From fb55337487e44f0ad091e52595dacabb150ac210 Mon Sep 17 00:00:00 2001
From: Stanislaw Halik <sthalik@misaki.pl>
Date: Tue, 15 Nov 2022 23:31:21 +0100
Subject: entity: more metaprogramming

---
 src/entity.hpp  | 25 ++++++++++++++++++++-----
 test/entity.cpp | 29 +++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+), 5 deletions(-)

diff --git a/src/entity.hpp b/src/entity.hpp
index 3c32ea23..51698651 100644
--- a/src/entity.hpp
+++ b/src/entity.hpp
@@ -6,6 +6,7 @@
 #include <utility>
 #include <algorithm>
 #include <tuple>
+#include <array>
 #include <Corrade/Containers/StringView.h>
 
 namespace floormat {}
@@ -314,14 +315,28 @@ struct except_nth_<0, parameter_pack<As...>, X<T, Ts...>> {
 template<std::size_t N, typename T>
 using except_nth = typename except_nth_<N, parameter_pack<>, T>::type;
 
-template<typename F, typename KeyT, typename Tuple>
-struct sort_tuple_;
-
-template<typename F, typename KeyT, template<typename...> class Tuple, typename... Ts>
-struct sort_tuple_<F, KeyT, Tuple<Ts...>> {
+template<typename Tuple, auto KeyFn, auto Comp>
+struct sort_tuple_ {
+    template<std::size_t... Is>
+    static consteval auto sort_indices(const Tuple& tuple, const std::index_sequence<Is...>&) {
+        std::array<std::size_t, sizeof...(Is)> indices = { Is..., };
+        using KeyT = decltype(KeyFn(std::get<0>(tuple)));
+        std::array<KeyT, sizeof...(Is)> keys = { KeyFn(std::get<Is>(tuple))..., };
+        std::sort(indices.begin(), indices.end(), [&](std::size_t a, std::size_t b) { return Comp(keys[a], keys[b]); });
+        return indices;
+    }
 
+    template<auto Array>
+    struct helper {
+        template<std::size_t... Is>
+        static consteval auto do_sort(const Tuple& tuple, const std::index_sequence<Is...>&) {
+            return std::make_tuple(std::get<Array[Is]>(tuple)...);
+        }
+    };
 };
 
+
+
 } // namespace detail
 
 template<typename F, typename Tuple>
diff --git a/test/entity.cpp b/test/entity.cpp
index 838d18cd..e1bbb055 100644
--- a/test/entity.cpp
+++ b/test/entity.cpp
@@ -64,10 +64,39 @@ static constexpr bool test_visitor()
     return true;
 }
 
+namespace test_sorting {
+
+template<std::size_t I>
+struct item {
+    static constexpr std::size_t size = I-1;
+    std::array<char, I> data;
+    consteval item(const char(&str)[I]) {
+        std::copy(str, str+I, data.data());
+    }
+    template<std::size_t J>
+    constexpr bool operator==(const item<J>& o) const { return data == o.data; }
+};
+
+static constexpr void test()
+{
+    using namespace floormat::entities::detail;
+    constexpr auto tuple = std::make_tuple(item{"bb"}, item{"aaa"}, item{"cccc"}, item{"d"});
+    constexpr auto size = std::tuple_size_v<std::decay_t<decltype(tuple)>>;
+    constexpr auto key = [](const auto& x) constexpr { return StringView(x.data.data(), x.data.size()); };
+    constexpr auto comp = [](auto a, auto b) constexpr { return a < b; };
+    using Sort = sort_tuple_<std::decay_t<decltype(tuple)>, key, comp>;
+    constexpr auto indices = Sort::sort_indices(tuple, std::make_index_sequence<size>());
+    constexpr auto tuple2 = Sort::helper<indices>::do_sort(tuple, std::make_index_sequence<size>());
+    static_assert(tuple2 == std::make_tuple(item{"aaa"}, item{"bb"}, item{"cccc"}, item{"d"}));
+}
+
+} // namespace test_sorting
+
 void test_app::test_entity()
 {
     static_assert(test_accessors());
     static_assert(test_visitor());
+    test_sorting::test();
 }
 
 namespace type_tests {
-- 
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