Port Seek word, add ctrl+left

src/text_editor/buffer.cpp

@@ -369,6 +369,55 @@ int64_t FindPos(Buffer &buffer, int64_t line_number, int64_t column) {
     return result;
 }
 
+int64_t Seek(Buffer &buffer, int64_t pos, int64_t direction = ITERATE_FORWARD) {
+    Assert(direction == ITERATE_FORWARD || direction == ITERATE_BACKWARD);
+    // ( - inclusive
+    // < - non-inclusive
+
+    int64_t min = 0;
+    int64_t max = 0;
+    char    c   = 0;
+    if (direction == ITERATE_FORWARD) {
+        // (pos + 1, end>
+        min = AdjustUTF8Pos(buffer, pos + 1, ITERATE_FORWARD);
+        max = buffer.len;
+        c   = GetChar(buffer, min);
+    } else {
+        // (0, pos>
+        max = pos;
+        min = 0;
+
+        int64_t next = AdjustUTF8Pos(buffer, max - 1, ITERATE_BACKWARD);
+        c            = GetChar(buffer, next);
+    }
+
+    bool standing_on_whitespace = IsWhitespace(c);
+    bool seek_whitespace        = standing_on_whitespace == false;
+    bool seek_word              = standing_on_whitespace;
+
+    int64_t    result   = max;
+    BufferIter iter     = Iterate(buffer, {min, max}, direction);
+    int64_t    prev_pos = iter.pos;
+    for (; IsValid(iter); Advance(&iter)) {
+        bool char_is_whitespace = iter.item < 255 && IsWhitespace(iter.item);
+
+        if (seek_word && char_is_whitespace == false) {
+            result = prev_pos;
+            break;
+        }
+        if (seek_whitespace && char_is_whitespace) {
+            if (direction == ITERATE_FORWARD) {
+                result = iter.pos;
+            } else {
+                result = prev_pos;
+            }
+            break;
+        }
+        prev_pos = iter.pos;
+    }
+    return result;
+}
+
 void RunBufferTests() {
     Scratch scratch;
     {