From 611601ec36a5603bc9c94cdac9a307c4bb07c929 Mon Sep 17 00:00:00 2001
From: Roland Reichwein <mail@reichwein.it>
Date: Sun, 31 Jan 2021 19:00:34 +0100
Subject: Add facet based interface

---
 include/unicode.h | 221 +++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 203 insertions(+), 18 deletions(-)

(limited to 'include')

diff --git a/include/unicode.h b/include/unicode.h
index f31cbac..4b676bf 100644
--- a/include/unicode.h
+++ b/include/unicode.h
@@ -3,8 +3,10 @@
 #pragma once
 
 #include <algorithm>
+#include <memory>
 #include <stdexcept>
 #include <string>
+#include <unordered_map>
 
 #ifdef __cpp_char8_t
 // char8_t available
@@ -31,7 +33,7 @@ namespace unicode::detail {
  template<typename T>
  struct utf_iterator
  {
-  typedef char32_t value_type;
+  typedef T value_type;
   typedef char32_t& reference;
   typedef std::basic_string<T> string_type;
 
@@ -201,6 +203,7 @@ namespace unicode::detail {
    return value;
   }
 
+ private:
   typename string_type::const_iterator iterator;
   typename string_type::const_iterator end_iterator;
 
@@ -211,13 +214,14 @@ namespace unicode::detail {
  template<typename T>
  struct utf_back_insert_iterator
  {
+  typedef T value_type;
   typedef std::basic_string<T> string_type;
   typedef utf_back_insert_iterator& reference;
 
   utf_back_insert_iterator(string_type& s): s(s) {}
 
   // no-op
-  utf_back_insert_iterator& operator++()
+  reference operator++()
   {
    return *this;
   }
@@ -302,39 +306,220 @@ namespace unicode::detail {
    return *this;
   }
 
+ private:
   typename utf_back_insert_iterator::string_type& s;
  };
 
- template<typename T>
- utf_back_insert_iterator<T> utf_back_inserter(std::basic_string<T>& s)
- {
-  return utf_back_insert_iterator<T>(s);
+ typedef std::unordered_map<utf8_t, char32_t> iso_map_type;
+ typedef std::unordered_map<char32_t, utf8_t> iso_map_type_reverse;
+
+ // ISO-8859-1 is lower 8-bit of Unicode, so no exceptions necessary
+ iso_map_type iso_8859_1_map;
+
+ // ISO-8859-15 is lower 8-bit of Unicode, except for:
+ iso_map_type iso_8859_15_map {
+  { '\xA4', U'\u20AC' }, // €
+  { '\xA6', U'\u0160' }, // Š
+  { '\xA8', U'\u0161' }, // š
+  { '\xB4', U'\u017D' }, // Ž
+  { '\xB8', U'\u017E' }, // ž
+  { '\xBC', U'\u0152' }, // Œ
+  { '\xBD', U'\u0153' }, // œ
+  { '\xBE', U'\u0178' }, // Ÿ
+ };
+
+ iso_map_type_reverse reverse_iso_map(const iso_map_type& map) {
+  iso_map_type_reverse result;
+  std::for_each(map.cbegin(), map.cend(),
+                [&](const iso_map_type::value_type& pair)
+                 {
+                  result.emplace(pair.second, pair.first);
+                 });
+  return result;
  }
 
- template<typename T>
- utf_iterator<T> utf_begin(const std::basic_string<T>& s)
+ iso_map_type_reverse iso_8859_15_map_reverse { reverse_iso_map(iso_8859_15_map) };
+ iso_map_type_reverse iso_8859_1_map_reverse { reverse_iso_map(iso_8859_1_map) };
+
+} // namespace unicode::detail
+
+namespace unicode {
+
+ using namespace detail;
+
+ template<unicode::detail::iso_map_type& Map=iso_8859_1_map>
+ struct iso_iterator {
+  typedef char32_t value_type;
+  typedef char32_t& reference;
+  typedef std::basic_string<utf8_t>::const_iterator iterator;
+
+  iso_iterator(const iterator& it): m_it(it) {}
+
+  // pre-increment
+  iso_iterator& operator++()
+  {
+   ++m_it;
+   return *this;
+  }
+
+  bool operator!=(const iso_iterator& other) const
+  {
+   return m_it != other.m_it;
+  }
+
+  // return reference?
+  value_type operator*()
+  {
+   utf8_t value{*m_it};
+
+   if constexpr(std::addressof(Map) != std::addressof(iso_8859_1_map)) // mapping of 128 <= x <= 255 needed
+   {
+    auto it{Map.find(value)};
+    if (it != Map.end())
+     return it->second;
+   }
+   return static_cast<value_type>(static_cast<uint8_t>(value));
+  }
+
+ private:
+  iterator m_it;
+ };
+
+ template<unicode::detail::iso_map_type_reverse& Map=iso_8859_1_map_reverse>
+ struct iso_back_insert_iterator {
+  typedef iso_back_insert_iterator& reference;
+  typedef std::basic_string<utf8_t> string_type;
+  
+  iso_back_insert_iterator(string_type& s): s(s) {}
+
+  // no-op
+  reference operator++()
+  {
+   return *this;
+  }
+
+  // support *x = value, together with operator=()
+  reference operator*()
+  {
+   return *this;
+  }
+
+  reference operator=(const char32_t& value)
+  {
+   if constexpr(std::addressof(Map) != std::addressof(iso_8859_1_map_reverse)) // mapping of 128 <= x <= 255 needed
+   {
+    auto it{Map.find(value)};
+    if (it != Map.end()) {
+     s.push_back(it->second);
+     return *this;
+    }
+   }
+
+   if (value > 255)
+    throw std::invalid_argument("Bad Unicode value above 255: "s + std::to_string(static_cast<uint32_t>(value)));
+
+   s.push_back(static_cast<utf8_t>(value));
+   return *this;
+  }
+
+ private:
+  typename iso_back_insert_iterator::string_type& s;
+ };
+
+ // Facet for convert() and ISO-8859-*
+ template<typename InputIt, typename OutputIt>
+ struct ISO_8859
+ {
+  typedef utf8_t value_type;
+
+  static InputIt begin(const std::basic_string<value_type>& s)
+  {
+   return InputIt(s.cbegin());
+  }
+
+  static InputIt end(const std::basic_string<value_type>& s)
+  {
+   return InputIt(s.cend());
+  }
+
+  static OutputIt back_inserter(std::basic_string<value_type>& s)
+  {
+   return OutputIt(s);
+  }
+ };
+
+ // Facet for convert() and UTF-*
+ template<typename InputIt, typename OutputIt>
+ struct UTF
  {
-  return utf_iterator<T>{s.cbegin(), s.cend()};
+  typedef typename InputIt::value_type value_type; // OutputIt::value_type is the same
+
+  static InputIt begin(const std::basic_string<value_type>& s)
+  {
+   return InputIt{s.cbegin(), s.cend()};
+  }
+
+  static InputIt end(const std::basic_string<value_type>& s)
+  {
+   return InputIt{s.cend(), s.cend()};
+  }
+
+  static OutputIt back_inserter(std::basic_string<value_type>& s)
+  {
+   return OutputIt(s);
+  }
+ };
+
+ // Facet for convert()
+ typedef ISO_8859<iso_iterator<>, iso_back_insert_iterator<>> ISO_8859_1;
+ typedef ISO_8859<iso_iterator<iso_8859_15_map>, iso_back_insert_iterator<iso_8859_15_map_reverse>> ISO_8859_15;
+ 
+ typedef UTF<utf_iterator<utf8_t>, utf_back_insert_iterator<utf8_t>> UTF_8;
+ typedef UTF<utf_iterator<char16_t>, utf_back_insert_iterator<char16_t>> UTF_16;
+ typedef UTF<utf_iterator<char32_t>, utf_back_insert_iterator<char32_t>> UTF_32;
+
+ // From and To are facets
+ template<typename From, typename To>
+ std::basic_string<typename To::value_type> convert(const std::basic_string<typename From::value_type>& s)
+ {
+  std::basic_string<typename To::value_type> result;
+
+  std::copy(From::begin(s), From::end(s), To::back_inserter(result));
+
+  return result;
  }
 
+ // Helper to get correct Facet from char type, e.g. Encoding<typename decltype(s)::value_type>::Facet
  template<typename T>
- utf_iterator<T> utf_end(const std::basic_string<T>& s)
+ struct Encoding
  {
-  return utf_iterator<T>{s.cend(), s.cend()};
- }
+ };
 
-} // namespace
+ template<>
+ struct Encoding<utf8_t>
+ {
+  typedef UTF_8 Facet;
+ };
 
-namespace unicode {
+ template<>
+ struct Encoding<char16_t>
+ {
+  typedef UTF_16 Facet;
+ };
 
- using namespace detail;
+ template<>
+ struct Encoding<char32_t>
+ {
+  typedef UTF_32 Facet;
+ };
 
+ // From and To are from: utf8_t, char16_t and char32_t
  template<typename From, typename To>
- std::basic_string<To> utf_to_utf(const std::basic_string<From>& s)
+ std::basic_string<To> convert(const std::basic_string<From>& s)
  {
   std::basic_string<To> result;
 
-  std::copy(utf_begin<From>(s), utf_end<From>(s), utf_back_inserter<To>(result));
+  std::copy(Encoding<From>::Facet::begin(s), Encoding<From>::Facet::end(s), Encoding<To>::Facet::back_inserter(result));
 
   return result;
  }
@@ -343,7 +528,7 @@ namespace unicode {
  bool is_valid_utf(const std::basic_string<T>& s)
  {
   try {
-   std::for_each(utf_begin<T>(s), utf_end<T>(s), [](const T& c){});
+   std::for_each(Encoding<T>::Facet::begin(s), Encoding<T>::Facet::end(s), [](const T& c){});
   } catch(...) {
    return false;
   }
-- 
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