Migrate observer_list.h from location/nearby to third_party/nearby

PiperOrigin-RevId: 500240685

Package.swift

@@ -417,6 +417,7 @@ let package = Package(
         "internal/platform/BUILD",
         "internal/analytics/BUILD",
         "internal/network/BUILD",
+        "internal/base/BUILD",
         // tests
         "connections/listeners_test.cc",
         "connections/strategy_test.cc",

internal/base/BUILD

@@ -0,0 +1,20 @@
+licenses(["notice"])
+
+cc_library(
+    name = "base",
+    srcs = [
+    ],
+    hdrs = [
+        "observer_list.h",
+    ],
+    copts = [
+        "-Ithird_party",
+    ],
+    visibility = [
+        "//internal:__pkg__",
+        "//location/nearby/cpp/fastpair:__subpackages__",
+    ],
+    deps = [
+        "@com_google_absl//absl/container:flat_hash_set",
+    ],
+)

internal/base/observer_list.h

@@ -0,0 +1,58 @@
+// Copyright 2021 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 THIRD_PARTY_NEARBY_INTERNAL_BASE_OBSERVER_LIST_H_
+#define THIRD_PARTY_NEARBY_INTERNAL_BASE_OBSERVER_LIST_H_
+
+#include <string>
+#include <vector>
+
+#include "absl/container/flat_hash_set.h"
+
+namespace nearby {
+
+template <class ObserverType>
+class ObserverList {
+ public:
+  using iterator = typename absl::flat_hash_set<ObserverType*>::iterator;
+  using const_iterator =
+      typename absl::flat_hash_set<ObserverType*>::const_iterator;
+
+  void AddObserver(ObserverType* observer) { observers_.emplace(observer); }
+
+  void RemoveObserver(ObserverType* observer) { observers_.erase(observer); }
+
+  bool HasObserver(ObserverType* observer) {
+    return observers_.contains(observer);
+  }
+
+  void Clear() { observers_.clear(); }
+
+  bool empty() const { return observers_.empty(); }
+
+  int size() const { return observers_.size(); }
+
+  // Supports iterators
+  iterator begin() { return observers_.begin(); }
+  iterator end() { return observers_.end(); }
+  const_iterator begin() const { return observers_.begin(); }
+  const_iterator end() const { return observers_.end(); }
+
+ private:
+  absl::flat_hash_set<ObserverType*> observers_;
+};
+
+}  // namespace nearby
+
+#endif  // THIRD_PARTY_NEARBY_INTERNAL_BASE_OBSERVER_LIST_H_