Optional ClassicAPI support

When ClassicAPI is installed and "Use ClassicAPI" is on (Mods tab, reload):
- Detect ClassicAPI and each feature separately; show it in the Mods tab
- Read auras with C_UnitAuras.GetAuraSlots (fill form) + UnitAuraBySlot,
  reusing entries, with ClassicAPI durations, expirations and casters
- UNIT_AURA_DELTA: refresh-only events update stacks and timers in place
  without rebuilding the aura icons or the health bar
- Aura timers without SuperWoW; native Cooldown frames with one shared
  text driver instead of a Model and OnUpdateModel per icon
- UNIT_IN_RANGE_UPDATE, UNIT_DISTANCE_CHECK_UPDATE, UNIT_CONNECTION and
  INCOMING_RESURRECT_CHANGED; UnitHasIncomingResurrection in res checks
- HealPredict learns heals from COMBAT_LOG_EVENT_UNFILTERED when the
  GUID formats match SuperWoW's
- Distance and line of sight when UnitXP SP3 and SuperWoW are missing

Without ClassicAPI, or with the option off, behaviour is unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019W3rwwTK1hwTEWHqsan2mV

core/EventHandler.lua

@@ -65,11 +65,8 @@ RegisterEventHandler({"UNIT_MANA", "UNIT_RAGE", "UNIT_ENERGY", "UNIT_FOCUS", "UN
         raidFrameGroup:RequestRaidManaUpdate()
     end
 end)
-RegisterEventHandler("UNIT_AURA", function()
-    local unit = arg1
-    if not IsRelevantUnit(unit) then
-        return
-    end
+-- Rescans the unit's auras and rebuilds its aura icons
+local function UpdateUnitAuras(unit)
     if unit == "player" then
         util.MarkSpellCostCacheDirty()
     end
@@ -78,7 +75,107 @@ RegisterEventHandler("UNIT_AURA", function()
         ui:UpdateAuras()
         ui:UpdateHealth() -- Update health because there may be an aura that changes health bar color
     end
+end
+
+-- True once UNIT_AURA_DELTA handles the real unit tokens (see RegisterClassicAPIEvents)
+local auraDeltaActive = false
+local AllRealUnitsSet = util.AllRealUnitsSet
+
+RegisterEventHandler("UNIT_AURA", function()
+    local unit = arg1
+    if not IsRelevantUnit(unit) then
+        return
+    end
+    -- ClassicAPI reports the same changes for these tokens through UNIT_AURA_DELTA, with what changed.
+    -- Other arguments (SuperWoW GUIDs of custom units) still come only through UNIT_AURA, and so do
+    -- members out of view, whose auras arrive with the party stats rather than the unit's own fields.
+    if auraDeltaActive and AllRealUnitsSet[unit] and UnitIsVisible(unit) then
+        return
+    end
+    UpdateUnitAuras(unit)
 end)
+
+-- ClassicAPI events, registered once options are loaded and the unit frames exist
+function RegisterClassicAPIEvents()
+    if util.IsClassicAPIActive("AuraDelta") then
+        auraDeltaActive = true
+        RegisterEventHandler("UNIT_AURA_DELTA", function()
+            local unit = arg1
+            if not IsRelevantUnit(unit) then
+                return
+            end
+            local info = arg2 -- Valid only during this handler
+            if info and not info.isFullUpdate and not info.addedAuraInstanceIDs and not info.removedAuraInstanceIDs then
+                -- Only refreshes and stack changes: update the timers and stacks in place
+                if PTUnit.Get(unit):RefreshClassicAuras() then
+                    if unit == "player" then
+                        util.MarkSpellCostCacheDirty()
+                    end
+                    for ui in UnitFrames(unit) do
+                        ui:RefreshAuras()
+                    end
+                    return
+                end
+            end
+            UpdateUnitAuras(unit)
+        end)
+    end
+
+    if util.IsClassicAPIActive("Resurrection") then
+        RegisterEventHandler("INCOMING_RESURRECT_CHANGED", function()
+            local unit = arg1
+            if not IsRelevantUnit(unit) then
+                return
+            end
+            for ui in UnitFrames(unit) do
+                ui:UpdateHealth()
+            end
+        end)
+    end
+
+    if util.IsClassicAPIActive("ConnectionEvent") then
+        RegisterEventHandler("UNIT_CONNECTION", function()
+            local unit = arg1
+            if not IsRelevantUnit(unit) then
+                return
+            end
+            PTUnit.Get(unit):UpdateDistance()
+            for ui in UnitFrames(unit) do
+                ui:UpdateHealth()
+                ui:UpdatePower()
+                ui:UpdateRange()
+            end
+        end)
+    end
+
+    -- Visibility and the 40 yard check change state right away instead of at the next tracking scan
+    local function UpdateUnitRange()
+        local unit = arg1
+        if not IsRelevantUnit(unit) then
+            return
+        end
+        local cache = PTUnit.Get(unit)
+        local distanceChanged = cache:UpdateDistance()
+        local sightChanged = cache:UpdateSight()
+        if distanceChanged or sightChanged then
+            for ui in UnitFrames(unit) do
+                if distanceChanged then
+                    ui:UpdateRange()
+                end
+                if sightChanged then
+                    ui:UpdateSight()
+                end
+            end
+        end
+    end
+    if util.IsClassicAPIActive("VisibilityEvent") then
+        RegisterEventHandler("UNIT_DISTANCE_CHECK_UPDATE", UpdateUnitRange)
+    end
+    if util.IsClassicAPIActive("RangeEvent") then
+        -- RegisterEvent covers pet, party and raid members and their pets, which ClassicAPI checks every frame
+        RegisterEventHandler("UNIT_IN_RANGE_UPDATE", UpdateUnitRange)
+    end
+end
 RegisterEventHandler({"PARTY_MEMBERS_CHANGED", "RAID_ROSTER_UPDATE"}, function()
     CheckGroupThrottled()
 end)