#ifndef ENTT_ENTITY_HANDLE_HPP
#define ENTT_ENTITY_HANDLE_HPP

#include <tuple>
#include <type_traits>
#include <utility>
#include "../config/config.h"
#include "../core/type_traits.hpp"
#include "fwd.hpp"
#include "registry.hpp"

namespace entt {

/**
 * @brief Non-owning handle to an entity.
 *
 * Tiny wrapper around a registry and an entity.
 *
 * @tparam Entity A valid entity type (see entt_traits for more details).
 * @tparam Type Types to which to restrict the scope of a handle.
 */
template<typename Entity, typename... Type>
struct basic_handle {
    /*! @brief Type of registry accepted by the handle. */
    using registry_type = constness_as_t<basic_registry<std::remove_const_t<Entity>>, Entity>;
    /*! @brief Underlying entity identifier. */
    using entity_type = typename registry_type::entity_type;
    /*! @brief Underlying version type. */
    using version_type = typename registry_type::version_type;
    /*! @brief Unsigned integer type. */
    using size_type = typename registry_type::size_type;

    /*! @brief Constructs an invalid handle. */
    basic_handle() ENTT_NOEXCEPT
        : reg{},
          entt{null} {}

    /**
     * @brief Constructs a handle from a given registry and entity.
     * @param ref An instance of the registry class.
     * @param value A valid identifier.
     */
    basic_handle(registry_type &ref, entity_type value) ENTT_NOEXCEPT
        : reg{&ref},
          entt{value} {}

    /**
     * @brief Constructs a const handle from a non-const one.
     * @tparam Other A valid entity type (see entt_traits for more details).
     * @tparam Args Scope of the handle to construct.
     * @return A const handle referring to the same registry and the same
     * entity.
     */
    template<typename Other, typename... Args>
    operator basic_handle<Other, Args...>() const ENTT_NOEXCEPT {
        static_assert(std::is_same_v<Other, Entity> || std::is_same_v<std::remove_const_t<Other>, Entity>, "Invalid conversion between different handles");
        static_assert((sizeof...(Type) == 0 || ((sizeof...(Args) != 0 && sizeof...(Args) <= sizeof...(Type)) && ... && (type_list_contains_v<type_list<Type...>, Args>))), "Invalid conversion between different handles");

        return reg ? basic_handle<Other, Args...>{*reg, entt} : basic_handle<Other, Args...>{};
    }

    /**
     * @brief Converts a handle to its underlying entity.
     * @return The contained identifier.
     */
    [[nodiscard]] operator entity_type() const ENTT_NOEXCEPT {
        return entity();
    }

    /**
     * @brief Checks if a handle refers to non-null registry pointer and entity.
     * @return True if the handle refers to non-null registry and entity, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
        return reg && reg->valid(entt);
    }

    /**
     * @brief Checks if a handle refers to a valid entity or not.
     * @return True if the handle refers to a valid entity, false otherwise.
     */
    [[nodiscard]] bool valid() const {
        return reg->valid(entt);
    }

    /**
     * @brief Returns a pointer to the underlying registry, if any.
     * @return A pointer to the underlying registry, if any.
     */
    [[nodiscard]] registry_type *registry() const ENTT_NOEXCEPT {
        return reg;
    }

    /**
     * @brief Returns the entity associated with a handle.
     * @return The entity associated with the handle.
     */
    [[nodiscard]] entity_type entity() const ENTT_NOEXCEPT {
        return entt;
    }

    /**
     * @brief Destroys the entity associated with a handle.
     * @sa basic_registry::destroy
     */
    void destroy() {
        reg->destroy(entt);
    }

    /**
     * @brief Destroys the entity associated with a handle.
     * @sa basic_registry::destroy
     * @param version A desired version upon destruction.
     */
    void destroy(const version_type version) {
        reg->destroy(entt, version);
    }

    /**
     * @brief Assigns the given component to a handle.
     * @sa basic_registry::emplace
     * @tparam Component Type of component to create.
     * @tparam Args Types of arguments to use to construct the component.
     * @param args Parameters to use to initialize the component.
     * @return A reference to the newly created component.
     */
    template<typename Component, typename... Args>
    decltype(auto) emplace(Args &&...args) const {
        static_assert(((sizeof...(Type) == 0) || ... || std::is_same_v<Component, Type>), "Invalid type");
        return reg->template emplace<Component>(entt, std::forward<Args>(args)...);
    }

    /**
     * @brief Assigns or replaces the given component for a handle.
     * @sa basic_registry::emplace_or_replace
     * @tparam Component Type of component to assign or replace.
     * @tparam Args Types of arguments to use to construct the component.
     * @param args Parameters to use to initialize the component.
     * @return A reference to the newly created component.
     */
    template<typename Component, typename... Args>
    decltype(auto) emplace_or_replace(Args &&...args) const {
        static_assert(((sizeof...(Type) == 0) || ... || std::is_same_v<Component, Type>), "Invalid type");
        return reg->template emplace_or_replace<Component>(entt, std::forward<Args>(args)...);
    }

    /**
     * @brief Patches the given component for a handle.
     * @sa basic_registry::patch
     * @tparam Component Type of component to patch.
     * @tparam Func Types of the function objects to invoke.
     * @param func Valid function objects.
     * @return A reference to the patched component.
     */
    template<typename Component, typename... Func>
    decltype(auto) patch(Func &&...func) const {
        static_assert(((sizeof...(Type) == 0) || ... || std::is_same_v<Component, Type>), "Invalid type");
        return reg->template patch<Component>(entt, std::forward<Func>(func)...);
    }

    /**
     * @brief Replaces the given component for a handle.
     * @sa basic_registry::replace
     * @tparam Component Type of component to replace.
     * @tparam Args Types of arguments to use to construct the component.
     * @param args Parameters to use to initialize the component.
     * @return A reference to the component being replaced.
     */
    template<typename Component, typename... Args>
    decltype(auto) replace(Args &&...args) const {
        static_assert(((sizeof...(Type) == 0) || ... || std::is_same_v<Component, Type>), "Invalid type");
        return reg->template replace<Component>(entt, std::forward<Args>(args)...);
    }

    /**
     * @brief Removes the given components from a handle.
     * @sa basic_registry::remove
     * @tparam Component Types of components to remove.
     * @return The number of components actually removed.
     */
    template<typename... Component>
    size_type remove() const {
        static_assert(sizeof...(Type) == 0 || (type_list_contains_v<type_list<Type...>, Component> && ...), "Invalid type");
        return reg->template remove<Component...>(entt);
    }

    /**
     * @brief Erases the given components from a handle.
     * @sa basic_registry::erase
     * @tparam Component Types of components to erase.
     */
    template<typename... Component>
    void erase() const {
        static_assert(sizeof...(Type) == 0 || (type_list_contains_v<type_list<Type...>, Component> && ...), "Invalid type");
        reg->template erase<Component...>(entt);
    }

    /**
     * @brief Checks if a handle has all the given components.
     * @sa basic_registry::all_of
     * @tparam Component Components for which to perform the check.
     * @return True if the handle has all the components, false otherwise.
     */
    template<typename... Component>
    [[nodiscard]] decltype(auto) all_of() const {
        return reg->template all_of<Component...>(entt);
    }

    /**
     * @brief Checks if a handle has at least one of the given components.
     * @sa basic_registry::any_of
     * @tparam Component Components for which to perform the check.
     * @return True if the handle has at least one of the given components,
     * false otherwise.
     */
    template<typename... Component>
    [[nodiscard]] decltype(auto) any_of() const {
        return reg->template any_of<Component...>(entt);
    }

    /**
     * @brief Returns references to the given components for a handle.
     * @sa basic_registry::get
     * @tparam Component Types of components to get.
     * @return References to the components owned by the handle.
     */
    template<typename... Component>
    [[nodiscard]] decltype(auto) get() const {
        static_assert(sizeof...(Type) == 0 || (type_list_contains_v<type_list<Type...>, Component> && ...), "Invalid type");
        return reg->template get<Component...>(entt);
    }

    /**
     * @brief Returns a reference to the given component for a handle.
     * @sa basic_registry::get_or_emplace
     * @tparam Component Type of component to get.
     * @tparam Args Types of arguments to use to construct the component.
     * @param args Parameters to use to initialize the component.
     * @return Reference to the component owned by the handle.
     */
    template<typename Component, typename... Args>
    [[nodiscard]] decltype(auto) get_or_emplace(Args &&...args) const {
        static_assert(((sizeof...(Type) == 0) || ... || std::is_same_v<Component, Type>), "Invalid type");
        return reg->template get_or_emplace<Component>(entt, std::forward<Args>(args)...);
    }

    /**
     * @brief Returns pointers to the given components for a handle.
     * @sa basic_registry::try_get
     * @tparam Component Types of components to get.
     * @return Pointers to the components owned by the handle.
     */
    template<typename... Component>
    [[nodiscard]] auto try_get() const {
        static_assert(sizeof...(Type) == 0 || (type_list_contains_v<type_list<Type...>, Component> && ...), "Invalid type");
        return reg->template try_get<Component...>(entt);
    }

    /**
     * @brief Checks if a handle has components assigned.
     * @return True if the handle has no components assigned, false otherwise.
     */
    [[nodiscard]] bool orphan() const {
        return reg->orphan(entt);
    }

    /**
     * @brief Visits a handle and returns the pools for its components.
     *
     * The signature of the function should be equivalent to the following:
     *
     * @code{.cpp}
     * void(id_type, const basic_sparse_set<entity_type> &);
     * @endcode
     *
     * Returned pools are those that contain the entity associated with the
     * handle.
     *
     * @tparam Func Type of the function object to invoke.
     * @param func A valid function object.
     */
    template<typename Func>
    void visit(Func &&func) const {
        for(auto [id, storage]: reg->storage()) {
            if(storage.contains(entt)) {
                func(id, storage);
            }
        }
    }

private:
    registry_type *reg;
    entity_type entt;
};

/**
 * @brief Compares two handles.
 * @tparam Args Scope of the first handle.
 * @tparam Other Scope of the second handle.
 * @param lhs A valid handle.
 * @param rhs A valid handle.
 * @return True if both handles refer to the same registry and the same
 * entity, false otherwise.
 */
template<typename... Args, typename... Other>
[[nodiscard]] bool operator==(const basic_handle<Args...> &lhs, const basic_handle<Other...> &rhs) ENTT_NOEXCEPT {
    return lhs.registry() == rhs.registry() && lhs.entity() == rhs.entity();
}

/**
 * @brief Compares two handles.
 * @tparam Args Scope of the first handle.
 * @tparam Other Scope of the second handle.
 * @param lhs A valid handle.
 * @param rhs A valid handle.
 * @return False if both handles refer to the same registry and the same
 * entity, true otherwise.
 */
template<typename... Args, typename... Other>
[[nodiscard]] bool operator!=(const basic_handle<Args...> &lhs, const basic_handle<Other...> &rhs) ENTT_NOEXCEPT {
    return !(lhs == rhs);
}

/**
 * @brief Deduction guide.
 * @tparam Entity A valid entity type (see entt_traits for more details).
 */
template<typename Entity>
basic_handle(basic_registry<Entity> &, Entity) -> basic_handle<Entity>;

/**
 * @brief Deduction guide.
 * @tparam Entity A valid entity type (see entt_traits for more details).
 */
template<typename Entity>
basic_handle(const basic_registry<Entity> &, Entity) -> basic_handle<const Entity>;

} // namespace entt

#endif