# vim: ft=python fileencoding=utf-8 sts=4 sw=4 et:

# Copyright 2014-2017 Florian Bruhin (The Compiler) <mail@qutebrowser.org>
#
# This file is part of qutebrowser.
#
# qutebrowser is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# qutebrowser is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with qutebrowser.  If not, see <http://www.gnu.org/licenses/>.

"""The tab widget used for TabbedBrowser from browser.py."""

import collections
import functools

from PyQt5.QtCore import (pyqtSignal, pyqtSlot, Qt, QSize, QRect, QPoint,
                          QTimer, QUrl)
from PyQt5.QtWidgets import (QTabWidget, QTabBar, QSizePolicy, QCommonStyle,
                             QStyle, QStylePainter, QStyleOptionTab,
                             QStyleFactory, QWidget)
from PyQt5.QtGui import QIcon, QPalette, QColor

from qutebrowser.utils import qtutils, objreg, utils, usertypes, log
from qutebrowser.config import config
from qutebrowser.misc import objects


PixelMetrics = usertypes.enum('PixelMetrics', ['icon_padding'],
                              start=QStyle.PM_CustomBase, is_int=True)


class TabWidget(QTabWidget):

    """The tab widget used for TabbedBrowser.

    Signals:
        tab_index_changed: Emitted when the current tab was changed.
                           arg 0: The index of the tab which is now focused.
                           arg 1: The total count of tabs.
    """

    tab_index_changed = pyqtSignal(int, int)

    def __init__(self, win_id, parent=None):
        super().__init__(parent)
        bar = TabBar(win_id, self)
        self.setStyle(TabBarStyle())
        self.setTabBar(bar)
        bar.tabCloseRequested.connect(self.tabCloseRequested)
        bar.tabMoved.connect(functools.partial(
            QTimer.singleShot, 0, self.update_tab_titles))
        bar.currentChanged.connect(self._on_current_changed)
        self.setSizePolicy(QSizePolicy.Expanding, QSizePolicy.Fixed)
        self.setDocumentMode(True)
        self.setElideMode(Qt.ElideRight)
        self.setUsesScrollButtons(True)
        bar.setDrawBase(False)
        self.init_config()
        objreg.get('config').changed.connect(self.init_config)

    @config.change_filter('tabs')
    def init_config(self):
        """Initialize attributes based on the config."""
        if self is None:  # pragma: no cover
            # WORKAROUND for PyQt 5.2
            return
        tabbar = self.tabBar()
        self.setMovable(config.get('tabs', 'movable'))
        self.setTabsClosable(False)
        position = config.get('tabs', 'position')
        selection_behavior = config.get('tabs', 'select-on-remove')
        self.setTabPosition(position)
        tabbar.vertical = position in [QTabWidget.West, QTabWidget.East]
        tabbar.setSelectionBehaviorOnRemove(selection_behavior)
        tabbar.refresh()

    def set_tab_indicator_color(self, idx, color):
        """Set the tab indicator color.

        Args:
            idx: The tab index.
            color: A QColor.
        """
        bar = self.tabBar()
        bar.set_tab_data(idx, 'indicator-color', color)
        bar.update(bar.tabRect(idx))

    def set_tab_pinned(self, tab: QWidget,
                       pinned: bool, *, loading: bool = False) -> None:
        """Set the tab status as pinned.

        Args:
            tab: The tab to pin
            pinned: Pinned tab state to set.
            loading: Whether to ignore current data state when
                     counting pinned_count.
        """
        bar = self.tabBar()
        idx = self.indexOf(tab)

        # Only modify pinned_count if we had a change
        # always modify pinned_count if we are loading
        if tab.data.pinned != pinned or loading:
            if pinned:
                bar.pinned_count += 1
            elif not pinned:
                bar.pinned_count -= 1

        bar.set_tab_data(idx, 'pinned', pinned)
        tab.data.pinned = pinned
        self.update_tab_title(idx)

        bar.refresh()

    def tab_indicator_color(self, idx):
        """Get the tab indicator color for the given index."""
        return self.tabBar().tab_indicator_color(idx)

    def set_page_title(self, idx, title):
        """Set the tab title user data."""
        self.tabBar().set_tab_data(idx, 'page-title', title)
        self.update_tab_title(idx)

    def page_title(self, idx):
        """Get the tab title user data."""
        return self.tabBar().page_title(idx)

    def update_tab_title(self, idx):
        """Update the tab text for the given tab."""
        tab = self.widget(idx)
        fields = self.get_tab_fields(idx)
        fields['title'] = fields['title'].replace('&', '&&')
        fields['index'] = idx + 1

        fmt = config.get('tabs', 'title-format')
        fmt_pinned = config.get('tabs', 'title-format-pinned')

        if tab.data.pinned:
            title = '' if fmt_pinned is None else fmt_pinned.format(**fields)
        else:
            title = '' if fmt is None else fmt.format(**fields)

        self.tabBar().setTabText(idx, title)

    def get_tab_fields(self, idx):
        """Get the tab field data."""
        tab = self.widget(idx)
        if tab is None:
            log.misc.debug("Got None-tab in get_tab_fields!")

        page_title = self.page_title(idx)

        fields = {}
        fields['id'] = tab.tab_id
        fields['title'] = page_title
        fields['title_sep'] = ' - ' if page_title else ''
        fields['perc_raw'] = tab.progress()
        fields['backend'] = objects.backend.name
        fields['private'] = ' [Private Mode] ' if tab.private else ''

        if tab.load_status() == usertypes.LoadStatus.loading:
            fields['perc'] = '[{}%] '.format(tab.progress())
        else:
            fields['perc'] = ''

        try:
            fields['host'] = self.tab_url(idx).host()
        except qtutils.QtValueError:
            fields['host'] = ''

        y = tab.scroller.pos_perc()[1]
        if y is None:
            scroll_pos = '???'
        elif y <= 0:
            scroll_pos = 'top'
        elif y >= 100:
            scroll_pos = 'bot'
        else:
            scroll_pos = '{:2}%'.format(y)

        fields['scroll_pos'] = scroll_pos
        return fields

    def update_tab_titles(self, section='tabs', option='title-format'):
        """Update all texts."""
        if section == 'tabs' and option in ['title-format',
                                            'title-format-pinned']:
            for idx in range(self.count()):
                self.update_tab_title(idx)

    def tabInserted(self, idx):
        """Update titles when a tab was inserted."""
        super().tabInserted(idx)
        self.update_tab_titles()

    def tabRemoved(self, idx):
        """Update titles when a tab was removed."""
        super().tabRemoved(idx)
        self.update_tab_titles()

    def addTab(self, page, icon_or_text, text_or_empty=None):
        """Override addTab to use our own text setting logic.

        Unfortunately QTabWidget::addTab has these two overloads:
            - QWidget * page, const QIcon & icon, const QString & label
            - QWidget * page, const QString & label

        This means we'll get different arguments based on the chosen overload.

        Args:
            page: The QWidget to add.
            icon_or_text: Either the QIcon to add or the label.
            text_or_empty: Either the label or None.

        Return:
            The index of the newly added tab.
        """
        if text_or_empty is None:
            icon = None
            text = icon_or_text
            new_idx = super().addTab(page, '')
        else:
            icon = icon_or_text
            text = text_or_empty
            new_idx = super().addTab(page, icon, '')
        self.set_page_title(new_idx, text)
        return new_idx

    def insertTab(self, idx, page, icon_or_text, text_or_empty=None):
        """Override insertTab to use our own text setting logic.

        Unfortunately QTabWidget::insertTab has these two overloads:
            - int index, QWidget * page, const QIcon & icon,
              const QString & label
            - int index, QWidget * page, const QString & label

        This means we'll get different arguments based on the chosen overload.

        Args:
            idx: Where to insert the widget.
            page: The QWidget to add.
            icon_or_text: Either the QIcon to add or the label.
            text_or_empty: Either the label or None.

        Return:
            The index of the newly added tab.
        """
        if text_or_empty is None:
            icon = None
            text = icon_or_text
            new_idx = super().insertTab(idx, page, '')
        else:
            icon = icon_or_text
            text = text_or_empty
            new_idx = super().insertTab(idx, page, icon, '')
        self.set_page_title(new_idx, text)
        return new_idx

    @pyqtSlot(int)
    def _on_current_changed(self, index):
        """Emit the tab_index_changed signal if the current tab changed."""
        self.tabBar().on_current_changed()
        self.tab_index_changed.emit(index, self.count())

    def tab_url(self, idx):
        """Get the URL of the tab at the given index.

        Return:
            The tab URL as QUrl.
        """
        tab = self.widget(idx)
        if tab is None:
            url = QUrl()
        else:
            url = tab.url()
        # It's possible for url to be invalid, but the caller will handle that.
        qtutils.ensure_valid(url)
        return url


class TabBar(QTabBar):

    """Custom tab bar with our own style.

    FIXME: Dragging tabs doesn't look as nice as it does in QTabBar.  However,
    fixing this would be a lot of effort, so we'll postpone it until we're
    reimplementing drag&drop for other reasons.

    https://github.com/qutebrowser/qutebrowser/issues/126

    Attributes:
        vertical: When the tab bar is currently vertical.
        win_id: The window ID this TabBar belongs to.
    """

    def __init__(self, win_id, parent=None):
        super().__init__(parent)
        self._win_id = win_id
        self.setStyle(TabBarStyle())
        self.set_font()
        config_obj = objreg.get('config')
        config_obj.changed.connect(self.set_font)
        config_obj.changed.connect(self.set_icon_size)
        self.vertical = False
        self._auto_hide_timer = QTimer()
        self._auto_hide_timer.setSingleShot(True)
        self._auto_hide_timer.setInterval(
            config.get('tabs', 'show-switching-delay'))
        self._auto_hide_timer.timeout.connect(self.maybe_hide)
        self.setAutoFillBackground(True)
        self.set_colors()
        self.pinned_count = 0
        config_obj.changed.connect(self.set_colors)
        QTimer.singleShot(0, self.maybe_hide)
        config_obj.changed.connect(self.on_tab_colors_changed)
        config_obj.changed.connect(self.on_show_switching_delay_changed)
        config_obj.changed.connect(self.tabs_show)

    def __repr__(self):
        return utils.get_repr(self, count=self.count())

    def _current_tab(self):
        """Get the current tab object."""
        return self.parent().currentWidget()

    @config.change_filter('tabs', 'show')
    def tabs_show(self):
        """Hide or show tab bar if needed when tabs->show got changed."""
        self.maybe_hide()

    @config.change_filter('tabs', 'show-switching-delay')
    def on_show_switching_delay_changed(self):
        """Set timer interval when tabs->show-switching-delay got changed."""
        self._auto_hide_timer.setInterval(
            config.get('tabs', 'show-switching-delay'))

    def on_current_changed(self):
        """Show tab bar when current tab got changed."""
        self.maybe_hide()  # for fullscreen tabs
        show = config.get('tabs', 'show')
        if show == 'switching':
            self.show()
            self._auto_hide_timer.start()

    @pyqtSlot()
    def maybe_hide(self):
        """Hide the tab bar if needed."""
        show = config.get('tabs', 'show')
        tab = self._current_tab()
        if (show in ['never', 'switching'] or
                (show == 'multiple' and self.count() == 1) or
                (tab and tab.data.fullscreen)):
            self.hide()
        else:
            self.show()

    def set_tab_data(self, idx, key, value):
        """Set tab data as a dictionary."""
        if not 0 <= idx < self.count():
            raise IndexError("Tab index ({}) out of range ({})!".format(
                idx, self.count()))
        data = self.tabData(idx)
        if data is None:
            data = {}
        data[key] = value
        self.setTabData(idx, data)

    def tab_data(self, idx, key):
        """Get tab data for a given key."""
        if not 0 <= idx < self.count():
            raise IndexError("Tab index ({}) out of range ({})!".format(
                idx, self.count()))
        data = self.tabData(idx)
        if data is None:
            data = {}
        return data[key]

    def tab_indicator_color(self, idx):
        """Get the tab indicator color for the given index."""
        try:
            return self.tab_data(idx, 'indicator-color')
        except KeyError:
            return QColor()

    def page_title(self, idx):
        """Get the tab title user data.

        Args:
            idx: The tab index to get the title for.
            handle_unset: Whether to return an empty string on KeyError.
        """
        try:
            return self.tab_data(idx, 'page-title')
        except KeyError:
            return ''

    def refresh(self):
        """Properly repaint the tab bar and relayout tabs."""
        # This is a horrible hack, but we need to do this so the underlying Qt
        # code sets layoutDirty so it actually relayouts the tabs.
        self.setIconSize(self.iconSize())

    @config.change_filter('fonts', 'tabbar')
    def set_font(self):
        """Set the tab bar font."""
        self.setFont(config.get('fonts', 'tabbar'))
        self.set_icon_size()

    @config.change_filter('tabs', 'favicon-scale')
    def set_icon_size(self):
        """Set the tab bar favicon size."""
        size = self.fontMetrics().height() - 2
        size *= config.get('tabs', 'favicon-scale')
        self.setIconSize(QSize(size, size))

    @config.change_filter('colors', 'tabs.bg.bar')
    def set_colors(self):
        """Set the tab bar colors."""
        p = self.palette()
        p.setColor(QPalette.Window, config.get('colors', 'tabs.bg.bar'))
        self.setPalette(p)

    @pyqtSlot(str, str)
    def on_tab_colors_changed(self, section, option):
        """Set the tab colors."""
        if section == 'colors' and option.startswith('tabs.'):
            self.update()

    def mousePressEvent(self, e):
        """Override mousePressEvent to close tabs if configured."""
        button = config.get('tabs', 'close-mouse-button')
        if (e.button() == Qt.RightButton and button == 'right' or
                e.button() == Qt.MiddleButton and button == 'middle'):
            e.accept()
            idx = self.tabAt(e.pos())
            if idx == -1:
                idx = self.currentIndex()
            self.tabCloseRequested.emit(idx)
            return
        super().mousePressEvent(e)

    def minimumTabSizeHint(self, index):
        """Set the minimum tab size to indicator/icon/... text.

        Args:
            index: The index of the tab to get a size hint for.

        Return:
            A QSize.
        """
        icon = self.tabIcon(index)
        padding = config.get('tabs', 'padding')
        padding_h = padding.left + padding.right
        padding_v = padding.top + padding.bottom
        if icon.isNull():
            icon_size = QSize(0, 0)
        else:
            extent = self.style().pixelMetric(QStyle.PM_TabBarIconSize, None,
                                              self)
            icon_size = icon.actualSize(QSize(extent, extent))
            padding_h += self.style().pixelMetric(
                PixelMetrics.icon_padding, None, self)
        indicator_width = config.get('tabs', 'indicator-width')
        height = self.fontMetrics().height() + padding_v
        width = (self.fontMetrics().width('\u2026') + icon_size.width() +
                 padding_h + indicator_width)
        return QSize(width, height)

    def tabSizeHint(self, index):
        """Override tabSizeHint so all tabs are the same size.

        https://wiki.python.org/moin/PyQt/Customising%20tab%20bars

        Args:
            index: The index of the tab.

        Return:
            A QSize.
        """
        minimum_size = self.minimumTabSizeHint(index)
        height = minimum_size.height()
        if self.vertical:
            confwidth = str(config.get('tabs', 'width'))
            if confwidth.endswith('%'):
                main_window = objreg.get('main-window', scope='window',
                                         window=self._win_id)
                perc = int(confwidth.rstrip('%'))
                width = main_window.width() * perc / 100
            else:
                width = int(confwidth)
            size = QSize(max(minimum_size.width(), width), height)
        elif self.count() == 0:
            # This happens on startup on macOS.
            # We return it directly rather than setting `size' because we don't
            # want to ensure it's valid in this special case.
            return QSize()
        else:
            tab_width_pinned_conf = config.get('tabs', 'pinned-width')

            try:
                pinned = self.tab_data(index, 'pinned')
            except KeyError:
                pinned = False

            no_pinned_count = self.count() - self.pinned_count
            pinned_width = tab_width_pinned_conf * self.pinned_count
            no_pinned_width = self.width() - pinned_width

            if pinned:
                width = tab_width_pinned_conf
            else:

                # Tabs should attempt to occupy the whole window width. If
                # there are pinned tabs their size will be subtracted from the
                # total window width.  During shutdown the self.count goes
                # down, but the self.pinned_count not - this generates some odd
                # behavior. To avoid this we compare self.count against
                # self.pinned_count. If we end up having too little space, we
                # set the minimum size below.
                if self.pinned_count > 0 and no_pinned_count > 0:
                    width = no_pinned_width / no_pinned_count
                else:
                    width = self.width() / self.count()

            # If no_pinned_width is not divisible by no_pinned_count, add a
            # pixel to some tabs so that there is no ugly leftover space.
            if (no_pinned_count > 0 and
                    index < no_pinned_width % no_pinned_count):
                width += 1

            # If we don't have enough space, we return the minimum size so we
            # get scroll buttons as soon as needed.
            width = max(width, minimum_size.width())

            size = QSize(width, height)
        qtutils.ensure_valid(size)
        return size

    def paintEvent(self, _e):
        """Override paintEvent to draw the tabs like we want to."""
        # pylint: disable=bad-config-call
        # WORKAROUND for https://bitbucket.org/logilab/astroid/issue/104
        p = QStylePainter(self)
        selected = self.currentIndex()
        for idx in range(self.count()):
            tab = QStyleOptionTab()
            self.initStyleOption(tab, idx)

            bg_parts = ['tabs', 'bg']
            fg_parts = ['tabs', 'fg']
            if idx == selected:
                bg_parts.append('selected')
                fg_parts.append('selected')

            if idx % 2:
                bg_parts.append('odd')
                fg_parts.append('odd')
            else:
                bg_parts.append('even')
                fg_parts.append('even')

            bg_color = config.get('colors', '.'.join(bg_parts))
            fg_color = config.get('colors', '.'.join(fg_parts))
            tab.palette.setColor(QPalette.Window, bg_color)
            tab.palette.setColor(QPalette.WindowText, fg_color)

            indicator_color = self.tab_indicator_color(idx)
            tab.palette.setColor(QPalette.Base, indicator_color)
            if tab.rect.right() < 0 or tab.rect.left() > self.width():
                # Don't bother drawing a tab if the entire tab is outside of
                # the visible tab bar.
                continue
            p.drawControl(QStyle.CE_TabBarTab, tab)

    def tabInserted(self, idx):
        """Update visibility when a tab was inserted."""
        super().tabInserted(idx)
        self.maybe_hide()

    def tabRemoved(self, idx):
        """Update visibility when a tab was removed."""
        super().tabRemoved(idx)
        self.maybe_hide()

    def wheelEvent(self, e):
        """Override wheelEvent to make the action configurable.

        Args:
            e: The QWheelEvent
        """
        if config.get('tabs', 'mousewheel-tab-switching'):
            super().wheelEvent(e)
        else:
            tabbed_browser = objreg.get('tabbed-browser', scope='window',
                                        window=self._win_id)
            tabbed_browser.wheelEvent(e)


# Used by TabBarStyle._tab_layout().
Layouts = collections.namedtuple('Layouts', ['text', 'icon', 'indicator'])


class TabBarStyle(QCommonStyle):

    """Qt style used by TabBar to fix some issues with the default one.

    This fixes the following things:
        - Remove the focus rectangle Ubuntu draws on tabs.
        - Force text to be left-aligned even though Qt has "centered"
          hardcoded.

    Unfortunately PyQt doesn't support QProxyStyle, so we need to do this the
    hard way...

    Based on:

    http://stackoverflow.com/a/17294081
    https://code.google.com/p/makehuman/source/browse/trunk/makehuman/lib/qtgui.py
    """

    def __init__(self):
        """Initialize all functions we're not overriding.

        This simply calls the corresponding function in self._style.
        """
        self._style = QStyleFactory.create('Fusion')
        for method in ['drawComplexControl', 'drawItemPixmap',
                       'generatedIconPixmap', 'hitTestComplexControl',
                       'itemPixmapRect', 'itemTextRect', 'polish', 'styleHint',
                       'subControlRect', 'unpolish', 'drawItemText',
                       'sizeFromContents', 'drawPrimitive']:
            target = getattr(self._style, method)
            setattr(self, method, functools.partial(target))
        super().__init__()

    def _draw_indicator(self, layouts, opt, p):
        """Draw the tab indicator.

        Args:
            layouts: The layouts from _tab_layout.
            opt: QStyleOption from drawControl.
            p: QPainter from drawControl.
        """
        color = opt.palette.base().color()
        rect = layouts.indicator
        if color.isValid() and rect.isValid():
            p.fillRect(rect, color)

    def _draw_icon(self, layouts, opt, p):
        """Draw the tab icon.

        Args:
            layouts: The layouts from _tab_layout.
            opt: QStyleOption
            p: QPainter
        """
        qtutils.ensure_valid(layouts.icon)
        icon_mode = (QIcon.Normal if opt.state & QStyle.State_Enabled
                     else QIcon.Disabled)
        icon_state = (QIcon.On if opt.state & QStyle.State_Selected
                      else QIcon.Off)
        icon = opt.icon.pixmap(opt.iconSize, icon_mode, icon_state)
        p.drawPixmap(layouts.icon.x(), layouts.icon.y(), icon)

    def drawControl(self, element, opt, p, widget=None):
        """Override drawControl to draw odd tabs in a different color.

        Draws the given element with the provided painter with the style
        options specified by option.

        Args:
            element: ControlElement
            opt: QStyleOption
            p: QPainter
            widget: QWidget
        """
        if element not in [QStyle.CE_TabBarTab, QStyle.CE_TabBarTabShape,
                           QStyle.CE_TabBarTabLabel]:
            # Let the real style draw it.
            self._style.drawControl(element, opt, p, widget)
            return

        layouts = self._tab_layout(opt)
        if layouts is None:
            log.misc.warning("Could not get layouts for tab!")
            return

        if element == QStyle.CE_TabBarTab:
            # We override this so we can control TabBarTabShape/TabBarTabLabel.
            self.drawControl(QStyle.CE_TabBarTabShape, opt, p, widget)
            self.drawControl(QStyle.CE_TabBarTabLabel, opt, p, widget)
        elif element == QStyle.CE_TabBarTabShape:
            p.fillRect(opt.rect, opt.palette.window())
            self._draw_indicator(layouts, opt, p)
            # We use super() rather than self._style here because we don't want
            # any sophisticated drawing.
            super().drawControl(QStyle.CE_TabBarTabShape, opt, p, widget)
        elif element == QStyle.CE_TabBarTabLabel:
            if not opt.icon.isNull() and layouts.icon.isValid():
                self._draw_icon(layouts, opt, p)
            alignment = (config.get('tabs', 'title-alignment') |
                         Qt.AlignVCenter | Qt.TextHideMnemonic)
            self._style.drawItemText(p, layouts.text, alignment, opt.palette,
                                     opt.state & QStyle.State_Enabled,
                                     opt.text, QPalette.WindowText)
        else:
            raise ValueError("Invalid element {!r}".format(element))

    def pixelMetric(self, metric, option=None, widget=None):
        """Override pixelMetric to not shift the selected tab.

        Args:
            metric: PixelMetric
            option: const QStyleOption *
            widget: const QWidget *

        Return:
            An int.
        """
        if metric in [QStyle.PM_TabBarTabShiftHorizontal,
                      QStyle.PM_TabBarTabShiftVertical,
                      QStyle.PM_TabBarTabHSpace,
                      QStyle.PM_TabBarTabVSpace,
                      QStyle.PM_TabBarScrollButtonWidth]:
            return 0
        elif metric == PixelMetrics.icon_padding:
            return 4
        else:
            return self._style.pixelMetric(metric, option, widget)

    def subElementRect(self, sr, opt, widget=None):
        """Override subElementRect to use our own _tab_layout implementation.

        Args:
            sr: SubElement
            opt: QStyleOption
            widget: QWidget

        Return:
            A QRect.
        """
        if sr == QStyle.SE_TabBarTabText:
            layouts = self._tab_layout(opt)
            if layouts is None:
                log.misc.warning("Could not get layouts for tab!")
                return QRect()
            return layouts.text
        elif sr == QStyle.SE_TabWidgetTabBar:
            # Need to use super() because we also use super() to render
            # element in drawControl(); otherwise, we may get bit by
            # style differences...
            rct = super().subElementRect(sr, opt, widget)
            return rct
        else:
            try:
                # We need this so the left scroll button is aligned properly.
                # Otherwise, empty space will be shown after the last tab even
                # though the button width is set to 0
                #
                # QStyle.SE_TabBarScrollLeftButton was added in Qt 5.7
                if sr == QStyle.SE_TabBarScrollLeftButton:
                    return super().subElementRect(sr, opt, widget)
            except AttributeError:
                pass

            return self._style.subElementRect(sr, opt, widget)

    def _tab_layout(self, opt):
        """Compute the text/icon rect from the opt rect.

        This is based on Qt's QCommonStylePrivate::tabLayout
        (qtbase/src/widgets/styles/qcommonstyle.cpp) as we can't use the
        private implementation.

        Args:
            opt: QStyleOptionTab

        Return:
            A Layout namedtuple with two QRects.
        """
        padding = config.get('tabs', 'padding')
        indicator_padding = config.get('tabs', 'indicator-padding')

        text_rect = QRect(opt.rect)
        if not text_rect.isValid():
            # This happens sometimes according to crash reports, but no idea
            # why...
            return None

        text_rect.adjust(padding.left, padding.top, -padding.right,
                         -padding.bottom)

        indicator_width = config.get('tabs', 'indicator-width')
        if indicator_width == 0:
            indicator_rect = QRect()
        else:
            indicator_rect = QRect(opt.rect)
            qtutils.ensure_valid(indicator_rect)
            indicator_rect.adjust(padding.left + indicator_padding.left,
                                  padding.top + indicator_padding.top,
                                  0,
                                  -(padding.bottom + indicator_padding.bottom))
            indicator_rect.setWidth(indicator_width)

            text_rect.adjust(indicator_width + indicator_padding.left +
                             indicator_padding.right, 0, 0, 0)

        icon_rect = self._get_icon_rect(opt, text_rect)
        if icon_rect.isValid():
            icon_padding = self.pixelMetric(PixelMetrics.icon_padding, opt)
            text_rect.adjust(icon_rect.width() + icon_padding, 0, 0, 0)

        text_rect = self._style.visualRect(opt.direction, opt.rect, text_rect)
        return Layouts(text=text_rect, icon=icon_rect,
                       indicator=indicator_rect)

    def _get_icon_rect(self, opt, text_rect):
        """Get a QRect for the icon to draw.

        Args:
            opt: QStyleOptionTab
            text_rect: The QRect for the text.

        Return:
            A QRect.
        """
        icon_size = opt.iconSize
        if not icon_size.isValid():
            icon_extent = self.pixelMetric(QStyle.PM_SmallIconSize)
            icon_size = QSize(icon_extent, icon_extent)
        icon_mode = (QIcon.Normal if opt.state & QStyle.State_Enabled
                     else QIcon.Disabled)
        icon_state = (QIcon.On if opt.state & QStyle.State_Selected
                      else QIcon.Off)
        # reserve space for favicon when tab bar is vertical (issue #1968)
        position = config.get('tabs', 'position')
        if (opt.icon.isNull() and
                position in [QTabWidget.East, QTabWidget.West] and
                config.get('tabs', 'show-favicons')):
            tab_icon_size = icon_size
        else:
            actual_size = opt.icon.actualSize(icon_size, icon_mode, icon_state)
            tab_icon_size = QSize(
                min(actual_size.width(), icon_size.width()),
                min(actual_size.height(), icon_size.height()))
        icon_top = text_rect.center().y() + 1 - tab_icon_size.height() / 2
        icon_rect = QRect(QPoint(text_rect.left(), icon_top), tab_icon_size)
        icon_rect = self._style.visualRect(opt.direction, opt.rect, icon_rect)
        return icon_rect