ObjectCache.hpp

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/*
    MIT License
 
    DiscordCoreAPI, A bot library for Discord, written in C++, and featuring explicit multithreading through the usage of custom, asynchronous C++ CoRoutines.
 
    Copyright 2022, 2023 Chris M. (RealTimeChris)
 
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/// ObjectCache.hpp - Header file for the "object_cache" stuff.
/// Dec 12, 2021
/// https://discordcoreapi.com
/// \file ObjectCache.hpp
#pragma once
 
#include <discordcoreapi/Utilities/Base.hpp>
#include <discordcoreapi/Utilities/Etf.hpp>
#include <discordcoreapi/Utilities/UniquePtr.hpp>
 
namespace discord_core_api {
 
    /// @brief A template class representing an object cache.
    /// @tparam value_type the type of values stored in the cache.
    template<typename value_type> class object_cache {
      public:
        using mapped_type     = value_type;
        using reference       = mapped_type&;
        using const_reference = const mapped_type&;
        using pointer         = mapped_type*;
 
        /// @brief Default constructor for the object_cache class.
        DCA_INLINE object_cache() : cacheMap{} {};
 
        /// @brief Move assignment operator for the object_cache class.
        /// @param other another object_cache instance to be moved.
        /// @return reference to the current object_cache instance.
        DCA_INLINE object_cache& operator=(object_cache&& other) noexcept {
            if (this != &other) {
                std::unique_lock lock01{ other.cacheMutex };
                std::unique_lock lock02{ cacheMutex };
                std::swap(cacheMap, other.cacheMap);
            }
            return *this;
        }
 
        /// @brief Move constructor for the object_cache class.
        /// @param other another object_cache instance to be moved.
        DCA_INLINE object_cache(object_cache&& other) noexcept {
            *this = std::move(other);
        }
 
        /// @brief Add an object to the cache.
        /// @tparam mapped_type_new the type of the object to be added.
        /// @param object the object to be added to the cache.
        /// @return an iterator pointing to the newly added object in the cache.
        template<typename mapped_type_new> DCA_INLINE auto emplace(mapped_type_new&& object) {
            std::unique_lock lock(cacheMutex);
            return cacheMap.emplace(makeUnique<std::remove_cvref_t<mapped_type_new>>(std::forward<mapped_type_new>(object)));
        }
 
        /// @brief Access an object in the cache using a key.
        /// @tparam mapped_type_new the type of the key used for access.
        /// @param key the key used for accessing the object in the cache.
        /// @return reference to the object associated with the provided key.
        template<typename mapped_type_new> DCA_INLINE reference operator[](mapped_type_new&& key) {
            std::shared_lock lock(cacheMutex);
            if (!cacheMap.contains(key)) {
                cacheMap.emplace(makeUnique<mapped_type>());
            }
            return *cacheMap.operator[](key);
        }
 
        /// @brief Check if the cache contains an object with a given key.
        /// @tparam mapped_type_new the type of the key to be checked.
        /// @param key the key to check for existence in the cache.
        /// @return `true` if the cache contains the key, `false` otherwise.
        template<typename mapped_type_new> DCA_INLINE bool contains(mapped_type_new&& key) {
            std::shared_lock lock(cacheMutex);
            return cacheMap.contains(std::forward<mapped_type_new>(key));
        }
 
        /// @brief Remove an object from the cache using a key.
        /// @tparam mapped_type_new the type of the key used for removal.
        /// @param key the key used to remove the object from the cache.
        template<typename mapped_type_new> DCA_INLINE void erase(mapped_type_new&& key) {
            std::unique_lock lock(cacheMutex);
            cacheMap.erase(std::forward<mapped_type_new>(key));
        }
 
        /// @brief Get the number of objects currently in the cache.
        /// @return the number of objects in the cache.
        DCA_INLINE uint64_t count() {
            std::shared_lock lock(cacheMutex);
            return cacheMap.size();
        }
 
        /// @brief Get an iterator to the beginning of the cache.
        /// @return an iterator to the beginning of the cache.
        DCA_INLINE auto begin() {
            return cacheMap.begin();
        }
 
        /// @brief Get an iterator to the end of the cache.
        /// @return an iterator to the end of the cache.
        DCA_INLINE auto end() {
            return cacheMap.end();
        }
 
        /// @brief Destructor for the object_cache class.
        DCA_INLINE ~object_cache(){};
 
      protected:
        unordered_set<unique_ptr<mapped_type>> cacheMap{};///< The underlying container for storing objects.
        std::shared_mutex cacheMutex{};///< Mutex for ensuring thread-safe access to the cache.
    };
 
 
}