Add shop shield handling, credits counter, softlock protection

shopkeeper.asm

@@ -436,7 +436,7 @@ Shopkeeper_BuyItem:
         BRA +
     .refill
         JSL Sprite_GetEmptyBottleIndex : BMI .full_bottles
-        LDA.b #$1 : STA.l ShopkeeperRefill ; If this is on, don't toggle bit to remove from shop
+        LDA.b #$01 : STA.l ShopkeeperRefill ; If this is on, don't toggle bit to remove from shop
     +
 
         LDA.l ShopType : AND.b #$80 : BNE .buy ; don't charge if this is a take-any
@@ -453,6 +453,16 @@ Shopkeeper_BuyItem:
     LDA.b #$3C : STA.w SFX2 ; error sound
     JMP .done
     .buy
+
+    LDA.l ShopInventory, X
+    TAY
+    JSL ShieldCheck
+    BCS +
+        JMP .done
+    +
+    ; Y now has the (possibly-substituted) item ID
+
+
     LDA.l ShopType : AND.b #$80 : BNE ++ ; don't charge if this is a take-any
         REP #$20 : LDA.l CurrentRupees : !SUB.l ShopInventory+1, X : STA.l CurrentRupees : SEP #$20 ; Take price away
     ++
@@ -464,9 +474,9 @@ Shopkeeper_BuyItem:
             LDA.l EnableShopItemCount, X : STA.l ShopEnableCount ; If so, store the permission to count the item here.
         +++
     PLX
-    LDA.l ShopInventory, X
-    JSL AttemptItemSubstitution
-    TAY : JSL Link_ReceiveItem
+
+    ; Y still has item ID
+    JSL Link_ReceiveItem
     LDA.l ShopInventory+3, X : INC : STA.l ShopInventory+3, X
     LDA.b #$00 : STA.l ShopEnableCount
     TXA : LSR #2 : TAX