Add ContentSuggestionsCategoryFactory; Store categories as ints

components/ntp_snippets/content_suggestions_category.h

 // Copyright 2016 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_NTP_SNIPPETS_CONTENT_SUGGESTIONS_CATEGORY_H_
 #define COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_CATEGORY_H_
 
+#include <ostream>
+
 namespace ntp_snippets {
 
-// A category groups ContentSuggestions which belong together.
-enum class ContentSuggestionsCategory { ARTICLES, OFFLINE_PAGES, COUNT };
+class ContentSuggestionsCategoryFactory;
+
+// These are the categories that the client knows about.
+// The values before LOCAL_CATEGORIES_COUNT are the categories that are provided
+// locally on the device. Those values need to be listed in the
+// ContentSuggestionsCategoryFactory constructor!
+// Categories provided by the server (IDs strictly larger than
+// REMOTE_CATEGORIES_OFFSET) only need to be hard-coded here if they need to be
+// recognized by the client implementation.
+enum class KnownSuggestionsCategories {
+  OFFLINE_PAGES,
+  LOCAL_CATEGORIES_COUNT,
+
+  REMOTE_CATEGORIES_OFFSET = 10000,
+  ARTICLES = REMOTE_CATEGORIES_OFFSET + 1,
+};
+
+// A category groups ContentSuggestions which belong together. Use the
+// ContentSuggestionsCategoryFactory to obtain instances.
+class ContentSuggestionsCategory {
+ public:
+  // Returns a non-negative identifier that is unique for the category and can
+  // be converted back to a ContentSuggestionsCategory instance using
+  // |ContentSuggestionsCategoryFactory::FromIDValue(id)|.
+  // Note that these IDs are not necessarily stable across multiple runs of
+  // the application, so they should not be persisted.
+  int id() const { return id_; }
+
+  bool IsKnownCategory(KnownSuggestionsCategories known_category) const;
+
+ private:
+  friend class ContentSuggestionsCategoryFactory;
+
+  ContentSuggestionsCategory(int id);
+
+  int id_;
+
+  // Allow copy and assignment.
+};
+
+bool operator==(const ContentSuggestionsCategory& left,
+                const ContentSuggestionsCategory& right);
+
+bool operator!=(const ContentSuggestionsCategory& left,
+                const ContentSuggestionsCategory& right);
+
+std::ostream& operator<<(std::ostream& os,
+                         const ContentSuggestionsCategory& obj);
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_CATEGORY_H_