Add wielded, wieldable items

Split the character's inventory up into wielded items (in one or both
hands) and the backpack, and display wielded items when drawing the
inventory panel. Currently there's no way to actually *wield* items
though, so this is all unused/untested.

Also, add the ability for items to be "wieldable", which gives specific
descriptions for when attacking with them and also modified damage.

src/Xanthous/Game/Draw.hs

@@ -14,6 +14,7 @@ import           Xanthous.Data.EntityMap (EntityMap, atPosition)
 import qualified Xanthous.Data.EntityMap as EntityMap
 import           Xanthous.Game.State
 import           Xanthous.Entities.Character
+import           Xanthous.Entities.Item (Item)
 import           Xanthous.Game
                  ( GameState(..)
                  , entities
@@ -105,16 +106,36 @@ drawPanel game panel
   . viewport (Resource.Panel panel) Vertical
   $ case panel of
       InventoryPanel ->
-        let items = game ^. character . inventory
-        in if null items
-           then txtWrap "Your inventory is empty right now."
-           else
-             txtWrap "You are currently carrying the following items:"
-             <=> txt " "
-             <=> foldl' (<=>) emptyWidget
-                 (map
-                  (txtWrap . ((bullet <| " ") <>) . description)
-                  items)
+        drawWielded (game ^. character . inventory . wielded)
+        <=> drawBackpack (game ^. character . inventory . backpack)
+  where
+    drawWielded :: Wielded -> Widget Name
+    drawWielded (Hands Nothing Nothing) = emptyWidget
+    drawWielded (DoubleHanded i) =
+      txt $ "You are holding " <> description i <> " in both hands"
+    drawWielded (Hands l r) =
+      maybe
+        emptyWidget
+        (\i ->
+           txt $ "You are holding " <> description i <> " in your left hand")
+        l
+      <=>
+      maybe
+        emptyWidget
+        (\i ->
+           txt $ "You are holding " <> description i <> " in your right hand")
+        r
+
+    drawBackpack :: Vector Item -> Widget Name
+    drawBackpack Empty = txtWrap "Your backpack is empty right now."
+    drawBackpack backpackItems
+      = txtWrap ( "You are currently carrying the following items in your "
+                <> "backpack:")
+        <=> txt " "
+        <=> foldl' (<=>) emptyWidget
+            (map
+              (txtWrap . ((bullet <| " ") <>) . description)
+              backpackItems)
 
 drawCharacterInfo :: Character -> Widget Name
 drawCharacterInfo ch = txt " " <+> charName <+> charHitpoints