DepthGuide/src/core_v2/meta_helper.hpp

#ifndef META_HELPER_H
#define META_HELPER_H

#include <boost/any.hpp>

#include <shared_mutex>
#include <string>
#include <unordered_map>

struct meta_base_v2 {
    // using key_type = std::size_t;
    using key_type = std::string;
    using value_type = boost::any;

    using meta_map_type = std::unordered_map<key_type, value_type>;
    meta_map_type meta;
    std::shared_mutex mu;

    void insert(auto &&key, const value_type &value) {
        using Key = decltype(key);
        auto lock = std::unique_lock(mu);
        if constexpr (std::is_convertible_v<Key, key_type>) {
            const auto key_hash = (key_type) key;
            meta[key_hash] = value;
        } else {
            // const auto key_hash = std::hash<Key>()(key);
            const auto key_hash = std::to_string(key);
            meta[key_hash] = value;
        }
    }

    void merge(meta_base_v2 &o) {
        if (this == &o) return;
        //@formatter:off
        auto read_lock = std::shared_lock(o.mu, std::defer_lock);
        auto write_lock = std::unique_lock(mu, std::defer_lock);
        assert(&o.mu != &mu);
        if (&o.mu < &mu) { read_lock.lock(); write_lock.lock(); }
        else { write_lock.lock(); read_lock.lock(); } // prevent deadlock
        //@formatter:on
        meta.insert(o.meta.begin(), o.meta.end());
    }

    template<typename T = value_type>
    T query(auto &&key) {
        using Key = decltype(key);
        auto lock = std::shared_lock(mu);
        auto iter = meta_map_type::const_iterator();
        if constexpr (std::is_convertible_v<Key, key_type>) {
            const auto key_hash = (key_type) key;
            iter = meta.find(key_hash);
        } else {
            // const auto key_hash = std::hash<Key>()(key);
            const auto key_hash = std::to_string(key);
            iter = meta.find(key_hash);
        }
        if constexpr (!std::is_same_v<T, value_type>) {
            assert(iter != meta.end());
            return boost::any_cast<T>(iter->second);
        } else {
            if (iter != meta.end()) {
                return iter->second;
            } else {
                return {};
            }
        }
    }
};

struct meta_proxy {
    using meta_base_type = meta_base_v2;
    using meta_key_type = meta_base_type::key_type;
    using meta_value_type = meta_base_type::value_type;

    using meta_ptr_type = std::shared_ptr<meta_base_type>;
    meta_ptr_type meta;

    void insert_meta(auto &&key, auto &&value) {
        get_meta().insert(key, value);
    }

    void merge_meta(const meta_proxy &o) {
        if (o.meta == nullptr) return;
        get_meta().merge(*o.meta);
    }

    template<typename T = meta_value_type>
    T query_meta(auto &&key) const {
        if (meta == nullptr) {
            if constexpr (std::is_same_v<T, meta_value_type>) {
                return {};
            }
            assert(false);
        }
        return meta->query<T>(key);
    }

    void initialize_meta() {
        get_meta();
    }

private:
    meta_base_type &get_meta() {
        if (meta == nullptr) [[unlikely]] {
            meta = std::make_shared<meta_base_type>();
        }
        return *meta;
    }
};

#endif //META_HELPER_H