Use pipe as ID separator and add inverse functions for MakeUniqueID

components/ntp_snippets/content_suggestions_provider.cc

 // 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.
 
 #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
 
 ContentSuggestionsProvider::ContentSuggestionsProvider(
     const std::vector<ContentSuggestionsCategory>& provided_categories)
     : provided_categories_(provided_categories) {}
 
 ContentSuggestionsProvider::~ContentSuggestionsProvider() {}
 
+// static
 std::string ContentSuggestionsProvider::MakeUniqueID(
     ContentSuggestionsCategory category,
     const std::string& within_category_id) {
   return base::StringPrintf(kCombinedIDFormat,
                             static_cast<int>(category),
                             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