Translate: language list smart updater

chrome/browser/translate/translate_language_list.h

 // Copyright 2013 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 CHROME_BROWSER_TRANSLATE_TRANSLATE_LANGUAGE_LIST_H_
 #define CHROME_BROWSER_TRANSLATE_TRANSLATE_LANGUAGE_LIST_H_
 
 #include <set>
 #include <string>
 #include <vector>
 
+#include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
+#include "googleurl/src/gurl.h"
+#include "net/base/network_change_notifier.h"
 #include "net/url_request/url_fetcher_delegate.h"
 
 namespace net {
 class URLFetcher;
 }
 
 // The TranslateLanguageList class is responsible for maintaining the latest
 // supporting language list.
 // This class is defined to be owned only by TranslateManager.
-class TranslateLanguageList : public net::URLFetcherDelegate {
+class TranslateLanguageList
+    : public net::NetworkChangeNotifier::NetworkChangeObserver {
  public:
   TranslateLanguageList();
   virtual ~TranslateLanguageList();
 
-  // net::URLFetcherDelegate implementation:
-  virtual void OnURLFetchComplete(const net::URLFetcher* source) OVERRIDE;
-
   // Fills |languages| with the list of languages that the translate server can
   // translate to and from. |languages| will include alpha languages.
   void GetSupportedLanguages(std::vector<std::string>* languages);
 
   // Returns the language code that can be used with the Translate method for a
   // specified |chrome_locale|.
   std::string GetLanguageCode(const std::string& chrome_locale);
 
   // Returns true if |language| is supported by the translation server. It also
   // returns true against alpha languages.
   bool IsSupportedLanguage(const std::string& language);
 
   // Returns true if |language| is supported by the translation server as a
   // alpha language.
   bool IsAlphaLanguage(const std::string& language);
 
   // Fetches the language list from the translate server. It will not retry
-  // more than kMaxRetryLanguageListFetch times.
+  // more than kMaxRetryLanguageListFetch times. Do nothing if the list is
+  // already updated.
   void RequestLanguageList();
 
+  // net::NetworkChangeObserver implementation:
+  virtual void OnNetworkChanged(
+      net::NetworkChangeNotifier::ConnectionType type) OVERRIDE;
+
   // static const values shared with our browser tests.
   static const char kLanguageListCallbackName[];
   static const char kTargetLanguagesKey[];
 
  private:
+  // The LanguageListFetcher class implements a client to fetch a server
+  // supported language list. It also maintains state to represent if the fetch
+  // is completed successfully to try again later.
+  class LanguageListFetcher : public net::URLFetcherDelegate {
+   public:
+    // Callback type for Request().
+    typedef base::Callback<void(bool, bool, const std::string&)> Callback;
+
+    // Represents internal state if the fetch is completed successfully.
+    enum State {
+      IDLE,        // No fetch request was issued.
+      REQUESTING,  // A fetch request was issued, but not finished yet.
+      COMPLETED,   // The last fetch request was finished successfully.
+      FAILED,      // The last fetch request was finished with a failure.
+    };
+
+    explicit LanguageListFetcher(bool include_alpha_languages);
+    virtual ~LanguageListFetcher();
+
+    // Requests to fetch a server supported language list. |callback| will be
+    // invoked when the function returns true, and the request is finished
+    // asynchronously.
+    // Returns false if the previous request is not finished, or the request
+    // is omitted due to retry limitation.
+    bool Request(const Callback& callback);
+
+    // Gets internal state.
+    State state() { return state_; }
+
+    // net::URLFetcherDelegate implementation:
+    virtual void OnURLFetchComplete(const net::URLFetcher* source) OVERRIDE;
+
+   private:
+    // Represents if this instance should fetch a supported language list
+    // including alpha languages.
+    bool include_alpha_languages_;
+
+    // Internal state.
+    enum State state_;
+
+    // URLFetcher instance.
+    scoped_ptr<net::URLFetcher> fetcher_;
+
+    // Callback passed at Request(). It will be invoked when asynchronous
+    // fetch operation is finished.
+    Callback callback_;
+
+    // Counts how many times did it try to fetch the language list.
+    int retry_count_;
+
+    DISALLOW_COPY_AND_ASSIGN(LanguageListFetcher);
+  };
+
+  // Callback function called when LanguageListFetcher::Request() is finished.
+  void OnLanguageListFetchComplete(bool include_alpha_languages,
+                                   bool success,
+                                   const std::string& data);
+
   // Updates |all_supported_languages_| to contain the union of
   // |supported_languages_| and |supported_alpha_languages_|.
   void UpdateSupportedLanguages();
 
   // The languages supported by the translation server.
   std::set<std::string> supported_languages_;
 
   // The alpha languages supported by the translation server.
   std::set<std::string> supported_alpha_languages_;
 
   // All the languages supported by the translation server. It contains the
   // union of |supported_languages_| and |supported_alpha_languages_|.
   std::set<std::string> all_supported_languages_;
 
-  // An URLFetcher instance to fetch a server providing supported language list.
-  scoped_ptr<net::URLFetcher> language_list_fetcher_;
+  // A LanguageListFetcher instance to fetch a server providing supported
+  // language list.
+  scoped_ptr<LanguageListFetcher> language_list_fetcher_;
 
-  // An URLFetcher instance to fetch a server providing supported alpha language
-  // list.
-  scoped_ptr<net::URLFetcher> alpha_language_list_fetcher_;
+  // A LanguageListFetcher instance to fetch a server providing supported alpha
+  // language list.
+  scoped_ptr<LanguageListFetcher> alpha_language_list_fetcher_;
 
   DISALLOW_COPY_AND_ASSIGN(TranslateLanguageList);
 };
 
 #endif  // CHROME_BROWSER_TRANSLATE_TRANSLATE_LANGUAGE_LIST_H_