Core/Movement: Fix issues where creatures cancel spell casts chasing target and Implement SPELL_ATTR5_CAN_CHANNEL_WHEN_MOVING

(cherry picked from commit bf2cee8cce39e64590dc68bc35e5d3d2dd19cbaf)

src/server/game/Entities/Unit/Unit.cpp

@@ -2983,6 +2983,15 @@ int32 Unit::GetCurrentSpellCastTime(uint32 spell_id) const
     return 0;
 }
 
+bool Unit::CanMoveDuringChannel() const
+{
+    if (Spell* spell = m_currentSpells[CURRENT_CHANNELED_SPELL])
+        if (spell->getState() != SPELL_STATE_FINISHED)
+            return spell->GetSpellInfo()->HasAttribute(SPELL_ATTR5_CAN_CHANNEL_WHEN_MOVING) && spell->IsChannelActive();
+
+    return false;
+}
+
 bool Unit::isInFrontInMap(Unit const* target, float distance,  float arc) const
 {
     return IsWithinDistInMap(target, distance) && HasInArc(arc, target);

src/server/game/Entities/Unit/Unit.h

@@ -1957,6 +1957,9 @@ class TC_GAME_API Unit : public WorldObject
         virtual SpellInfo const* GetCastSpellInfo(SpellInfo const* spellInfo) const;
         uint32 GetCastSpellXSpellVisualId(SpellInfo const* spellInfo) const;
 
+        // Check if our current channel spell has attribute SPELL_ATTR5_CAN_CHANNEL_WHEN_MOVING
+        bool CanMoveDuringChannel() const;
+
         SpellHistory* GetSpellHistory() { return _spellHistory; }
         SpellHistory const* GetSpellHistory() const { return _spellHistory; }
 

src/server/game/Miscellaneous/SharedDefines.h

@@ -540,7 +540,7 @@ enum SpellAttr4
 
 enum SpellAttr5
 {
-    SPELL_ATTR5_UNK0                             = 0x00000001, //  0
+    SPELL_ATTR5_CAN_CHANNEL_WHEN_MOVING          = 0x00000001, //  0 available casting channel spell when moving
     SPELL_ATTR5_NO_REAGENT_WHILE_PREP            = 0x00000002, //  1 not need reagents if UNIT_FLAG_PREPARATION
     SPELL_ATTR5_UNK2                             = 0x00000004, //  2
     SPELL_ATTR5_USABLE_WHILE_STUNNED             = 0x00000008, //  3 usable while stunned

src/server/game/Movement/MovementGenerators/TargetedMovementGenerator.cpp

@@ -36,6 +36,9 @@ void TargetedMovementGeneratorMedium<T, D>::_setTargetLocation(T* owner, bool up
     if (owner->HasUnitState(UNIT_STATE_NOT_MOVE))
         return;
 
+    if (owner->HasUnitState(UNIT_STATE_CASTING) && !owner->CanMoveDuringChannel())
+        return;
+
     if (owner->GetTypeId() == TYPEID_UNIT && !i_target->isInAccessiblePlaceFor(owner->ToCreature()))
     {
         owner->ToCreature()->SetCannotReachTarget(true);
@@ -146,7 +149,7 @@ bool TargetedMovementGeneratorMedium<T, D>::DoUpdate(T* owner, uint32 time_diff)
     }
 
     // prevent movement while casting spells with cast time or channel time
-    if (owner->HasUnitState(UNIT_STATE_CASTING))
+    if (owner->HasUnitState(UNIT_STATE_CASTING) && !owner->CanMoveDuringChannel())
     {
         if (!owner->IsStopped())
             owner->StopMoving();

src/server/game/Spells/Spell.cpp

@@ -3036,14 +3036,19 @@ void Spell::prepare(SpellCastTargets const* targets, AuraEffect const* triggered
         }
 
     // don't allow channeled spells / spells with cast time to be cast while moving
+    // exception are only channeled spells that have no casttime and SPELL_ATTR5_CAN_CHANNEL_WHEN_MOVING
     // (even if they are interrupted on moving, spells with almost immediate effect get to have their effect processed before movement interrupter kicks in)
     // don't cancel spells which are affected by a SPELL_AURA_CAST_WHILE_WALKING effect
     if (((m_spellInfo->IsChanneled() || m_casttime) && m_caster->GetTypeId() == TYPEID_PLAYER && m_caster->isMoving() &&
         m_spellInfo->InterruptFlags & SPELL_INTERRUPT_FLAG_MOVEMENT) && !m_caster->HasAuraTypeWithAffectMask(SPELL_AURA_CAST_WHILE_WALKING, m_spellInfo))
     {
-        SendCastResult(SPELL_FAILED_MOVING);
-        finish(false);
-        return;
+        // 1. Is a channel spell, 2. Has no casttime, 3. And has flag to allow movement during channel
+        if (!(m_spellInfo->IsChanneled() && !m_casttime && m_spellInfo->HasAttribute(SPELL_ATTR5_CAN_CHANNEL_WHEN_MOVING)))
+        {
+            SendCastResult(SPELL_FAILED_MOVING);
+            finish(false);
+            return;
+        }
     }
 
     // set timer base at cast time
@@ -3589,7 +3594,7 @@ void Spell::update(uint32 difftime)
         !m_caster->HasAuraTypeWithAffectMask(SPELL_AURA_CAST_WHILE_WALKING, m_spellInfo))
     {
         // don't cancel for melee, autorepeat, triggered and instant spells
-        if (!IsNextMeleeSwingSpell() && !IsAutoRepeat() && !IsTriggered())
+        if (!IsNextMeleeSwingSpell() && !IsAutoRepeat() && !IsTriggered() && !(IsChannelActive() && m_spellInfo->HasAttribute(SPELL_ATTR5_CAN_CHANNEL_WHEN_MOVING)))
             cancel();
     }