[Doodle] Introduce a DoodleService

components/doodle/doodle_service.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/doodle/doodle_service.h"
+
+#include <utility>
+
+#include "base/bind.h"
+
+namespace doodle {
+
+DoodleService::DoodleService(std::unique_ptr<DoodleFetcher> fetcher)
+    : fetcher_(std::move(fetcher)) {
+  DCHECK(fetcher_);
+}
+
+DoodleService::~DoodleService() = default;
+
+void DoodleService::AddObserver(Observer* observer) {
+  observers_.AddObserver(observer);
+}
+
+void DoodleService::RemoveObserver(Observer* observer) {
+  observers_.RemoveObserver(observer);
+}
+
+void DoodleService::Refresh() {
+  fetcher_->FetchDoodle(
+      base::BindOnce(&DoodleService::DoodleFetched, base::Unretained(this)));
+}
+
+void DoodleService::DoodleFetched(
+    DoodleState state,
+    const base::Optional<DoodleConfig>& doodle_config) {
+  // If there is no config before or after the update, there's nothing to do.

[vitaliii, 2017/02/28 11:37:17]

s/or/and

[Marc Treib, 2017/02/28 13:06:49]

Actually, neither formulation is really unambiguous.

I made it: "If there isn't a config either before or after the update, there's
nothing to do."

[vitaliii, 2017/02/28 13:13:28]

Both messages feel to me like !cached_config_.has_value() ||
!doodle_config.has_value().
What about "There was no config before and we did not get a new one, there's
nothing to do"? 

Overall it may be my English problem, not your message, so feel free to ignore.

[Marc Treib, 2017/02/28 13:34:22]

I agree that your formulation is much better. Done.

+  if (!cached_config_.has_value() && !doodle_config.has_value()) {
+    return;
+  }
+
+  bool notify = false;
+  if (cached_config_.has_value() != doodle_config.has_value()) {
+    // We got a new config, or an existing one went away.
+    notify = true;
+  } else {
+    // There was a config both before and after the update. Notify observers
+    // only if something relevant changed.
+    notify = !cached_config_.value().IsEquivalent(doodle_config.value());
+  }
+
+  // In any case, update the cache.
+  cached_config_ = doodle_config;
+
+  if (notify) {
+    for (auto& observer : observers_) {
+      observer.OnDoodleConfigUpdated(cached_config_);
+    }
+  }
+}
+
+}  // namespace doodle