From 4c83259acb509693be14e9b6c273ca16b2b2e95a Mon Sep 17 00:00:00 2001
From: Peter Johnson <johnson.peter@gmail.com>
Date: Sat, 19 Sep 2015 12:18:25 -0700
Subject: [PATCH] C++ NetworkTable: Provide AddSubTableListener().

This matches the implementation provided by Java NetworkTable, with the
exception that the subtable is not provided (because it's not a value).
The listener still can get access to the subtable by calling
source->getSubTable(key).
---
 include/networktables/NetworkTable.h |  1 +
 include/tables/ITable.h              |  6 ++++++
 src/networktables/NetworkTable.cpp   | 28 ++++++++++++++++++++++++++++
 3 files changed, 35 insertions(+)

diff --git a/include/networktables/NetworkTable.h b/include/networktables/NetworkTable.h
index 76309f7a9f..fbaf906dea 100644
--- a/include/networktables/NetworkTable.h
+++ b/include/networktables/NetworkTable.h
@@ -139,6 +139,7 @@ class NetworkTable : public ITable {
   void AddTableListener(ITableListener* listener, bool immediateNotify);
   void AddTableListener(llvm::StringRef key, ITableListener* listener,
                         bool immediateNotify);
+  void AddSubTableListener(ITableListener* listener);
   void RemoveTableListener(ITableListener* listener);
 
   /**
diff --git a/include/tables/ITable.h b/include/tables/ITable.h
index 73eb1d83d9..cb1a0ddad0 100644
--- a/include/tables/ITable.h
+++ b/include/tables/ITable.h
@@ -220,6 +220,12 @@ class ITable {
   virtual void AddTableListener(llvm::StringRef key, ITableListener* listener,
                                 bool immediateNotify) = 0;
 
+  /**
+   * This will immediately notify the listener of all current sub tables
+   * @param listener the listener to add
+   */
+  virtual void AddSubTableListener(ITableListener* listener) = 0;
+
   /**
    * Remove a listener from receiving table events
    *
diff --git a/src/networktables/NetworkTable.cpp b/src/networktables/NetworkTable.cpp
index ddfa0c928e..33bbb32f0d 100644
--- a/src/networktables/NetworkTable.cpp
+++ b/src/networktables/NetworkTable.cpp
@@ -3,6 +3,7 @@
 #include <algorithm>
 
 #include "llvm/SmallString.h"
+#include "llvm/StringMap.h"
 #include "tables/ITableListener.h"
 #include "ntcore.h"
 
@@ -136,6 +137,33 @@ void NetworkTable::AddTableListener(StringRef key,
   m_listeners.emplace_back(listener, id);
 }
 
+void NetworkTable::AddSubTableListener(ITableListener* listener) {
+  std::lock_guard<std::mutex> lock(m_mutex);
+  llvm::SmallString<128> path(m_path);
+  path += PATH_SEPARATOR_CHAR;
+  std::size_t prefix_len = path.size();
+
+  // The lambda needs to be copyable, but StringMap is not, so use
+  // a shared_ptr to it.
+  auto notified_tables = std::make_shared<llvm::StringMap<char>>();
+
+  unsigned int id = nt::AddEntryListener(
+      path,
+      [=](unsigned int uid, StringRef name, std::shared_ptr<nt::Value> value,
+          bool is_new) mutable {
+        StringRef relative_key = name.substr(prefix_len);
+        auto end_sub_table = relative_key.find(PATH_SEPARATOR_CHAR);
+        if (end_sub_table == StringRef::npos) return;
+        StringRef sub_table_key = relative_key.substr(0, end_sub_table);
+        if (notified_tables->find(sub_table_key) == notified_tables->end())
+          return;
+        notified_tables->insert(std::make_pair(sub_table_key, '\0'));
+        listener->ValueChanged(this, sub_table_key, nullptr, true);
+      },
+      true);
+  m_listeners.emplace_back(listener, id);
+}
+
 void NetworkTable::RemoveTableListener(ITableListener* listener) {
   std::lock_guard<std::mutex> lock(m_mutex);
   auto matches_begin =