Core/AI: Fix assertion triggered with PetAI derived scripts (#21254)

* Core/AI: Fix assertion triggered with PetAI derived scripts

Fix an assertion triggered when spawning through ".npc add" or from SQL db table a Creature with AI set to a custom AI inheriting from PetAI.

(cherry picked from commit 95a76a83fcbad0e52c6013697544e3c5691e7e24)

4 files changed, 78 insertions, 3 deletions

diff --git a/src/server/game/AI/AIException.cpp b/src/server/game/AI/AIException.cpp
new file mode 100644
index 00000000000..3af2deda12c
--- /dev/null
+++ b/src/server/game/AI/AIException.cpp
@@ -0,0 +1,23 @@
+/*
+ * This file is part of the TrinityCore Project. See AUTHORS file for Copyright information
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "AIException.h"
+
+InvalidAIException::InvalidAIException(char const* _message)
+{
+    message().assign(_message);
+}
diff --git a/src/server/game/AI/AIException.h b/src/server/game/AI/AIException.h
new file mode 100644
index 00000000000..b3bc318a112
--- /dev/null
+++ b/src/server/game/AI/AIException.h
@@ -0,0 +1,40 @@
+/*
+ * This file is part of the TrinityCore Project. See AUTHORS file for Copyright information
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef TRINITY_AIEXCEPTION_H
+#define TRINITY_AIEXCEPTION_H
+
+#include "Define.h"
+#include <exception>
+#include <string>
+
+class TC_GAME_API InvalidAIException : public std::exception
+{
+public:
+    InvalidAIException(char const* _message);
+    ~InvalidAIException() throw() { }
+
+    char const* what() const noexcept override { return msg_.c_str(); }
+
+protected:
+    std::string & message() throw() { return msg_; }
+
+private:
+    std::string msg_;
+};
+
+#endif
diff --git a/src/server/game/AI/CoreAI/PetAI.cpp b/src/server/game/AI/CoreAI/PetAI.cpp
index 50cad20bae1..7c16b7bfa86 100644
--- a/src/server/game/AI/CoreAI/PetAI.cpp
+++ b/src/server/game/AI/CoreAI/PetAI.cpp
@@ -16,6 +16,7 @@
  */
 
 #include "PetAI.h"
+#include "AIException.h"
 #include "Creature.h"
 #include "Errors.h"
 #include "Group.h"
@@ -45,6 +46,8 @@ int32 PetAI::Permissible(Creature const* creature)
 
 PetAI::PetAI(Creature* c) : CreatureAI(c), i_tracker(TIME_INTERVAL_LOOK)
 {
+    if (!me->GetCharmInfo())
+        throw InvalidAIException("Creature doesn't have a valid charm info");
     UpdateAllies();
 }
 
@@ -153,7 +156,7 @@ void PetAI::UpdateAI(uint32 diff)
             if (!spellInfo)
                 continue;
 
-            if (me->GetCharmInfo() && me->GetSpellHistory()->HasGlobalCooldown(spellInfo))
+            if (me->GetSpellHistory()->HasGlobalCooldown(spellInfo))
                 continue;
 
             // check spell cooldown
diff --git a/src/server/game/AI/CreatureAISelector.cpp b/src/server/game/AI/CreatureAISelector.cpp
index b7181a35f76..fd298c86ed3 100644
--- a/src/server/game/AI/CreatureAISelector.cpp
+++ b/src/server/game/AI/CreatureAISelector.cpp
@@ -15,6 +15,7 @@
  * with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include "AIException.h"
 #include "Creature.h"
 #include "CreatureAISelector.h"
 #include "CreatureAIFactory.h"
@@ -83,8 +84,16 @@ namespace FactorySelector
             return ASSERT_NOTNULL(sCreatureAIRegistry->GetRegistryItem("PetAI"))->Create(creature);
 
         // scriptname in db
-        if (CreatureAI* scriptedAI = sScriptMgr->GetCreatureAI(creature))
-            return scriptedAI;
+        try
+        {
+            if (CreatureAI* scriptedAI = sScriptMgr->GetCreatureAI(creature))
+                return scriptedAI;
+        }
+        catch (InvalidAIException const& e)
+        {
+            TC_LOG_ERROR("entities.unit", "Exception trying to assign script '%s' to Creature (Entry: %u), this Creature will have a default AI. Exception message: %s",
+                creature->GetScriptName().c_str(), creature->GetEntry(), e.what());
+        }
 
         return SelectFactory<CreatureAI>(creature)->Create(creature);
     }