// Copyright (c) 2012 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 "ui/gfx/render_text.h"

#include <algorithm>
#include <climits>

#include "base/command_line.h"
#include "base/i18n/break_iterator.h"
#include "base/logging.h"
#include "base/stl_util.h"
#include "base/strings/string_util.h"
#include "base/strings/utf_string_conversions.h"
#include "third_party/icu/source/common/unicode/rbbi.h"
#include "third_party/icu/source/common/unicode/utf16.h"
#include "third_party/skia/include/core/SkTypeface.h"
#include "third_party/skia/include/effects/SkGradientShader.h"
#include "ui/gfx/canvas.h"
#include "ui/gfx/insets.h"
#include "ui/gfx/render_text_harfbuzz.h"
#include "ui/gfx/scoped_canvas.h"
#include "ui/gfx/skia_util.h"
#include "ui/gfx/switches.h"
#include "ui/gfx/text_elider.h"
#include "ui/gfx/text_utils.h"
#include "ui/gfx/utf16_indexing.h"

namespace gfx {

namespace {

// All chars are replaced by this char when the password style is set.
// TODO(benrg): GTK uses the first of U+25CF, U+2022, U+2731, U+273A, '*'
// that's available in the font (find_invisible_char() in gtkentry.c).
const base::char16 kPasswordReplacementChar = '*';

// Default color used for the text and cursor.
const SkColor kDefaultColor = SK_ColorBLACK;

// Default color used for drawing selection background.
const SkColor kDefaultSelectionBackgroundColor = SK_ColorGRAY;

// Fraction of the text size to lower a strike through below the baseline.
const SkScalar kStrikeThroughOffset = (-SK_Scalar1 * 6 / 21);
// Fraction of the text size to lower an underline below the baseline.
const SkScalar kUnderlineOffset = (SK_Scalar1 / 9);
// Fraction of the text size to use for a strike through or under-line.
const SkScalar kLineThickness = (SK_Scalar1 / 18);
// Fraction of the text size to use for a top margin of a diagonal strike.
const SkScalar kDiagonalStrikeMarginOffset = (SK_Scalar1 / 4);

// Invalid value of baseline.  Assigning this value to |baseline_| causes
// re-calculation of baseline.
const int kInvalidBaseline = INT_MAX;

// Returns the baseline, with which the text best appears vertically centered.
int DetermineBaselineCenteringText(const Rect& display_rect,
                                   const FontList& font_list) {
  const int display_height = display_rect.height();
  const int font_height = font_list.GetHeight();
  // Lower and upper bound of baseline shift as we try to show as much area of
  // text as possible.  In particular case of |display_height| == |font_height|,
  // we do not want to shift the baseline.
  const int min_shift = std::min(0, display_height - font_height);
  const int max_shift = std::abs(display_height - font_height);
  const int baseline = font_list.GetBaseline();
  const int cap_height = font_list.GetCapHeight();
  const int internal_leading = baseline - cap_height;
  // Some platforms don't support getting the cap height, and simply return
  // the entire font ascent from GetCapHeight().  Centering the ascent makes
  // the font look too low, so if GetCapHeight() returns the ascent, center
  // the entire font height instead.
  const int space =
      display_height - ((internal_leading != 0) ? cap_height : font_height);
  const int baseline_shift = space / 2 - internal_leading;
  return baseline + std::max(min_shift, std::min(max_shift, baseline_shift));
}

// Converts |Font::FontStyle| flags to |SkTypeface::Style| flags.
SkTypeface::Style ConvertFontStyleToSkiaTypefaceStyle(int font_style) {
  int skia_style = SkTypeface::kNormal;
  skia_style |= (font_style & Font::BOLD) ? SkTypeface::kBold : 0;
  skia_style |= (font_style & Font::ITALIC) ? SkTypeface::kItalic : 0;
  return static_cast<SkTypeface::Style>(skia_style);
}

// Given |font| and |display_width|, returns the width of the fade gradient.
int CalculateFadeGradientWidth(const FontList& font_list, int display_width) {
  // Fade in/out about 2.5 characters of the beginning/end of the string.
  // The .5 here is helpful if one of the characters is a space.
  // Use a quarter of the display width if the display width is very short.
  const int average_character_width = font_list.GetExpectedTextWidth(1);
  const double gradient_width = std::min(average_character_width * 2.5,
                                         display_width / 4.0);
  DCHECK_GE(gradient_width, 0.0);
  return static_cast<int>(floor(gradient_width + 0.5));
}

// Appends to |positions| and |colors| values corresponding to the fade over
// |fade_rect| from color |c0| to color |c1|.
void AddFadeEffect(const Rect& text_rect,
                   const Rect& fade_rect,
                   SkColor c0,
                   SkColor c1,
                   std::vector<SkScalar>* positions,
                   std::vector<SkColor>* colors) {
  const SkScalar left = static_cast<SkScalar>(fade_rect.x() - text_rect.x());
  const SkScalar width = static_cast<SkScalar>(fade_rect.width());
  const SkScalar p0 = left / text_rect.width();
  const SkScalar p1 = (left + width) / text_rect.width();
  // Prepend 0.0 to |positions|, as required by Skia.
  if (positions->empty() && p0 != 0.0) {
    positions->push_back(0.0);
    colors->push_back(c0);
  }
  positions->push_back(p0);
  colors->push_back(c0);
  positions->push_back(p1);
  colors->push_back(c1);
}

// Creates a SkShader to fade the text, with |left_part| specifying the left
// fade effect, if any, and |right_part| specifying the right fade effect.
skia::RefPtr<SkShader> CreateFadeShader(const Rect& text_rect,
                                        const Rect& left_part,
                                        const Rect& right_part,
                                        SkColor color) {
  // Fade alpha of 51/255 corresponds to a fade of 0.2 of the original color.
  const SkColor fade_color = SkColorSetA(color, 51);
  std::vector<SkScalar> positions;
  std::vector<SkColor> colors;

  if (!left_part.IsEmpty())
    AddFadeEffect(text_rect, left_part, fade_color, color,
                  &positions, &colors);
  if (!right_part.IsEmpty())
    AddFadeEffect(text_rect, right_part, color, fade_color,
                  &positions, &colors);
  DCHECK(!positions.empty());

  // Terminate |positions| with 1.0, as required by Skia.
  if (positions.back() != 1.0) {
    positions.push_back(1.0);
    colors.push_back(colors.back());
  }

  SkPoint points[2];
  points[0].iset(text_rect.x(), text_rect.y());
  points[1].iset(text_rect.right(), text_rect.y());

  return skia::AdoptRef(
      SkGradientShader::CreateLinear(&points[0], &colors[0], &positions[0],
                                     colors.size(), SkShader::kClamp_TileMode));
}

// Converts a FontRenderParams::Hinting value to the corresponding
// SkPaint::Hinting value.
SkPaint::Hinting FontRenderParamsHintingToSkPaintHinting(
    FontRenderParams::Hinting params_hinting) {
  switch (params_hinting) {
    case FontRenderParams::HINTING_NONE:   return SkPaint::kNo_Hinting;
    case FontRenderParams::HINTING_SLIGHT: return SkPaint::kSlight_Hinting;
    case FontRenderParams::HINTING_MEDIUM: return SkPaint::kNormal_Hinting;
    case FontRenderParams::HINTING_FULL:   return SkPaint::kFull_Hinting;
  }
  return SkPaint::kNo_Hinting;
}

}  // namespace

namespace internal {

// Value of |underline_thickness_| that indicates that underline metrics have
// not been set explicitly.
const SkScalar kUnderlineMetricsNotSet = -1.0f;

SkiaTextRenderer::SkiaTextRenderer(Canvas* canvas)
    : canvas_(canvas),
      canvas_skia_(canvas->sk_canvas()),
      underline_thickness_(kUnderlineMetricsNotSet),
      underline_position_(0.0f) {
  DCHECK(canvas_skia_);
  paint_.setTextEncoding(SkPaint::kGlyphID_TextEncoding);
  paint_.setStyle(SkPaint::kFill_Style);
  paint_.setAntiAlias(true);
  paint_.setSubpixelText(true);
  paint_.setLCDRenderText(true);
  paint_.setHinting(SkPaint::kNormal_Hinting);
}

SkiaTextRenderer::~SkiaTextRenderer() {
}

void SkiaTextRenderer::SetDrawLooper(SkDrawLooper* draw_looper) {
  paint_.setLooper(draw_looper);
}

void SkiaTextRenderer::SetFontRenderParams(const FontRenderParams& params,
                                           bool background_is_transparent) {
  ApplyRenderParams(params, background_is_transparent, &paint_);
}

void SkiaTextRenderer::SetTypeface(SkTypeface* typeface) {
  paint_.setTypeface(typeface);
}

void SkiaTextRenderer::SetTextSize(SkScalar size) {
  paint_.setTextSize(size);
}

void SkiaTextRenderer::SetFontFamilyWithStyle(const std::string& family,
                                              int style) {
  DCHECK(!family.empty());

  skia::RefPtr<SkTypeface> typeface = CreateSkiaTypeface(family.c_str(), style);
  if (typeface) {
    // |paint_| adds its own ref. So don't |release()| it from the ref ptr here.
    SetTypeface(typeface.get());

    // Enable fake bold text if bold style is needed but new typeface does not
    // have it.
    paint_.setFakeBoldText((style & Font::BOLD) && !typeface->isBold());
  }
}

void SkiaTextRenderer::SetForegroundColor(SkColor foreground) {
  paint_.setColor(foreground);
}

void SkiaTextRenderer::SetShader(SkShader* shader) {
  paint_.setShader(shader);
}

void SkiaTextRenderer::SetUnderlineMetrics(SkScalar thickness,
                                           SkScalar position) {
  underline_thickness_ = thickness;
  underline_position_ = position;
}

void SkiaTextRenderer::DrawPosText(const SkPoint* pos,
                                   const uint16* glyphs,
                                   size_t glyph_count) {
  const size_t byte_length = glyph_count * sizeof(glyphs[0]);
  canvas_skia_->drawPosText(&glyphs[0], byte_length, &pos[0], paint_);
}

void SkiaTextRenderer::DrawDecorations(int x, int y, int width, bool underline,
                                       bool strike, bool diagonal_strike) {
  if (underline)
    DrawUnderline(x, y, width);
  if (strike)
    DrawStrike(x, y, width);
  if (diagonal_strike) {
    if (!diagonal_)
      diagonal_.reset(new DiagonalStrike(canvas_, Point(x, y), paint_));
    diagonal_->AddPiece(width, paint_.getColor());
  } else if (diagonal_) {
    EndDiagonalStrike();
  }
}

void SkiaTextRenderer::EndDiagonalStrike() {
  if (diagonal_) {
    diagonal_->Draw();
    diagonal_.reset();
  }
}

void SkiaTextRenderer::DrawUnderline(int x, int y, int width) {
  SkRect r = SkRect::MakeLTRB(x, y + underline_position_, x + width,
                              y + underline_position_ + underline_thickness_);
  if (underline_thickness_ == kUnderlineMetricsNotSet) {
    const SkScalar text_size = paint_.getTextSize();
    r.fTop = SkScalarMulAdd(text_size, kUnderlineOffset, y);
    r.fBottom = r.fTop + SkScalarMul(text_size, kLineThickness);
  }
  canvas_skia_->drawRect(r, paint_);
}

void SkiaTextRenderer::DrawStrike(int x, int y, int width) const {
  const SkScalar text_size = paint_.getTextSize();
  const SkScalar height = SkScalarMul(text_size, kLineThickness);
  const SkScalar offset = SkScalarMulAdd(text_size, kStrikeThroughOffset, y);
  const SkRect r = SkRect::MakeLTRB(x, offset, x + width, offset + height);
  canvas_skia_->drawRect(r, paint_);
}

SkiaTextRenderer::DiagonalStrike::DiagonalStrike(Canvas* canvas,
                                                 Point start,
                                                 const SkPaint& paint)
    : canvas_(canvas),
      start_(start),
      paint_(paint),
      total_length_(0) {
}

SkiaTextRenderer::DiagonalStrike::~DiagonalStrike() {
}

void SkiaTextRenderer::DiagonalStrike::AddPiece(int length, SkColor color) {
  pieces_.push_back(Piece(length, color));
  total_length_ += length;
}

void SkiaTextRenderer::DiagonalStrike::Draw() {
  const SkScalar text_size = paint_.getTextSize();
  const SkScalar offset = SkScalarMul(text_size, kDiagonalStrikeMarginOffset);
  const int thickness =
      SkScalarCeilToInt(SkScalarMul(text_size, kLineThickness) * 2);
  const int height = SkScalarCeilToInt(text_size - offset);
  const Point end = start_ + Vector2d(total_length_, -height);
  const int clip_height = height + 2 * thickness;

  paint_.setAntiAlias(true);
  paint_.setStrokeWidth(thickness);

  const bool clipped = pieces_.size() > 1;
  SkCanvas* sk_canvas = canvas_->sk_canvas();
  int x = start_.x();

  for (size_t i = 0; i < pieces_.size(); ++i) {
    paint_.setColor(pieces_[i].second);

    if (clipped) {
      canvas_->Save();
      sk_canvas->clipRect(RectToSkRect(
          Rect(x, end.y() - thickness, pieces_[i].first, clip_height)));
    }

    canvas_->DrawLine(start_, end, paint_);

    if (clipped)
      canvas_->Restore();

    x += pieces_[i].first;
  }
}

StyleIterator::StyleIterator(const BreakList<SkColor>& colors,
                             const std::vector<BreakList<bool> >& styles)
    : colors_(colors),
      styles_(styles) {
  color_ = colors_.breaks().begin();
  for (size_t i = 0; i < styles_.size(); ++i)
    style_.push_back(styles_[i].breaks().begin());
}

StyleIterator::~StyleIterator() {}

Range StyleIterator::GetRange() const {
  Range range(colors_.GetRange(color_));
  for (size_t i = 0; i < NUM_TEXT_STYLES; ++i)
    range = range.Intersect(styles_[i].GetRange(style_[i]));
  return range;
}

void StyleIterator::UpdatePosition(size_t position) {
  color_ = colors_.GetBreak(position);
  for (size_t i = 0; i < NUM_TEXT_STYLES; ++i)
    style_[i] = styles_[i].GetBreak(position);
}

LineSegment::LineSegment() : run(0) {}

LineSegment::~LineSegment() {}

Line::Line() : preceding_heights(0), baseline(0) {}

Line::~Line() {}

skia::RefPtr<SkTypeface> CreateSkiaTypeface(const std::string& family,
                                            int style) {
  SkTypeface::Style skia_style = ConvertFontStyleToSkiaTypefaceStyle(style);
  return skia::AdoptRef(SkTypeface::CreateFromName(family.c_str(), skia_style));
}

void ApplyRenderParams(const FontRenderParams& params,
                       bool background_is_transparent,
                       SkPaint* paint) {
  paint->setAntiAlias(params.antialiasing);
  paint->setLCDRenderText(!background_is_transparent &&
      params.subpixel_rendering != FontRenderParams::SUBPIXEL_RENDERING_NONE);
  paint->setSubpixelText(params.subpixel_positioning);
  paint->setAutohinted(params.autohinter);
  paint->setHinting(FontRenderParamsHintingToSkPaintHinting(params.hinting));
}

}  // namespace internal

RenderText::~RenderText() {
}

RenderText* RenderText::CreateInstance() {
  return CommandLine::ForCurrentProcess()->HasSwitch(
      switches::kDisableHarfBuzzRenderText) ? CreateNativeInstance() :
      new RenderTextHarfBuzz;
}

void RenderText::SetText(const base::string16& text) {
  DCHECK(!composition_range_.IsValid());
  if (text_ == text)
    return;
  text_ = text;

  // Adjust ranged styles and colors to accommodate a new text length.
  // Clear style ranges as they might break new text graphemes and apply
  // the first style to the whole text instead.
  const size_t text_length = text_.length();
  colors_.SetMax(text_length);
  for (size_t style = 0; style < NUM_TEXT_STYLES; ++style) {
    BreakList<bool>& break_list = styles_[style];
    break_list.SetValue(break_list.breaks().begin()->second);
    break_list.SetMax(text_length);
  }
  cached_bounds_and_offset_valid_ = false;

  // Reset selection model. SetText should always followed by SetSelectionModel
  // or SetCursorPosition in upper layer.
  SetSelectionModel(SelectionModel());

  // Invalidate the cached text direction if it depends on the text contents.
  if (directionality_mode_ == DIRECTIONALITY_FROM_TEXT)
    text_direction_ = base::i18n::UNKNOWN_DIRECTION;

  obscured_reveal_index_ = -1;
  UpdateLayoutText();
}

void RenderText::SetHorizontalAlignment(HorizontalAlignment alignment) {
  if (horizontal_alignment_ != alignment) {
    horizontal_alignment_ = alignment;
    display_offset_ = Vector2d();
    cached_bounds_and_offset_valid_ = false;
  }
}

void RenderText::SetFontList(const FontList& font_list) {
  font_list_ = font_list;
  const int font_style = font_list.GetFontStyle();
  SetStyle(BOLD, (font_style & gfx::Font::BOLD) != 0);
  SetStyle(ITALIC, (font_style & gfx::Font::ITALIC) != 0);
  SetStyle(UNDERLINE, (font_style & gfx::Font::UNDERLINE) != 0);
  baseline_ = kInvalidBaseline;
  cached_bounds_and_offset_valid_ = false;
  ResetLayout();
}

void RenderText::SetCursorEnabled(bool cursor_enabled) {
  cursor_enabled_ = cursor_enabled;
  cached_bounds_and_offset_valid_ = false;
}

void RenderText::ToggleInsertMode() {
  insert_mode_ = !insert_mode_;
  cached_bounds_and_offset_valid_ = false;
}

void RenderText::SetObscured(bool obscured) {
  if (obscured != obscured_) {
    obscured_ = obscured;
    obscured_reveal_index_ = -1;
    cached_bounds_and_offset_valid_ = false;
    UpdateLayoutText();
  }
}

void RenderText::SetObscuredRevealIndex(int index) {
  if (obscured_reveal_index_ == index)
    return;

  obscured_reveal_index_ = index;
  cached_bounds_and_offset_valid_ = false;
  UpdateLayoutText();
}

void RenderText::SetReplaceNewlineCharsWithSymbols(bool replace) {
  replace_newline_chars_with_symbols_ = replace;
  cached_bounds_and_offset_valid_ = false;
  UpdateLayoutText();
}

void RenderText::SetMultiline(bool multiline) {
  if (multiline != multiline_) {
    multiline_ = multiline;
    cached_bounds_and_offset_valid_ = false;
    lines_.clear();
  }
}

void RenderText::SetElideBehavior(ElideBehavior elide_behavior) {
  // TODO(skanuj) : Add a test for triggering layout change.
  if (elide_behavior_ != elide_behavior) {
    elide_behavior_ = elide_behavior;
    UpdateLayoutText();
  }
}

void RenderText::SetDisplayRect(const Rect& r) {
  if (r != display_rect_) {
    display_rect_ = r;
    baseline_ = kInvalidBaseline;
    cached_bounds_and_offset_valid_ = false;
    lines_.clear();
    if (elide_behavior_ != NO_ELIDE)
      UpdateLayoutText();
  }
}

void RenderText::SetCursorPosition(size_t position) {
  MoveCursorTo(position, false);
}

void RenderText::MoveCursor(BreakType break_type,
                            VisualCursorDirection direction,
                            bool select) {
  SelectionModel cursor(cursor_position(), selection_model_.caret_affinity());
  // Cancelling a selection moves to the edge of the selection.
  if (break_type != LINE_BREAK && !selection().is_empty() && !select) {
    SelectionModel selection_start = GetSelectionModelForSelectionStart();
    int start_x = GetCursorBounds(selection_start, true).x();
    int cursor_x = GetCursorBounds(cursor, true).x();
    // Use the selection start if it is left (when |direction| is CURSOR_LEFT)
    // or right (when |direction| is CURSOR_RIGHT) of the selection end.
    if (direction == CURSOR_RIGHT ? start_x > cursor_x : start_x < cursor_x)
      cursor = selection_start;
    // Use the nearest word boundary in the proper |direction| for word breaks.
    if (break_type == WORD_BREAK)
      cursor = GetAdjacentSelectionModel(cursor, break_type, direction);
    // Use an adjacent selection model if the cursor is not at a valid position.
    if (!IsValidCursorIndex(cursor.caret_pos()))
      cursor = GetAdjacentSelectionModel(cursor, CHARACTER_BREAK, direction);
  } else {
    cursor = GetAdjacentSelectionModel(cursor, break_type, direction);
  }
  if (select)
    cursor.set_selection_start(selection().start());
  MoveCursorTo(cursor);
}

bool RenderText::MoveCursorTo(const SelectionModel& model) {
  // Enforce valid selection model components.
  size_t text_length = text().length();
  Range range(std::min(model.selection().start(), text_length),
              std::min(model.caret_pos(), text_length));
  // The current model only supports caret positions at valid cursor indices.
  if (!IsValidCursorIndex(range.start()) || !IsValidCursorIndex(range.end()))
    return false;
  SelectionModel sel(range, model.caret_affinity());
  bool changed = sel != selection_model_;
  SetSelectionModel(sel);
  return changed;
}

bool RenderText::SelectRange(const Range& range) {
  Range sel(std::min(range.start(), text().length()),
            std::min(range.end(), text().length()));
  // Allow selection bounds at valid indicies amid multi-character graphemes.
  if (!IsValidLogicalIndex(sel.start()) || !IsValidLogicalIndex(sel.end()))
    return false;
  LogicalCursorDirection affinity =
      (sel.is_reversed() || sel.is_empty()) ? CURSOR_FORWARD : CURSOR_BACKWARD;
  SetSelectionModel(SelectionModel(sel, affinity));
  return true;
}

bool RenderText::IsPointInSelection(const Point& point) {
  if (selection().is_empty())
    return false;
  SelectionModel cursor = FindCursorPosition(point);
  return RangeContainsCaret(
      selection(), cursor.caret_pos(), cursor.caret_affinity());
}

void RenderText::ClearSelection() {
  SetSelectionModel(SelectionModel(cursor_position(),
                                   selection_model_.caret_affinity()));
}

void RenderText::SelectAll(bool reversed) {
  const size_t length = text().length();
  const Range all = reversed ? Range(length, 0) : Range(0, length);
  const bool success = SelectRange(all);
  DCHECK(success);
}

void RenderText::SelectWord() {
  if (obscured_) {
    SelectAll(false);
    return;
  }

  size_t selection_max = selection().GetMax();

  base::i18n::BreakIterator iter(text(), base::i18n::BreakIterator::BREAK_WORD);
  bool success = iter.Init();
  DCHECK(success);
  if (!success)
    return;

  size_t selection_min = selection().GetMin();
  if (selection_min == text().length() && selection_min != 0)
    --selection_min;

  for (; selection_min != 0; --selection_min) {
    if (iter.IsStartOfWord(selection_min) ||
        iter.IsEndOfWord(selection_min))
      break;
  }

  if (selection_min == selection_max && selection_max != text().length())
    ++selection_max;

  for (; selection_max < text().length(); ++selection_max)
    if (iter.IsEndOfWord(selection_max) || iter.IsStartOfWord(selection_max))
      break;

  const bool reversed = selection().is_reversed();
  MoveCursorTo(reversed ? selection_max : selection_min, false);
  MoveCursorTo(reversed ? selection_min : selection_max, true);
}

const Range& RenderText::GetCompositionRange() const {
  return composition_range_;
}

void RenderText::SetCompositionRange(const Range& composition_range) {
  CHECK(!composition_range.IsValid() ||
        Range(0, text_.length()).Contains(composition_range));
  composition_range_.set_end(composition_range.end());
  composition_range_.set_start(composition_range.start());
  ResetLayout();
}

void RenderText::SetColor(SkColor value) {
  colors_.SetValue(value);
}

void RenderText::ApplyColor(SkColor value, const Range& range) {
  colors_.ApplyValue(value, range);
}

void RenderText::SetStyle(TextStyle style, bool value) {
  styles_[style].SetValue(value);

  cached_bounds_and_offset_valid_ = false;
  ResetLayout();
}

void RenderText::ApplyStyle(TextStyle style, bool value, const Range& range) {
  // Do not change styles mid-grapheme to avoid breaking ligatures.
  const size_t start = IsValidCursorIndex(range.start()) ? range.start() :
      IndexOfAdjacentGrapheme(range.start(), CURSOR_BACKWARD);
  const size_t end = IsValidCursorIndex(range.end()) ? range.end() :
      IndexOfAdjacentGrapheme(range.end(), CURSOR_FORWARD);
  styles_[style].ApplyValue(value, Range(start, end));

  cached_bounds_and_offset_valid_ = false;
  ResetLayout();
}

bool RenderText::GetStyle(TextStyle style) const {
  return (styles_[style].breaks().size() == 1) &&
      styles_[style].breaks().front().second;
}

void RenderText::SetDirectionalityMode(DirectionalityMode mode) {
  if (mode == directionality_mode_)
    return;

  directionality_mode_ = mode;
  text_direction_ = base::i18n::UNKNOWN_DIRECTION;
  cached_bounds_and_offset_valid_ = false;
  ResetLayout();
}

base::i18n::TextDirection RenderText::GetTextDirection() {
  if (text_direction_ == base::i18n::UNKNOWN_DIRECTION) {
    switch (directionality_mode_) {
      case DIRECTIONALITY_FROM_TEXT:
        // Derive the direction from the display text, which differs from text()
        // in the case of obscured (password) textfields.
        text_direction_ =
            base::i18n::GetFirstStrongCharacterDirection(GetLayoutText());
        break;
      case DIRECTIONALITY_FROM_UI:
        text_direction_ = base::i18n::IsRTL() ? base::i18n::RIGHT_TO_LEFT :
                                                base::i18n::LEFT_TO_RIGHT;
        break;
      case DIRECTIONALITY_FORCE_LTR:
        text_direction_ = base::i18n::LEFT_TO_RIGHT;
        break;
      case DIRECTIONALITY_FORCE_RTL:
        text_direction_ = base::i18n::RIGHT_TO_LEFT;
        break;
      default:
        NOTREACHED();
    }
  }

  return text_direction_;
}

VisualCursorDirection RenderText::GetVisualDirectionOfLogicalEnd() {
  return GetTextDirection() == base::i18n::LEFT_TO_RIGHT ?
      CURSOR_RIGHT : CURSOR_LEFT;
}

SizeF RenderText::GetStringSizeF() {
  const Size size = GetStringSize();
  return SizeF(size.width(), size.height());
}

float RenderText::GetContentWidth() {
  return GetStringSizeF().width() + (cursor_enabled_ ? 1 : 0);
}

int RenderText::GetBaseline() {
  if (baseline_ == kInvalidBaseline)
    baseline_ = DetermineBaselineCenteringText(display_rect(), font_list());
  DCHECK_NE(kInvalidBaseline, baseline_);
  return baseline_;
}

void RenderText::Draw(Canvas* canvas) {
  EnsureLayout();

  if (clip_to_display_rect()) {
    Rect clip_rect(display_rect());
    clip_rect.Inset(ShadowValue::GetMargin(shadows_));

    canvas->Save();
    canvas->ClipRect(clip_rect);
  }

  if (!text().empty() && focused())
    DrawSelection(canvas);

  if (cursor_enabled() && cursor_visible() && focused())
    DrawCursor(canvas, selection_model_);

  if (!text().empty())
    DrawVisualText(canvas);

  if (clip_to_display_rect())
    canvas->Restore();
}

void RenderText::DrawCursor(Canvas* canvas, const SelectionModel& position) {
  // Paint cursor. Replace cursor is drawn as rectangle for now.
  // TODO(msw): Draw a better cursor with a better indication of association.
  canvas->FillRect(GetCursorBounds(position, true), cursor_color_);
}

bool RenderText::IsValidLogicalIndex(size_t index) {
  // Check that the index is at a valid code point (not mid-surrgate-pair) and
  // that it's not truncated from the layout text (its glyph may be shown).
  //
  // Indices within truncated text are disallowed so users can easily interact
  // with the underlying truncated text using the ellipsis as a proxy. This lets
  // users select all text, select the truncated text, and transition from the
  // last rendered glyph to the end of the text without getting invisible cursor
  // positions nor needing unbounded arrow key presses to traverse the ellipsis.
  return index == 0 || index == text().length() ||
      (index < text().length() &&
       (truncate_length_ == 0 || index < truncate_length_) &&
       IsValidCodePointIndex(text(), index));
}

Rect RenderText::GetCursorBounds(const SelectionModel& caret,
                                 bool insert_mode) {
  // TODO(ckocagil): Support multiline. This function should return the height
  //                 of the line the cursor is on. |GetStringSize()| now returns
  //                 the multiline size, eliminate its use here.

  EnsureLayout();
  size_t caret_pos = caret.caret_pos();
  DCHECK(IsValidLogicalIndex(caret_pos));
  // In overtype mode, ignore the affinity and always indicate that we will
  // overtype the next character.
  LogicalCursorDirection caret_affinity =
      insert_mode ? caret.caret_affinity() : CURSOR_FORWARD;
  int x = 0, width = 1;
  Size size = GetStringSize();
  if (caret_pos == (caret_affinity == CURSOR_BACKWARD ? 0 : text().length())) {
    // The caret is attached to the boundary. Always return a 1-dip width caret,
    // since there is nothing to overtype.
    if ((GetTextDirection() == base::i18n::RIGHT_TO_LEFT) == (caret_pos == 0))
      x = size.width();
  } else {
    size_t grapheme_start = (caret_affinity == CURSOR_FORWARD) ?
        caret_pos : IndexOfAdjacentGrapheme(caret_pos, CURSOR_BACKWARD);
    Range xspan(GetGlyphBounds(grapheme_start));
    if (insert_mode) {
      x = (caret_affinity == CURSOR_BACKWARD) ? xspan.end() : xspan.start();
    } else {  // overtype mode
      x = xspan.GetMin();
      width = xspan.length();
    }
  }
  return Rect(ToViewPoint(Point(x, 0)), Size(width, size.height()));
}

const Rect& RenderText::GetUpdatedCursorBounds() {
  UpdateCachedBoundsAndOffset();
  return cursor_bounds_;
}

size_t RenderText::IndexOfAdjacentGrapheme(size_t index,
                                           LogicalCursorDirection direction) {
  if (index > text().length())
    return text().length();

  EnsureLayout();

  if (direction == CURSOR_FORWARD) {
    while (index < text().length()) {
      index++;
      if (IsValidCursorIndex(index))
        return index;
    }
    return text().length();
  }

  while (index > 0) {
    index--;
    if (IsValidCursorIndex(index))
      return index;
  }
  return 0;
}

SelectionModel RenderText::GetSelectionModelForSelectionStart() {
  const Range& sel = selection();
  if (sel.is_empty())
    return selection_model_;
  return SelectionModel(sel.start(),
                        sel.is_reversed() ? CURSOR_BACKWARD : CURSOR_FORWARD);
}

const Vector2d& RenderText::GetUpdatedDisplayOffset() {
  UpdateCachedBoundsAndOffset();
  return display_offset_;
}

void RenderText::SetDisplayOffset(int horizontal_offset) {
  const int extra_content = GetContentWidth() - display_rect_.width();
  const int cursor_width = cursor_enabled_ ? 1 : 0;

  int min_offset = 0;
  int max_offset = 0;
  if (extra_content > 0) {
    switch (GetCurrentHorizontalAlignment()) {
      case ALIGN_LEFT:
        min_offset = -extra_content;
        break;
      case ALIGN_RIGHT:
        max_offset = extra_content;
        break;
      case ALIGN_CENTER:
        // The extra space reserved for cursor at the end of the text is ignored
        // when centering text. So, to calculate the valid range for offset, we
        // exclude that extra space, calculate the range, and add it back to the
        // range (if cursor is enabled).
        min_offset = -(extra_content - cursor_width + 1) / 2 - cursor_width;
        max_offset = (extra_content - cursor_width) / 2;
        break;
      default:
        break;
    }
  }
  if (horizontal_offset < min_offset)
    horizontal_offset = min_offset;
  else if (horizontal_offset > max_offset)
    horizontal_offset = max_offset;

  cached_bounds_and_offset_valid_ = true;
  display_offset_.set_x(horizontal_offset);
  cursor_bounds_ = GetCursorBounds(selection_model_, insert_mode_);
}

RenderText::RenderText()
    : horizontal_alignment_(base::i18n::IsRTL() ? ALIGN_RIGHT : ALIGN_LEFT),
      directionality_mode_(DIRECTIONALITY_FROM_TEXT),
      text_direction_(base::i18n::UNKNOWN_DIRECTION),
      cursor_enabled_(true),
      cursor_visible_(false),
      insert_mode_(true),
      cursor_color_(kDefaultColor),
      selection_color_(kDefaultColor),
      selection_background_focused_color_(kDefaultSelectionBackgroundColor),
      focused_(false),
      composition_range_(Range::InvalidRange()),
      colors_(kDefaultColor),
      styles_(NUM_TEXT_STYLES),
      composition_and_selection_styles_applied_(false),
      obscured_(false),
      obscured_reveal_index_(-1),
      truncate_length_(0),
      elide_behavior_(NO_ELIDE),
      replace_newline_chars_with_symbols_(true),
      multiline_(false),
      background_is_transparent_(false),
      clip_to_display_rect_(true),
      baseline_(kInvalidBaseline),
      cached_bounds_and_offset_valid_(false) {
}

SelectionModel RenderText::GetAdjacentSelectionModel(
    const SelectionModel& current,
    BreakType break_type,
    VisualCursorDirection direction) {
  EnsureLayout();

  if (break_type == LINE_BREAK || text().empty())
    return EdgeSelectionModel(direction);
  if (break_type == CHARACTER_BREAK)
    return AdjacentCharSelectionModel(current, direction);
  DCHECK(break_type == WORD_BREAK);
  return AdjacentWordSelectionModel(current, direction);
}

SelectionModel RenderText::EdgeSelectionModel(
    VisualCursorDirection direction) {
  if (direction == GetVisualDirectionOfLogicalEnd())
    return SelectionModel(text().length(), CURSOR_FORWARD);
  return SelectionModel(0, CURSOR_BACKWARD);
}

void RenderText::SetSelectionModel(const SelectionModel& model) {
  DCHECK_LE(model.selection().GetMax(), text().length());
  selection_model_ = model;
  cached_bounds_and_offset_valid_ = false;
}

const base::string16& RenderText::GetLayoutText() const {
  return layout_text_;
}

const BreakList<size_t>& RenderText::GetLineBreaks() {
  if (line_breaks_.max() != 0)
    return line_breaks_;

  const base::string16& layout_text = GetLayoutText();
  const size_t text_length = layout_text.length();
  line_breaks_.SetValue(0);
  line_breaks_.SetMax(text_length);
  base::i18n::BreakIterator iter(layout_text,
                                 base::i18n::BreakIterator::BREAK_LINE);
  const bool success = iter.Init();
  DCHECK(success);
  if (success) {
    do {
      line_breaks_.ApplyValue(iter.pos(), Range(iter.pos(), text_length));
    } while (iter.Advance());
  }
  return line_breaks_;
}

void RenderText::ApplyCompositionAndSelectionStyles() {
  // Save the underline and color breaks to undo the temporary styles later.
  DCHECK(!composition_and_selection_styles_applied_);
  saved_colors_ = colors_;
  saved_underlines_ = styles_[UNDERLINE];

  // Apply an underline to the composition range in |underlines|.
  if (composition_range_.IsValid() && !composition_range_.is_empty())
    styles_[UNDERLINE].ApplyValue(true, composition_range_);

  // Apply the selected text color to the [un-reversed] selection range.
  if (!selection().is_empty() && focused()) {
    const Range range(selection().GetMin(), selection().GetMax());
    colors_.ApplyValue(selection_color_, range);
  }
  composition_and_selection_styles_applied_ = true;
}

void RenderText::UndoCompositionAndSelectionStyles() {
  // Restore the underline and color breaks to undo the temporary styles.
  DCHECK(composition_and_selection_styles_applied_);
  colors_ = saved_colors_;
  styles_[UNDERLINE] = saved_underlines_;
  composition_and_selection_styles_applied_ = false;
}

Vector2d RenderText::GetLineOffset(size_t line_number) {
  Vector2d offset = display_rect().OffsetFromOrigin();
  // TODO(ckocagil): Apply the display offset for multiline scrolling.
  if (!multiline())
    offset.Add(GetUpdatedDisplayOffset());
  else
    offset.Add(Vector2d(0, lines_[line_number].preceding_heights));
  offset.Add(GetAlignmentOffset(line_number));
  return offset;
}

Point RenderText::ToTextPoint(const Point& point) {
  return point - GetLineOffset(0);
  // TODO(ckocagil): Convert multiline view space points to text space.
}

Point RenderText::ToViewPoint(const Point& point) {
  if (!multiline())
    return point + GetLineOffset(0);

  // TODO(ckocagil): Traverse individual line segments for RTL support.
  DCHECK(!lines_.empty());
  int x = point.x();
  size_t line = 0;
  for (; line < lines_.size() && x > lines_[line].size.width(); ++line)
    x -= lines_[line].size.width();
  return Point(x, point.y()) + GetLineOffset(line);
}

std::vector<Rect> RenderText::TextBoundsToViewBounds(const Range& x) {
  std::vector<Rect> rects;

  if (!multiline()) {
    rects.push_back(Rect(ToViewPoint(Point(x.GetMin(), 0)),
                         Size(x.length(), GetStringSize().height())));
    return rects;
  }

  EnsureLayout();

  // Each line segment keeps its position in text coordinates. Traverse all line
  // segments and if the segment intersects with the given range, add the view
  // rect corresponding to the intersection to |rects|.
  for (size_t line = 0; line < lines_.size(); ++line) {
    int line_x = 0;
    const Vector2d offset = GetLineOffset(line);
    for (size_t i = 0; i < lines_[line].segments.size(); ++i) {
      const internal::LineSegment* segment = &lines_[line].segments[i];
      const Range intersection = segment->x_range.Intersect(x);
      if (!intersection.is_empty()) {
        Rect rect(line_x + intersection.start() - segment->x_range.start(),
                  0, intersection.length(), lines_[line].size.height());
        rects.push_back(rect + offset);
      }
      line_x += segment->x_range.length();
    }
  }

  return rects;
}

HorizontalAlignment RenderText::GetCurrentHorizontalAlignment() {
  if (horizontal_alignment_ != ALIGN_TO_HEAD)
    return horizontal_alignment_;
  return GetTextDirection() == base::i18n::RIGHT_TO_LEFT ? ALIGN_RIGHT
                                                         : ALIGN_LEFT;
}

Vector2d RenderText::GetAlignmentOffset(size_t line_number) {
  // TODO(ckocagil): Enable |lines_| usage in other platforms.
#if defined(OS_WIN)
  DCHECK_LT(line_number, lines_.size());
#endif
  Vector2d offset;
  HorizontalAlignment horizontal_alignment = GetCurrentHorizontalAlignment();
  if (horizontal_alignment != ALIGN_LEFT) {
#if defined(OS_WIN)
    const int width = lines_[line_number].size.width() +
        (cursor_enabled_ ? 1 : 0);
#else
    const int width = GetContentWidth();
#endif
    offset.set_x(display_rect().width() - width);
    // Put any extra margin pixel on the left to match legacy behavior.
    if (horizontal_alignment == ALIGN_CENTER)
      offset.set_x((offset.x() + 1) / 2);
  }

  // Vertically center the text.
  if (multiline_) {
    const int text_height = lines_.back().preceding_heights +
        lines_.back().size.height();
    offset.set_y((display_rect_.height() - text_height) / 2);
  } else {
    offset.set_y(GetBaseline() - GetLayoutTextBaseline());
  }

  return offset;
}

void RenderText::ApplyFadeEffects(internal::SkiaTextRenderer* renderer) {
  const int width = display_rect().width();
  if (multiline() || elide_behavior_ != FADE_TAIL ||
      static_cast<int>(GetContentWidth()) <= width)
    return;

  const int gradient_width = CalculateFadeGradientWidth(font_list(), width);
  if (gradient_width == 0)
    return;

  HorizontalAlignment horizontal_alignment = GetCurrentHorizontalAlignment();
  Rect solid_part = display_rect();
  Rect left_part;
  Rect right_part;
  if (horizontal_alignment != ALIGN_LEFT) {
    left_part = solid_part;
    left_part.Inset(0, 0, solid_part.width() - gradient_width, 0);
    solid_part.Inset(gradient_width, 0, 0, 0);
  }
  if (horizontal_alignment != ALIGN_RIGHT) {
    right_part = solid_part;
    right_part.Inset(solid_part.width() - gradient_width, 0, 0, 0);
    solid_part.Inset(0, 0, gradient_width, 0);
  }

  Rect text_rect = display_rect();
  text_rect.Inset(GetAlignmentOffset(0).x(), 0, 0, 0);

  // TODO(msw): Use the actual text colors corresponding to each faded part.
  skia::RefPtr<SkShader> shader = CreateFadeShader(
      text_rect, left_part, right_part, colors_.breaks().front().second);
  if (shader)
    renderer->SetShader(shader.get());
}

void RenderText::ApplyTextShadows(internal::SkiaTextRenderer* renderer) {
  skia::RefPtr<SkDrawLooper> looper = CreateShadowDrawLooper(shadows_);
  renderer->SetDrawLooper(looper.get());
}

// static
bool RenderText::RangeContainsCaret(const Range& range,
                                    size_t caret_pos,
                                    LogicalCursorDirection caret_affinity) {
  // NB: exploits unsigned wraparound (WG14/N1124 section 6.2.5 paragraph 9).
  size_t adjacent = (caret_affinity == CURSOR_BACKWARD) ?
      caret_pos - 1 : caret_pos + 1;
  return range.Contains(Range(caret_pos, adjacent));
}

void RenderText::MoveCursorTo(size_t position, bool select) {
  size_t cursor = std::min(position, text().length());
  if (IsValidCursorIndex(cursor))
    SetSelectionModel(SelectionModel(
        Range(select ? selection().start() : cursor, cursor),
        (cursor == 0) ? CURSOR_FORWARD : CURSOR_BACKWARD));
}

void RenderText::UpdateLayoutText() {
  layout_text_.clear();
  line_breaks_.SetMax(0);

  if (obscured_) {
    size_t obscured_text_length =
        static_cast<size_t>(UTF16IndexToOffset(text_, 0, text_.length()));
    layout_text_.assign(obscured_text_length, kPasswordReplacementChar);

    if (obscured_reveal_index_ >= 0 &&
        obscured_reveal_index_ < static_cast<int>(text_.length())) {
      // Gets the index range in |text_| to be revealed.
      size_t start = obscured_reveal_index_;
      U16_SET_CP_START(text_.data(), 0, start);
      size_t end = start;
      UChar32 unused_char;
      U16_NEXT(text_.data(), end, text_.length(), unused_char);

      // Gets the index in |layout_text_| to be replaced.
      const size_t cp_start =
          static_cast<size_t>(UTF16IndexToOffset(text_, 0, start));
      if (layout_text_.length() > cp_start)
        layout_text_.replace(cp_start, 1, text_.substr(start, end - start));
    }
  } else {
    layout_text_ = text_;
  }

  const base::string16& text = layout_text_;
  if (truncate_length_ > 0 && truncate_length_ < text.length()) {
    // Truncate the text at a valid character break and append an ellipsis.
    icu::StringCharacterIterator iter(text.c_str());
    // Respect ELIDE_HEAD and ELIDE_MIDDLE preferences during truncation.
    if (elide_behavior_ == ELIDE_HEAD) {
      iter.setIndex32(text.length() - truncate_length_ + 1);
      layout_text_.assign(kEllipsisUTF16 + text.substr(iter.getIndex()));
    } else if (elide_behavior_ == ELIDE_MIDDLE) {
      iter.setIndex32(truncate_length_ / 2);
      const size_t ellipsis_start = iter.getIndex();
      iter.setIndex32(text.length() - (truncate_length_ / 2));
      const size_t ellipsis_end = iter.getIndex();
      DCHECK_LE(ellipsis_start, ellipsis_end);
      layout_text_.assign(text.substr(0, ellipsis_start) + kEllipsisUTF16 +
                          text.substr(ellipsis_end));
    } else {
      iter.setIndex32(truncate_length_ - 1);
      layout_text_.assign(text.substr(0, iter.getIndex()) + kEllipsisUTF16);
    }
  }

  if (elide_behavior_ != NO_ELIDE &&
      elide_behavior_ != FADE_TAIL &&
      !layout_text_.empty() &&
      static_cast<int>(GetContentWidth()) > display_rect_.width()) {
    // This doesn't trim styles so ellipsis may get rendered as a different
    // style than the preceding text. See crbug.com/327850.
    layout_text_.assign(
        Elide(layout_text_, display_rect_.width(), elide_behavior_));
  }

  // Replace the newline character with a newline symbol in single line mode.
  static const base::char16 kNewline[] = { '\n', 0 };
  static const base::char16 kNewlineSymbol[] = { 0x2424, 0 };
  if (!multiline_ && replace_newline_chars_with_symbols_)
    base::ReplaceChars(layout_text_, kNewline, kNewlineSymbol, &layout_text_);

  ResetLayout();
}

base::string16 RenderText::Elide(const base::string16& text,
                                 float available_width,
                                 ElideBehavior behavior) {
  if (available_width <= 0 || text.empty())
    return base::string16();
  if (behavior == ELIDE_EMAIL)
    return ElideEmail(text, available_width);

  // Create a RenderText copy with attributes that affect the rendering width.
  scoped_ptr<RenderText> render_text(CreateInstance());
  render_text->SetFontList(font_list_);
  render_text->SetDirectionalityMode(directionality_mode_);
  render_text->SetCursorEnabled(cursor_enabled_);
  render_text->set_truncate_length(truncate_length_);
  render_text->styles_ = styles_;
  render_text->colors_ = colors_;
  render_text->SetText(text);
  if (render_text->GetContentWidth() <= available_width)
    return text;

  const base::string16 ellipsis = base::string16(kEllipsisUTF16);
  const bool insert_ellipsis = (behavior != TRUNCATE);
  const bool elide_in_middle = (behavior == ELIDE_MIDDLE);
  const bool elide_at_beginning = (behavior == ELIDE_HEAD);
  StringSlicer slicer(text, ellipsis, elide_in_middle, elide_at_beginning);

  render_text->SetText(ellipsis);
  const float ellipsis_width = render_text->GetContentWidth();

  if (insert_ellipsis && (ellipsis_width > available_width))
    return base::string16();

  // Use binary search to compute the elided text.
  size_t lo = 0;
  size_t hi = text.length() - 1;
  const base::i18n::TextDirection text_direction = GetTextDirection();
  for (size_t guess = (lo + hi) / 2; lo <= hi; guess = (lo + hi) / 2) {
    // Restore colors. They will be truncated to size by SetText.
    render_text->colors_ = colors_;
    base::string16 new_text =
        slicer.CutString(guess, insert_ellipsis && behavior != ELIDE_TAIL);
    render_text->SetText(new_text);

    // This has to be an additional step so that the ellipsis is rendered with
    // same style as trailing part of the text.
    if (insert_ellipsis && behavior == ELIDE_TAIL) {
      // When ellipsis follows text whose directionality is not the same as that
      // of the whole text, it will be rendered with the directionality of the
      // whole text. Since we want ellipsis to indicate continuation of the
      // preceding text, we force the directionality of ellipsis to be same as
      // the preceding text using LTR or RTL markers.
      base::i18n::TextDirection trailing_text_direction =
          base::i18n::GetLastStrongCharacterDirection(new_text);
      new_text.append(ellipsis);
      if (trailing_text_direction != text_direction) {
        if (trailing_text_direction == base::i18n::LEFT_TO_RIGHT)
          new_text += base::i18n::kLeftToRightMark;
        else
          new_text += base::i18n::kRightToLeftMark;
      }
      render_text->SetText(new_text);
    }

    // Restore styles. Make sure style ranges don't break new text graphemes.
    render_text->styles_ = styles_;
    for (size_t style = 0; style < NUM_TEXT_STYLES; ++style) {
      BreakList<bool>& break_list = render_text->styles_[style];
      break_list.SetMax(render_text->text_.length());
      Range range;
      while (range.end() < break_list.max()) {
        BreakList<bool>::const_iterator current_break =
            break_list.GetBreak(range.end());
        range = break_list.GetRange(current_break);
        if (range.end() < break_list.max() &&
            !render_text->IsValidCursorIndex(range.end())) {
          range.set_end(render_text->IndexOfAdjacentGrapheme(range.end(),
                                                             CURSOR_FORWARD));
          break_list.ApplyValue(current_break->second, range);
        }
      }
    }

    // We check the width of the whole desired string at once to ensure we
    // handle kerning/ligatures/etc. correctly.
    const float guess_width = render_text->GetContentWidth();
    if (guess_width == available_width)
      break;
    if (guess_width > available_width) {
      hi = guess - 1;
      // Move back on the loop terminating condition when the guess is too wide.
      if (hi < lo)
        lo = hi;
    } else {
      lo = guess + 1;
    }
  }

  return render_text->text();
}

base::string16 RenderText::ElideEmail(const base::string16& email,
                                      float available_width) {
  // The returned string will have at least one character besides the ellipsis
  // on either side of '@'; if that's impossible, a single ellipsis is returned.
  // If possible, only the username is elided. Otherwise, the domain is elided
  // in the middle, splitting available width equally with the elided username.
  // If the username is short enough that it doesn't need half the available
  // width, the elided domain will occupy that extra width.

  // Split the email into its local-part (username) and domain-part. The email
  // spec allows for @ symbols in the username under some special requirements,
  // but not in the domain part, so splitting at the last @ symbol is safe.
  const size_t split_index = email.find_last_of('@');
  DCHECK_NE(split_index, base::string16::npos);
  base::string16 username = email.substr(0, split_index);
  base::string16 domain = email.substr(split_index + 1);
  DCHECK(!username.empty());
  DCHECK(!domain.empty());

  // Subtract the @ symbol from the available width as it is mandatory.
  const base::string16 kAtSignUTF16 = base::ASCIIToUTF16("@");
  available_width -= GetStringWidthF(kAtSignUTF16, font_list());

  // Check whether eliding the domain is necessary: if eliding the username
  // is sufficient, the domain will not be elided.
  const float full_username_width = GetStringWidthF(username, font_list());
  const float available_domain_width = available_width -
      std::min(full_username_width,
          GetStringWidthF(username.substr(0, 1) + kEllipsisUTF16, font_list()));
  if (GetStringWidthF(domain, font_list()) > available_domain_width) {
    // Elide the domain so that it only takes half of the available width.
    // Should the username not need all the width available in its half, the
    // domain will occupy the leftover width.
    // If |desired_domain_width| is greater than |available_domain_width|: the
    // minimal username elision allowed by the specifications will not fit; thus
    // |desired_domain_width| must be <= |available_domain_width| at all cost.
    const float desired_domain_width =
        std::min<float>(available_domain_width,
            std::max<float>(available_width - full_username_width,
                            available_width / 2));
    domain = Elide(domain, desired_domain_width, ELIDE_MIDDLE);
    // Failing to elide the domain such that at least one character remains
    // (other than the ellipsis itself) remains: return a single ellipsis.
    if (domain.length() <= 1U)
      return base::string16(kEllipsisUTF16);
  }

  // Fit the username in the remaining width (at this point the elided username
  // is guaranteed to fit with at least one character remaining given all the
  // precautions taken earlier).
  available_width -= GetStringWidthF(domain, font_list());
  username = Elide(username, available_width, ELIDE_TAIL);
  return username + kAtSignUTF16 + domain;
}

void RenderText::UpdateCachedBoundsAndOffset() {
  if (cached_bounds_and_offset_valid_)
    return;

  // TODO(ckocagil): Add support for scrolling multiline text.

  int delta_x = 0;

  if (cursor_enabled()) {
    // When cursor is enabled, ensure it is visible. For this, set the valid
    // flag true and calculate the current cursor bounds using the stale
    // |display_offset_|. Then calculate the change in offset needed to move the
    // cursor into the visible area.
    cached_bounds_and_offset_valid_ = true;
    cursor_bounds_ = GetCursorBounds(selection_model_, insert_mode_);

    // TODO(bidi): Show RTL glyphs at the cursor position for ALIGN_LEFT, etc.
    if (cursor_bounds_.right() > display_rect_.right())
      delta_x = display_rect_.right() - cursor_bounds_.right();
    else if (cursor_bounds_.x() < display_rect_.x())
      delta_x = display_rect_.x() - cursor_bounds_.x();
  }

  SetDisplayOffset(display_offset_.x() + delta_x);
}

void RenderText::DrawSelection(Canvas* canvas) {
  const std::vector<Rect> sel = GetSubstringBounds(selection());
  for (std::vector<Rect>::const_iterator i = sel.begin(); i < sel.end(); ++i)
    canvas->FillRect(*i, selection_background_focused_color_);
}

}  // namespace gfx