From 71646fbcff9cab79983bf1aa04dbfabd23d63aa4 Mon Sep 17 00:00:00 2001
From: Dennis Snell <dennis.snell@automattic.com>
Date: Sat, 9 Nov 2019 14:54:38 -0600
Subject: [PATCH] Add fixes for Java client

---
 .../neil/plaintext/diff_match_patch.java       | 18 ++++++++++++++++++
 .../neil/plaintext/diff_match_patch_test.java  |  4 ++++
 2 files changed, 22 insertions(+)

diff --git a/java/src/name/fraser/neil/plaintext/diff_match_patch.java b/java/src/name/fraser/neil/plaintext/diff_match_patch.java
index 9d07867..c7935ed 100644
--- a/java/src/name/fraser/neil/plaintext/diff_match_patch.java
+++ b/java/src/name/fraser/neil/plaintext/diff_match_patch.java
@@ -19,6 +19,7 @@
 package name.fraser.neil.plaintext;
 
 import java.io.UnsupportedEncodingException;
+import java.lang.Character;
 import java.net.URLDecoder;
 import java.net.URLEncoder;
 import java.util.*;
@@ -1429,7 +1430,24 @@ public int diff_levenshtein(List<Diff> diffs) {
    */
   public String diff_toDelta(List<Diff> diffs) {
     StringBuilder text = new StringBuilder();
+    char lastEnd = 0;
+    boolean isFirst = true;
     for (Diff aDiff : diffs) {
+
+      char thisTop = aDiff.text.charAt(0);
+      char thisEnd = aDiff.text.charAt(aDiff.text.length() - 1);
+
+      if (Character.isHighSurrogate(thisEnd)) {
+        aDiff.text = aDiff.text.substring(0, aDiff.text.length() - 1);
+      }
+
+      if (! isFirst && Character.isHighSurrogate(lastEnd) && Character.isLowSurrogate(thisTop)) {
+        aDiff.text = lastEnd + aDiff.text;
+      }
+
+      isFirst = false;
+      lastEnd = thisEnd;
+
       switch (aDiff.operation) {
       case INSERT:
         try {
diff --git a/java/tests/name/fraser/neil/plaintext/diff_match_patch_test.java b/java/tests/name/fraser/neil/plaintext/diff_match_patch_test.java
index 2f38793..aef98ce 100644
--- a/java/tests/name/fraser/neil/plaintext/diff_match_patch_test.java
+++ b/java/tests/name/fraser/neil/plaintext/diff_match_patch_test.java
@@ -424,6 +424,10 @@ public static void testDiffDelta() {
 
     assertEquals("diff_fromDelta: Unicode.", diffs, dmp.diff_fromDelta(text1, delta));
 
+    diffs = diffList(new Diff(EQUAL, "\ud83d\ude4b\ud83d"), new Diff(INSERT, "\ude4c\ud83d"), new Diff(EQUAL, "\ude4b"));
+    delta = dmp.diff_toDelta(diffs);
+    assertEquals("diff_toDelta: Surrogate Pairs.", "=2\t+%F0%9F%99%8C\t=2", delta);
+
     // Verify pool of unchanged characters.
     diffs = diffList(new Diff(INSERT, "A-Z a-z 0-9 - _ . ! ~ * ' ( ) ; / ? : @ & = + $ , # "));
     String text2 = dmp.diff_text2(diffs);