// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "core/editing/EditingUtilities.h"

#include "core/dom/StaticNodeList.h"
#include "core/editing/EditingTestBase.h"

namespace blink {

class EditingUtilitiesTest : public EditingTestBase {};

TEST_F(EditingUtilitiesTest, directionOfEnclosingBlock) {
  const char* bodyContent =
      "<p id='host'><b id='one'></b><b id='two'>22</b></p>";
  const char* shadowContent =
      "<content select=#two></content><p dir=rtl><content "
      "select=#one></content><p>";
  setBodyContent(bodyContent);
  setShadowContent(shadowContent, "host");
  Node* one = document().getElementById("one");

  EXPECT_EQ(TextDirection::kLtr, directionOfEnclosingBlock(Position(one, 0)));
  EXPECT_EQ(TextDirection::kRtl,
            directionOfEnclosingBlock(PositionInFlatTree(one, 0)));
}

TEST_F(EditingUtilitiesTest, firstEditablePositionAfterPositionInRoot) {
  const char* bodyContent =
      "<p id='host' contenteditable><b id='one'>1</b><b id='two'>22</b></p>";
  const char* shadowContent =
      "<content select=#two></content><content select=#one></content><b "
      "id='three'>333</b>";
  setBodyContent(bodyContent);
  ShadowRoot* shadowRoot = setShadowContent(shadowContent, "host");
  Element* host = document().getElementById("host");
  Node* one = document().getElementById("one");
  Node* two = document().getElementById("two");
  Node* three = shadowRoot->getElementById("three");

  EXPECT_EQ(Position(one, 0),
            firstEditablePositionAfterPositionInRoot(Position(one, 0), *host));
  EXPECT_EQ(
      Position(one->firstChild(), 0),
      firstEditableVisiblePositionAfterPositionInRoot(Position(one, 0), *host)
          .deepEquivalent());

  EXPECT_EQ(PositionInFlatTree(one, 0),
            firstEditablePositionAfterPositionInRoot(PositionInFlatTree(one, 0),
                                                     *host));
  EXPECT_EQ(PositionInFlatTree(two->firstChild(), 2),
            firstEditableVisiblePositionAfterPositionInRoot(
                PositionInFlatTree(one, 0), *host)
                .deepEquivalent());

  EXPECT_EQ(
      Position::firstPositionInNode(host),
      firstEditablePositionAfterPositionInRoot(Position(three, 0), *host));
  EXPECT_EQ(
      Position(one->firstChild(), 0),
      firstEditableVisiblePositionAfterPositionInRoot(Position(three, 0), *host)
          .deepEquivalent());
  EXPECT_EQ(PositionInFlatTree::afterNode(host),
            firstEditablePositionAfterPositionInRoot(
                PositionInFlatTree(three, 0), *host));
  EXPECT_EQ(PositionInFlatTree::lastPositionInNode(host),
            firstEditableVisiblePositionAfterPositionInRoot(
                PositionInFlatTree(three, 0), *host)
                .deepEquivalent());
}

TEST_F(EditingUtilitiesTest, enclosingBlock) {
  const char* bodyContent = "<p id='host'><b id='one'>11</b></p>";
  const char* shadowContent =
      "<content select=#two></content><div id='three'><content "
      "select=#one></content></div>";
  setBodyContent(bodyContent);
  ShadowRoot* shadowRoot = setShadowContent(shadowContent, "host");
  Node* host = document().getElementById("host");
  Node* one = document().getElementById("one");
  Node* three = shadowRoot->getElementById("three");

  EXPECT_EQ(host, enclosingBlock(Position(one, 0), CannotCrossEditingBoundary));
  EXPECT_EQ(three, enclosingBlock(PositionInFlatTree(one, 0),
                                  CannotCrossEditingBoundary));
}

TEST_F(EditingUtilitiesTest, enclosingNodeOfType) {
  const char* bodyContent = "<p id='host'><b id='one'>11</b></p>";
  const char* shadowContent =
      "<content select=#two></content><div id='three'><content "
      "select=#one></div></content>";
  setBodyContent(bodyContent);
  ShadowRoot* shadowRoot = setShadowContent(shadowContent, "host");
  Node* host = document().getElementById("host");
  Node* one = document().getElementById("one");
  Node* three = shadowRoot->getElementById("three");

  EXPECT_EQ(host, enclosingNodeOfType(Position(one, 0), isEnclosingBlock));
  EXPECT_EQ(three,
            enclosingNodeOfType(PositionInFlatTree(one, 0), isEnclosingBlock));
}

TEST_F(EditingUtilitiesTest, isEditablePositionWithTable) {
  // We would like to have below DOM tree without HTML, HEAD and BODY element.
  //   <table id=table><caption>foo</caption></table>
  // However, |setBodyContent()| automatically creates HTML, HEAD and BODY
  // element. So, we build DOM tree manually.
  // Note: This is unusual HTML taken from http://crbug.com/574230
  Element* table = document().createElement("table");
  table->setInnerHTML("<caption>foo</caption>");
  while (document().firstChild())
    document().firstChild()->remove();
  document().appendChild(table);
  document().setDesignMode("on");
  updateAllLifecyclePhases();

  EXPECT_FALSE(isEditablePosition(Position(table, 0)));
}

TEST_F(EditingUtilitiesTest, tableElementJustBefore) {
  const char* bodyContent =
      "<div contenteditable id=host><table "
      "id=table><tr><td>1</td></tr></table><b id=two>22</b></div>";
  const char* shadowContent =
      "<content select=#two></content><content select=#table></content>";
  setBodyContent(bodyContent);
  setShadowContent(shadowContent, "host");
  Node* host = document().getElementById("host");
  Node* table = document().getElementById("table");

  EXPECT_EQ(table, tableElementJustBefore(VisiblePosition::afterNode(table)));
  EXPECT_EQ(table, tableElementJustBefore(
                       VisiblePositionInFlatTree::afterNode(table)));

  EXPECT_EQ(table,
            tableElementJustBefore(VisiblePosition::lastPositionInNode(table)));
  EXPECT_EQ(table, tableElementJustBefore(createVisiblePosition(
                       PositionInFlatTree::lastPositionInNode(table))));

  EXPECT_EQ(nullptr,
            tableElementJustBefore(createVisiblePosition(Position(host, 2))));
  EXPECT_EQ(table, tableElementJustBefore(
                       createVisiblePosition(PositionInFlatTree(host, 2))));

  EXPECT_EQ(nullptr, tableElementJustBefore(VisiblePosition::afterNode(host)));
  EXPECT_EQ(nullptr,
            tableElementJustBefore(VisiblePositionInFlatTree::afterNode(host)));

  EXPECT_EQ(nullptr,
            tableElementJustBefore(VisiblePosition::lastPositionInNode(host)));
  EXPECT_EQ(table, tableElementJustBefore(createVisiblePosition(
                       PositionInFlatTree::lastPositionInNode(host))));
}

TEST_F(EditingUtilitiesTest, lastEditablePositionBeforePositionInRoot) {
  const char* bodyContent =
      "<p id='host' contenteditable><b id='one'>1</b><b id='two'>22</b></p>";
  const char* shadowContent =
      "<content select=#two></content><content select=#one></content><b "
      "id='three'>333</b>";
  setBodyContent(bodyContent);
  ShadowRoot* shadowRoot = setShadowContent(shadowContent, "host");
  Element* host = document().getElementById("host");
  Node* one = document().getElementById("one");
  Node* two = document().getElementById("two");
  Node* three = shadowRoot->getElementById("three");

  EXPECT_EQ(Position(one, 0),
            lastEditablePositionBeforePositionInRoot(Position(one, 0), *host));
  EXPECT_EQ(
      Position(one->firstChild(), 0),
      lastEditableVisiblePositionBeforePositionInRoot(Position(one, 0), *host)
          .deepEquivalent());

  EXPECT_EQ(PositionInFlatTree(one, 0),
            lastEditablePositionBeforePositionInRoot(PositionInFlatTree(one, 0),
                                                     *host));
  EXPECT_EQ(PositionInFlatTree(two->firstChild(), 2),
            lastEditableVisiblePositionBeforePositionInRoot(
                PositionInFlatTree(one, 0), *host)
                .deepEquivalent());

  EXPECT_EQ(
      Position::firstPositionInNode(host),
      lastEditablePositionBeforePositionInRoot(Position(three, 0), *host));
  EXPECT_EQ(
      Position(one->firstChild(), 0),
      lastEditableVisiblePositionBeforePositionInRoot(Position(three, 0), *host)
          .deepEquivalent());
  EXPECT_EQ(PositionInFlatTree::firstPositionInNode(host),
            lastEditablePositionBeforePositionInRoot(
                PositionInFlatTree(three, 0), *host));
  EXPECT_EQ(PositionInFlatTree(two->firstChild(), 0),
            lastEditableVisiblePositionBeforePositionInRoot(
                PositionInFlatTree(three, 0), *host)
                .deepEquivalent());
}

TEST_F(EditingUtilitiesTest, NextNodeIndex) {
  const char* bodyContent =
      "<p id='host'>00<b id='one'>11</b><b id='two'>22</b>33</p>";
  const char* shadowContent =
      "<content select=#two></content><content select=#one></content>";
  setBodyContent(bodyContent);
  setShadowContent(shadowContent, "host");
  Node* host = document().getElementById("host");
  Node* two = document().getElementById("two");

  EXPECT_EQ(
      Position(host, 3),
      nextPositionOf(Position(two, 2), PositionMoveType::GraphemeCluster));
  EXPECT_EQ(PositionInFlatTree(host, 1),
            nextPositionOf(PositionInFlatTree(two, 2),
                           PositionMoveType::GraphemeCluster));
}

TEST_F(EditingUtilitiesTest, NextVisuallyDistinctCandidate) {
  const char* bodyContent =
      "<p id='host'>00<b id='one'>11</b><b id='two'>22</b><b "
      "id='three'>33</b></p>";
  const char* shadowContent =
      "<content select=#two></content><content select=#one></content><content "
      "select=#three></content>";
  setBodyContent(bodyContent);
  setShadowContent(shadowContent, "host");
  Node* one = document().getElementById("one");
  Node* two = document().getElementById("two");
  Node* three = document().getElementById("three");

  EXPECT_EQ(Position(two->firstChild(), 1),
            nextVisuallyDistinctCandidate(Position(one, 1)));
  EXPECT_EQ(PositionInFlatTree(three->firstChild(), 1),
            nextVisuallyDistinctCandidate(PositionInFlatTree(one, 1)));
}

TEST_F(EditingUtilitiesTest, AreaIdenticalElements) {
  setBodyContent(
      "<style>li:nth-child(even) { -webkit-user-modify: read-write; "
      "}</style><ul><li>first item</li><li>second item</li><li "
      "class=foo>third</li><li>fourth</li></ul>");
  StaticElementList* items =
      document().querySelectorAll("li", ASSERT_NO_EXCEPTION);
  DCHECK_EQ(items->length(), 4u);

  EXPECT_FALSE(areIdenticalElements(*items->item(0)->firstChild(),
                                    *items->item(1)->firstChild()))
      << "Can't merge non-elements.  e.g. Text nodes";

  // Compare a LI and a UL.
  EXPECT_FALSE(
      areIdenticalElements(*items->item(0), *items->item(0)->parentNode()))
      << "Can't merge different tag names.";

  EXPECT_FALSE(areIdenticalElements(*items->item(0), *items->item(2)))
      << "Can't merge a element with no attributes and another element with an "
         "attribute.";

  // We can't use contenteditable attribute to make editability difference
  // because the hasEquivalentAttributes check is done earier.
  EXPECT_FALSE(areIdenticalElements(*items->item(0), *items->item(1)))
      << "Can't merge non-editable nodes.";

  EXPECT_TRUE(areIdenticalElements(*items->item(1), *items->item(3)));
}

TEST_F(EditingUtilitiesTest, uncheckedPreviousNextOffset_FirstLetter) {
  setBodyContent(
      "<style>p::first-letter {color:red;}</style><p id='target'>abc</p>");
  Node* node = document().getElementById("target")->firstChild();
  EXPECT_EQ(2, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(2, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 2));

  updateAllLifecyclePhases();
  EXPECT_NE(nullptr, node->layoutObject());
  EXPECT_EQ(2, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(2, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 2));
}

TEST_F(EditingUtilitiesTest, uncheckedPreviousNextOffset_textTransform) {
  setBodyContent(
      "<style>p {text-transform:uppercase}</style><p id='target'>abc</p>");
  Node* node = document().getElementById("target")->firstChild();
  EXPECT_EQ(2, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(2, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 2));

  updateAllLifecyclePhases();
  EXPECT_NE(nullptr, node->layoutObject());
  EXPECT_EQ(2, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(2, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 2));
}

// Following breaking rules come from http://unicode.org/reports/tr29/
// Note that some of rules are in draft. Also see
// http://www.unicode.org/reports/tr29/proposed.html
TEST_F(EditingUtilitiesTest, uncheckedPreviousNextOffset) {
  // GB1: Break at the start of text.
  setBodyContent("<p id='target'>a</p>");
  Node* node = document().getElementById("target")->firstChild();
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));

  // GB2: Break at the end of text.
  setBodyContent("<p id='target'>a</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));

  // GB3: Do not break between CR and LF.
  setBodyContent("<p id='target'>a&#x0D;&#x0A;b</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(3, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(4, nextGraphemeBoundaryOf(node, 3));

  // GB4,GB5: Break before and after CR/LF/Control.
  setBodyContent("<p id='target'>a&#x0D;b</p>");  // CR
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(2, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(2, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 2));
  setBodyContent("<p id='target'>a&#x0A;b</p>");  // LF
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(2, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(2, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 2));
  // U+00AD(SOFT HYPHEN) has Control property.
  setBodyContent("<p id='target'>a&#xAD;b</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(2, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(2, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 2));

  // GB6: Don't break Hangul sequence.
  const std::string L =
      "&#x1100;";  // U+1100 (HANGUL CHOSEONG KIYEOK) has L property.
  const std::string V =
      "&#x1160;";  // U+1160 (HANGUL JUNGSEONG FILLER) has V property.
  const std::string LV =
      "&#xAC00;";  // U+AC00 (HANGUL SYLLABLE GA) has LV property.
  const std::string LVT =
      "&#xAC01;";  // U+AC01 (HANGUL SYLLABLE GAG) has LVT property.
  const std::string T =
      "&#x11A8;";  // U+11A8 (HANGUL JONGSEONG KIYEOK) has T property.
  setBodyContent("<p id='target'>a" + L + L + "b</p>");  // L x L
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(3, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(4, nextGraphemeBoundaryOf(node, 3));
  setBodyContent("<p id='target'>a" + L + V + "b</p>");  // L x V
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(3, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(4, nextGraphemeBoundaryOf(node, 3));
  setBodyContent("<p id='target'>a" + L + LV + "b</p>");  // L x LV
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(3, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(4, nextGraphemeBoundaryOf(node, 3));
  setBodyContent("<p id='target'>a" + L + LVT + "b</p>");  // L x LVT
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(3, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(4, nextGraphemeBoundaryOf(node, 3));

  // GB7: Don't break Hangul sequence.
  setBodyContent("<p id='target'>a" + LV + V + "b</p>");  // LV x V
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(3, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(4, nextGraphemeBoundaryOf(node, 3));
  setBodyContent("<p id='target'>a" + LV + T + "b</p>");  // LV x T
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(3, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(4, nextGraphemeBoundaryOf(node, 3));
  setBodyContent("<p id='target'>a" + V + V + "b</p>");  // V x V
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(3, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(4, nextGraphemeBoundaryOf(node, 3));
  setBodyContent("<p id='target'>a" + V + T + "b</p>");  // V x T
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(3, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(4, nextGraphemeBoundaryOf(node, 3));

  // GB8: Don't break Hangul sequence.
  setBodyContent("<p id='target'>a" + LVT + T + "b</p>");  // LVT x T
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(3, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(4, nextGraphemeBoundaryOf(node, 3));
  setBodyContent("<p id='target'>a" + T + T + "b</p>");  // T x T
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(3, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(4, nextGraphemeBoundaryOf(node, 3));

  // Break other Hangul syllable combination. See test of GB999.

  // GB8a: Don't break between regional indicator if there are even numbered
  // regional indicator symbols before.
  // U+1F1FA is REGIONAL INDICATOR SYMBOL LETTER U.
  // U+1F1F8 is REGIONAL INDICATOR SYMBOL LETTER S.
  const std::string flag = "&#x1F1FA;&#x1F1F8;";  // US flag.
  // ^(RI RI)* RI x RI
  setBodyContent("<p id='target'>" + flag + flag + flag + flag + "a</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(16, previousGraphemeBoundaryOf(node, 17));
  EXPECT_EQ(12, previousGraphemeBoundaryOf(node, 16));
  EXPECT_EQ(8, previousGraphemeBoundaryOf(node, 12));
  EXPECT_EQ(4, previousGraphemeBoundaryOf(node, 8));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(4, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(8, nextGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(12, nextGraphemeBoundaryOf(node, 8));
  EXPECT_EQ(16, nextGraphemeBoundaryOf(node, 12));
  EXPECT_EQ(17, nextGraphemeBoundaryOf(node, 16));

  // GB8c: Don't break between regional indicator if there are even numbered
  // regional indicator symbols before.
  // [^RI] (RI RI)* RI x RI
  setBodyContent("<p id='target'>a" + flag + flag + flag + flag + "b</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(17, previousGraphemeBoundaryOf(node, 18));
  EXPECT_EQ(13, previousGraphemeBoundaryOf(node, 17));
  EXPECT_EQ(9, previousGraphemeBoundaryOf(node, 13));
  EXPECT_EQ(5, previousGraphemeBoundaryOf(node, 9));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 5));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(5, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(9, nextGraphemeBoundaryOf(node, 5));
  EXPECT_EQ(13, nextGraphemeBoundaryOf(node, 9));
  EXPECT_EQ(17, nextGraphemeBoundaryOf(node, 13));
  EXPECT_EQ(18, nextGraphemeBoundaryOf(node, 17));

  // GB8c: Break if there is an odd number of regional indicator symbols before.
  setBodyContent("<p id='target'>a" + flag + flag + flag + flag +
                 "&#x1F1F8;b</p>");  // RI ÷ RI
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(19, previousGraphemeBoundaryOf(node, 20));
  EXPECT_EQ(17, previousGraphemeBoundaryOf(node, 19));
  EXPECT_EQ(13, previousGraphemeBoundaryOf(node, 17));
  EXPECT_EQ(9, previousGraphemeBoundaryOf(node, 13));
  EXPECT_EQ(5, previousGraphemeBoundaryOf(node, 9));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 5));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(5, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(9, nextGraphemeBoundaryOf(node, 5));
  EXPECT_EQ(13, nextGraphemeBoundaryOf(node, 9));
  EXPECT_EQ(17, nextGraphemeBoundaryOf(node, 13));
  EXPECT_EQ(19, nextGraphemeBoundaryOf(node, 17));
  EXPECT_EQ(20, nextGraphemeBoundaryOf(node, 19));

  // GB9: Do not break before extending characters or ZWJ.
  // U+0300(COMBINING GRAVE ACCENT) has Extend property.
  setBodyContent("<p id='target'>a&#x0300;b</p>");  // x Extend
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(2, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(2, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 2));
  // U+200D is ZERO WIDTH JOINER.
  setBodyContent("<p id='target'>a&#x200D;b</p>");  // x ZWJ
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(2, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(2, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 2));

  // GB9a: Do not break before SpacingMarks.
  // U+0903(DEVANAGARI SIGN VISARGA) has SpacingMark property.
  setBodyContent("<p id='target'>a&#x0903;b</p>");  // x SpacingMark
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(2, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(2, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 2));

  // GB9b: Do not break after Prepend.
  // TODO(nona): Introduce Prepend test case once ICU grabs Unicode 9.0.

  // For https://bugs.webkit.org/show_bug.cgi?id=24342
  // The break should happens after Thai character.
  setBodyContent("<p id='target'>a&#x0E40;b</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(2, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(2, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 2));

  // Blink customization: Don't break before Japanese half-width katakana voiced
  // marks.
  setBodyContent("<p id='target'>a&#xFF76;&#xFF9E;b</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(3, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(4, nextGraphemeBoundaryOf(node, 3));

  // Additional rule for IndicSyllabicCategory=Virama: Do not break after that.
  // See
  // http://www.unicode.org/Public/9.0.0/ucd/IndicSyllabicCategory-9.0.0d2.txt
  // U+0905 is DEVANAGARI LETTER A. This has Extend property.
  // U+094D is DEVANAGARI SIGN VIRAMA. This has Virama property.
  // U+0915 is DEVANAGARI LETTER KA.
  setBodyContent("<p id='target'>a&#x0905;&#x094D;&#x0915;b</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(4, previousGraphemeBoundaryOf(node, 5));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(4, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(5, nextGraphemeBoundaryOf(node, 4));
  // U+0E01 is THAI CHARACTER KO KAI
  // U+0E3A is THAI CHARACTER PHINTHU
  // Should break after U+0E3A since U+0E3A has Virama property but not listed
  // in IndicSyllabicCategory=Virama.
  setBodyContent("<p id='target'>a&#x0E01;&#x0E3A;&#x0E01;b</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(4, previousGraphemeBoundaryOf(node, 5));
  EXPECT_EQ(3, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(4, nextGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(5, nextGraphemeBoundaryOf(node, 4));

  // GB10: Do not break within emoji modifier.
  // U+1F385(FATHER CHRISTMAS) has E_Base property.
  // U+1F3FB(EMOJI MODIFIER FITZPATRICK TYPE-1-2) has E_Modifier property.
  setBodyContent(
      "<p id='target'>a&#x1F385;&#x1F3FB;b</p>");  // E_Base x E_Modifier
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(5, previousGraphemeBoundaryOf(node, 6));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 5));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(5, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(6, nextGraphemeBoundaryOf(node, 5));
  // U+1F466(BOY) has EBG property.
  setBodyContent(
      "<p id='target'>a&#x1F466;&#x1F3FB;b</p>");  // EBG x E_Modifier
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(5, previousGraphemeBoundaryOf(node, 6));
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 5));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(5, nextGraphemeBoundaryOf(node, 1));
  EXPECT_EQ(6, nextGraphemeBoundaryOf(node, 5));

  // GB11: Do not break within ZWJ emoji sequence.
  // U+2764(HEAVY BLACK HEART) has Glue_After_Zwj property.
  setBodyContent(
      "<p id='target'>a&#x200D;&#x2764;b</p>");  // ZWJ x Glue_After_Zwj
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(3, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(4, nextGraphemeBoundaryOf(node, 3));
  setBodyContent("<p id='target'>a&#x200D;&#x1F466;b</p>");  // ZWJ x EBG
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(4, previousGraphemeBoundaryOf(node, 5));
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(4, nextGraphemeBoundaryOf(node, 0));
  EXPECT_EQ(5, nextGraphemeBoundaryOf(node, 4));

  // Not only Glue_After_ZWJ or EBG but also other emoji shouldn't break
  // before ZWJ.
  // U+1F5FA(WORLD MAP) doesn't have either Glue_After_Zwj or EBG but has
  // Emoji property.
  setBodyContent("<p id='target'>&#x200D;&#x1F5FA;</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(0, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(3, nextGraphemeBoundaryOf(node, 0));

  // GB999: Otherwise break everywhere.
  // Breaks between Hangul syllable except for GB6, GB7, GB8.
  setBodyContent("<p id='target'>" + L + T + "</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  setBodyContent("<p id='target'>" + V + L + "</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  setBodyContent("<p id='target'>" + V + LV + "</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  setBodyContent("<p id='target'>" + V + LVT + "</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  setBodyContent("<p id='target'>" + LV + L + "</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  setBodyContent("<p id='target'>" + LV + LV + "</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  setBodyContent("<p id='target'>" + LV + LVT + "</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  setBodyContent("<p id='target'>" + LVT + L + "</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  setBodyContent("<p id='target'>" + LVT + V + "</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  setBodyContent("<p id='target'>" + LVT + LV + "</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  setBodyContent("<p id='target'>" + LVT + LVT + "</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  setBodyContent("<p id='target'>" + T + L + "</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  setBodyContent("<p id='target'>" + T + V + "</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  setBodyContent("<p id='target'>" + T + LV + "</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  setBodyContent("<p id='target'>" + T + LVT + "</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));

  // For GB10, if base emoji character is not E_Base or EBG, break happens
  // before E_Modifier.
  setBodyContent("<p id='target'>a&#x1F3FB;</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 3));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
  // U+1F5FA(WORLD MAP) doesn't have either E_Base or EBG property.
  setBodyContent("<p id='target'>&#x1F5FA;&#x1F3FB;</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(2, previousGraphemeBoundaryOf(node, 4));
  EXPECT_EQ(2, nextGraphemeBoundaryOf(node, 0));

  // For GB11, if trailing character is not Glue_After_Zwj or EBG, break happens
  // after ZWJ.
  // U+1F5FA(WORLD MAP) doesn't have either Glue_After_Zwj or EBG.
  setBodyContent("<p id='target'>&#x200D;a</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(1, previousGraphemeBoundaryOf(node, 2));
  EXPECT_EQ(1, nextGraphemeBoundaryOf(node, 0));
}

TEST_F(EditingUtilitiesTest, previousPositionOf_Backspace) {
  // BMP characters. Only one code point should be deleted.
  setBodyContent("<p id='target'>abc</p>");
  Node* node = document().getElementById("target")->firstChild();
  EXPECT_EQ(Position(node, 2),
            previousPositionOf(Position(node, 3),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 1),
            previousPositionOf(Position(node, 2),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 0),
            previousPositionOf(Position(node, 1),
                               PositionMoveType::BackwardDeletion));
}

TEST_F(EditingUtilitiesTest, previousPositionOf_Backspace_FirstLetter) {
  setBodyContent(
      "<style>p::first-letter {color:red;}</style><p id='target'>abc</p>");
  Node* node = document().getElementById("target")->firstChild();
  EXPECT_EQ(Position(node, 2),
            previousPositionOf(Position(node, 3),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 1),
            previousPositionOf(Position(node, 2),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 0),
            previousPositionOf(Position(node, 1),
                               PositionMoveType::BackwardDeletion));

  setBodyContent(
      "<style>p::first-letter {color:red;}</style><p id='target'>(a)bc</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(Position(node, 4),
            previousPositionOf(Position(node, 5),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 3),
            previousPositionOf(Position(node, 4),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 2),
            previousPositionOf(Position(node, 3),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 1),
            previousPositionOf(Position(node, 2),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 0),
            previousPositionOf(Position(node, 1),
                               PositionMoveType::BackwardDeletion));
}

TEST_F(EditingUtilitiesTest, previousPositionOf_Backspace_TextTransform) {
  // Uppercase of &#x00DF; will be transformed to SS.
  setBodyContent(
      "<style>p {text-transform:uppercase}</style><p "
      "id='target'>&#x00DF;abc</p>");
  Node* node = document().getElementById("target")->firstChild();
  EXPECT_EQ(Position(node, 3),
            previousPositionOf(Position(node, 4),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 2),
            previousPositionOf(Position(node, 3),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 1),
            previousPositionOf(Position(node, 2),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 0),
            previousPositionOf(Position(node, 1),
                               PositionMoveType::BackwardDeletion));
}

TEST_F(EditingUtilitiesTest, previousPositionOf_Backspace_SurrogatePairs) {
  // Supplementary plane characters. Only one code point should be deleted.
  // &#x1F441; is EYE.
  setBodyContent("<p id='target'>&#x1F441;&#x1F441;&#x1F441;</p>");
  Node* node = document().getElementById("target")->firstChild();
  EXPECT_EQ(Position(node, 4),
            previousPositionOf(Position(node, 6),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 2),
            previousPositionOf(Position(node, 4),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 0),
            previousPositionOf(Position(node, 2),
                               PositionMoveType::BackwardDeletion));

  // BMP and Supplementary plane case.
  setBodyContent("<p id='target'>&#x1F441;a&#x1F441;a</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(Position(node, 5),
            previousPositionOf(Position(node, 6),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 3),
            previousPositionOf(Position(node, 5),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 2),
            previousPositionOf(Position(node, 3),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 0),
            previousPositionOf(Position(node, 2),
                               PositionMoveType::BackwardDeletion));

  // Edge case: broken surrogate pairs.
  setBodyContent(
      "<p id='target'>&#xD83D;</p>");  // &#xD83D; is unpaired lead surrogate.
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(Position(node, 0),
            previousPositionOf(Position(node, 1),
                               PositionMoveType::BackwardDeletion));

  // &#xD83D; is unpaired lead surrogate.
  setBodyContent("<p id='target'>&#x1F441;&#xD83D;&#x1F441;</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(Position(node, 3),
            previousPositionOf(Position(node, 5),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 2),
            previousPositionOf(Position(node, 3),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 0),
            previousPositionOf(Position(node, 2),
                               PositionMoveType::BackwardDeletion));

  setBodyContent(
      "<p id='target'>a&#xD83D;a</p>");  // &#xD83D; is unpaired lead surrogate.
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(Position(node, 2),
            previousPositionOf(Position(node, 3),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 1),
            previousPositionOf(Position(node, 2),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 0),
            previousPositionOf(Position(node, 1),
                               PositionMoveType::BackwardDeletion));

  setBodyContent(
      "<p id='target'>&#xDC41;</p>");  // &#xDC41; is unpaired trail surrogate.
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(Position(node, 0),
            previousPositionOf(Position(node, 1),
                               PositionMoveType::BackwardDeletion));

  // &#xDC41; is unpaired trail surrogate.
  setBodyContent("<p id='target'>&#x1F441;&#xDC41;&#x1F441;</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(Position(node, 3),
            previousPositionOf(Position(node, 5),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 2),
            previousPositionOf(Position(node, 3),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 0),
            previousPositionOf(Position(node, 2),
                               PositionMoveType::BackwardDeletion));

  // &#xDC41; is unpaired trail surrogate.
  setBodyContent("<p id='target'>a&#xDC41;a</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(Position(node, 2),
            previousPositionOf(Position(node, 3),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 1),
            previousPositionOf(Position(node, 2),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 0),
            previousPositionOf(Position(node, 1),
                               PositionMoveType::BackwardDeletion));

  // Edge case: specify middle of surrogate pairs.
  setBodyContent("<p id='target'>&#x1F441;&#x1F441;&#x1F441</p>");
  node = document().getElementById("target")->firstChild();
  EXPECT_EQ(Position(node, 4),
            previousPositionOf(Position(node, 5),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 2),
            previousPositionOf(Position(node, 3),
                               PositionMoveType::BackwardDeletion));
  EXPECT_EQ(Position(node, 0),
            previousPositionOf(Position(node, 1),
                               PositionMoveType::BackwardDeletion));
}

}  // namespace blink