netrunner/src/LRUCache.h

#pragma once
#ifndef CACHE_H
#define CACHE_H

#include <unordered_map>
#include <list>
#include <utility>
#include <iostream>

template<class K, class V>
class LRUCache {
	using Key_list = std::list<std::pair<K, V>>;
	Key_list key_values;
	std::unordered_map<K, typename Key_list::iterator> positions;
	size_t max_values;

	void remove_oldest() {
		while (positions.size() >= max_values) {
			positions.erase(key_values.back().first);
			key_values.pop_back();
		}
	}

public:
	LRUCache(const size_t max_values) : max_values(max_values) {
	}

	template<class VV>
	void insert(const K& key, VV&& value) {
		remove_oldest();
		key_values.emplace_front(key, value);
		positions[key] = key_values.begin();
	}

	std::pair<V*, bool> find(const K& key) {
		auto p = positions.find(key);
		if (p == positions.end())
			return {nullptr, false};
		auto iter = p->second;
		auto& value = iter->second;
		// If the iterator is not at the front of the list, move it there.
		if (iter != key_values.begin()) {
			key_values.splice(
					key_values.begin(), 
					key_values, 
					iter, 
					std::next(iter));
		}
		positions[key] = key_values.begin();
		return {&(iter->second), true};
	}

	void debug_cache() {
		for (auto& p : key_values) {
			std::cout << p.first << ":" << p.second << std::endl;
		}
	}
};

#endif