1 files changed, 12 insertions, 13 deletions
diff --git a/java/com/android/incallui/rtt/impl/RttChatMessage.java b/java/com/android/incallui/rtt/impl/RttChatMessage.java
index fe30364b8..6c852cf92 100644
--- a/java/com/android/incallui/rtt/impl/RttChatMessage.java
+++ b/java/com/android/incallui/rtt/impl/RttChatMessage.java
@@ -18,7 +18,6 @@ package com.android.incallui.rtt.impl;
 
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
-import android.text.TextWatcher;
 import com.android.incallui.rtt.protocol.Constants;
 import com.google.common.base.Splitter;
 import java.util.ArrayList;
@@ -59,10 +58,7 @@ final class RttChatMessage {
   }
 
   /**
-   * Generates delta change to a text.
-   *
-   * <p>This is used to track text change of input. See more details in {@link
-   * TextWatcher#onTextChanged}
+   * Computes delta change of two string.
    *
    * <p>e.g. "hello world" -> "hello" : "\b\b\b\b\b\b"
    *
@@ -72,16 +68,19 @@ final class RttChatMessage {
    *
    * <p>"hello world" -> "hello new world" : "\b\b\b\b\bnew world"
    */
-  static String getChangedString(CharSequence s, int start, int before, int count) {
+  static String computeChangedString(String oldMessage, String newMesssage) {
     StringBuilder modify = new StringBuilder();
-    char c = '\b';
-    int oldLength = s.length() - count + before;
-    for (int i = 0; i < oldLength - start; i++) {
-      modify.append(c);
+    int indexChangeStart = 0;
+    while (indexChangeStart < oldMessage.length()
+        && indexChangeStart < newMesssage.length()
+        && oldMessage.charAt(indexChangeStart) == newMesssage.charAt(indexChangeStart)) {
+      indexChangeStart++;
+    }
+    for (int i = indexChangeStart; i < oldMessage.length(); i++) {
+      modify.append('\b');
     }
-    modify.append(s, start, start + count);
-    if (start + count < s.length()) {
-      modify.append(s, start + count, s.length());
+    for (int i = indexChangeStart; i < newMesssage.length(); i++) {
+      modify.append(newMesssage.charAt(i));
     }
     return modify.toString();
   }