feat(vf): add SlotFilter and StackSlot

core/include/vf/ContainerMenu.h

@@ -0,0 +1,160 @@
+#pragma once
+
+#include <cstdint>
+#include <vector>
+
+#include "Container.h"
+#include "Crafting.h"
+#include "ItemStack.h"
+
+namespace vf {
+
+// A menu is the screen an open container puts in front of the player. It does
+// not replace Container: a Container is still the storage that lives in the
+// world and that hoppers, droppers and comparators read. The menu binds one for
+// the duration of the screen, adds the player's own sections next to it, and
+// gives every cell a role and an admission rule.
+
+// What a slot is willing to accept. The result of a craft, a smelt or a trade
+// takes Nothing, which is what makes it take-only.
+struct SlotFilter {
+    enum class Kind : uint8_t {
+        Any,
+        Nothing,
+        Fuel,           // furnace fuel, per Crafting.h isFuel
+        Smeltable,      // has a smelting recipe in the bound registry
+        Lapis,          // enchanting table payment
+        Enchantable,    // enchantabilityOf > 0
+        Repairable,     // anvil input: tools carry durability, so they repair
+        BrewIngredient, // the brewing ingredients that exist as items here
+        Count
+    };
+
+    Kind kind = Kind::Any;
+
+    // `registry` is only consulted by Smeltable; every other kind answers from
+    // the item tables alone and accepts a null registry.
+    bool accepts(const MetaStack& stack, const CraftingRegistry* registry) const;
+};
+
+const char* slotFilterKindName(SlotFilter::Kind kind);
+
+// One storage cell: a stack plus a cap. `capacity` of zero defers to the item's
+// own limit, anything else clamps below it (a brewing bottle holds exactly one).
+struct StackSlot {
+    MetaStack stack;
+    int capacity = 0;
+
+    bool empty() const { return stack.empty(); }
+    int limitFor(const MetaStack& candidate) const;
+    int room(const MetaStack& candidate) const;
+
+    // Merges what fits from `incoming`, leaving the rest in it. Returns moved.
+    int insert(MetaStack& incoming);
+    MetaStack take(int amount);
+    MetaStack takeAll();
+    MetaStack swapWith(const MetaStack& incoming);
+};
+
+enum class MenuKind : uint8_t {
+    PlayerInventory,
+    CraftingTable,
+    Chest,
+    LargeChest,
+    Furnace,
+    BrewingStand,
+    EnchantingTable,
+    Anvil,
+    Villager,
+    Hopper,
+    Count
+};
+
+const char* menuKindName(MenuKind kind);
+
+struct MenuSlot {
+    // Which part of the screen the slot belongs to. Shift-clicking moves items
+    // between the container half and the player half, so the roles have to be
+    // distinguishable at runtime, not just visually.
+    enum class Role : uint8_t {
+        Storage,        // the bound container, or the menu's own storage
+        Inventory,      // the player's three rows
+        Hotbar,         // the player's bottom row
+        CraftInput,
+        CraftResult,
+        FuelInput,
+        SmeltInput,
+        SmeltOutput,
+        BrewBottle,
+        BrewIngredient,
+        EnchantItem,
+        EnchantLapis,
+        AnvilInput,
+        AnvilResult,
+        TradeInput,
+        TradeResult,
+        OffHand,
+        Count
+    };
+
+    StackSlot cell;
+    Role role = Role::Storage;
+    SlotFilter filter;
+    // A take-only slot never accepts a placement, however empty it is.
+    bool takeOnly = false;
+    // Index into the bound Container, or -1 when the menu owns the stack.
+    int backingIndex = -1;
+};
+
+const char* menuSlotRoleName(MenuSlot::Role role);
+
+// Where each section starts and how long it is, so callers can iterate a
+// section without knowing the slot order by heart.
+struct MenuLayout {
+    MenuKind kind = MenuKind::Chest;
+
+    int storageFirst = -1;
+    int storageCount = 0;
+    int inventoryFirst = -1;
+    int inventoryCount = 0;
+    int hotbarFirst = -1;
+    int hotbarCount = 0;
+    int craftFirst = -1;
+    int craftWidth = 0;
+    int craftHeight = 0;
+    int resultSlot = -1;
+    int offHandSlot = -1;
+
+    int totalSlots = 0;
+
+    int craftCells() const { return craftWidth * craftHeight; }
+    bool hasCrafting() const { return craftFirst >= 0 && craftCells() > 0; }
+};
+
+MenuLayout layoutFor(MenuKind kind);
+
+constexpr int playerInventoryRows = 3;
+constexpr int playerInventoryColumns = 9;
+constexpr int playerInventorySlots = playerInventoryRows * playerInventoryColumns;
+constexpr int playerHotbarSlots = 9;
+
+class ContainerMenu;
+
+// The crafting half of a menu, wired to the existing CraftingRegistry. It owns
+// no stacks and no lifetime: it reads and writes the menu's craft slots in
+// place, so the grid the player sees and the grid the recipe matcher sees are
+// the same cells. A menu without a crafting section hands out a view whose
+// cellCount is zero and whose operations therefore do nothing.
+class CraftingView {
+public:
+    explicit CraftingView(ContainerMenu& menu);
+
+    int width() const;
+    int height() const;
+    int cellCount() const;
+
+    MetaStack& input(int x, int y);
+    const MetaStack& input(int x, int y) const;
+    MetaStack& inputAt(int cell);
+    const MetaStack& inputAt(int cell) const;
+