/* -*- Mode: C++; tab-width: 40; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "ScrollbarUtil.h"

#include "mozilla/Maybe.h"
#include "mozilla/RelativeLuminanceUtils.h"
#include "mozilla/StaticPrefs_widget.h"
#include "nsLayoutUtils.h"
#include "nsNativeTheme.h"
#include "nsNativeBasicTheme.h"

using mozilla::ComputedStyle;
using mozilla::EventStates;
using mozilla::Maybe;
using mozilla::Nothing;
using mozilla::RelativeLuminanceUtils;
using mozilla::Some;
using mozilla::StyleAppearance;
using mozilla::StyleScrollbarWidth;

namespace StaticPrefs = mozilla::StaticPrefs;

/*static*/
bool ScrollbarUtil::IsScrollbarWidthThin(ComputedStyle* aStyle) {
  auto scrollbarWidth = aStyle->StyleUIReset()->mScrollbarWidth;
  return scrollbarWidth == StyleScrollbarWidth::Thin;
}

/*static*/
bool ScrollbarUtil::IsScrollbarWidthThin(nsIFrame* aFrame) {
  ComputedStyle* style = nsLayoutUtils::StyleForScrollbar(aFrame);
  return IsScrollbarWidthThin(style);
}

/*static*/
ComputedStyle* ScrollbarUtil::GetCustomScrollbarStyle(nsIFrame* aFrame,
                                                      bool* aDarkScrollbar) {
  ComputedStyle* style = nsLayoutUtils::StyleForScrollbar(aFrame);
  if (style->StyleUI()->HasCustomScrollbars()) {
    return style;
  }
  bool useDarkScrollbar = !StaticPrefs::widget_disable_dark_scrollbar() &&
                          nsNativeTheme::IsDarkBackground(aFrame);
  if (useDarkScrollbar || IsScrollbarWidthThin(style)) {
    if (aDarkScrollbar) {
      *aDarkScrollbar = useDarkScrollbar;
    }
    return style;
  }
  return nullptr;
}

/*static*/
nscolor ScrollbarUtil::GetScrollbarTrackColor(nsIFrame* aFrame) {
  bool darkScrollbar = false;
  ComputedStyle* style = GetCustomScrollbarStyle(aFrame, &darkScrollbar);
  if (style) {
    const nsStyleUI* ui = style->StyleUI();
    auto* customColors = ui->mScrollbarColor.IsAuto()
                             ? nullptr
                             : &ui->mScrollbarColor.AsColors();
    if (customColors) {
      return customColors->track.CalcColor(*style);
    }
  }
  return darkScrollbar ? NS_RGBA(20, 20, 25, 77) : NS_RGB(240, 240, 240);
}

/*static*/
nscolor ScrollbarUtil::GetScrollbarThumbColor(nsIFrame* aFrame,
                                              EventStates aEventStates) {
  bool darkScrollbar = false;
  ComputedStyle* style = GetCustomScrollbarStyle(aFrame, &darkScrollbar);
  nscolor color =
      darkScrollbar ? NS_RGBA(249, 249, 250, 102) : NS_RGB(205, 205, 205);
  if (style) {
    const nsStyleUI* ui = style->StyleUI();
    auto* customColors = ui->mScrollbarColor.IsAuto()
                             ? nullptr
                             : &ui->mScrollbarColor.AsColors();
    if (customColors) {
      color = customColors->thumb.CalcColor(*style);
    }
  }
  return nsNativeBasicTheme::AdjustUnthemedScrollbarThumbColor(color,
                                                               aEventStates);
}

/*static*/
Maybe<nsITheme::Transparency> ScrollbarUtil::GetScrollbarPartTransparency(
    nsIFrame* aFrame, StyleAppearance aAppearance) {
  if (nsNativeTheme::IsWidgetScrollbarPart(aAppearance)) {
    if (ComputedStyle* style = ScrollbarUtil::GetCustomScrollbarStyle(aFrame)) {
      auto* ui = style->StyleUI();
      if (ui->mScrollbarColor.IsAuto() ||
          ui->mScrollbarColor.AsColors().track.MaybeTransparent()) {
        return Some(nsITheme::eTransparent);
      }
      // These widgets may be thinner than the track, so we need to return
      // transparent for them to make the track visible.
      switch (aAppearance) {
        case StyleAppearance::ScrollbarthumbHorizontal:
        case StyleAppearance::ScrollbarthumbVertical:
        case StyleAppearance::ScrollbarbuttonUp:
        case StyleAppearance::ScrollbarbuttonDown:
        case StyleAppearance::ScrollbarbuttonLeft:
        case StyleAppearance::ScrollbarbuttonRight:
          return Some(nsITheme::eTransparent);
        default:
          break;
      }
    }
  }

  switch (aAppearance) {
    case StyleAppearance::ScrollbarHorizontal:
    case StyleAppearance::ScrollbarVertical:
    case StyleAppearance::Scrollcorner:
    case StyleAppearance::Statusbar:
      // Knowing that scrollbars and statusbars are opaque improves
      // performance, because we create layers for them. This better be
      // true across all Windows themes! If it's not true, we should
      // paint an opaque background for them to make it true!
      return Some(nsITheme::eOpaque);
    default:
      break;
  }

  return Nothing();
}