nearby sdk refactor

PiperOrigin-RevId: 425434260

connections/implementation/mediums/lost_entity_tracker.h

@@ -0,0 +1,94 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef CORE_INTERNAL_MEDIUMS_LOST_ENTITY_TRACKER_H_
+#define CORE_INTERNAL_MEDIUMS_LOST_ENTITY_TRACKER_H_
+
+#include "absl/container/flat_hash_set.h"
+#include "internal/platform/mutex.h"
+#include "internal/platform/mutex_lock.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+// Tracks "lost" entities based on a manual update/compute model. Used by
+// mediums that only report found devices. Lost entities are computed based off
+// of whether a specific entity was rediscovered since the last call to
+// ComputeLostEntities.
+//
+// Note: Entity must overload the < and == operators.
+template <typename Entity>
+class LostEntityTracker {
+ public:
+  using EntitySet = absl::flat_hash_set<Entity>;
+
+  LostEntityTracker();
+  ~LostEntityTracker();
+
+  // Records the given entity as being recently found, whether or not this is
+  // our first time discovering the entity.
+  void RecordFoundEntity(const Entity& entity) ABSL_LOCKS_EXCLUDED(mutex_);
+
+  // Computes and returns the set of entities considered lost since the last
+  // time this method was called.
+  EntitySet ComputeLostEntities() ABSL_LOCKS_EXCLUDED(mutex_);
+
+ private:
+  Mutex mutex_;
+  EntitySet current_entities_ ABSL_GUARDED_BY(mutex_);
+  EntitySet previously_found_entities_ ABSL_GUARDED_BY(mutex_);
+};
+
+template <typename Entity>
+LostEntityTracker<Entity>::LostEntityTracker()
+    : current_entities_{}, previously_found_entities_{} {}
+
+template <typename Entity>
+LostEntityTracker<Entity>::~LostEntityTracker() {
+  previously_found_entities_.clear();
+  current_entities_.clear();
+}
+
+template <typename Entity>
+void LostEntityTracker<Entity>::RecordFoundEntity(const Entity& entity) {
+  MutexLock lock(&mutex_);
+
+  current_entities_.insert(entity);
+}
+
+template <typename Entity>
+typename LostEntityTracker<Entity>::EntitySet
+LostEntityTracker<Entity>::ComputeLostEntities() {
+  MutexLock lock(&mutex_);
+
+  // The set of lost entities is the previously found set MINUS the currently
+  // found set.
+  for (const auto& item : current_entities_) {
+    previously_found_entities_.erase(item);
+  }
+  auto lost_entities = std::move(previously_found_entities_);
+  previously_found_entities_ = std::move(current_entities_);
+  current_entities_ = {};
+
+  return lost_entities;
+}
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#endif  // CORE_INTERNAL_MEDIUMS_LOST_ENTITY_TRACKER_H_