1 files changed, 280 insertions, 0 deletions
diff --git a/entity/entity.hpp b/entity/entity.hpp
new file mode 100644
index 00000000..8f0980ae
--- /dev/null
+++ b/entity/entity.hpp
@@ -0,0 +1,280 @@
+#pragma once
+#include "name-of.hpp"
+#include "compat/integer-types.hpp"
+#include "accessor.hpp"
+#include "util.hpp"
+#include <concepts>
+#include <compare>
+#include <type_traits>
+#include <utility>
+#include <tuple>
+#include <typeinfo>
+#include <array>
+#include <compat/function2.hpp>
+#include <Corrade/Containers/StringView.h>
+
+namespace floormat::entities {
+
+template<typename F, typename T, typename FieldType>
+concept FieldReader_memfn = requires(const T x, F f) {
+    { (x.*f)() } -> std::convertible_to<FieldType>;
+};
+
+template<typename F, typename T, typename FieldType>
+concept FieldReader_ptr = requires(const T x, F f) {
+    { x.*f } -> std::convertible_to<FieldType>;
+};
+
+template<typename F, typename T, typename FieldType>
+concept FieldReader_function = requires(const T x, F f) {
+    { f(x) } -> std::convertible_to<FieldType>;
+};
+
+template<typename F, typename T, typename FieldType>
+concept FieldReader = requires {
+    requires FieldReader_memfn<F, T, FieldType> ||
+             FieldReader_ptr<F, T, FieldType> ||
+             FieldReader_function<F, T, FieldType>;
+};
+
+template<typename F, typename T, typename FieldType>
+concept FieldWriter_memfn = requires(T x, move_qualified<FieldType> value, F f) {
+    { (x.*f)(value) } -> std::same_as<void>;
+};
+
+template<typename F, typename T, typename FieldType>
+concept FieldWriter_ptr = requires(T x, move_qualified<FieldType> value, F f) {
+    { x.*f = value };
+};
+
+template<typename F, typename T, typename FieldType>
+concept FieldWriter_function = requires(T x, move_qualified<FieldType> value, F f) {
+    { f(x, value) } -> std::same_as<void>;
+};
+
+template<typename F, typename T, typename FieldType>
+concept FieldWriter = requires {
+    requires FieldWriter_memfn<F, T, FieldType> ||
+             FieldWriter_ptr<F, T, FieldType> ||
+             FieldWriter_function<F, T, FieldType>;
+};
+
+namespace detail {
+
+template<typename Obj, typename Type, FieldReader<Obj, Type> R>
+struct read_field {
+    static constexpr Type read(const Obj& x, R r) { return r(x); }
+};
+
+template<typename Obj, typename Type>
+struct read_field<Obj, Type, Type (Obj::*)() const> {
+    static constexpr Type read(const Obj& x, Type (Obj::*r)() const) { return (x.*r)(); }
+};
+
+template<typename Obj, typename Type>
+struct read_field<Obj, Type, Type Obj::*> {
+    static constexpr Type read(const Obj& x, Type Obj::*r) { return x.*r; }
+};
+
+template<typename Obj, typename Type, bool IsOwning, bool IsCopyable, typename Capacity, bool IsThrowing, bool HasStrongExceptionGuarantee>
+struct read_field<Obj, Type, fu2::function_base<IsOwning, IsCopyable, Capacity, IsThrowing, HasStrongExceptionGuarantee, void(const Obj&, move_qualified<Type>) const>> {
+    template<typename F> static constexpr Type read(const Obj& x, F&& fun) { return fun(x); }
+};
+
+template<typename Obj, typename FieldType, FieldWriter<Obj, FieldType> W> struct write_field {
+    static constexpr void write(Obj& x, W w, move_qualified<FieldType> value) { w(x, value); }
+};
+
+template<typename Obj, typename FieldType>
+struct write_field<Obj, FieldType, void(Obj::*)(move_qualified<FieldType>)> {
+    static constexpr void write(Obj& x, void(Obj::*w)(move_qualified<FieldType>), move_qualified<FieldType> value) { (x.*w)(value); }
+};
+
+template<typename Obj, typename FieldType>
+struct write_field<Obj, FieldType, FieldType Obj::*> {
+    static constexpr void write(Obj& x, FieldType Obj::* w, move_qualified<FieldType> value) { x.*w = value; }
+};
+
+template<typename Obj, typename Type, bool IsOwning, bool IsCopyable, typename Capacity, bool IsThrowing, bool HasStrongExceptionGuarantee>
+struct write_field<Obj, Type, fu2::function_base<IsOwning, IsCopyable, Capacity, IsThrowing, HasStrongExceptionGuarantee, void(Obj&, move_qualified<Type>) const>> {
+    template<typename F> static constexpr void write(Obj& x, F&& fun, move_qualified<Type> value) { fun(x, value); }
+};
+
+template<typename F, typename Tuple, std::size_t N>
+requires std::invocable<F, decltype(std::get<N>(std::declval<Tuple>()))>
+constexpr CORRADE_ALWAYS_INLINE void visit_tuple(F&& fun, Tuple&& tuple)
+{
+    using Size = std::tuple_size<std::remove_cvref_t<Tuple>>;
+    static_assert(N < Size());
+
+    fun(std::get<N>(tuple));
+    if constexpr(N+1 < Size())
+        visit_tuple<F, Tuple, N+1>(std::forward<F>(fun), std::forward<Tuple>(tuple));
+}
+
+template<typename F, typename Tuple, std::size_t N>
+requires std::is_invocable_r_v<bool, F, decltype(std::get<N>(std::declval<Tuple>()))>
+constexpr CORRADE_ALWAYS_INLINE bool find_in_tuple(F&& fun, Tuple&& tuple)
+{
+    using Size = std::tuple_size<std::remove_cvref_t<Tuple>>;
+    static_assert(N < Size());
+
+    if (fun(std::get<N>(tuple)))
+        return true;
+    if constexpr(N+1 < Size())
+        return find_in_tuple<F, Tuple, N+1>(std::forward<F>(fun), std::forward<Tuple>(tuple));
+    return false;
+}
+
+template<typename T> struct decay_tuple_;
+template<typename... Ts> struct decay_tuple_<std::tuple<Ts...>> {
+    using type = std::tuple<std::decay_t<Ts>...>;
+};
+
+template<typename T>
+using decay_tuple = typename decay_tuple_<T>::type;
+
+template<typename T>
+struct accessors_for_
+{
+    using type = decay_tuple<std::decay_t<decltype(T::accessors())>>;
+};
+
+template<typename T>
+using accessors_for = typename accessors_for_<T>::type;
+
+} // namespace detail
+
+template<typename Obj, typename Type> struct entity_field_base {};
+
+template<typename Obj, typename Type, FieldReader<Obj, Type> R, FieldWriter<Obj, Type> W>
+struct entity_field : entity_field_base<Obj, Type> {
+    using ObjectType = Obj;
+    using FieldType = Type;
+    using Reader = R;
+    using Writer = W;
+
+    StringView name;
+    [[no_unique_address]] R reader;
+    [[no_unique_address]] W writer;
+
+    constexpr entity_field(const entity_field&) = default;
+    constexpr entity_field& operator=(const entity_field&) = default;
+    static constexpr decltype(auto) read(const R& reader, const Obj& x) { return detail::read_field<Obj, Type, R>::read(x, reader); }
+    static constexpr void write(const W& writer, Obj& x, move_qualified<Type> v) { detail::write_field<Obj, Type, W>::write(x, writer, v); }
+    constexpr decltype(auto) read(const Obj& x) const { return read(reader, x); }
+    constexpr void write(Obj& x, move_qualified<Type> value) const { write(writer, x, value); }
+    constexpr entity_field(StringView name, R r, W w) noexcept : name{name}, reader{r}, writer{w} {}
+
+    constexpr erased_accessor erased() const {
+        using reader_t = typename erased_accessor::erased_reader_t;
+        using writer_t = typename erased_accessor::erased_writer_t;
+        constexpr auto obj_name = name_of<Obj>, field_name = name_of<Type>;
+
+        constexpr auto reader_fn = [](const void* obj, const reader_t* reader, void* value)
+        {
+            const auto& obj_ = *reinterpret_cast<const Obj*>(obj);
+            const auto& reader_ = *reinterpret_cast<const R*>(reader);
+            auto& value_ = *reinterpret_cast<Type*>(value);
+            value_ = read(reader_, obj_);
+        };
+        constexpr auto writer_fn = [](void* obj, const writer_t* writer, void* value)
+        {
+            auto& obj_ = *reinterpret_cast<Obj*>(obj);
+            const auto& writer_ = *reinterpret_cast<const W*>(writer);
+            move_qualified<Type> value_ = std::move(*reinterpret_cast<Type*>(value));
+            write(writer_, obj_, value_);
+        };
+        return erased_accessor{
+            (void*)&reader, (void*)&writer,
+            obj_name, field_name,
+            reader_fn, writer_fn,
+        };
+    }
+};
+
+template<typename Obj>
+struct Entity final {
+    static_assert(std::is_same_v<Obj, std::decay_t<Obj>>);
+
+    template<typename Type>
+    struct type final
+    {
+        template<FieldReader<Obj, Type> R, FieldWriter<Obj, Type> W>
+        struct field final : entity_field<Obj, Type, R, W>
+        {
+            constexpr field(StringView field_name, R r, W w) noexcept :
+                entity_field<Obj, Type, R, W>{field_name, r, w}
+            {}
+        };
+
+        template<FieldReader<Obj, Type> R, FieldWriter<Obj, Type> W>
+        field(StringView name, R r, W w) -> field<R, W>;
+    };
+};
+
+template<typename F, typename Tuple>
+constexpr void visit_tuple(F&& fun, Tuple&& tuple)
+{
+    using Size = std::tuple_size<std::decay_t<Tuple>>;
+    if constexpr(Size() > 0)
+        detail::visit_tuple<F, Tuple, 0>(std::forward<F>(fun), std::forward<Tuple>(tuple));
+}
+
+template<typename F, typename Tuple>
+constexpr bool find_in_tuple(F&& fun, Tuple&& tuple)
+{
+    using Size = std::tuple_size<std::decay_t<Tuple>>;
+    if constexpr(Size() > 0)
+        return detail::find_in_tuple<F, Tuple, 0>(std::forward<F>(fun), std::forward<Tuple>(tuple));
+    else
+        return false;
+}
+
+enum class erased_field_type : std::uint32_t {
+    none,
+    string,
+    u8, u16, u32, u64, s8, s16, s32, s64,
+    user_type_start,
+    MAX = (1u << 31) - 1u,
+    DYNAMIC = (std::uint32_t)-1,
+};
+
+template<erased_field_type> struct type_of_erased_field;
+template<typename T> struct erased_field_type_v_ : std::integral_constant<erased_field_type, erased_field_type::DYNAMIC> {};
+
+#define FM_ERASED_FIELD_TYPE(TYPE, ENUM)                                                                                    \
+    template<> struct erased_field_type_v_<TYPE> : std::integral_constant<erased_field_type, erased_field_type::ENUM> {};   \
+    template<> struct type_of_erased_field<erased_field_type::ENUM> { using type = TYPE; }
+FM_ERASED_FIELD_TYPE(std::uint8_t, u8);
+FM_ERASED_FIELD_TYPE(std::uint16_t, u16);
+FM_ERASED_FIELD_TYPE(std::uint32_t, u32);
+FM_ERASED_FIELD_TYPE(std::uint64_t, u64);
+FM_ERASED_FIELD_TYPE(std::int8_t, s8);
+FM_ERASED_FIELD_TYPE(std::int16_t, s16);
+FM_ERASED_FIELD_TYPE(std::int32_t, s32);
+FM_ERASED_FIELD_TYPE(std::int64_t, s64);
+FM_ERASED_FIELD_TYPE(StringView, string);
+#undef FM_ERASED_FIELD_TYPE
+
+} // namespace floormat::entities
+
+namespace floormat {
+
+template<typename T>
+requires std::is_same_v<T, std::decay_t<T>>
+class entity_metadata final {
+    template<typename... Ts>
+    static constexpr auto erased_helper(const std::tuple<Ts...>& tuple)
+    {
+        std::array<entities::erased_accessor, sizeof...(Ts)> array { std::get<Ts>(tuple).erased()..., };
+        return array;
+    }
+public:
+    static constexpr StringView class_name = name_of<T>;
+    static constexpr std::size_t size = std::tuple_size_v<entities::detail::accessors_for<T>>;
+    static constexpr entities::detail::accessors_for<T> accessors = T::accessors();
+    static constexpr auto erased_accessors = erased_helper(accessors);
+};
+
+} // namespace floormat