Improper singletons migration to clean Meyer's singletons (cherry-pick) (#2082)

# Pull Request

- Applies the clean and corrected singletons, Meyer pattern. (cherry
picked from @SmashingQuasar )

Testing by just playing the game in various ways. Been tested by myself
@Celandriel and @SmashingQuasar
---

## Complexity & Impact

- Does this change add new decision branches?
    - [x] No
    - [ ] Yes (**explain below**)

- Does this change increase per-bot or per-tick processing?
    - [x] No
    - [ ] Yes (**describe and justify impact**)

- Could this logic scale poorly under load?
    - [x] No
    - [ ] Yes (**explain why**)

---

## Defaults & Configuration

- Does this change modify default bot behavior?
    - [x] No
    - [ ] Yes (**explain why**)

---

## AI Assistance

- Was AI assistance (e.g. ChatGPT or similar tools) used while working
on this change?
    - [x] No
    - [ ] Yes (**explain below**)
---

## Final Checklist

- [x] Stability is not compromised
- [x] Performance impact is understood, tested, and acceptable
- [x] Added logic complexity is justified and explained
- [x] Documentation updated if needed

---

## Notes for Reviewers

Anything that significantly improves realism at the cost of stability or
performance should be carefully discussed
before merging.

---------

Co-authored-by: Nicolas Lebacq <nicolas.cordier@outlook.com>
Co-authored-by: Keleborn <22352763+Celandriel@users.noreply.github.com>

src/Db/FlightMasterCache.h

@@ -8,10 +8,11 @@
 class FlightMasterCache
 {
 public:
-    static FlightMasterCache* Instance()
+    static FlightMasterCache& Instance()
     {
         static FlightMasterCache instance;
-        return &instance;
+
+        return instance;
     }
 
     Creature* GetNearestFlightMaster(Player* bot);
@@ -19,9 +20,17 @@ public:
     void AddAllianceFlightMaster(uint32 entry, WorldPosition pos);
 
 private:
+    FlightMasterCache() = default;
+    ~FlightMasterCache() = default;
+
+    FlightMasterCache(const FlightMasterCache&) = delete;
+    FlightMasterCache& operator=(const FlightMasterCache&) = delete;
+
+    FlightMasterCache(FlightMasterCache&&) = delete;
+    FlightMasterCache& operator=(FlightMasterCache&&) = delete;
+
     std::map<uint32, WorldPosition> allianceFlightMasterCache;
     std::map<uint32, WorldPosition> hordeFlightMasterCache;
 };
 
-#define sFlightMasterCache FlightMasterCache::Instance()
 #endif

src/Db/PlayerbotDungeonRepository.cpp

@@ -3,9 +3,15 @@
  * and/or modify it under version 3 of the License, or (at your option), any later version.
  */
 
-#include "PlayerbotDungeonRepository.h"
+#include "Log.h"
+#include "Timer.h"
+#include "DatabaseEnv.h"
+#include "Field.h"
+#include "World.h"
+// Required import due to poor implementation by AC
+#include "QueryResult.h"
 
-#include "Playerbots.h"
+#include "PlayerbotDungeonRepository.h"
 
 std::vector<DungeonSuggestion> const PlayerbotDungeonRepository::GetDungeonSuggestions()
 {

src/Db/PlayerbotDungeonRepository.h

@@ -6,10 +6,9 @@
 #ifndef _PLAYERBOT_PLAYERBOTDUNGEONREPOSITORY_H
 #define _PLAYERBOT_PLAYERBOTDUNGEONREPOSITORY_H
 
-#include <map>
 #include <vector>
+#include <string>
 
-#include "Common.h"
 #include "DBCEnums.h"
 
 struct DungeonSuggestion
@@ -22,24 +21,31 @@ struct DungeonSuggestion
     std::string strategy;
 };
 
+// @TODO: Completely unused at this moment.
 class PlayerbotDungeonRepository
 {
 public:
-    PlayerbotDungeonRepository(){};
-    ~PlayerbotDungeonRepository(){};
-    static PlayerbotDungeonRepository* instance()
+    static PlayerbotDungeonRepository& instance()
     {
         static PlayerbotDungeonRepository instance;
-        return &instance;
+
+        return instance;
     }
 
     void LoadDungeonSuggestions();
     std::vector<DungeonSuggestion> const GetDungeonSuggestions();
 
 private:
+    PlayerbotDungeonRepository() = default;
+    ~PlayerbotDungeonRepository() = default;
+
+    PlayerbotDungeonRepository(const PlayerbotDungeonRepository&) = delete;
+    PlayerbotDungeonRepository& operator=(const PlayerbotDungeonRepository&) = delete;
+
+    PlayerbotDungeonRepository(PlayerbotDungeonRepository&&) = delete;
+    PlayerbotDungeonRepository& operator=(PlayerbotDungeonRepository&&) = delete;
+
     std::vector<DungeonSuggestion> m_dungeonSuggestions;
 };
 
-#define sPlayerbotDungeonRepository PlayerbotDungeonRepository::instance()
-
 #endif

src/Db/PlayerbotRepository.h

@@ -6,21 +6,20 @@
 #ifndef _PLAYERBOT_PLAYERBOTREPOSITORY_H
 #define _PLAYERBOT_PLAYERBOTREPOSITORY_H
 
+#include <cstdint>
+#include <string>
 #include <vector>
 
-#include "Common.h"
-
-class PlayerbotAI;
+#include "PlayerbotAI.h"
 
 class PlayerbotRepository
 {
 public:
-    PlayerbotRepository() {}
-    virtual ~PlayerbotRepository() {}
-    static PlayerbotRepository* instance()
+    static PlayerbotRepository& instance()
     {
         static PlayerbotRepository instance;
-        return &instance;
+
+        return instance;
     }
 
     void Save(PlayerbotAI* botAI);
@@ -28,10 +27,17 @@ public:
     void Reset(PlayerbotAI* botAI);
 
 private:
-    void SaveValue(uint32 guid, std::string const key, std::string const value);
+    PlayerbotRepository() = default;
+    ~PlayerbotRepository() = default;
+
+    PlayerbotRepository(const PlayerbotRepository&) = delete;
+    PlayerbotRepository& operator=(const PlayerbotRepository&) = delete;
+
+    PlayerbotRepository(PlayerbotRepository&&) = delete;
+    PlayerbotRepository& operator=(PlayerbotRepository&&) = delete;
+
+    void SaveValue(uint32_t guid, std::string const key, std::string const value);
     std::string const FormatStrategies(std::string const type, std::vector<std::string> strategies);
 };
 
-#define sPlayerbotRepository PlayerbotRepository::instance()
-
 #endif

src/Db/PlayerbotSpellRepository.cpp

@@ -1,3 +1,10 @@
+#include "Log.h"
+#include "DBCStores.h"
+#include "DatabaseEnv.h"
+#include "Field.h"
+// Required due to poor implementation on AC side
+#include "QueryResult.h"
+
 #include "PlayerbotSpellRepository.h"
 
 //  caches the result set

src/Db/PlayerbotSpellRepository.h

@@ -6,29 +6,37 @@
 #ifndef _PLAYERBOT_PLAYERBOTSPELLREPOSITORY_H
 #define _PLAYERBOT_PLAYERBOTSPELLREPOSITORY_H
 
-#include "Playerbots.h"
+#include <cstdint>
+
+#include "DBCStructure.h"
 
 class PlayerbotSpellRepository
 {
 public:
-    static PlayerbotSpellRepository* Instance()
+    static PlayerbotSpellRepository& Instance()
     {
         static PlayerbotSpellRepository instance;
-        return &instance;
+
+        return instance;
     }
 
-    void Initialize(); // call once on startup
+    void Initialize();
 
-    SkillLineAbilityEntry const* GetSkillLine(uint32 spellId) const;
-    bool IsItemBuyable(uint32 itemId) const;
+    SkillLineAbilityEntry const* GetSkillLine(uint32_t spellId) const;
+    bool IsItemBuyable(uint32_t itemId) const;
 
 private:
     PlayerbotSpellRepository() = default;
+    ~PlayerbotSpellRepository() = default;
 
-    std::map<uint32, SkillLineAbilityEntry const*> skillSpells;
-    std::set<uint32> vendorItems;
+    PlayerbotSpellRepository(const PlayerbotSpellRepository&) = delete;
+    PlayerbotSpellRepository& operator=(const PlayerbotSpellRepository&) = delete;
+
+    PlayerbotSpellRepository(PlayerbotSpellRepository&&) = delete;
+    PlayerbotSpellRepository& operator=(PlayerbotSpellRepository&&) = delete;
+
+    std::map<uint32_t, SkillLineAbilityEntry const*> skillSpells;
+    std::set<uint32_t> vendorItems;
 };
 
-#define sPlayerbotSpellRepository PlayerbotSpellRepository::Instance()
-
 #endif