From 742f1e0421f06aae4ee38a3ef211a9ae68d1f4b7 Mon Sep 17 00:00:00 2001
From: massaraksh111 <amironochev@yandex.ru>
Date: Mon, 15 Jun 2020 13:49:04 +0300
Subject: [PATCH] Add constexpr version of ozo::detail::ltob36

---
 include/ozo/detail/base36.h | 19 +++++++++++++++++++
 include/ozo/error.h         |  4 +++-
 tests/detail/base36.cpp     |  3 +++
 3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/include/ozo/detail/base36.h b/include/ozo/detail/base36.h
index a6a1c20db..75384015e 100644
--- a/include/ozo/detail/base36.h
+++ b/include/ozo/detail/base36.h
@@ -1,6 +1,8 @@
 #pragma once
 
 #include <boost/range/algorithm/reverse.hpp>
+#include <boost/hana/string.hpp>
+#include <boost/hana/if.hpp>
 #include <string_view>
 #include <string>
 
@@ -10,6 +12,23 @@ inline long b36tol(std::string_view in) {
     return strtol(in.data(), nullptr, 36);
 }
 
+template<unsigned long i>
+constexpr auto ultob36() {
+    constexpr int base = 36;
+    constexpr int d = i % base;
+    if constexpr (i > 0) {
+        const char sym = boost::hana::if_(d < 10, '0' + d, 'A' + d - 10);
+        return ultob36<i / base>() + boost::hana::string_c<sym>;
+    } else {
+        return BOOST_HANA_STRING("");
+    }
+}
+
+template<long i>
+constexpr auto ltob36() {
+    return ultob36<static_cast<unsigned long>(i)>();
+}
+
 inline std::string ltob36(long i) {
     auto u = static_cast<unsigned long>(i);
     std::string out ;
diff --git a/include/ozo/error.h b/include/ozo/error.h
index 64e1900ea..bf953c574 100644
--- a/include/ozo/error.h
+++ b/include/ozo/error.h
@@ -524,7 +524,9 @@ class category final : public error_category {
     const char* name() const noexcept override final { return "ozo::sqlstate::category"; }
 
     std::string message(int value) const override final {
-        #define OZO_SQLSTATE_NAME(value) case value: return std::string(#value) + "(" + detail::ltob36(value) + ")";
+        #define OZO_SQLSTATE_NAME(value) case value: return boost::hana::to<char const*>(\
+                BOOST_HANA_STRING(#value) + BOOST_HANA_STRING("(") +\
+                detail::ltob36<value>() + BOOST_HANA_STRING(")"));
         switch (value) {
             OZO_SQLSTATE_NAME(successful_completion)
             OZO_SQLSTATE_NAME(warning)
diff --git a/tests/detail/base36.cpp b/tests/detail/base36.cpp
index eb2fd8deb..7812227e1 100644
--- a/tests/detail/base36.cpp
+++ b/tests/detail/base36.cpp
@@ -1,4 +1,5 @@
 #include <ozo/detail/base36.h>
+#include <boost/hana.hpp>
 
 #include <gtest/gtest.h>
 
@@ -16,4 +17,6 @@ TEST(ltob36, should_with_29999809_return_HV001) {
     EXPECT_EQ("HV001", ozo::detail::ltob36(29999809));
 }
 
+static_assert(BOOST_HANA_STRING("HV001") == ozo::detail::ltob36<29999809>());
+
 } // namespace