42.20 and Towtrucks

42.20/media/lua/client/TowBar/TowSyncClient.lua

@@ -4,6 +4,23 @@ if not TowBarMod then TowBarMod = {} end
 TowBarMod.Sync = TowBarMod.Sync or {}
 if TowBarMod.Sync._towSyncClientLoaded then return end
 TowBarMod.Sync._towSyncClientLoaded = true
+TowBarMod.Sync.appliedPairs = TowBarMod.Sync.appliedPairs or {}
+
+local function pairKeyContainsVehicle(key, vehicleId)
+    local id = tostring(vehicleId)
+    return string.sub(key, 1, #id + 1) == id .. ":"
+        or string.sub(key, -(#id + 1)) == ":" .. id
+end
+
+local function clearAppliedPairForVehicle(vehicle)
+    if not vehicle then return end
+    local vehicleId = vehicle:getId()
+    for key in pairs(TowBarMod.Sync.appliedPairs) do
+        if pairKeyContainsVehicle(key, vehicleId) then
+            TowBarMod.Sync.appliedPairs[key] = nil
+        end
+    end
+end
 
 local function resolveVehicle(id)
     if not id then return nil end
@@ -89,6 +106,8 @@ local function reconcilePairState(vehicleA, vehicleB, attachmentA, attachmentB)
     end
 end
 
+local breakTowBarPair
+
 local function applyAttachSync(args)
     if not args then return end
 
@@ -102,8 +121,25 @@ local function applyAttachSync(args)
         return
     end
 
-    if not isLinked(vehicleA, vehicleB) then
-        vehicleA:addPointConstraint(nil, vehicleB, attachmentA, attachmentB)
+    local key = tostring(vehicleA:getId()) .. ":" .. tostring(vehicleB:getId())
+    if TowBarMod.Sync.appliedPairs[key] and not isLinked(vehicleA, vehicleB) then
+        -- Vehicle streaming can remove the native constraint while the Lua
+        -- module remains loaded. Allow the authoritative recovery sync to
+        -- rebuild local physics for the returning pair.
+        TowBarMod.Sync.appliedPairs[key] = nil
+    end
+    if not TowBarMod.Sync.appliedPairs[key] then
+        -- The server initially creates a normal Build 42 tow relation. It may
+        -- also restore one from the save. Replace that native rope exactly
+        -- once with this mod's rigid fake-trailer constraint.
+        breakTowBarPair(vehicleA, vehicleB)
+        if TowBarMod.Hook and TowBarMod.Hook.setVehicleScriptWithTowBarHidden then
+            TowBarMod.Hook.setVehicleScriptWithTowBarHidden(vehicleB, "notTowingA_Trailer")
+        end
+        -- The final true keeps this a local physics rebuild. The server owns
+        -- the persisted logical relation and must not receive a detach/attach race.
+        vehicleA:addPointConstraint(nil, vehicleB, attachmentA, attachmentB, true)
+        TowBarMod.Sync.appliedPairs[key] = true
     end
 
     reconcilePairState(vehicleA, vehicleB, attachmentA, attachmentB)
@@ -130,18 +166,17 @@ local function hasConflictingTowLink(vehicle, expectedOther)
             and modData["towBarTowingVehicleId"] ~= expectedOtherId)
 end
 
-local function breakTowBarPair(vehicleA, vehicleB)
+breakTowBarPair = function(vehicleA, vehicleB)
     if not vehicleA or not vehicleB then return end
 
     local vehicleAReferencesB = vehicleA:getVehicleTowing() == vehicleB
         or vehicleA:getVehicleTowedBy() == vehicleB
     local vehicleBReferencesA = vehicleB:getVehicleTowing() == vehicleA
         or vehicleB:getVehicleTowedBy() == vehicleA
-    if vehicleBReferencesA then
-        vehicleB:breakConstraint(true, true)
-    end
     if vehicleAReferencesB then
         vehicleA:breakConstraint(true, true)
+    elseif vehicleBReferencesA then
+        vehicleB:breakConstraint(true, true)
     end
 end
 
@@ -154,6 +189,7 @@ local function applyDetachSync(args)
         return
     end
     breakTowBarPair(vehicleA, vehicleB)
+    TowBarMod.Sync.appliedPairs[tostring(vehicleA:getId()) .. ":" .. tostring(vehicleB:getId())] = nil
 
     if TowBarMod.Hook and TowBarMod.Hook.cleanupDetachedTowBar then
         pcall(TowBarMod.Hook.cleanupDetachedTowBar, vehicleA, vehicleB)
@@ -170,4 +206,10 @@ local function onServerCommand(module, command, args)
     end
 end
 
+TowBarMod.Sync.applyAttachSync = applyAttachSync
+TowBarMod.Sync.applyDetachSync = applyDetachSync
+
 Events.OnServerCommand.Add(onServerCommand)
+if Events.OnSpawnVehicleEnd then
+    Events.OnSpawnVehicleEnd.Add(clearAppliedPairForVehicle)
+end