Update spell book requirements when refreshing stash items

Source/items.cpp

@@ -4626,6 +4626,23 @@ void Item::setNewAnimation(bool showAnimation)
 	}
 }
 
+void Item::updateRequiredStatsCacheForPlayer(const Player &player)
+{
+	if (_itype == ItemType::Misc && _iMiscId == IMISC_BOOK) {
+		_iMinMag = spelldata[_iSpell].sMinInt;
+		int8_t spellLevel = player._pSplLvl[_iSpell];
+		while (spellLevel != 0) {
+			_iMinMag += 20 * _iMinMag / 100;
+			spellLevel--;
+			if (_iMinMag + 20 * _iMinMag / 100 > 255) {
+				_iMinMag = 255;
+				spellLevel = 0;
+			}
+		}
+	}
+	_iStatFlag = player.CanUseItem(*this);
+}
+
 void initItemGetRecords()
 {
 	memset(itemrecord, 0, sizeof(itemrecord));

Source/items.h

@@ -171,6 +171,9 @@ enum icreateinfo_flag2 {
 // All item animation frames have this width.
 constexpr int ItemAnimWidth = 96;
 
+// Defined in player.h, forward declared here to allow for functions which operate in the context of a player.
+struct Player;
+
 struct Item {
 	/** Randomly generated identifier */
 	int32_t _iSeed = 0;
@@ -414,6 +417,12 @@ struct Item {
 	 * @param showAnimation Definies if the Animation (Flipping) is shown or if only the final Frame (item on the ground) is shown
 	 */
 	void setNewAnimation(bool showAnimation);
+
+	/**
+	 * @brief If this item is a spell book, calculates the magic requirement to learn a new level, then for all items sets _iStatFlag
+	 * @param player Player to compare stats against requirements
+	 */
+	void updateRequiredStatsCacheForPlayer(const Player &player);
 };
 
 struct ItemGetRecordStruct {
@@ -429,8 +438,6 @@ struct CornerStoneStruct {
 	Item item;
 };
 
-struct Player;
-
 /** Contains the items on ground in the current game. */
 extern Item Items[MAXITEMS + 1];
 extern uint8_t ActiveItems[MAXITEMS];

Source/qol/stash.cpp

@@ -561,7 +561,7 @@ void StashStruct::PreviousPage(unsigned offset)
 void StashStruct::RefreshItemStatFlags()
 {
 	for (auto &item : Stash.stashList) {
-		item._iStatFlag = MyPlayer->CanUseItem(item);
+		item.updateRequiredStatsCacheForPlayer(*MyPlayer);
 	}
 }