Introduce SerializeDictionaryForest for devtools_target_ui

chrome/browser/devtools/serialize_host_descriptions.cc

+// Copyright 2017 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 "chrome/browser/devtools/serialize_host_descriptions.h"
+
+#include <map>
+#include <utility>
+
+#include "base/memory/ptr_util.h"
+#include "base/strings/string_piece.h"
+
+namespace {
+
+// Returns the serialization of |root|. It expects |children[x]| to be the
+// vector of child nodes for all descendants |x| of |root|. The serialization
+// consists of taking the |representation| value of each node, starting in
+// leaves, and injecting children's representations into a ListValue under the
+// key |child_key| in the parent's |representation|. This is desctructive to the
+// representation stored with the nodes (which gets moved out of them).
+base::DictionaryValue Serialize(
+    base::StringPiece child_key,
+    base::DictionaryValue* root,
+    const std::map<base::DictionaryValue*, std::vector<base::DictionaryValue*>>&
+        children) {
+  auto children_list = base::MakeUnique<base::ListValue>();
+  auto child_it = children.find(root);
+  if (child_it != children.end()) {
+    for (base::DictionaryValue* child : child_it->second) {
+      children_list->base::Value::GetList().push_back(
+          Serialize(child_key, child, children));
+    }
+  }
+
+  if (!children_list->empty())
+    root->Set(child_key, std::move(children_list));
+  return std::move(*root);
+}
+
+// Takes a vector of host description and converts it into:
+// |children|: a map from a host's representation to representations of its
+//             children,
+// |roots|: a vector of representations of hosts with no parents, and
+// |representations|: a vector actually storing all those representations to
+//                    which the rest just points.
+void CreateDictionaryForest(
+    std::vector<HostDescriptionNode> hosts,
+    std::map<base::DictionaryValue*, std::vector<base::DictionaryValue*>>*
+        children,
+    std::vector<base::DictionaryValue*>* roots,
+    std::vector<base::DictionaryValue>* representations) {
+  representations->reserve(hosts.size());
+  children->clear();
+  roots->clear();
+  representations->clear();
+
+  std::map<base::StringPiece, base::DictionaryValue*> name_to_representation;
+
+  // First move the representations and map the names to them.
+  for (HostDescriptionNode& node : hosts) {
+    representations->push_back(std::move(node.representation));
+    name_to_representation[node.name] = &representations->back();
+  }
+
+  // Now compute children.
+  for (HostDescriptionNode& node : hosts) {
+    base::DictionaryValue* node_rep = name_to_representation[node.name];
+    base::StringPiece parent_name = node.parent_name;
+    if (parent_name.empty()) {
+      roots->push_back(node_rep);
+      continue;
+    }
+    auto node_it = name_to_representation.find(parent_name);
+    if (node_it == name_to_representation.end()) {
+      roots->push_back(node_rep);
+      continue;
+    }
+    (*children)[name_to_representation[parent_name]].push_back(node_rep);
+  }
+}
+
+}  // namespace
+
+base::ListValue SerializeHostDescriptions(
+    std::vector<HostDescriptionNode> hosts,
+    base::StringPiece child_key) {
+  // |representations| must outlive |children| and |roots|, which contain
+  // pointers to objects in |representations|.
+  std::vector<base::DictionaryValue> representations;
+  std::map<base::DictionaryValue*, std::vector<base::DictionaryValue*>>
+      children;
+  std::vector<base::DictionaryValue*> roots;
+
+  CreateDictionaryForest(std::move(hosts), &children, &roots, &representations);
+
+  base::ListValue list_value;
+  for (auto* root : roots) {
+    list_value.base::Value::GetList().push_back(
+        Serialize(child_key, root, children));
+  }
+  return list_value;
+}