4 files changed, 145 insertions, 78 deletions
diff --git a/include/cru/common/Format.hpp b/include/cru/common/Format.hpp
new file mode 100644
index 00000000..c2fd2e09
--- /dev/null
+++ b/include/cru/common/Format.hpp
@@ -0,0 +1,142 @@
+#pragma once
+
+#include "Exception.hpp"
+#include "String.hpp"
+#include "cru/common/Base.hpp"
+
+namespace cru {
+inline String ToString(bool value) {
+  return value ? String(u"true") : String(u"false");
+}
+
+template <typename T>
+std::enable_if_t<std::is_integral_v<T>, String> ToString(T value) {
+  std::array<char, 50> buffer;
+  auto result =
+      std::to_chars(buffer.data(), buffer.data() + buffer.size(), value);
+
+  if (result.ec == std::errc{}) {
+  } else {
+    throw std::invalid_argument("Failed to convert value to chars.");
+  }
+
+  auto size = result.ptr - buffer.data();
+  auto b = new char16_t[size + 1];
+  b[size] = 0;
+  std::copy(buffer.data(), result.ptr, b);
+  return String::FromBuffer(b, size, size);
+}
+
+template <typename T>
+std::enable_if_t<std::is_floating_point_v<T>, String> ToString(T value) {
+  auto str = std::to_string(value);
+  return String(str.cbegin(), str.cend());
+}
+
+template <typename T>
+std::enable_if_t<
+    std::is_convertible_v<decltype(ToString(std::declval<const T&>)), String>,
+    String>
+ToString(const T& value, StringView option) {
+  CRU_UNUSED(option)
+  return ToString(value);
+}
+
+inline String ToString(String value) { return value; }
+
+namespace details {
+enum class FormatTokenType { PlaceHolder, Text };
+enum class FormatPlaceHolderType { None, Positioned, Named };
+
+struct FormatToken {
+  static FormatToken Text() {
+    return FormatToken{FormatTokenType::Text, {}, {}, 0, {}, {}};
+  }
+
+  static FormatToken NonePlaceHolder(String option) {
+    return FormatToken(FormatTokenType::PlaceHolder, {},
+                       FormatPlaceHolderType::None, 0, {}, std::move(option));
+  }
+
+  static FormatToken PositionedPlaceHolder(int position, String option) {
+    return FormatToken(FormatTokenType::PlaceHolder, {},
+                       FormatPlaceHolderType::Positioned, position, {},
+                       std::move(option));
+  }
+
+  static FormatToken NamedPlaceHolder(String name, String option) {
+    return FormatToken(FormatTokenType::PlaceHolder, {},
+                       FormatPlaceHolderType::Named, 0, std::move(name),
+                       std::move(option));
+  }
+
+  FormatToken(FormatTokenType type, String data,
+              FormatPlaceHolderType place_holder_type,
+              int place_holder_position, String place_holder_name,
+              String place_holder_option)
+      : type(type),
+        data(std::move(data)),
+        place_holder_type(place_holder_type),
+        place_holder_position(place_holder_position),
+        place_holder_name(std::move(place_holder_name)),
+        place_holder_option(std::move(place_holder_option)) {}
+
+  CRU_DEFAULT_COPY(FormatToken)
+  CRU_DEFAULT_MOVE(FormatToken)
+
+  CRU_DEFAULT_DESTRUCTOR(FormatToken)
+
+  FormatTokenType type;
+  String data;
+  FormatPlaceHolderType place_holder_type;
+  int place_holder_position;
+  String place_holder_name;
+  String place_holder_option;
+};
+
+std::vector<FormatToken> CRU_BASE_API ParseToFormatTokenList(const String& str);
+
+void CRU_BASE_API FormatAppendFromFormatTokenList(
+    String& current, const std::vector<FormatToken>& format_token_list,
+    Index index);
+
+template <typename TA, typename... T>
+void FormatAppendFromFormatTokenList(
+    String& current, const std::vector<FormatToken>& format_token_list,
+    Index index, TA&& args0, T&&... args) {
+  for (Index i = index; i < static_cast<Index>(format_token_list.size()); i++) {
+    const auto& token = format_token_list[i];
+    if (token.type == FormatTokenType::PlaceHolder) {
+      if (token.place_holder_type == FormatPlaceHolderType::None) {
+        current += ToString(std::forward<TA>(args0), token.place_holder_option);
+        FormatAppendFromFormatTokenList(current, format_token_list, i + 1,
+                                        std::forward<T>(args)...);
+
+        return;
+      } else {
+        throw Exception(
+            u"Currently do not support positional or named place holder.");
+      }
+    } else {
+      current += token.data;
+    }
+  }
+}
+}  // namespace details
+
+template <typename... T>
+String Format(const String& format, T&&... args) {
+  String result;
+
+  details::FormatAppendFromFormatTokenList(
+      result, details::ParseToFormatTokenList(format), 0,
+      std::forward<T>(args)...);
+
+  return result;
+}
+
+template <typename... T>
+String String::Format(T&&... args) const {
+  return cru::Format(*this, std::forward<T>(args)...);
+}
+}  // namespace cru
diff --git a/include/cru/common/Logger.hpp b/include/cru/common/Logger.hpp
index 7d43fc5a..c4a3e54a 100644
--- a/include/cru/common/Logger.hpp
+++ b/include/cru/common/Logger.hpp
@@ -2,6 +2,7 @@
 #include "Base.hpp"
 
 #include "String.hpp"
+#include "Format.hpp"
 
 #include <list>
 #include <memory>
diff --git a/include/cru/common/String.hpp b/include/cru/common/String.hpp
index dd3da52f..8db012cb 100644
--- a/include/cru/common/String.hpp
+++ b/include/cru/common/String.hpp
@@ -14,6 +14,7 @@
 #include <string>
 #include <string_view>
 #include <system_error>
+#include <tuple>
 #include <type_traits>
 #include <vector>
 
@@ -320,84 +321,6 @@ inline String operator+(const String& left, const String& right) {
   return result;
 }
 
-inline String ToString(bool value) {
-  return value ? String(u"true") : String(u"false");
-}
-
-template <typename T>
-std::enable_if_t<std::is_integral_v<T>, String> ToString(T value) {
-  std::array<char, 50> buffer;
-  auto result =
-      std::to_chars(buffer.data(), buffer.data() + buffer.size(), value);
-
-  if (result.ec == std::errc{}) {
-  } else {
-    throw std::invalid_argument("Failed to convert value to chars.");
-  }
-
-  auto size = result.ptr - buffer.data();
-  auto b = new char16_t[size + 1];
-  b[size] = 0;
-  std::copy(buffer.data(), result.ptr, b);
-  return String::FromBuffer(b, size, size);
-}
-
-template <typename T>
-std::enable_if_t<std::is_floating_point_v<T>, String> ToString(T value) {
-  auto str = std::to_string(value);
-  return String(str.cbegin(), str.cend());
-}
-
-inline String ToString(String value) { return value; }
-
-namespace details {
-enum class FormatTokenType { PlaceHolder, Text };
-
-struct FormatToken {
-  FormatTokenType type;
-  String data;
-};
-
-std::vector<FormatToken> CRU_BASE_API ParseToFormatTokenList(const String& str);
-
-void CRU_BASE_API FormatAppendFromFormatTokenList(
-    String& current, const std::vector<FormatToken>& format_token_list,
-    Index index);
-
-template <typename TA, typename... T>
-void FormatAppendFromFormatTokenList(
-    String& current, const std::vector<FormatToken>& format_token_list,
-    Index index, TA&& args0, T&&... args) {
-  for (Index i = index; i < static_cast<Index>(format_token_list.size()); i++) {
-    const auto& token = format_token_list[i];
-    if (token.type == FormatTokenType::PlaceHolder) {
-      current += ToString(std::forward<TA>(args0));
-      FormatAppendFromFormatTokenList(current, format_token_list, i + 1,
-                                      std::forward<T>(args)...);
-      return;
-    } else {
-      current += token.data;
-    }
-  }
-}
-}  // namespace details
-
-template <typename... T>
-String Format(const String& format, T&&... args) {
-  String result;
-
-  details::FormatAppendFromFormatTokenList(
-      result, details::ParseToFormatTokenList(format), 0,
-      std::forward<T>(args)...);
-
-  return result;
-}
-
-template <typename... T>
-String String::Format(T&&... args) const {
-  return cru::Format(*this, std::forward<T>(args)...);
-}
-
 CRU_DEFINE_COMPARE_OPERATORS(StringView)
 
 inline String::iterator String::insert(const_iterator pos, StringView str) {
diff --git a/include/cru/common/StringUtil.hpp b/include/cru/common/StringUtil.hpp
index 3c673db1..2d53fc2b 100644
--- a/include/cru/common/StringUtil.hpp
+++ b/include/cru/common/StringUtil.hpp
@@ -223,6 +223,7 @@ char16_t CRU_BASE_API ToLower(char16_t c);
 char16_t CRU_BASE_API ToUpper(char16_t c);
 
 bool CRU_BASE_API IsWhitespace(char16_t c);
+bool CRU_BASE_API IsDigit(char16_t c);
 
 Utf8CodePointIterator CRU_BASE_API CreateUtf8Iterator(const std::byte* buffer,
                                                       Index size);