Cursor improvements in pad (Beta)

www/common/cursor.js

@@ -124,6 +124,7 @@ define([
 
         cursor.pushDelta = function (oldVal, newVal) {
             if (oldVal === newVal) { return; }
+
             var commonStart = 0;
             while (oldVal.charAt(commonStart) === newVal.charAt(commonStart)) {
                 commonStart++;
@@ -156,6 +157,31 @@ define([
             };
         };
 
+        cursor.transformRange = function (cursorRange, ops) {
+            var transformCursor = function (cursor, op) {
+                if (!op) { return cursor; }
+
+                var pos = op.offset;
+                var remove = op.toRemove;
+                var insert = op.toInsert.length;
+                if (typeof cursor === 'undefined') { return; }
+                if (typeof remove === 'number' && pos < cursor) {
+                    cursor -= Math.min(remove, cursor - pos);
+                }
+                if (typeof insert === 'number' && pos < cursor) {
+                    cursor += insert;
+                }
+                return cursor;
+            };
+            var c = cursorRange.offset;
+            if (Array.isArray(ops)) {
+                for (var i = ops.length - 1; i >= 0; i--) {
+                    c = transformCursor(c, ops[i]);
+                }
+                cursorRange.offset = c;
+            }
+        };
+
         cursor.brFix = function () {
             cursor.update();
             var start = Range.start;