1 files changed, 123 insertions, 0 deletions
diff --git a/third_party/libwebrtc/api/environment/environment_factory.cc b/third_party/libwebrtc/api/environment/environment_factory.cc
new file mode 100644
index 0000000000..c0b681aa08
--- /dev/null
+++ b/third_party/libwebrtc/api/environment/environment_factory.cc
@@ -0,0 +1,123 @@
+/*
+ *  Copyright 2023 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "api/environment/environment_factory.h"
+
+#include <memory>
+#include <utility>
+#include <vector>
+
+#include "api/make_ref_counted.h"
+#include "api/rtc_event_log/rtc_event_log.h"
+#include "api/task_queue/default_task_queue_factory.h"
+#include "api/transport/field_trial_based_config.h"
+#include "rtc_base/checks.h"
+#include "system_wrappers/include/clock.h"
+
+namespace webrtc {
+namespace {
+
+template <typename T>
+void Store(absl::Nonnull<std::unique_ptr<T>> value,
+           scoped_refptr<const rtc::RefCountedBase>& leaf) {
+  class StorageNode : public rtc::RefCountedBase {
+   public:
+    StorageNode(scoped_refptr<const rtc::RefCountedBase> parent,
+                absl::Nonnull<std::unique_ptr<T>> value)
+        : parent_(std::move(parent)), value_(std::move(value)) {}
+
+    StorageNode(const StorageNode&) = delete;
+    StorageNode& operator=(const StorageNode&) = delete;
+
+    ~StorageNode() override = default;
+
+   private:
+    scoped_refptr<const rtc::RefCountedBase> parent_;
+    absl::Nonnull<std::unique_ptr<T>> value_;
+  };
+
+  // Utilities provided with ownership form a tree:
+  // Root is nullptr, each node keeps an ownership of one utility.
+  // Each child node has a link to the parent, but parent is unaware of its
+  // children. Each `EnvironmentFactory` and `Environment` keep a reference to a
+  // 'leaf_' - node with the last provided utility. This way `Environment` keeps
+  // ownership of a single branch of the storage tree with each used utiltity
+  // owned by one of the nodes on that branch.
+  leaf = rtc::make_ref_counted<StorageNode>(std::move(leaf), std::move(value));
+}
+
+}  // namespace
+
+EnvironmentFactory::EnvironmentFactory(const Environment& env)
+    : leaf_(env.storage_),
+      field_trials_(env.field_trials_),
+      clock_(env.clock_),
+      task_queue_factory_(env.task_queue_factory_),
+      event_log_(env.event_log_) {}
+
+void EnvironmentFactory::Set(
+    absl::Nullable<std::unique_ptr<const FieldTrialsView>> utility) {
+  if (utility != nullptr) {
+    field_trials_ = utility.get();
+    Store(std::move(utility), leaf_);
+  }
+}
+
+void EnvironmentFactory::Set(absl::Nullable<std::unique_ptr<Clock>> utility) {
+  if (utility != nullptr) {
+    clock_ = utility.get();
+    Store(std::move(utility), leaf_);
+  }
+}
+
+void EnvironmentFactory::Set(
+    absl::Nullable<std::unique_ptr<TaskQueueFactory>> utility) {
+  if (utility != nullptr) {
+    task_queue_factory_ = utility.get();
+    Store(std::move(utility), leaf_);
+  }
+}
+
+void EnvironmentFactory::Set(
+    absl::Nullable<std::unique_ptr<RtcEventLog>> utility) {
+  if (utility != nullptr) {
+    event_log_ = utility.get();
+    Store(std::move(utility), leaf_);
+  }
+}
+
+Environment EnvironmentFactory::CreateWithDefaults() && {
+  if (field_trials_ == nullptr) {
+    Set(std::make_unique<FieldTrialBasedConfig>());
+  }
+  if (clock_ == nullptr) {
+    Set(Clock::GetRealTimeClock());
+  }
+  if (task_queue_factory_ == nullptr) {
+    Set(CreateDefaultTaskQueueFactory(field_trials_));
+  }
+  if (event_log_ == nullptr) {
+    Set(std::make_unique<RtcEventLogNull>());
+  }
+
+  RTC_DCHECK(field_trials_ != nullptr);
+  RTC_DCHECK(clock_ != nullptr);
+  RTC_DCHECK(task_queue_factory_ != nullptr);
+  RTC_DCHECK(event_log_ != nullptr);
+  return Environment(std::move(leaf_),  //
+                     field_trials_, clock_, task_queue_factory_, event_log_);
+}
+
+Environment EnvironmentFactory::Create() const {
+  // Create a temporary copy to avoid mutating `this` with default utilities.
+  return EnvironmentFactory(*this).CreateWithDefaults();
+}
+
+}  // namespace webrtc