enum_metadata.hpp

// Copyright Take Vos 2021.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)
 
#pragma once
 
#include "required.hpp"
#include "cast.hpp"
#include "assert.hpp"
#include <cstddef>
#include <type_traits>
#include <array>
#include <algorithm>
#include <string_view>
 
hi_warning_push();
// C26445: Do not assign gsl::span or std::string_view to a reference. They are cheap to construct and are not owners of
// the underlying data. (gsl.view).
// False positive, sometimes the template is instantiated with string_view, sometimes not.
hi_warning_ignore_msvc(26445);
 
namespace hi::inline v1 {
 
template<typename ValueType, typename NameType, std::size_t N>
class enum_metadata {
public:
    using value_type = ValueType;
    using name_type = NameType;
 
    static constexpr std::size_t count = N;
 
    bool values_are_continues;
 
    static_assert(std::is_enum_v<value_type>, "value_type Must be an enum");
    static_assert(N != 0);
 
    [[nodiscard]] constexpr size_t size() const noexcept
    {
        return count;
    }
 
    [[nodiscard]] constexpr value_type minimum() const noexcept
    {
        return std::get<0>(_by_value).value;
    }
 
    [[nodiscard]] constexpr value_type maximum() const noexcept
    {
        return std::get<N - 1>(_by_value).value;
    }
 
    template<typename... Args>
    [[nodiscard]] constexpr enum_metadata(Args const&...args) noexcept
    {
        static_assert(sizeof...(Args) == N * 2);
        add_value_name<0>(args...);
 
        std::sort(_by_name.begin(), _by_name.end(), [](hilet& a, hilet& b) {
            return a.name < b.name;
        });
 
        std::sort(_by_value.begin(), _by_value.end(), [](hilet& a, hilet& b) {
            return to_underlying(a.value) < to_underlying(b.value);
        });
 
        values_are_continues = check_values_are_continues();
    }
 
    [[nodiscard]] constexpr bool contains(std::convertible_to<name_type> auto&& name) const noexcept
    {
        return find(name_type{hi_forward(name)}) != nullptr;
    }
 
    [[nodiscard]] constexpr bool contains(value_type value) const noexcept
    {
        return find(value) != nullptr;
    }
 
    [[nodiscard]] constexpr value_type at(std::convertible_to<name_type> auto&& name) const
    {
        if (hilet *value = find(name_type{hi_forward(name)})) {
            return *value;
        } else {
            throw std::out_of_range{"enum_metadata::at"};
        }
    }
 
    [[nodiscard]] constexpr name_type const& at(value_type value) const
    {
        if (hilet *name = find(value)) {
            return *name;
        } else {
            throw std::out_of_range{"enum_metadata::at"};
        }
    }
 
    [[nodiscard]] constexpr value_type at(std::convertible_to<name_type> auto&& name, value_type default_value) const noexcept
    {
        if (hilet *value = find(name_type{hi_forward(name)})) {
            return *value;
        } else {
            return default_value;
        }
    }
 
    [[nodiscard]] constexpr name_type at(value_type value, std::convertible_to<name_type> auto&& default_name) const noexcept
    {
        if (hilet *name = find(value)) {
            return *name;
        } else {
            return hi_forward(default_name);
        }
    }
 
    [[nodiscard]] constexpr value_type operator[](std::convertible_to<name_type> auto&& name) const noexcept
    {
        auto *value = find(name_type{hi_forward(name)});
        hi_axiom(value != nullptr);
        return *value;
    }
 
    [[nodiscard]] constexpr name_type const& operator[](value_type value) const noexcept
    {
        auto *name = find(value);
        hi_axiom(name != nullptr);
        return *name;
    }
 
private:
    struct value_name {
        value_type value;
        name_type name;
 
        constexpr value_name() noexcept : value(), name() {}
        constexpr value_name(value_type value, name_type name) noexcept : value(value), name(std::move(name)) {}
    };
 
    std::array<value_name, N> _by_name;
    std::array<value_name, N> _by_value;
 
    [[nodiscard]] constexpr name_type const *find(value_type value) const noexcept
    {
        if (values_are_continues) {
            // If the enum values are continues we can do an associative lookup.
            hilet it = _by_value.begin();
            hilet offset = to_underlying(it->value);
            hilet i = to_underlying(value) - offset;
            return (i >= 0 and i < N) ? &(it + i)->name : nullptr;
 
        } else {
            hilet it = std::lower_bound(_by_value.begin(), _by_value.end(), value, [](hilet& item, hilet& key) {
                return item.value < key;
            });
 
            return (it != _by_value.end() and it->value == value) ? &it->name : nullptr;
        }
    }
 
    [[nodiscard]] constexpr value_type const *find(name_type const& name) const noexcept
    {
        hilet it = std::lower_bound(_by_name.begin(), _by_name.end(), name, [](hilet& item, hilet& key) {
            return item.name < key;
        });
 
        return (it != _by_name.end() and it->name == name) ? &it->value : nullptr;
    }
 
    template<std::size_t I, typename... Rest>
    constexpr void add_value_name(value_type value, name_type name, Rest const&...rest) noexcept
    {
        static_assert(sizeof...(Rest) % 2 == 0);
 
        std::get<I>(_by_name) = {value, name};
        std::get<I>(_by_value) = {value, std::move(name)};
 
        if constexpr (sizeof...(Rest) > 0) {
            add_value_name<I + 1>(rest...);
        }
    }
 
    [[nodiscard]] constexpr bool check_values_are_continues() const noexcept
    {
        auto check_value = to_underlying(minimum());
        for (hilet& item : _by_value) {
            if (to_underlying(item.value) != check_value++) {
                return false;
            }
        }
        return true;
    }
};
 
template<typename T>
struct enum_metadata_name {
    using type = std::decay_t<T>;
};
 
// clang-format off
template<> struct enum_metadata_name<char const *> { using type = std::string_view; };
template<> struct enum_metadata_name<char *> { using type = std::string_view; };
template<size_t N> struct enum_metadata_name<char [N]> { using type = std::string_view; };
template<size_t N> struct enum_metadata_name<char const [N]> { using type = std::string_view; };
// clang-format on
 
template<typename T>
using enum_metadata_name_t = enum_metadata_name<T>::type;
 
template<typename ValueType, typename NameType, typename... Rest>
enum_metadata(ValueType const&, NameType const&, Rest const&...)
    -> enum_metadata<ValueType, enum_metadata_name_t<NameType>, (sizeof...(Rest) + 2) / 2>;
 
} // namespace hi::inline v1
 
hi_warning_pop();