From 640cb3bf7f551bf40caee034d022c78187d6cf5c Mon Sep 17 00:00:00 2001
From: geeksville <kevinh@geeksville.com>
Date: Fri, 10 Apr 2020 12:40:44 -0700
Subject: [PATCH] allow observers to return an error code to abort further
 processing

Will allow me to use observers to generalize the various hooks
that need to run to preflight sleep entry.
---
 src/MeshService.cpp                |  4 +++-
 src/MeshService.h                  |  3 ++-
 src/Observer.h                     | 20 +++++++++++++++-----
 src/esp32/MeshBluetoothService.cpp |  3 ++-
 4 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/src/MeshService.cpp b/src/MeshService.cpp
index 6b9dabdc6..38fdc3473 100644
--- a/src/MeshService.cpp
+++ b/src/MeshService.cpp
@@ -322,7 +322,7 @@ void MeshService::sendOurPosition(NodeNum dest, bool wantReplies)
     sendToMesh(p);
 }
 
-void MeshService::onGPSChanged(void *unused)
+int MeshService::onGPSChanged(void *unused)
 {
     DEBUG_MSG("got gps notify\n");
 
@@ -354,4 +354,6 @@ void MeshService::onGPSChanged(void *unused)
 
         releaseToPool(p);
     }
+
+    return 0;
 }
diff --git a/src/MeshService.h b/src/MeshService.h
index 30e03017c..e8f8721eb 100644
--- a/src/MeshService.h
+++ b/src/MeshService.h
@@ -80,7 +80,8 @@ class MeshService
     void sendToMesh(MeshPacket *p);
 
     /// Called when our gps position has changed - updates nodedb and sends Location message out into the mesh
-    void onGPSChanged(void *arg);
+    /// returns 0 to allow futher processing
+    int onGPSChanged(void *arg);
 
     /// handle all the packets that just arrived from the mesh radio
     void handleFromRadio();
diff --git a/src/Observer.h b/src/Observer.h
index b20fe818d..eab1a4a30 100644
--- a/src/Observer.h
+++ b/src/Observer.h
@@ -24,7 +24,11 @@ template <class T> class Observer
     friend class Observable<T>;
 
   protected:
-    virtual void onNotify(T arg) = 0;
+    /**
+     * returns 0 if other observers should continue to be called
+     * returns !0 if the observe calls should be aborted and this result code returned for notifyObservers
+     **/
+    virtual int onNotify(T arg) = 0;
 };
 
 /**
@@ -32,7 +36,7 @@ template <class T> class Observer
  */
 template <class Callback, class T> class CallbackObserver : public Observer<T>
 {
-    typedef void (Callback::*ObserverCallback)(T arg);
+    typedef int (Callback::*ObserverCallback)(T arg);
 
     Callback *objPtr;
     ObserverCallback method;
@@ -41,7 +45,7 @@ template <class Callback, class T> class CallbackObserver : public Observer<T>
     CallbackObserver(Callback *_objPtr, ObserverCallback _method) : objPtr(_objPtr), method(_method) {}
 
   protected:
-    virtual void onNotify(T arg) { (objPtr->*method)(arg); }
+    virtual int onNotify(T arg) { return (objPtr->*method)(arg); }
 };
 
 /**
@@ -55,13 +59,19 @@ template <class T> class Observable
   public:
     /**
      * Tell all observers about a change, observers can process arg as they wish
+     *
+     * returns !0 if an observer chose to abort processing by returning this code
      */
-    void notifyObservers(T arg)
+    int notifyObservers(T arg)
     {
         for (typename std::list<Observer<T> *>::const_iterator iterator = observers.begin(); iterator != observers.end();
              ++iterator) {
-            (*iterator)->onNotify(arg);
+            int result = (*iterator)->onNotify(arg);
+            if (result != 0)
+                return result;
         }
+
+        return 0;
     }
 
   private:
diff --git a/src/esp32/MeshBluetoothService.cpp b/src/esp32/MeshBluetoothService.cpp
index d1bd273b6..086f0afe6 100644
--- a/src/esp32/MeshBluetoothService.cpp
+++ b/src/esp32/MeshBluetoothService.cpp
@@ -222,10 +222,11 @@ class FromNumCharacteristic : public CallbackCharacteristic, public Observer<uin
     }
 
     /// If the mesh service tells us fromNum has changed, tell the phone
-    virtual void onNotify(uint32_t newValue)
+    virtual int onNotify(uint32_t newValue)
     {
         setValue(newValue);
         notify();
+        return 0;
     }
 };