From 3a7708c0827407733fb0e498c013290d6cfc5cfd Mon Sep 17 00:00:00 2001
From: Alexander Karatarakis <alex@karatarakis.com>
Date: Sun, 30 Jun 2024 14:43:32 -0700
Subject: [PATCH] WIP

---
 test/sub_struct_view_test.cpp | 134 +++++++++++++++++++++++++++++++---
 1 file changed, 122 insertions(+), 12 deletions(-)

diff --git a/test/sub_struct_view_test.cpp b/test/sub_struct_view_test.cpp
index c2bca572..bcc77b4e 100644
--- a/test/sub_struct_view_test.cpp
+++ b/test/sub_struct_view_test.cpp
@@ -1,10 +1,13 @@
 #include "fixed_containers/sub_struct_view.hpp"
 
 #include "fixed_containers/fixed_map.hpp"
+#include "fixed_containers/fixed_set.hpp"
+#include "fixed_containers/fixed_vector.hpp"
 #include "fixed_containers/reflection.hpp"
 
 #include <gtest/gtest.h>
 
+#include <cstddef>
 #include <iterator>
 
 namespace fixed_containers::sub_struct_view
@@ -25,8 +28,27 @@ struct FlatSubStruct1
     const double* retain1;
     const float* retain2;
 };
+
 }  // namespace
 
+template <typename S>
+static auto extract_field_to_offset_map(const S& instance = {})
+{
+    FixedMap<std::string_view, std::ptrdiff_t, reflection::field_count_of<S>()> field_to_offset{};
+    reflection::for_each_field(instance,
+                               [&]<class T>(const std::string_view& name, T& field)
+                               {
+                                   const std::byte* base_pointer =
+                                       reinterpret_cast<const std::byte*>(&instance);
+                                   const std::byte* field_pointer =
+                                       reinterpret_cast<const std::byte*>(&field);
+                                   field_to_offset.try_emplace(
+                                       name, std::distance(base_pointer, field_pointer));
+                               });
+
+    return field_to_offset;
+}
+
 TEST(SubStructView, Flat)
 {
     FlatSuperStruct1 flat_super_struct_1{};
@@ -35,33 +57,121 @@ TEST(SubStructView, Flat)
 
     FlatSubStruct1 flat_sub_struct_1{};
 
-    FixedMap<std::string_view, std::size_t, 10> field_to_offset{};
-    std::size_t current_offset{};
-
-    reflection::for_each_field(flat_sub_struct_1,
-                               [&]<class T>(const std::string_view& name, T& /*field*/)
-                               {
-                                   field_to_offset.try_emplace(name, current_offset);
-                                   current_offset += sizeof(T);
-                               });
+    auto field_to_offset_map = extract_field_to_offset_map(flat_sub_struct_1);
 
     reflection::for_each_field(flat_super_struct_1,
                                [&]<class T>(const std::string_view& name, T& field)
                                {
-                                   auto it = field_to_offset.find(name);
-                                   if (it == field_to_offset.cend())
+                                   auto it = field_to_offset_map.find(name);
+                                   if (it == field_to_offset_map.cend())
                                    {
                                        return;
                                    }
 
                                    std::byte* byte_ptr =
                                        reinterpret_cast<std::byte*>(&flat_sub_struct_1);
-                                   const std::size_t offset = it->second;
+                                   const std::ptrdiff_t offset = it->second;
                                    std::advance(byte_ptr, offset);
                                    T** field_in_struct = reinterpret_cast<T**>(byte_ptr);
                                    *field_in_struct = &field;
                                });
+
     ASSERT_TRUE(flat_sub_struct_1.retain1 == &flat_super_struct_1.retain1);
     ASSERT_TRUE(flat_sub_struct_1.retain2 == &flat_super_struct_1.retain2);
 }
+
+namespace
+{
+struct PointXYZ
+{
+    double x{};
+    double y{};
+    double z{};
+};
+
+struct FlatSuperStruct2
+{
+    int ignore1{};
+    std::array<PointXYZ, 5> retain1{};
+    float ignore2{};
+};
+
+struct PointXZ
+{
+    const double* x{};
+    const double* z{};
+};
+
+
+template <class T>
+class StridedArrayView
+{
+    FixedVector<std::byte*, reflection::field_count_of<T>()> field_pointers_{};
+    std::ptrdiff_t stride_;
+
+public:
+    template <class P>
+    void update(P& parent)
+    {
+        field_pointers_.clear();
+        stride_ = sizeof(P);
+
+        T flat_sub_struct_1{};
+
+        auto field_to_offset_map = extract_field_to_offset_map(flat_sub_struct_1);
+
+        reflection::for_each_field(parent,
+                                   [&]<class F>(const std::string_view& name, F& field)
+                                   {
+                                       auto it = field_to_offset_map.find(name);
+                                       if (it == field_to_offset_map.cend())
+                                       {
+                                           return;
+                                       }
+
+                                       std::byte* byte_ptr =
+                                           reinterpret_cast<std::byte*>(&flat_sub_struct_1);
+                                       const std::ptrdiff_t offset = it->second;
+                                       std::advance(byte_ptr, offset);
+                                       F** field_in_struct = reinterpret_cast<F**>(byte_ptr);
+                                       *field_in_struct = &field;
+                                   });
+    }
+
+    T at(const std::size_t i) const
+    {
+        T instance{};
+        std::size_t field_i = 0;
+        reflection::for_each_field(instance,
+                                   [&]<class F>(const std::string_view& /*name*/, F& field)
+                                   {
+                                       const PointerAndStride& current_pointer_and_stride =
+                                           field_pointers_and_strides_.at(field_i);
+                                       std::byte* byte_ptr = reinterpret_cast<std::byte*>(
+                                           current_pointer_and_stride.pointer);
+                                       const auto offset = current_pointer_and_stride.stride *
+                                                           static_cast<std::ptrdiff_t>(i);
+                                       std::advance(byte_ptr, offset);
+                                       F* field_in_struct = reinterpret_cast<F*>(byte_ptr);
+                                       field = *field_in_struct;
+                                       field_i++;
+                                   });
+
+        return instance;
+    }
+};
+
+struct FlatSubStruct2
+{
+    StridedArrayView<PointXZ> retain1{};
+};
+
+}  // namespace
+
+TEST(SubStructView, ArraysOfStructs)
+{
+    StridedArrayView<PointXZ> view{};
+    (void)view.at(0).x;
+}
+
 }  // namespace fixed_containers::sub_struct_view