[fix] prevent stale device online status

apps/desktop/src/gui/runtime/device_presence_cache.h

@@ -7,6 +7,7 @@
 #ifndef _DEVICE_PRESENCE_CACHE_H_
 #define _DEVICE_PRESENCE_CACHE_H_
 
+#include <chrono>
 #include <mutex>
 #include <string>
 #include <unordered_map>
@@ -15,15 +16,29 @@ namespace crossdesk {
 
 class DevicePresenceCache {
 public:
-  void SetOnline(const std::string &device_id, bool online) {
+  using Clock = std::chrono::steady_clock;
+  static constexpr auto kMaxAge = std::chrono::seconds(60);
+
+  void SetSignalConnected(bool connected) {
     std::lock_guard<std::mutex> lock(mutex_);
-    cache_[device_id] = online;
+    signal_connected_ = connected;
+    cache_.clear();
   }
 
-  bool IsOnline(const std::string &device_id) const {
+  void SetOnline(const std::string &device_id, bool online,
+                 Clock::time_point now = Clock::now()) {
+    std::lock_guard<std::mutex> lock(mutex_);
+    if (signal_connected_) {
+      cache_[device_id] = {online, now};
+    }
+  }
+
+  bool IsOnline(const std::string &device_id,
+                Clock::time_point now = Clock::now()) const {
     std::lock_guard<std::mutex> lock(mutex_);
     const auto it = cache_.find(device_id);
-    return it != cache_.end() && it->second;
+    return signal_connected_ && it != cache_.end() && it->second.online &&
+           now - it->second.updated_at < kMaxAge;
   }
 
   void Clear() {
@@ -32,7 +47,12 @@ public:
   }
 
 private:
-  std::unordered_map<std::string, bool> cache_;
+  struct Entry {
+    bool online;
+    Clock::time_point updated_at;
+  };
+  bool signal_connected_ = false;
+  std::unordered_map<std::string, Entry> cache_;
   mutable std::mutex mutex_;
 };