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// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
// SPDX-License-Identifier: GPL-3.0-or-later
#pragma once
#include <list>
#include <optional>
#include <shared_mutex>
#include <unordered_map>
#include <utility>
#include "common/logging/log.h"
template <typename KeyType, typename ValueType>
class LRUCache {
public:
using key_type = KeyType;
using value_type = ValueType;
using size_type = std::size_t;
struct Statistics {
size_type hits = 0;
size_type misses = 0;
void reset() noexcept { hits = misses = 0; }
};
explicit LRUCache(size_type capacity, bool enabled = true)
: enabled_{enabled}, capacity_{capacity} {
cache_map_.reserve(capacity_);
LOG_WARNING(Core, "LRU Cache initialised (state: {} | capacity: {})", enabled_ ? "enabled" : "disabled", capacity_);
}
// Non-movable copy semantics
LRUCache(const LRUCache&) = delete;
LRUCache& operator=(const LRUCache&) = delete;
LRUCache(LRUCache&& other) noexcept { *this = std::move(other); }
LRUCache& operator=(LRUCache&& other) noexcept {
if (this == &other) return *this;
std::unique_lock this_lock(mutex_, std::defer_lock);
std::unique_lock other_lock(other.mutex_, std::defer_lock);
std::lock(this_lock, other_lock);
enabled_ = other.enabled_;
capacity_ = other.capacity_;
cache_list_ = std::move(other.cache_list_);
cache_map_ = std::move(other.cache_map_);
stats_ = other.stats_;
return *this;
}
~LRUCache() = default;
[[nodiscard]] value_type* get(const key_type& key) {
if (!enabled_) [[unlikely]] return nullptr;
std::unique_lock lock(mutex_);
auto it = cache_map_.find(key);
if (it == cache_map_.end()) {
++stats_.misses;
return nullptr;
}
move_to_front(it);
++stats_.hits;
return &it->second.second;
}
[[nodiscard]] value_type* peek(const key_type& key) const {
if (!enabled_) [[unlikely]] return nullptr;
std::shared_lock lock(mutex_);
auto it = cache_map_.find(key);
return it == cache_map_.end() ? nullptr : &it->second.second;
}
template <typename V>
void put(const key_type& key, V&& value) {
if (!enabled_) [[unlikely]] return;
std::unique_lock lock(mutex_);
insert_or_update(key, std::forward<V>(value));
}
template <typename ValueFactory>
value_type& get_or_emplace(const key_type& key, ValueFactory&& factory) {
std::unique_lock lock(mutex_);
auto it = cache_map_.find(key);
if (it != cache_map_.end()) {
move_to_front(it);
return it->second.second;
}
value_type new_value = factory();
insert_or_update(key, std::move(new_value));
return cache_map_.find(key)->second.second;
}
[[nodiscard]] bool contains(const key_type& key) const {
if (!enabled_) return false;
std::shared_lock lock(mutex_);
return cache_map_.find(key) != cache_map_.end();
}
bool erase(const key_type& key) {
if (!enabled_) return false;
std::unique_lock lock(mutex_);
auto it = cache_map_.find(key);
if (it == cache_map_.end()) return false;
cache_list_.erase(it->second.first);
cache_map_.erase(it);
return true;
}
void clear() {
std::unique_lock lock(mutex_);
cache_list_.clear();
cache_map_.clear();
stats_.reset();
}
[[nodiscard]] size_type size() const {
if (!enabled_) return 0;
std::shared_lock lock(mutex_);
return cache_map_.size();
}
[[nodiscard]] size_type get_capacity() const { return capacity_; }
void resize(size_type new_capacity) {
if (!enabled_) return;
std::unique_lock lock(mutex_);
capacity_ = new_capacity;
shrink_if_needed();
cache_map_.reserve(capacity_);
}
void setEnabled(bool state) {
std::unique_lock lock(mutex_);
enabled_ = state;
LOG_WARNING(Core, "LRU Cache state changed to: {}", state ? "enabled" : "disabled");
if (!enabled_) clear();
}
[[nodiscard]] bool isEnabled() const { return enabled_; }
[[nodiscard]] Statistics stats() const {
std::shared_lock lock(mutex_);
return stats_;
}
private:
using list_type = std::list<key_type>;
using list_iterator = typename list_type::iterator;
using map_value_type = std::pair<list_iterator, value_type>;
using map_type = std::unordered_map<key_type, map_value_type>;
template <typename V>
void insert_or_update(const key_type& key, V&& value) {
auto it = cache_map_.find(key);
if (it != cache_map_.end()) {
it->second.second = std::forward<V>(value);
move_to_front(it);
return;
}
// evict LRU if full
if (cache_map_.size() >= capacity_) {
const auto& lru_key = cache_list_.back();
cache_map_.erase(lru_key);
cache_list_.pop_back();
}
cache_list_.push_front(key);
cache_map_[key] = {cache_list_.begin(), std::forward<V>(value)};
}
void move_to_front(typename map_type::iterator it) {
cache_list_.splice(cache_list_.begin(), cache_list_, it->second.first);
it->second.first = cache_list_.begin();
}
void shrink_if_needed() {
while (cache_map_.size() > capacity_) {
const auto& lru_key = cache_list_.back();
cache_map_.erase(lru_key);
cache_list_.pop_back();
}
}
private:
mutable std::shared_mutex mutex_;
bool enabled_{true};
size_type capacity_;
list_type cache_list_;
map_type cache_map_;
mutable Statistics stats_;
};
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