From 1849a0383555aa1ddab91f4dcc2af14467611b05 Mon Sep 17 00:00:00 2001
From: "Alexander A. Klimov" <alexander.klimov@icinga.com>
Date: Wed, 8 Feb 2023 15:28:09 +0100
Subject: [PATCH] Introduce HybridMap

A tree- and hash-map. Ordered iteration combined with O(1) lookup.
---
 lib/base/CMakeLists.txt |   1 +
 lib/base/hybrid-map.hpp | 152 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 153 insertions(+)
 create mode 100644 lib/base/hybrid-map.hpp

diff --git a/lib/base/CMakeLists.txt b/lib/base/CMakeLists.txt
index 18e884de2..98e6a9981 100644
--- a/lib/base/CMakeLists.txt
+++ b/lib/base/CMakeLists.txt
@@ -37,6 +37,7 @@ set(base_SOURCES
   fifo.cpp fifo.hpp
   filelogger.cpp filelogger.hpp filelogger-ti.hpp
   function.cpp function.hpp function-ti.hpp function-script.cpp functionwrapper.hpp
+  hybrid-map.hpp
   initialize.cpp initialize.hpp
   io-engine.cpp io-engine.hpp
   journaldlogger.cpp journaldlogger.hpp journaldlogger-ti.hpp
diff --git a/lib/base/hybrid-map.hpp b/lib/base/hybrid-map.hpp
new file mode 100644
index 000000000..5f85e369f
--- /dev/null
+++ b/lib/base/hybrid-map.hpp
@@ -0,0 +1,152 @@
+/* Icinga 2 | (c) 2023 Icinga GmbH | GPLv2+ */
+
+#pragma once
+
+#include <functional>
+#include <map>
+#include <unordered_map>
+#include <utility>
+
+namespace icinga
+{
+
+/**
+ * Proxies == and std::hash to *this->Target. Useful not to duplicate hash table keys.
+ *
+ * @ingroup base
+ */
+template<class T>
+struct HashProxy
+{
+	T const * Target;
+
+	inline HashProxy(T const * target) : Target(target)
+	{
+	}
+
+	inline bool operator==(const HashProxy& rhs) const
+	{
+		return *Target == *rhs.Target;
+	}
+};
+
+/**
+ * A tree- and hash-map. Ordered iteration combined with O(1) lookup.
+ *
+ * @ingroup base
+ */
+template<class K, class V>
+class HybridMap
+{
+public:
+	typedef typename std::map<K, V>::value_type ValueType;
+	typedef typename std::map<K, V>::iterator Iterator;
+
+	auto Contains(const K& k) const
+	{
+		return m_Fast.find(&k) != m_Fast.end();
+	}
+
+	auto Get(const K& k, V& v) const
+	{
+		auto pos (m_Fast.find(&k));
+
+		if (pos == m_Fast.end()) {
+			return false;
+		}
+
+		v = pos->second->second;
+		return true;
+	}
+
+	inline auto GetLength() const
+	{
+		return m_Fast.size();
+	}
+
+	inline auto begin()
+	{
+		return m_Ordered.begin();
+	}
+
+	inline auto end()
+	{
+		return m_Ordered.end();
+	}
+
+	inline auto begin() const
+	{
+		return m_Ordered.begin();
+	}
+
+	inline auto end() const
+	{
+		return m_Ordered.end();
+	}
+
+	void Set(const K& k, V v)
+	{
+		auto pos (m_Fast.find(&k));
+
+		if (pos == m_Fast.end()) {
+			auto pos (m_Ordered.emplace(k, std::move(v)).first);
+
+			m_Fast.emplace(&pos->first, pos);
+		} else {
+			pos->second->second = std::move(v);
+		}
+	}
+
+	void Set(K&& k, V v)
+	{
+		auto pos (m_Fast.find(&k));
+
+		if (pos == m_Fast.end()) {
+			auto pos (m_Ordered.emplace(std::move(k), std::move(v)).first);
+
+			m_Fast.emplace(&pos->first, pos);
+		} else {
+			pos->second->second = std::move(v);
+		}
+	}
+
+	void Remove(const K& k)
+	{
+		auto pos (m_Fast.find(&k));
+
+		if (pos != m_Fast.end()) {
+			m_Ordered.erase(pos->second);
+			m_Fast.erase(pos);
+		}
+	}
+
+	void Remove(Iterator i)
+	{
+		m_Fast.erase(&i->first);
+		m_Ordered.erase(i);
+	}
+
+	void Clear()
+	{
+		m_Ordered.clear();
+		m_Fast.clear();
+	}
+
+private:
+	std::map<K, V> m_Ordered;
+	std::unordered_map<HashProxy<K>, Iterator> m_Fast;
+};
+
+}
+
+namespace std
+{
+	template<class T>
+	struct hash<icinga::HashProxy<T>>
+	{
+		inline std::size_t operator()(const icinga::HashProxy<T>& hp) const noexcept
+		{
+			return std::hash<T>{}(*hp.Target);
+		}
+	};
+}