From 0ce6fed70d4f52038e6acbb1b403fdf655081eee Mon Sep 17 00:00:00 2001
From: Mateusz Pusz <mateusz.pusz@gmail.com>
Date: Tue, 23 Jan 2024 21:19:45 +0100
Subject: [PATCH] fix: quantity alignment formatting fixed

---
 src/core/include/mp-units/bits/fmt.h |  4 +++-
 src/core/include/mp-units/format.h   | 34 +++++++++++++++++++++++-----
 2 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/src/core/include/mp-units/bits/fmt.h b/src/core/include/mp-units/bits/fmt.h
index 5b7305b4..e570a0ef 100644
--- a/src/core/include/mp-units/bits/fmt.h
+++ b/src/core/include/mp-units/bits/fmt.h
@@ -341,7 +341,8 @@ constexpr int code_point_length(It begin)
 
 // Parses fill and alignment.
 template<typename Char, typename Specs>
-[[nodiscard]] constexpr const Char* parse_align(const Char* begin, const Char* end, Specs& specs)
+[[nodiscard]] constexpr const Char* parse_align(const Char* begin, const Char* end, Specs& specs,
+                                                fmt_align default_align = fmt_align::none)
 {
   gsl_Expects(begin != end);
   auto align = fmt_align::none;
@@ -378,6 +379,7 @@ template<typename Char, typename Specs>
     }
     p = begin;
   }
+  if (align == fmt_align::none) align = default_align;  // mp-units extension
   specs.align = align;
   return begin;
 }
diff --git a/src/core/include/mp-units/format.h b/src/core/include/mp-units/format.h
index 21a95e53..c3bc9d7c 100644
--- a/src/core/include/mp-units/format.h
+++ b/src/core/include/mp-units/format.h
@@ -40,6 +40,30 @@ struct fill_align_width_format_specs {
   fmt_arg_ref<Char> width_ref;
 };
 
+template<typename OutputIt, typename Char>
+OutputIt format_global_buffer(OutputIt out, const fill_align_width_format_specs<Char>& specs)
+{
+  MP_UNITS_STD_FMT::format_to(out, "{{:");
+  if (specs.fill.size() != 1 || specs.fill[0] != ' ') {
+    MP_UNITS_STD_FMT::format_to(out, "{}", specs.fill.data());
+  }
+  switch (specs.align) {
+    case fmt_align::left:
+      MP_UNITS_STD_FMT::format_to(out, "<");
+      break;
+    case fmt_align::right:
+      MP_UNITS_STD_FMT::format_to(out, ">");
+      break;
+    case fmt_align::center:
+      MP_UNITS_STD_FMT::format_to(out, "^");
+      break;
+    default:
+      break;
+  }
+  if (specs.width >= 1) MP_UNITS_STD_FMT::format_to(out, "{}", specs.width);
+  return MP_UNITS_STD_FMT::format_to(out, "}}");
+}
+
 template<typename Char>
 [[nodiscard]] constexpr const Char* at_most_one_of(const Char* begin, const Char* end, std::string_view modifiers)
 {
@@ -215,7 +239,6 @@ class MP_UNITS_STD_FMT::formatter<mp_units::quantity<Reference, Rep>, Char> {
 
   using format_specs = mp_units::detail::fill_align_width_format_specs<Char>;
 
-  std::basic_string_view<Char> fill_align_width_format_str_;
   std::basic_string_view<Char> modifiers_format_str_;
   std::vector<size_t> format_str_lengths_;
   format_specs specs_{};
@@ -370,14 +393,12 @@ public:
     auto it = begin, end = ctx.end();
     if (it == end || *it == '}') return it;
 
-    it = mp_units::detail::parse_align(it, end, specs_);
+    it = mp_units::detail::parse_align(it, end, specs_, mp_units::detail::fmt_align::right);
     if (it == end) return it;
 
     it = mp_units::detail::parse_dynamic_spec(it, end, specs_.width, specs_.width_ref, ctx);
     if (it == end) return it;
 
-    fill_align_width_format_str_ = {begin, it};
-
     format_checker checker(ctx, format_str_lengths_);
     end = parse_quantity_specs(it, end, checker);
     modifiers_format_str_ = {it, end};
@@ -397,8 +418,9 @@ public:
       std::basic_string<Char> quantity_buffer;
       format_quantity(std::back_inserter(quantity_buffer), q, ctx);
 
-      std::basic_string<Char> global_format_buffer = "{:" + std::basic_string<Char>{fill_align_width_format_str_} + "}";
-      return MP_UNITS_STD_FMT::vformat_to(ctx.out(), global_format_buffer,
+      std::basic_string<Char> fill_align_width_format_str;
+      mp_units::detail::format_global_buffer(std::back_inserter(fill_align_width_format_str), specs);
+      return MP_UNITS_STD_FMT::vformat_to(ctx.out(), fill_align_width_format_str,
                                           MP_UNITS_STD_FMT::make_format_args(quantity_buffer));
     }
   }