Add SpyReader methods for inserting/removing by char index

spec/runtime/helpers/spy_reader.cc

@@ -1,6 +1,7 @@
 #include "runtime/helpers/spy_reader.h"
 #include <string.h>
 #include <algorithm>
+#include "utf8proc.h"
 
 using std::string;
 
@@ -41,6 +42,37 @@ TSInput SpyReader::input() {
   return result;
 }
 
+long position_for_char_index(string str, size_t goal_index) {
+  size_t index = 0, position = 0;
+  int32_t dest_char;
+
+  while (index < goal_index) {
+    if (position >= str.size())
+      return -1;
+    position += utf8proc_iterate(
+        (uint8_t *)(str.data() + position),
+        str.size() - position,
+        &dest_char);
+    index++;
+  }
+
+  return position;
+}
+
+bool SpyReader::insert(size_t char_index, string text) {
+  long pos = position_for_char_index(content, char_index);
+  if (pos < 0) return false;
+  content.insert(pos, text);
+  return true;
+}
+
+bool SpyReader::erase(size_t char_index, size_t len) {
+  long pos = position_for_char_index(content, char_index);
+  if (pos < 0) return false;
+  content.erase(pos, len);
+  return true;
+}
+
 SpyReader::~SpyReader() {
   delete buffer;
 }

spec/runtime/helpers/spy_reader.h

@@ -12,6 +12,8 @@ class SpyReader {
 
   void clear();
   TSInput input();
+  bool insert(size_t position, std::string text);
+  bool erase(size_t position, size_t len);
 
   char *buffer;
   std::string content;

tests.gyp

@@ -28,6 +28,7 @@
         'examples',
         'spec',
         'externals/bandit',
+        'externals/utf8proc',
       ],
       'sources': [
         '<!@(find spec/runtime -name "*.cc")',