Add ContentSuggestionsCategoryFactory; Store categories as ints

components/ntp_snippets/content_suggestions_category.h

Index: components/ntp_snippets/content_suggestions_category.h
diff --git a/components/ntp_snippets/content_suggestions_category.h b/components/ntp_snippets/content_suggestions_category.h
index 70bb23d06fedc97de38433c46551ea6fc347af2c..fc4802ca84d592b7738aa9d107e090ca705401a3 100644
--- a/components/ntp_snippets/content_suggestions_category.h
+++ b/components/ntp_snippets/content_suggestions_category.h
@@ -5,10 +5,51 @@
 #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:
+  int id() const { return id_; }

[tschumann, 2016/07/28 15:36:10]

we should document this id. To make clear which properties clients can assume
(hopefully none besides uniquely identifying the category).

[Philipp Keck, 2016/07/28 16:59:58]

Done.

+
+  bool IsKnownCategory(KnownSuggestionsCategories known_category) const;
+
+ private:
+  friend class ContentSuggestionsCategoryFactory;
+
+  ContentSuggestionsCategory(int id);
+
+  int id_;
+};
+
+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