Add a PersistentStore to FeatureEngagementTracker

components/feature_engagement_tracker/internal/persistent_store.cc

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "components/feature_engagement_tracker/internal/persistent_store.h"
+
+#include <vector>
+
+#include "base/bind.h"
+#include "base/memory/ptr_util.h"
+
+namespace feature_engagement_tracker {
+namespace {
+// Corresponds to a UMA suffix "LevelDBOpenResults" in histograms.xml.
+// Please do not change.
+const char kDatabaseUMAName[] = "FeatureEngagementTrackerStore";
+
+using KeyEventPair = std::pair<std::string, Event>;
+using KeyEventList = std::vector<KeyEventPair>;
+
+void NoopUpdateCallback(bool success) {}
+}  // namespace
+
+PersistentStore::PersistentStore(
+    const base::FilePath& storage_dir,
+    std::unique_ptr<leveldb_proto::ProtoDatabase<Event>> db)
+    : storage_dir_(storage_dir),
+      db_(std::move(db)),
+      ready_(false),
+      weak_ptr_factory_(this) {}
+
+PersistentStore::~PersistentStore() = default;
+
+void PersistentStore::Load(const OnLoadedCallback& callback) {
+  DCHECK(!ready_);
+
+  db_->Init(kDatabaseUMAName, storage_dir_,
+            base::Bind(&PersistentStore::OnInitComplete,
+                       weak_ptr_factory_.GetWeakPtr(), callback));
+}
+
+bool PersistentStore::IsReady() const {
+  return ready_;
+}
+
+void PersistentStore::WriteEvent(const Event& event) {
+  DCHECK(IsReady());
+  std::unique_ptr<KeyEventList> entries = base::MakeUnique<KeyEventList>();
+  entries->push_back(KeyEventPair(event.name(), event));
+
+  // TODO(dtrainor, nyquist): Consider tracking failures here and storing UMA.
+  db_->UpdateEntries(std::move(entries),
+                     base::MakeUnique<std::vector<std::string>>(),
+                     base::Bind(&NoopUpdateCallback));
+}
+
+void PersistentStore::OnInitComplete(const OnLoadedCallback& callback,
+                                     bool success) {
+  if (!success) {
+    callback.Run(false, base::MakeUnique<std::vector<Event>>());
+    return;
+  }
+
+  db_->LoadEntries(base::Bind(&PersistentStore::OnLoadComplete,
+                              weak_ptr_factory_.GetWeakPtr(), callback));
+}
+
+void PersistentStore::OnLoadComplete(
+    const OnLoadedCallback& callback,
+    bool success,
+    std::unique_ptr<std::vector<Event>> entries) {
+  ready_ = success;
+  callback.Run(success, std::move(entries));
+}
+
+}  // namespace feature_engagement_tracker