[Doodle] Introduce a DoodleService

components/doodle/doodle_service.h

Index: components/doodle/doodle_service.h
diff --git a/components/doodle/doodle_service.h b/components/doodle/doodle_service.h
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+++ b/components/doodle/doodle_service.h
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+// 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.
+
+#ifndef COMPONENTS_DOODLE_DOODLE_SERVICE_H_
+#define COMPONENTS_DOODLE_DOODLE_SERVICE_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "base/observer_list.h"
+#include "base/optional.h"
+#include "components/doodle/doodle_fetcher.h"
+#include "components/doodle/doodle_types.h"
+
+namespace doodle {
+
+class DoodleService {
+ public:
+  class Observer {
+   public:
+    virtual void OnDoodleConfigUpdated(const base::Optional<DoodleConfig>&) = 0;
+  };
+
+  DoodleService(std::unique_ptr<DoodleFetcher> fetcher);
+  ~DoodleService();
+
+  // Returns the current (cached) config, if any.
+  const base::Optional<DoodleConfig>& config() const { return cached_config_; }
+
+  // Adds a new observer to the service. It'll only be called when the config
+  // changes; to get the current (cached) config, call |config()|.
+  void AddObserver(Observer* observer);
+
+  // Prevents |observer| from receiving future updates. This is safe to call
+  // even when the observer is being notified of an update.
+  void RemoveObserver(Observer* observer);
+
+  // Requests an asynchronous refresh of the DoodleConfig from the network.
+  // After the update completes, the observers will be notified only if the
+  // config changed.
+  void Refresh();
+
+ private:
+  void DoodleFetched(DoodleState state,
+                     const base::Optional<DoodleConfig>& doodle_config);
+
+  // The fetcher for getting fresh DoodleConfigs from the network.
+  std::unique_ptr<DoodleFetcher> fetcher_;
+
+  // The result of the last network fetch.
+  base::Optional<DoodleConfig> cached_config_;
+
+  // The list of observers to be notified when the DoodleConfig changes.
+  base::ObserverList<Observer> observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(DoodleService);
+};
+
+}  // namespace doodle
+
+#endif  // COMPONENTS_DOODLE_DOODLE_SERVICE_H_