From 0cafb9bcd75925bef5c5513197e6ce63d6ef0c41 Mon Sep 17 00:00:00 2001
From: Kurt Sassenrath <ksassenrath@roku.com>
Date: Tue, 2 Jan 2024 20:59:45 -0800
Subject: [PATCH] Additional concepts work

---
 .../core/detail/builtin_packable_types.h      | 12 +--
 .../msgpack/core/detail/packable_concepts.h   | 86 +++++++++++++++++++
 .../msgpack/core/detail/packable_ranges.h     |  8 +-
 include/parselink/msgpack/core/packer.h       | 14 +--
 tests/msgpack/test_packer.cpp                 | 25 +++++-
 5 files changed, 121 insertions(+), 24 deletions(-)
 create mode 100644 include/parselink/msgpack/core/detail/packable_concepts.h

diff --git a/include/parselink/msgpack/core/detail/builtin_packable_types.h b/include/parselink/msgpack/core/detail/builtin_packable_types.h
index 1a2fb44..acd591c 100644
--- a/include/parselink/msgpack/core/detail/builtin_packable_types.h
+++ b/include/parselink/msgpack/core/detail/builtin_packable_types.h
@@ -18,6 +18,7 @@
 #ifndef msgpack_core_detail_builtin_packable_types_41bd88d512497527
 #define msgpack_core_detail_builtin_packable_types_41bd88d512497527
 
+#include "parselink/msgpack/core/detail/packable_concepts.h"
 #include "parselink/msgpack/core/format.h"
 #include "parselink/msgpack/util/endianness.h"
 
@@ -284,17 +285,6 @@ struct builtin_packer<map_desc> : builtin_packer_base {
     }
 };
 
-// Requirements for builtin_packable types.
-template <typename T, typename Packer = detail::dummy_packer>
-concept builtin_packable = requires(T&& value, Packer& dest) {
-    {
-        builtin_packer<std::remove_cvref_t<T>>::total_size(value)
-    } -> std::same_as<std::size_t>;
-    {
-        builtin_packer<std::remove_cvref_t<T>>::pack(value, dest)
-    } -> std::same_as<void>;
-};
-
 } // namespace msgpack
 
 #endif // msgpack_core_detail_builtin_packable_types_41bd88d512497527
diff --git a/include/parselink/msgpack/core/detail/packable_concepts.h b/include/parselink/msgpack/core/detail/packable_concepts.h
new file mode 100644
index 0000000..2c769f1
--- /dev/null
+++ b/include/parselink/msgpack/core/detail/packable_concepts.h
@@ -0,0 +1,86 @@
+
+//-----------------------------------------------------------------------------
+//     ___                      __ _       _
+//    / _ \__ _ _ __ ___  ___  / /(_)_ __ | | __
+//   / /_)/ _` | '__/ __|/ _ \/ / | | '_ \| |/ /
+//  / ___/ (_| | |  \__ \  __/ /__| | | | |   <
+//  \/    \__,_|_|  |___/\___\____/_|_| |_|_|\_\ .
+//
+//-----------------------------------------------------------------------------
+// Author: Kurt Sassenrath
+// Module: msgpack
+//
+// Concepts used for types that are packable by a packer.
+//
+// Copyright (c) 2023 Kurt Sassenrath.
+//
+// License TBD.
+//-----------------------------------------------------------------------------
+#ifndef msgpack_core_detail_packable_concepts_397b5e0ae6de61bf
+#define msgpack_core_detail_packable_concepts_397b5e0ae6de61bf
+
+#include <concepts>
+#include <cstddef>
+#include <type_traits>
+
+namespace msgpack {
+namespace detail {
+
+// This structure models a minimal packer context. It is used to validate
+// whether a particular type is considered packable or not.
+struct packer_context_model {
+    std::byte* out;
+};
+
+} // namespace detail
+
+// Packers with built-in support will specialize builtin_packer.
+template <typename>
+struct builtin_packer;
+
+// Packers
+template <typename>
+struct packer_adapter;
+
+template <typename T, template <typename> typename Packer,
+        typename Context = detail::packer_context_model>
+concept packable_with = requires(T&& value, Context& dest) {
+    {
+        Packer<std::remove_cvref_t<T>>::total_size(value)
+    } -> std::same_as<std::size_t>;
+    {
+        Packer<std::remove_cvref_t<T>>::pack(value, dest)
+    } -> std::same_as<void>;
+};
+
+template <typename T>
+concept custom_packable = packable_with<T, packer_adapter>;
+
+template <typename T>
+concept builtin_packable = packable_with<T, builtin_packer>;
+
+template <typename T>
+concept packable = builtin_packable<T> || custom_packable<T>;
+
+namespace detail {
+
+    template <typename>
+    struct packer_impl_s;
+
+    template <custom_packable T>
+    struct packer_impl_s<T> {
+        using type = packer_adapter<T>;
+    };
+
+    template <builtin_packable T>
+    struct packer_impl_s<T> {
+        using type = builtin_packer<T>;
+    };
+
+    template <typename T>
+    using packer_impl = packer_impl_s<T>::type;
+} // namespace detail
+
+} // namespace msgpack
+
+#endif // msgpack_core_detail_packable_concepts_397b5e0ae6de61bf
diff --git a/include/parselink/msgpack/core/detail/packable_ranges.h b/include/parselink/msgpack/core/detail/packable_ranges.h
index cef11ac..75115b1 100644
--- a/include/parselink/msgpack/core/detail/packable_ranges.h
+++ b/include/parselink/msgpack/core/detail/packable_ranges.h
@@ -21,7 +21,8 @@
 #ifndef msgpack_core_detail_packable_ranges_10d28c24498828c7
 #define msgpack_core_detail_packable_ranges_10d28c24498828c7
 
-#include "builtin_packable_types.h"
+#include "parselink/msgpack/core/detail/packable_concepts.h"
+#include "parselink/msgpack/core/detail/builtin_packable_types.h"
 #include <ranges>
 #include <tuple>
 
@@ -31,10 +32,7 @@ namespace detail {
 //
 template <typename T>
 concept packable_array = std::ranges::input_range<T>
-                      && builtin_packable<std::ranges::range_value_t<T>>;
-
-template <typename T>
-concept tuple_like = requires(T t) { typename std::tuple_size<T>::type; };
+                      && packable<std::ranges::range_value_t<T>>;
 
 template <typename T>
 concept key_value_pairlike = requires(T t) {
diff --git a/include/parselink/msgpack/core/packer.h b/include/parselink/msgpack/core/packer.h
index 05a67d4..c14064b 100644
--- a/include/parselink/msgpack/core/packer.h
+++ b/include/parselink/msgpack/core/packer.h
@@ -38,8 +38,10 @@
 #ifndef msgpack_core_packer_1d5939e9c1498568
 #define msgpack_core_packer_1d5939e9c1498568
 
+#include "parselink/msgpack/core/detail/packable_concepts.h"
 #include "parselink/msgpack/core/detail/builtin_packable_types.h"
 #include "parselink/msgpack/core/detail/packable_ranges.h"
+
 #include "parselink/msgpack/core/error.h"
 #include "parselink/msgpack/core/format.h"
 #include "parselink/msgpack/util/endianness.h"
@@ -54,9 +56,6 @@ namespace msgpack {
 template <typename T>
 struct pack_adapter {};
 
-template <typename T>
-concept packable_type = builtin_packable<T>;
-
 class packer {
     // Replace with output_range?
     using BufferType = std::span<std::byte>;
@@ -75,20 +74,21 @@ public:
             return std::ranges::distance(out, end);
         }
 
-        template <packable_type T>
+        template <packable T>
         constexpr tl::expected<tl::monostate, error> pack(T const& v) noexcept {
             auto rem = remaining();
-            decltype(rem) needed = builtin_packer<T>::total_size(v);
+            using packer_impl = detail::packer_impl<T>;
+            decltype(rem) needed = packer_impl::total_size(v);
             if (needed > rem) {
                 return tl::make_unexpected(error::out_of_space);
             } else {
-                builtin_packer<T>::pack(v, *this);
+                packer_impl::pack(v, *this);
                 return tl::monostate{};
             }
         }
     };
 
-    template <packable_type T>
+    template <packable T>
     constexpr tl::expected<tl::monostate, error> pack(T&& v) noexcept {
         context ctx{curr_, end_};
         // If packing is successful, it updates iterators.
diff --git a/tests/msgpack/test_packer.cpp b/tests/msgpack/test_packer.cpp
index 66a36f0..8e7fd2a 100644
--- a/tests/msgpack/test_packer.cpp
+++ b/tests/msgpack/test_packer.cpp
@@ -292,7 +292,7 @@ bool test_deduced() noexcept {
 
 } // anonymous namespace
 
-suite packer = [] {
+suite packer_single_format = [] {
     "packer::pack<bool>"_test = [] { expect(test_deduced<bool>()); };
     "packer::pack<nil>"_test = [] { expect(test_deduced<msgpack::nil>()); };
     "packer::pack<invalid>"_test = [] {
@@ -387,3 +387,26 @@ suite packer = [] {
         expect(test_deduced<msgpack::map_desc>());
     };
 };
+
+suite packer_ranges = [] {
+    "packer::pack<std::array/std::span<int>>"_test = [] {
+        constexpr auto data_array = std::to_array<int>({5, 10, 15, 20});
+        constexpr auto expected =
+                make_bytes(0x94, 0xd0, 0x05, 0xd0, 0xa, 0xd0, 0xf, 0xd0, 0x14);
+
+        {
+            std::array<std::byte, std::size(expected)> payload;
+            msgpack::packer packer(payload);
+            expect(!!packer.pack(data_array));
+            expect(std::ranges::equal(payload, expected));
+        }
+
+        {
+            std::span data_span{data_array};
+            std::array<std::byte, std::size(expected)> payload;
+            msgpack::packer packer(payload);
+            expect(!!packer.pack(data_span));
+            expect(std::ranges::equal(payload, expected));
+        }
+    };
+};