class_registrator.hh

/*
 * Copyright (C) 2015-present ScyllaDB
 */

/*
 * SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.0
 */

#pragma once

#include <memory>
#include <seastar/core/shared_ptr.hh>
#include <seastar/core/sstring.hh>

#include "seastarx.hh"

class no_such_class : public std::runtime_error {
public:
    using runtime_error::runtime_error;
};

inline bool is_class_name_qualified(std::string_view class_name) {
    return class_name.find_last_of('.') != std::string_view::npos;
}

// BaseType is a base type of a type hierarchy that this registry will hold
// Args... are parameters for object's constructor
template<typename BaseType, typename... Args>
class nonstatic_class_registry {
    template<typename T, typename ResultType = typename T::ptr_type>
    requires requires (typename T::ptr_type ptr) {
        { ptr.get() } -> std::same_as<T*>;
    }
    struct result_for;

    template<typename T>
    struct result_for<T, std::unique_ptr<T>> {
        typedef std::unique_ptr<T> type;
        template<typename Impl>
        static inline type make(Args&& ...args) {
            return std::make_unique<Impl>(std::forward<Args>(args)...);
        }
    };
    template<typename T>
    struct result_for<T, seastar::shared_ptr<T>> {
        typedef seastar::shared_ptr<T> type;
        template<typename Impl>
        static inline type make(Args&& ...args) {
            return seastar::make_shared<Impl>(std::forward<Args>(args)...);
        }
    };
    template<typename T>
    struct result_for<T, seastar::lw_shared_ptr<T>> {
        typedef seastar::lw_shared_ptr<T> type;
        // lw_shared is not (yet?) polymorph, thus having automatic
        // instantiation of it makes no sense. This way we get a nice
        // compilation error if someone messes up.
    };
    template<typename T>
    struct result_for<T, std::shared_ptr<T>> {
        typedef std::shared_ptr<T> type;
        template<typename Impl>
        static inline type make(Args&& ...args) {
            return std::make_shared<Impl>(std::forward<Args>(args)...);
        }
   };
    template<typename T, typename D>
    struct result_for<T, std::unique_ptr<T, D>> {
        typedef std::unique_ptr<T, D> type;
        template<typename Impl>
        static inline type make(Args&& ...args) {
            return std::make_unique<Impl, D>(std::forward<Args>(args)...);
        }
    };
public:
    using result_type = typename BaseType::ptr_type;
    using creator_type = std::function<result_type(Args...)>;
private:
    std::unordered_map<sstring, creator_type> _classes;
public:
    void register_class(sstring name, creator_type creator);
    template<typename T>
    void register_class(sstring name);
    result_type create(const sstring& name, Args&&...);

    std::unordered_map<sstring, creator_type>& classes() {
        return _classes;
    }
    const std::unordered_map<sstring, creator_type>& classes() const {
        return _classes;
    }

    sstring to_qualified_class_name(std::string_view class_name) const;
};

template<typename BaseType, typename... Args>
void nonstatic_class_registry<BaseType, Args...>::register_class(sstring name, typename nonstatic_class_registry<BaseType, Args...>::creator_type creator) {
    classes().emplace(name, std::move(creator));
}

template<typename BaseType, typename... Args>
template<typename T>
void nonstatic_class_registry<BaseType, Args...>::register_class(sstring name) {
    register_class(name, &result_for<BaseType>::template make<T>);
}

template<typename BaseType, typename... Args>
sstring nonstatic_class_registry<BaseType, Args...>::to_qualified_class_name(std::string_view class_name) const {
    if (is_class_name_qualified(class_name)) {
        return sstring(class_name);
    } else {
        const auto& classes{nonstatic_class_registry<BaseType, Args...>::classes()};

        const auto it = std::ranges::find_if(classes, [class_name](const auto& registered_class) {
            // the fully qualified name contains the short name
            auto i = registered_class.first.find_last_of('.');
            return i != sstring::npos && registered_class.first.compare(i + 1, sstring::npos, class_name) == 0;
        });
        if (it == classes.end()) {
            return sstring(class_name);
        }
        return it->first;
    }
}

// BaseType is a base type of a type hierarchy that this registry will hold
// Args... are parameters for object's constructor
template<typename BaseType, typename... Args>
class class_registry {
    using base_registry = nonstatic_class_registry<BaseType, Args...>;
    static base_registry& registry() {
        static base_registry the_registry;
        return the_registry;
    }
public:
    using result_type = typename base_registry::result_type;
    using creator_type = std::function<result_type(Args...)>;
public:
    static void register_class(sstring name, creator_type creator) {
        registry().register_class(std::move(name), std::move(creator));
    }
    template<typename T>
    static void register_class(sstring name) {
        registry().template register_class<T>(std::move(name));
    }
    template <typename... U>
    static result_type create(const sstring& name, U&&... a) {
        return registry().create(name, std::forward<U>(a)...);
    }

    static std::unordered_map<sstring, creator_type>& classes() {
        return registry().classes();
    }

    static sstring to_qualified_class_name(std::string_view class_name) {
        return registry().to_qualified_class_name(class_name);
    }
};

template<typename BaseType, typename T, typename... Args>
struct class_registrator {
    class_registrator(const sstring& name) {
        class_registry<BaseType, Args...>::template register_class<T>(name);
    }
    class_registrator(const sstring& name, typename class_registry<BaseType, Args...>::creator_type creator) {
        class_registry<BaseType, Args...>::register_class(name, creator);
    }
};

template<typename BaseType, typename... Args>
typename nonstatic_class_registry<BaseType, Args...>::result_type nonstatic_class_registry<BaseType, Args...>::create(const sstring& name, Args&&... args) {
    auto it = classes().find(name);
    if (it == classes().end()) {
        throw no_such_class(sstring("unable to find class '") + name + sstring("'"));
    }

    return it->second(std::forward<Args>(args)...);
}

template<typename BaseType, typename... Args>
typename class_registry<BaseType, Args...>::result_type  create_object(const sstring& name, Args&&... args) {
    return class_registry<BaseType, Args...>::create(name, std::forward<Args>(args)...);
}

class qualified_name {
    sstring _qname;
public:
    qualified_name(std::string_view pkg_pfx, std::string_view name)
        : _qname(is_class_name_qualified(name) ? name : make_sstring(pkg_pfx, name))
    {}
    operator const sstring&() const {
        return _qname;
    }
};

class unqualified_name {
    sstring _qname;
public:
    unqualified_name(std::string_view pkg_pfx, std::string_view name)
        : _qname(name.compare(0, pkg_pfx.size(), pkg_pfx) == 0 ? name.substr(pkg_pfx.size()) : name)
    {}
    operator const sstring&() const {
        return _qname;
    }
};