Use pipe as ID separator and add inverse functions for MakeUniqueID

components/ntp_snippets/content_suggestions_provider.cc

Index: components/ntp_snippets/content_suggestions_provider.cc
diff --git a/components/ntp_snippets/content_suggestions_provider.cc b/components/ntp_snippets/content_suggestions_provider.cc
index e4565e59d1c708b6f67650e3999940c5e44dd937..07947b860c71626564605cf121a2ececea7428b6 100644
--- a/components/ntp_snippets/content_suggestions_provider.cc
+++ b/components/ntp_snippets/content_suggestions_provider.cc
@@ -4,13 +4,15 @@
 
 #include "components/ntp_snippets/content_suggestions_provider.h"
 
+#include "base/strings/string_number_conversions.h"
 #include "base/strings/stringprintf.h"
 
 namespace ntp_snippets {
 
 namespace {
 
-const char kCombinedIDFormat[] = "%d:%s";
+const char kCombinedIDFormat[] = "%d|%s";
+const char kSeparator = '|';
 
 }  // namespace
 
@@ -20,6 +22,7 @@ ContentSuggestionsProvider::ContentSuggestionsProvider(
 
 ContentSuggestionsProvider::~ContentSuggestionsProvider() {}
 
+// static
 std::string ContentSuggestionsProvider::MakeUniqueID(
     ContentSuggestionsCategory category,
     const std::string& within_category_id) {
@@ -28,4 +31,27 @@ std::string ContentSuggestionsProvider::MakeUniqueID(
                             within_category_id.c_str());
 }
 
+// static
+ContentSuggestionsCategory ContentSuggestionsProvider::GetCategoryFromUniqueID(
+    const std::string& unique_id) {
+  size_t colon_index = unique_id.find(kSeparator);
+  DCHECK_NE(std::string::npos, colon_index) << "Not a valid unique_id: "
+                                            << unique_id;
+  int category = -1;
+  DCHECK(base::StringToInt(unique_id.substr(0, colon_index), &category))
+      << "Non-numeric category part in unique_id: " << unique_id;
+  DCHECK(0 <= category && category < int(ContentSuggestionsCategory::COUNT))
+      << "Category does not exist: " << category;
+  return ContentSuggestionsCategory(category);
+}
+
+// static
+std::string ContentSuggestionsProvider::GetWithinCategoryIDFromUniqueID(
+    const std::string& unique_id) {
+  size_t colon_index = unique_id.find(kSeparator);
+  DCHECK_NE(std::string::npos, colon_index) << "Not a valid unique_id: "
+                                            << unique_id;
+  return unique_id.substr(colon_index + 1);
+}
+
 }  // namespace ntp_snippets