Small improvements

src/text_editor/buffer.cpp

@@ -39,6 +39,14 @@ struct Edit {
     String string;
 };
 
+struct Cursor {
+    union {
+        Range   range;
+        int64_t pos[2];
+    };
+    int64_t ifront;
+};
+
 // - Buffer should be initialized before use!
 struct Buffer {
     Allocator    allocator;
@@ -83,6 +91,43 @@ Range MakeRange(int64_t a, int64_t b) {
     return result;
 }
 
+int64_t GetFront(Cursor cursor) {
+    int64_t result = cursor.pos[cursor.ifront];
+    return result;
+}
+
+int64_t GetBack(Cursor cursor) {
+    int64_t index  = (cursor.ifront + 1) % 2;
+    int64_t result = cursor.pos[index];
+    return result;
+}
+
+Cursor MakeCursor(int64_t front, int64_t back) {
+    Cursor result = {};
+    if (front >= back) {
+        result.range.min = back;
+        result.range.max = front;
+        result.ifront    = 1;
+    } else {
+        result.range.min = front;
+        result.range.max = back;
+        result.ifront    = 0;
+    }
+    return result;
+}
+
+Cursor ChangeBack(Cursor cursor, int64_t back) {
+    int64_t front  = GetFront(cursor);
+    Cursor  result = MakeCursor(front, back);
+    return result;
+}
+
+Cursor ChangeFront(Cursor cursor, int64_t front) {
+    int64_t back   = GetBack(cursor);
+    Cursor  result = MakeCursor(front, back);
+    return result;
+}
+
 void AddEdit(Array<Edit> *edits, Range range, String string) {
     edits->add({range, string});
 }