[bbr-local] simplify AddService() and its use (openthread#9477)

This commit contains smaller changes in `BackbonRouter::Local`:

- `AddService()` now gets a `RegisterationMode` enum as its input
  either decide based on current state or force registration.
- We remove the `NetworkData::Notifier::HandleServerDataUpdated()`
  calls after calling `AddService()` since `AddService()` method
  itself will already call this (when successfully adds the service
  to Network Data)
- We also remove the extra state check before calling `AddService()`
  as it is done by the `AddService()` method itself.

src/core/api/backbone_router_ftd_api.cpp

@@ -69,7 +69,7 @@ otError otBackboneRouterSetConfig(otInstance *aInstance, const otBackboneRouterC
 
 otError otBackboneRouterRegister(otInstance *aInstance)
 {
-    return AsCoreType(aInstance).Get<BackboneRouter::Local>().AddService(true /* Force registration */);
+    return AsCoreType(aInstance).Get<BackboneRouter::Local>().AddService(BackboneRouter::Local::kForceRegistration);
 }
 
 uint8_t otBackboneRouterGetRegistrationJitter(otInstance *aInstance)

src/core/backbone_router/bbr_local.cpp

@@ -87,7 +87,7 @@ void Local::SetEnabled(bool aEnable)
     {
         SetState(kStateSecondary);
         AddDomainPrefixToNetworkData();
-        IgnoreError(AddService());
+        IgnoreError(AddService(kDecideBasedOnState));
     }
     else
     {
@@ -163,26 +163,30 @@ Error Local::SetConfig(const Config &aConfig)
     {
         Get<Notifier>().Signal(kEventThreadBackboneRouterLocalChanged);
 
-        IgnoreError(AddService());
+        IgnoreError(AddService(kDecideBasedOnState));
     }
 
 exit:
     LogBackboneRouterService("Set", error);
     return error;
 }
 
-Error Local::AddService(bool aForce)
+Error Local::AddService(RegisterMode aMode)
 {
     Error                                            error = kErrorInvalidState;
     NetworkData::Service::BackboneRouter::ServerData serverData;
 
     VerifyOrExit(mState != kStateDisabled && Get<Mle::Mle>().IsAttached());
 
-    VerifyOrExit(aForce /* if register by force */ ||
-                 !Get<BackboneRouter::Leader>().HasPrimary() /* if no available Backbone Router service */ ||
-                 Get<BackboneRouter::Leader>().GetServer16() == Get<Mle::MleRouter>().GetRloc16()
-                 /* If the device itself should be BBR. */
-    );
+    switch (aMode)
+    {
+    case kDecideBasedOnState:
+        VerifyOrExit(!Get<BackboneRouter::Leader>().HasPrimary() ||
+                     Get<BackboneRouter::Leader>().GetServer16() == Get<Mle::MleRouter>().GetRloc16());
+        break;
+    case kForceRegistration:
+        break;
+    }
 
     serverData.SetSequenceNumber(mSequenceNumber);
     serverData.SetReregistrationDelay(mReregistrationDelay);
@@ -272,10 +276,7 @@ void Local::HandleBackboneRouterPrimaryUpdate(Leader::State aState, const Config
         mMlrTimeout          = aConfig.mMlrTimeout;
         SequenceNumberIncrease();
         Get<Notifier>().Signal(kEventThreadBackboneRouterLocalChanged);
-        if (AddService(true /* Force registration to refresh and restore Primary state */) == kErrorNone)
-        {
-            Get<NetworkData::Notifier>().HandleServerDataUpdated();
-        }
+        IgnoreError(AddService(kForceRegistration));
     }
     else
     {

src/core/backbone_router/bbr_local.hpp

@@ -84,6 +84,16 @@ class Local : public InstanceLocator, private NonCopyable
         kStatePrimary   = OT_BACKBONE_ROUTER_STATE_PRIMARY,   ///< The Primary Backbone Router.
     };
 
+    /**
+     * Represents registration mode used as input to `AddService()` method.
+     *
+     */
+    enum RegisterMode : uint8_t
+    {
+        kDecideBasedOnState, ///< Decide based on current state.
+        kForceRegistration,  ///< Force registration regardless of current state.
+    };
+
     /**
      * Initializes the local Backbone Router.
      *
@@ -137,16 +147,14 @@ class Local : public InstanceLocator, private NonCopyable
     /**
      * Registers Backbone Router Dataset to Leader.
      *
-     * @param[in]  aForce True to force registration regardless of current state.
-     *                    False to decide based on current state.
-     *
+     * @param[in]  aMode  The registration mode to use (decide based on current state or force registration).
      *
      * @retval kErrorNone            Successfully added the Service entry.
      * @retval kErrorInvalidState    Not in the ready state to register.
      * @retval kErrorNoBufs          Insufficient space to add the Service entry.
      *
      */
-    Error AddService(bool aForce = false);
+    Error AddService(RegisterMode aMode);
 
     /**
      * Indicates whether or not the Backbone Router is Primary.

src/core/thread/mle_router.cpp

@@ -1550,14 +1550,7 @@ void MleRouter::HandleTimeTick(void)
 
         if (mBackboneRouterRegistrationDelay == 0)
         {
-            // If no Backbone Router service after jitter, try to register its own Backbone Router Service.
-            if (!Get<BackboneRouter::Leader>().HasPrimary())
-            {
-                if (Get<BackboneRouter::Local>().AddService() == kErrorNone)
-                {
-                    Get<NetworkData::Notifier>().HandleServerDataUpdated();
-                }
-            }
+            IgnoreError(Get<BackboneRouter::Local>().AddService(BackboneRouter::Local::kDecideBasedOnState));
         }
     }
 #endif