1 files changed, 66 insertions, 2 deletions

diff --git a/src/common/StringUtil.cpp b/src/common/StringUtil.cpp
index fc6d6349..0cadc545 100644
--- a/src/common/StringUtil.cpp
+++ b/src/common/StringUtil.cpp
@@ -1,4 +1,6 @@
 #include "cru/common/StringUtil.hpp"
+#include "cru/common/Base.hpp"
+#include "gsl/gsl_util"
 
 namespace cru {
 namespace {
@@ -191,8 +193,8 @@ void Utf8EncodeCodePointAppend(CodePoint code_point, std::string& str) {
 }
 
 void Utf16EncodeCodePointAppend(CodePoint code_point, std::u16string& str) {
-  if (code_point >= 0 && code_point <= 0xD7FF ||
-      code_point >= 0xE000 && code_point <= 0xFFFF) {
+  if ((code_point >= 0 && code_point <= 0xD7FF) ||
+      (code_point >= 0xE000 && code_point <= 0xFFFF)) {
     str.push_back(static_cast<char16_t>(code_point));
   } else if (code_point >= 0x10000 && code_point <= 0x10FFFF) {
     std::uint32_t u = code_point - 0x10000;
@@ -220,4 +222,66 @@ std::u16string ToUtf16(std::string_view s) {
   }
   return result;
 }
+
+bool Utf16IsValidInsertPosition(std::u16string_view s, gsl::index position) {
+  if (position < 0) return false;
+  if (position > static_cast<gsl::index>(s.size())) return false;
+  if (position == 0) return true;
+  if (position == static_cast<gsl::index>(s.size())) return true;
+  return !IsUtf16SurrogatePairTrailing(s[position]);
+}
+
+gsl::index Utf16BackwardUntil(std::u16string_view str, gsl::index position,
+                              const std::function<bool(CodePoint)>& predicate) {
+  if (position <= 0) return position;
+  while (true) {
+    gsl::index p = position;
+    auto c = Utf16PreviousCodePoint(str, p, &position);
+    if (predicate(c)) return p;
+    if (c == k_invalid_code_point) return p;
+  }
+  UnreachableCode();
+}
+
+gsl::index Utf16ForwardUntil(std::u16string_view str, gsl::index position,
+                             const std::function<bool(CodePoint)>& predicate) {
+  if (position >= static_cast<gsl::index>(str.size())) return position;
+  while (true) {
+    gsl::index p = position;
+    auto c = Utf16NextCodePoint(str, p, &position);
+    if (predicate(c)) return p;
+    if (c == k_invalid_code_point) return p;
+  }
+  UnreachableCode();
+}
+
+inline bool IsSpace(CodePoint c) { return c == 0x20 || c == 0xA; }
+
+gsl::index Utf16PreviousWord(std::u16string_view str, gsl::index position,
+                             bool* is_space) {
+  if (position <= 0) return position;
+  auto c = Utf16PreviousCodePoint(str, position, nullptr);
+  if (IsSpace(c)) {  // TODO: Currently only test against 0x20(space).
+    if (is_space) *is_space = true;
+    return Utf16BackwardUntil(str, position,
+                              [](CodePoint c) { return !IsSpace(c); });
+  } else {
+    if (is_space) *is_space = false;
+    return Utf16BackwardUntil(str, position, IsSpace);
+  }
+}
+
+gsl::index Utf16NextWord(std::u16string_view str, gsl::index position,
+                         bool* is_space) {
+  if (position >= static_cast<gsl::index>(str.size())) return position;
+  auto c = Utf16NextCodePoint(str, position, nullptr);
+  if (IsSpace(c)) {  // TODO: Currently only test against 0x20(space).
+    if (is_space) *is_space = true;
+    return Utf16ForwardUntil(str, position,
+                             [](CodePoint c) { return !IsSpace(c); });
+  } else {
+    if (is_space) *is_space = false;
+    return Utf16ForwardUntil(str, position, IsSpace);
+  }
+}
 }  // namespace cru