addSlot);
 
         inventory.addListener(this::onBackpackInventoryChanged);
         inventory.loadInventoryFromMainHand(playerInventory);
     }
 
     @Override
     public ItemStack clicked(int slotId, int dragType, ClickType clickType, PlayerEntity player) {
-        return super.clicked(slotId, dragType, clickType, player);
-    }
+        // Required because vanilla's shyte handling of number hotbar quick swap.
+        // Apparently it only asks the target slot (the one hovered over) if it can accept the item, but it does not ask the
+        // hotbar slot (corresponding to number pressed) if it can take the stack (which would be denied by the custom slot class's canTakeStack implemented above).
+        // Additionally, if the target slot is empty, it calls that empty slot's canTakeStack. This is almost certainly
+        // a bug. canTakeStack should be called on BOTH slots, and isItemValid should be called on BOTH slots with the other slots contents.
 
-    @Override
-    public void slotsChanged(IInventory inventory) {
-        super.slotsChanged(inventory);
-        //TODO save bag on server
-        // Note: Not reliable, not always called
+        if (isHotbar(slotId)) {
+            int hotbarIndex = slotId - 27;
+            if (hotbarIndex == player.inventory.selected) {
+                return ItemStack.EMPTY;
+            }
+        }
+
+        if (clickType == ClickType.SWAP) {
+            if (dragType == player.inventory.selected) {
+                return ItemStack.EMPTY;
+            }
+        }
+
+        return super.clicked(slotId, dragType, clickType, player);
     }
 
     @Override
     public void removed(PlayerEntity player) {
         super.removed(player);
-        if (!player.level.isClientSide) {
-            inventory.saveInventoryToMainHand(playerInventory);
-        }
+        inventory.saveInventoryToMainHand(playerInventory);
     }
 
     @Override
@@ -60,6 +71,87 @@ public boolean stillValid(PlayerEntity player) {
     }
 
     protected void onBackpackInventoryChanged(IInventory backpackInventory) {
-        //TODO save bag on server
+        // Note: no need to save here. Inventory is saved on container close
+    }
+
+    @Override
+    public ItemStack quickMoveStack(PlayerEntity player, int slotIndex) {
+        Slot slot = slots.get(slotIndex);
+        if (slot == null || !slot.hasItem()) return ItemStack.EMPTY;
+
+        ItemStack stack = slot.getItem();
+        ItemStack originalStack = stack.copy();
+
+        if (isBag(slotIndex)) {
+            if (!moveToEntireInventory(stack, true)) return ItemStack.EMPTY;
+        } else {
+            if (!moveToBag(stack, false)) return ItemStack.EMPTY;
+        }
+
+        if (stack.isEmpty()) {
+            slot.set(ItemStack.EMPTY);
+        } else {
+            slot.setChanged();
+        }
+
+        if (stack.getCount() == originalStack.getCount()) {
+            return ItemStack.EMPTY;
+        }
+
+        slot.onTake(player, stack);
+        return originalStack;
+    }
+
+    //@formatter:off
+    private boolean isPlayerInventory(int slotIndex) {
+        return slotIndex >= 0 && slotIndex < 27;
+    }
+    private boolean isHotbar(int slotIndex) {
+        return slotIndex >= 27 && slotIndex < 36;
+    }
+    private boolean isBag(int slotIndex) {
+        return slotIndex >= 36 && slotIndex < 63;
+    }
+
+    private boolean moveToPlayerInventory(ItemStack stack, boolean reverse) {
+        return moveItemStackTo(stack, 0, 27, reverse);
+    }
+    private boolean moveToHotbar(ItemStack stack, boolean reverse) {
+        return moveItemStackTo(stack, 27, 36, reverse);
+    }
+    private boolean moveToEntireInventory(ItemStack stack, boolean reverse) {
+        return moveItemStackTo(stack, 0, 36, reverse);
+    }
+    private boolean moveToBag(ItemStack stack, boolean reverse) {
+        return moveItemStackTo(stack, 36, 63, reverse);
+    }
+    //@formatter:on
+
+    /**
+     * Slot for the actual player inventory. Disables picking up backpack from hotbar.
+     */
+    private static class BackpackPlayerSlot extends Slot {
+        public BackpackPlayerSlot(IInventory inventory, int slotIndex, int x, int y) {
+            super(inventory, slotIndex, x, y);
+        }
+        @Override
+        public boolean mayPickup(PlayerEntity player) {
+            // Dont allow pickup if this is the slot containing the selected backpack
+            return getSlotIndex() != player.inventory.selected;
+        }
+    }
+
+    /**
+     * Slot for the backpack contents inventory. Enforces the backpack blacklist.
+     */
+    private static class BackpackSlot extends Slot {
+        public BackpackSlot(IInventory inventory, int slotIndex, int x, int y) {
+            super(inventory, slotIndex, x, y);
+        }
+
+        @Override
+        public boolean mayPlace(ItemStack stack) {
+            return BackpackItem.isItemAllowedInBackpack(stack);
+        }
     }
 }

src/exploration/java/mrtjp/projectred/exploration/item/BackpackItem.java

@@ -3,6 +3,7 @@
 import codechicken.lib.util.ServerUtils;
 import mrtjp.projectred.ProjectRedExploration;
 import mrtjp.projectred.core.inventory.BaseInventory;
+import mrtjp.projectred.exploration.init.ExplorationTags;
 import mrtjp.projectred.exploration.inventory.container.BackpackContainer;
 import net.minecraft.client.util.ITooltipFlag;
 import net.minecraft.entity.player.PlayerEntity;
@@ -17,6 +18,9 @@
 import net.minecraft.util.ActionResultType;
 import net.minecraft.util.Hand;
 import net.minecraft.util.text.ITextComponent;
+import net.minecraft.util.text.StringTextComponent;
+import net.minecraft.util.text.TextFormatting;
+import net.minecraft.util.text.TranslationTextComponent;
 import net.minecraft.world.World;
 
 import javax.annotation.Nullable;
@@ -58,12 +62,13 @@ public ActionResult<ItemStack> use(World world, PlayerEntity player, Hand hand)
     private void openGui(ServerPlayerEntity player) {
         ServerUtils.openContainer(player,
                 new SimpleNamedContainerProvider((windowId, playerInventory, playerEntity) -> new BackpackContainer(windowId, playerInventory),
-                        getDescription()));
+                        new TranslationTextComponent(this.getDescriptionId())));
     }
 
     @Override
     public void appendHoverText(ItemStack stack, @Nullable World world, List<ITextComponent> tooltip, ITooltipFlag flag) {
-        super.appendHoverText(stack, world, tooltip, flag);
+        int itemCount = getBackpackItemCount(stack);
+        tooltip.add(new StringTextComponent(itemCount + " / 27").withStyle(TextFormatting.GRAY));
     }
 
     public DyeColor getDyeColor() {
@@ -101,4 +106,8 @@ public static void deleteBackpackInventory(ItemStack stack) {
             stack.getTag().remove(TAG_INVENTORY);
         }
     }
+
+    public static boolean isItemAllowedInBackpack(ItemStack stack) {
+        return !ExplorationTags.BACKPACKS_DISALLOWED_TAG.contains(stack.getItem());
+    }
 }