path: root/contrib/python/prompt-toolkit/py2/prompt_toolkit/layout/containers.py

"""
Container for the layout.
(Containers can contain other containers or user interface controls.)
"""
from __future__ import unicode_literals

from abc import ABCMeta, abstractmethod
from six import with_metaclass
from six.moves import range

from .controls import UIControl, TokenListControl, UIContent
from .dimension import LayoutDimension, sum_layout_dimensions, max_layout_dimensions
from .margins import Margin
from .screen import Point, WritePosition, _CHAR_CACHE
from .utils import token_list_to_text, explode_tokens
from prompt_toolkit.cache import SimpleCache
from prompt_toolkit.filters import to_cli_filter, ViInsertMode, EmacsInsertMode
from prompt_toolkit.mouse_events import MouseEvent, MouseEventType
from prompt_toolkit.reactive import Integer
from prompt_toolkit.token import Token
from prompt_toolkit.utils import take_using_weights, get_cwidth

__all__ = (
    'Container',
    'HSplit',
    'VSplit',
    'FloatContainer',
    'Float',
    'Window',
    'WindowRenderInfo',
    'ConditionalContainer',
    'ScrollOffsets',
    'ColorColumn',
)

Transparent = Token.Transparent


class Container(with_metaclass(ABCMeta, object)):
    """
    Base class for user interface layout.
    """
    @abstractmethod
    def reset(self):
        """
        Reset the state of this container and all the children.
        (E.g. reset scroll offsets, etc...)
        """

    @abstractmethod
    def preferred_width(self, cli, max_available_width):
        """
        Return a :class:`~prompt_toolkit.layout.dimension.LayoutDimension` that
        represents the desired width for this container.

        :param cli: :class:`~prompt_toolkit.interface.CommandLineInterface`.
        """

    @abstractmethod
    def preferred_height(self, cli, width, max_available_height):
        """
        Return a :class:`~prompt_toolkit.layout.dimension.LayoutDimension` that
        represents the desired height for this container.

        :param cli: :class:`~prompt_toolkit.interface.CommandLineInterface`.
        """

    @abstractmethod
    def write_to_screen(self, cli, screen, mouse_handlers, write_position):
        """
        Write the actual content to the screen.

        :param cli: :class:`~prompt_toolkit.interface.CommandLineInterface`.
        :param screen: :class:`~prompt_toolkit.layout.screen.Screen`
        :param mouse_handlers: :class:`~prompt_toolkit.layout.mouse_handlers.MouseHandlers`.
        """

    @abstractmethod
    def walk(self, cli):
        """
        Walk through all the layout nodes (and their children) and yield them.
        """


def _window_too_small():
    " Create a `Window` that displays the 'Window too small' text. "
    return Window(TokenListControl.static(
        [(Token.WindowTooSmall, ' Window too small... ')]))


class HSplit(Container):
    """
    Several layouts, one stacked above/under the other.

    :param children: List of child :class:`.Container` objects.
    :param window_too_small: A :class:`.Container` object that is displayed if
        there is not enough space for all the children. By default, this is a
        "Window too small" message.
    :param get_dimensions: (`None` or a callable that takes a
        `CommandLineInterface` and returns a list of `LayoutDimension`
        instances.) By default the dimensions are taken from the children and
        divided by the available space. However, when `get_dimensions` is specified,
        this is taken instead.
    :param report_dimensions_callback: When rendering, this function is called
        with the `CommandLineInterface` and the list of used dimensions. (As a
        list of integers.)
    """
    def __init__(self, children, window_too_small=None,
                 get_dimensions=None, report_dimensions_callback=None):
        assert all(isinstance(c, Container) for c in children)
        assert window_too_small is None or isinstance(window_too_small, Container)
        assert get_dimensions is None or callable(get_dimensions)
        assert report_dimensions_callback is None or callable(report_dimensions_callback)

        self.children = children
        self.window_too_small = window_too_small or _window_too_small()
        self.get_dimensions = get_dimensions
        self.report_dimensions_callback = report_dimensions_callback

    def preferred_width(self, cli, max_available_width):
        if self.children:
            dimensions = [c.preferred_width(cli, max_available_width) for c in self.children]
            return max_layout_dimensions(dimensions)
        else:
            return LayoutDimension(0)

    def preferred_height(self, cli, width, max_available_height):
        dimensions = [c.preferred_height(cli, width, max_available_height) for c in self.children]
        return sum_layout_dimensions(dimensions)

    def reset(self):
        for c in self.children:
            c.reset()

    def write_to_screen(self, cli, screen, mouse_handlers, write_position):
        """
        Render the prompt to a `Screen` instance.

        :param screen: The :class:`~prompt_toolkit.layout.screen.Screen` class
            to which the output has to be written.
        """
        sizes = self._divide_heigths(cli, write_position)

        if self.report_dimensions_callback:
            self.report_dimensions_callback(cli, sizes)

        if sizes is None:
            self.window_too_small.write_to_screen(
                cli, screen, mouse_handlers, write_position)
        else:
            # Draw child panes.
            ypos = write_position.ypos
            xpos = write_position.xpos
            width = write_position.width

            for s, c in zip(sizes, self.children):
                c.write_to_screen(cli, screen, mouse_handlers, WritePosition(xpos, ypos, width, s))
                ypos += s

    def _divide_heigths(self, cli, write_position):
        """
        Return the heights for all rows.
        Or None when there is not enough space.
        """
        if not self.children:
            return []

        # Calculate heights.
        given_dimensions = self.get_dimensions(cli) if self.get_dimensions else None

        def get_dimension_for_child(c, index):
            if given_dimensions and given_dimensions[index] is not None:
                return given_dimensions[index]
            else:
                return c.preferred_height(cli, write_position.width, write_position.extended_height)

        dimensions = [get_dimension_for_child(c, index) for index, c in enumerate(self.children)]

        # Sum dimensions
        sum_dimensions = sum_layout_dimensions(dimensions)

        # If there is not enough space for both.
        # Don't do anything.
        if sum_dimensions.min > write_position.extended_height:
            return

        # Find optimal sizes. (Start with minimal size, increase until we cover
        # the whole height.)
        sizes = [d.min for d in dimensions]

        child_generator = take_using_weights(
            items=list(range(len(dimensions))),
            weights=[d.weight for d in dimensions])

        i = next(child_generator)

        while sum(sizes) < min(write_position.extended_height, sum_dimensions.preferred):
            # Increase until we meet at least the 'preferred' size.
            if sizes[i] < dimensions[i].preferred:
                sizes[i] += 1
            i = next(child_generator)

        if not any([cli.is_returning, cli.is_exiting, cli.is_aborting]):
            while sum(sizes) < min(write_position.height, sum_dimensions.max):
                # Increase until we use all the available space. (or until "max")
                if sizes[i] < dimensions[i].max:
                    sizes[i] += 1
                i = next(child_generator)

        return sizes

    def walk(self, cli):
        """ Walk through children. """
        yield self
        for c in self.children:
            for i in c.walk(cli):
                yield i


class VSplit(Container):
    """
    Several layouts, one stacked left/right of the other.

    :param children: List of child :class:`.Container` objects.
    :param window_too_small: A :class:`.Container` object that is displayed if
        there is not enough space for all the children. By default, this is a
        "Window too small" message.
    :param get_dimensions: (`None` or a callable that takes a
        `CommandLineInterface` and returns a list of `LayoutDimension`
        instances.) By default the dimensions are taken from the children and
        divided by the available space. However, when `get_dimensions` is specified,
        this is taken instead.
    :param report_dimensions_callback: When rendering, this function is called
        with the `CommandLineInterface` and the list of used dimensions. (As a
        list of integers.)
    """
    def __init__(self, children, window_too_small=None,
                 get_dimensions=None, report_dimensions_callback=None):
        assert all(isinstance(c, Container) for c in children)
        assert window_too_small is None or isinstance(window_too_small, Container)
        assert get_dimensions is None or callable(get_dimensions)
        assert report_dimensions_callback is None or callable(report_dimensions_callback)

        self.children = children
        self.window_too_small = window_too_small or _window_too_small()
        self.get_dimensions = get_dimensions
        self.report_dimensions_callback = report_dimensions_callback

    def preferred_width(self, cli, max_available_width):
        dimensions = [c.preferred_width(cli, max_available_width) for c in self.children]
        return sum_layout_dimensions(dimensions)

    def preferred_height(self, cli, width, max_available_height):
        sizes = self._divide_widths(cli, width)
        if sizes is None:
            return LayoutDimension()
        else:
            dimensions = [c.preferred_height(cli, s, max_available_height)
                          for s, c in zip(sizes, self.children)]
            return max_layout_dimensions(dimensions)

    def reset(self):
        for c in self.children:
            c.reset()

    def _divide_widths(self, cli, width):
        """
        Return the widths for all columns.
        Or None when there is not enough space.
        """
        if not self.children:
            return []

        # Calculate widths.
        given_dimensions = self.get_dimensions(cli) if self.get_dimensions else None

        def get_dimension_for_child(c, index):
            if given_dimensions and given_dimensions[index] is not None:
                return given_dimensions[index]
            else:
                return c.preferred_width(cli, width)

        dimensions = [get_dimension_for_child(c, index) for index, c in enumerate(self.children)]

        # Sum dimensions
        sum_dimensions = sum_layout_dimensions(dimensions)

        # If there is not enough space for both.
        # Don't do anything.
        if sum_dimensions.min > width:
            return

        # Find optimal sizes. (Start with minimal size, increase until we cover
        # the whole height.)
        sizes = [d.min for d in dimensions]

        child_generator = take_using_weights(
            items=list(range(len(dimensions))),
            weights=[d.weight for d in dimensions])

        i = next(child_generator)

        while sum(sizes) < min(width, sum_dimensions.preferred):
            # Increase until we meet at least the 'preferred' size.
            if sizes[i] < dimensions[i].preferred:
                sizes[i] += 1
            i = next(child_generator)

        while sum(sizes) < min(width, sum_dimensions.max):
            # Increase until we use all the available space.
            if sizes[i] < dimensions[i].max:
                sizes[i] += 1
            i = next(child_generator)

        return sizes

    def write_to_screen(self, cli, screen, mouse_handlers, write_position):
        """
        Render the prompt to a `Screen` instance.

        :param screen: The :class:`~prompt_toolkit.layout.screen.Screen` class
            to which the output has to be written.
        """
        if not self.children:
            return

        sizes = self._divide_widths(cli, write_position.width)

        if self.report_dimensions_callback:
            self.report_dimensions_callback(cli, sizes)

        # If there is not enough space.
        if sizes is None:
            self.window_too_small.write_to_screen(
                cli, screen, mouse_handlers, write_position)
            return

        # Calculate heights, take the largest possible, but not larger than write_position.extended_height.
        heights = [child.preferred_height(cli, width, write_position.extended_height).preferred
                   for width, child in zip(sizes, self.children)]
        height = max(write_position.height, min(write_position.extended_height, max(heights)))

        # Draw child panes.
        ypos = write_position.ypos
        xpos = write_position.xpos

        for s, c in zip(sizes, self.children):
            c.write_to_screen(cli, screen, mouse_handlers, WritePosition(xpos, ypos, s, height))
            xpos += s

    def walk(self, cli):
        """ Walk through children. """
        yield self
        for c in self.children:
            for i in c.walk(cli):
                yield i


class FloatContainer(Container):
    """
    Container which can contain another container for the background, as well
    as a list of floating containers on top of it.

    Example Usage::

        FloatContainer(content=Window(...),
                       floats=[
                           Float(xcursor=True,
                                ycursor=True,
                                layout=CompletionMenu(...))
                       ])
    """
    def __init__(self, content, floats):
        assert isinstance(content, Container)
        assert all(isinstance(f, Float) for f in floats)

        self.content = content
        self.floats = floats

    def reset(self):
        self.content.reset()

        for f in self.floats:
            f.content.reset()

    def preferred_width(self, cli, write_position):
        return self.content.preferred_width(cli, write_position)

    def preferred_height(self, cli, width, max_available_height):
        """
        Return the preferred height of the float container.
        (We don't care about the height of the floats, they should always fit
        into the dimensions provided by the container.)
        """
        return self.content.preferred_height(cli, width, max_available_height)

    def write_to_screen(self, cli, screen, mouse_handlers, write_position):
        self.content.write_to_screen(cli, screen, mouse_handlers, write_position)

        for fl in self.floats:
            # When a menu_position was given, use this instead of the cursor
            # position. (These cursor positions are absolute, translate again
            # relative to the write_position.)
            # Note: This should be inside the for-loop, because one float could
            #       set the cursor position to be used for the next one.
            cursor_position = screen.menu_position or screen.cursor_position
            cursor_position = Point(x=cursor_position.x - write_position.xpos,
                                    y=cursor_position.y - write_position.ypos)

            fl_width = fl.get_width(cli)
            fl_height = fl.get_height(cli)

            # Left & width given.
            if fl.left is not None and fl_width is not None:
                xpos = fl.left
                width = fl_width
            # Left & right given -> calculate width.
            elif fl.left is not None and fl.right is not None:
                xpos = fl.left
                width = write_position.width - fl.left - fl.right
            # Width & right given -> calculate left.
            elif fl_width is not None and fl.right is not None:
                xpos = write_position.width - fl.right - fl_width
                width = fl_width
            elif fl.xcursor:
                width = fl_width
                if width is None:
                    width = fl.content.preferred_width(cli, write_position.width).preferred
                    width = min(write_position.width, width)

                xpos = cursor_position.x
                if xpos + width > write_position.width:
                    xpos = max(0, write_position.width - width)
            # Only width given -> center horizontally.
            elif fl_width:
                xpos = int((write_position.width - fl_width) / 2)
                width = fl_width
            # Otherwise, take preferred width from float content.
            else:
                width = fl.content.preferred_width(cli, write_position.width).preferred

                if fl.left is not None:
                    xpos = fl.left
                elif fl.right is not None:
                    xpos = max(0, write_position.width - width - fl.right)
                else:  # Center horizontally.
                    xpos = max(0, int((write_position.width - width) / 2))

                # Trim.
                width = min(width, write_position.width - xpos)

            # Top & height given.
            if fl.top is not None and fl_height is not None:
                ypos = fl.top
                height = fl_height
            # Top & bottom given -> calculate height.
            elif fl.top is not None and fl.bottom is not None:
                ypos = fl.top
                height = write_position.height - fl.top - fl.bottom
            # Height & bottom given -> calculate top.
            elif fl_height is not None and fl.bottom is not None:
                ypos = write_position.height - fl_height - fl.bottom
                height = fl_height
            # Near cursor
            elif fl.ycursor:
                ypos = cursor_position.y + 1

                height = fl_height
                if height is None:
                    height = fl.content.preferred_height(
                        cli, width, write_position.extended_height).preferred

                # Reduce height if not enough space. (We can use the
                # extended_height when the content requires it.)
                if height > write_position.extended_height - ypos:
                    if write_position.extended_height - ypos + 1 >= ypos:
                        # When the space below the cursor is more than
                        # the space above, just reduce the height.
                        height = write_position.extended_height - ypos
                    else:
                        # Otherwise, fit the float above the cursor.
                        height = min(height, cursor_position.y)
                        ypos = cursor_position.y - height

            # Only height given -> center vertically.
            elif fl_width:
                ypos = int((write_position.height - fl_height) / 2)
                height = fl_height
            # Otherwise, take preferred height from content.
            else:
                height = fl.content.preferred_height(
                    cli, width, write_position.extended_height).preferred

                if fl.top is not None:
                    ypos = fl.top
                elif fl.bottom is not None:
                    ypos = max(0, write_position.height - height - fl.bottom)
                else:  # Center vertically.
                    ypos = max(0, int((write_position.height - height) / 2))

                # Trim.
                height = min(height, write_position.height - ypos)

            # Write float.
            # (xpos and ypos can be negative: a float can be partially visible.)
            if height > 0 and width > 0:
                wp = WritePosition(xpos=xpos + write_position.xpos,
                                   ypos=ypos + write_position.ypos,
                                   width=width, height=height)

                if not fl.hide_when_covering_content or self._area_is_empty(screen, wp):
                    fl.content.write_to_screen(cli, screen, mouse_handlers, wp)

    def _area_is_empty(self, screen, write_position):
        """
        Return True when the area below the write position is still empty.
        (For floats that should not hide content underneath.)
        """
        wp = write_position
        Transparent = Token.Transparent

        for y in range(wp.ypos, wp.ypos + wp.height):
            if y in screen.data_buffer:
                row = screen.data_buffer[y]

                for x in range(wp.xpos, wp.xpos + wp.width):
                    c = row[x]
                    if c.char != ' ' or c.token != Transparent:
                        return False

        return True

    def walk(self, cli):
        """ Walk through children. """
        yield self

        for i in self.content.walk(cli):
            yield i

        for f in self.floats:
            for i in f.content.walk(cli):
                yield i


class Float(object):
    """
    Float for use in a :class:`.FloatContainer`.

    :param content: :class:`.Container` instance.
    :param hide_when_covering_content: Hide the float when it covers content underneath.
    """
    def __init__(self, top=None, right=None, bottom=None, left=None,
                 width=None, height=None, get_width=None, get_height=None,
                 xcursor=False, ycursor=False, content=None,
                 hide_when_covering_content=False):
        assert isinstance(content, Container)
        assert width is None or get_width is None
        assert height is None or get_height is None

        self.left = left
        self.right = right
        self.top = top
        self.bottom = bottom

        self._width = width
        self._height = height

        self._get_width = get_width
        self._get_height = get_height

        self.xcursor = xcursor
        self.ycursor = ycursor

        self.content = content
        self.hide_when_covering_content = hide_when_covering_content

    def get_width(self, cli):
        if self._width:
            return self._width
        if self._get_width:
            return self._get_width(cli)

    def get_height(self, cli):
        if self._height:
            return self._height
        if self._get_height:
            return self._get_height(cli)

    def __repr__(self):
        return 'Float(content=%r)' % self.content


class WindowRenderInfo(object):
    """
    Render information, for the last render time of this control.
    It stores mapping information between the input buffers (in case of a
    :class:`~prompt_toolkit.layout.controls.BufferControl`) and the actual
    render position on the output screen.

    (Could be used for implementation of the Vi 'H' and 'L' key bindings as
    well as implementing mouse support.)

    :param ui_content: The original :class:`.UIContent` instance that contains
        the whole input, without clipping. (ui_content)
    :param horizontal_scroll: The horizontal scroll of the :class:`.Window` instance.
    :param vertical_scroll: The vertical scroll of the :class:`.Window` instance.
    :param window_width: The width of the window that displays the content,
        without the margins.
    :param window_height: The height of the window that displays the content.
    :param configured_scroll_offsets: The scroll offsets as configured for the
        :class:`Window` instance.
    :param visible_line_to_row_col: Mapping that maps the row numbers on the
        displayed screen (starting from zero for the first visible line) to
        (row, col) tuples pointing to the row and column of the :class:`.UIContent`.
    :param rowcol_to_yx: Mapping that maps (row, column) tuples representing
        coordinates of the :class:`UIContent` to (y, x) absolute coordinates at
        the rendered screen.
    """
    def __init__(self, ui_content, horizontal_scroll, vertical_scroll,
                 window_width, window_height,
                 configured_scroll_offsets,
                 visible_line_to_row_col, rowcol_to_yx,
                 x_offset, y_offset, wrap_lines):
        assert isinstance(ui_content, UIContent)
        assert isinstance(horizontal_scroll, int)
        assert isinstance(vertical_scroll, int)
        assert isinstance(window_width, int)
        assert isinstance(window_height, int)
        assert isinstance(configured_scroll_offsets, ScrollOffsets)
        assert isinstance(visible_line_to_row_col, dict)
        assert isinstance(rowcol_to_yx, dict)
        assert isinstance(x_offset, int)
        assert isinstance(y_offset, int)
        assert isinstance(wrap_lines, bool)

        self.ui_content = ui_content
        self.vertical_scroll = vertical_scroll
        self.window_width = window_width  # Width without margins.
        self.window_height = window_height

        self.configured_scroll_offsets = configured_scroll_offsets
        self.visible_line_to_row_col = visible_line_to_row_col
        self.wrap_lines = wrap_lines

        self._rowcol_to_yx = rowcol_to_yx  # row/col from input to absolute y/x
                                           # screen coordinates.
        self._x_offset = x_offset
        self._y_offset = y_offset

    @property
    def visible_line_to_input_line(self):
        return dict(
            (visible_line, rowcol[0])
            for visible_line, rowcol in self.visible_line_to_row_col.items())

    @property
    def cursor_position(self):
        """
        Return the cursor position coordinates, relative to the left/top corner
        of the rendered screen.
        """
        cpos = self.ui_content.cursor_position
        y, x = self._rowcol_to_yx[cpos.y, cpos.x]
        return Point(x=x - self._x_offset, y=y - self._y_offset)

    @property
    def applied_scroll_offsets(self):
        """
        Return a :class:`.ScrollOffsets` instance that indicates the actual
        offset. This can be less than or equal to what's configured. E.g, when
        the cursor is completely at the top, the top offset will be zero rather
        than what's configured.
        """
        if self.displayed_lines[0] == 0:
            top = 0
        else:
            # Get row where the cursor is displayed.
            y = self.input_line_to_visible_line[self.ui_content.cursor_position.y]
            top = min(y, self.configured_scroll_offsets.top)

        return ScrollOffsets(
            top=top,
            bottom=min(self.ui_content.line_count - self.displayed_lines[-1] - 1,
                       self.configured_scroll_offsets.bottom),

            # For left/right, it probably doesn't make sense to return something.
            # (We would have to calculate the widths of all the lines and keep
            # double width characters in mind.)
            left=0, right=0)

    @property
    def displayed_lines(self):
        """
        List of all the visible rows. (Line numbers of the input buffer.)
        The last line may not be entirely visible.
        """
        return sorted(row for row, col in self.visible_line_to_row_col.values())

    @property
    def input_line_to_visible_line(self):
        """
        Return the dictionary mapping the line numbers of the input buffer to
        the lines of the screen. When a line spans several rows at the screen,
        the first row appears in the dictionary.
        """
        result = {}
        for k, v in self.visible_line_to_input_line.items():
            if v in result:
                result[v] = min(result[v], k)
            else:
                result[v] = k
        return result

    def first_visible_line(self, after_scroll_offset=False):
        """
        Return the line number (0 based) of the input document that corresponds
        with the first visible line.
        """
        if after_scroll_offset:
            return self.displayed_lines[self.applied_scroll_offsets.top]
        else:
            return self.displayed_lines[0]

    def last_visible_line(self, before_scroll_offset=False):
        """
        Like `first_visible_line`, but for the last visible line.
        """
        if before_scroll_offset:
            return self.displayed_lines[-1 - self.applied_scroll_offsets.bottom]
        else:
            return self.displayed_lines[-1]

    def center_visible_line(self, before_scroll_offset=False,
                            after_scroll_offset=False):
        """
        Like `first_visible_line`, but for the center visible line.
        """
        return (self.first_visible_line(after_scroll_offset) +
                (self.last_visible_line(before_scroll_offset) -
                 self.first_visible_line(after_scroll_offset)) // 2
               )

    @property
    def content_height(self):
        """
        The full height of the user control.
        """
        return self.ui_content.line_count

    @property
    def full_height_visible(self):
        """
        True when the full height is visible (There is no vertical scroll.)
        """
        return self.vertical_scroll == 0 and self.last_visible_line() == self.content_height

    @property
    def top_visible(self):
        """
        True when the top of the buffer is visible.
        """
        return self.vertical_scroll == 0

    @property
    def bottom_visible(self):
        """
        True when the bottom of the buffer is visible.
        """
        return self.last_visible_line() == self.content_height - 1

    @property
    def vertical_scroll_percentage(self):
        """
        Vertical scroll as a percentage. (0 means: the top is visible,
        100 means: the bottom is visible.)
        """
        if self.bottom_visible:
            return 100
        else:
            return (100 * self.vertical_scroll // self.content_height)

    def get_height_for_line(self, lineno):
        """
        Return the height of the given line.
        (The height that it would take, if this line became visible.)
        """
        if self.wrap_lines:
            return self.ui_content.get_height_for_line(lineno, self.window_width)
        else:
            return 1


class ScrollOffsets(object):
    """
    Scroll offsets for the :class:`.Window` class.

    Note that left/right offsets only make sense if line wrapping is disabled.
    """
    def __init__(self, top=0, bottom=0, left=0, right=0):
        assert isinstance(top, Integer)
        assert isinstance(bottom, Integer)
        assert isinstance(left, Integer)
        assert isinstance(right, Integer)

        self._top = top
        self._bottom = bottom
        self._left = left
        self._right = right

    @property
    def top(self):
        return int(self._top)

    @property
    def bottom(self):
        return int(self._bottom)

    @property
    def left(self):
        return int(self._left)

    @property
    def right(self):
        return int(self._right)

    def __repr__(self):
        return 'ScrollOffsets(top=%r, bottom=%r, left=%r, right=%r)' % (
            self.top, self.bottom, self.left, self.right)


class ColorColumn(object):
    def __init__(self, position, token=Token.ColorColumn):
        self.position = position
        self.token = token


_in_insert_mode = ViInsertMode() | EmacsInsertMode()


class Window(Container):
    """
    Container that holds a control.

    :param content: :class:`~prompt_toolkit.layout.controls.UIControl` instance.
    :param width: :class:`~prompt_toolkit.layout.dimension.LayoutDimension` instance.
    :param height: :class:`~prompt_toolkit.layout.dimension.LayoutDimension` instance.
    :param get_width: callable which takes a `CommandLineInterface` and returns a `LayoutDimension`.
    :param get_height: callable which takes a `CommandLineInterface` and returns a `LayoutDimension`.
    :param dont_extend_width: When `True`, don't take up more width then the
                              preferred width reported by the control.
    :param dont_extend_height: When `True`, don't take up more width then the
                               preferred height reported by the control.
    :param left_margins: A list of :class:`~prompt_toolkit.layout.margins.Margin`
        instance to be displayed on the left. For instance:
        :class:`~prompt_toolkit.layout.margins.NumberredMargin` can be one of
        them in order to show line numbers.
    :param right_margins: Like `left_margins`, but on the other side.
    :param scroll_offsets: :class:`.ScrollOffsets` instance, representing the
        preferred amount of lines/columns to be always visible before/after the
        cursor. When both top and bottom are a very high number, the cursor
        will be centered vertically most of the time.
    :param allow_scroll_beyond_bottom: A `bool` or
        :class:`~prompt_toolkit.filters.CLIFilter` instance. When True, allow
        scrolling so far, that the top part of the content is not visible
        anymore, while there is still empty space available at the bottom of
        the window. In the Vi editor for instance, this is possible. You will
        see tildes while the top part of the body is hidden.
    :param wrap_lines: A `bool` or :class:`~prompt_toolkit.filters.CLIFilter`
        instance. When True, don't scroll horizontally, but wrap lines instead.
    :param get_vertical_scroll: Callable that takes this window
        instance as input and returns a preferred vertical scroll.
        (When this is `None`, the scroll is only determined by the last and
        current cursor position.)
    :param get_horizontal_scroll: Callable that takes this window
        instance as input and returns a preferred vertical scroll.
    :param always_hide_cursor: A `bool` or
        :class:`~prompt_toolkit.filters.CLIFilter` instance. When True, never
        display the cursor, even when the user control specifies a cursor
        position.
    :param cursorline: A `bool` or :class:`~prompt_toolkit.filters.CLIFilter`
        instance. When True, display a cursorline.
    :param cursorcolumn: A `bool` or :class:`~prompt_toolkit.filters.CLIFilter`
        instance. When True, display a cursorcolumn.
    :param get_colorcolumns: A callable that takes a `CommandLineInterface` and
        returns a a list of :class:`.ColorColumn` instances that describe the
        columns to be highlighted.
    :param cursorline_token: The token to be used for highlighting the current line,
        if `cursorline` is True.
    :param cursorcolumn_token: The token to be used for highlighting the current line,
        if `cursorcolumn` is True.
    """
    def __init__(self, content, width=None, height=None, get_width=None,
                 get_height=None, dont_extend_width=False, dont_extend_height=False,
                 left_margins=None, right_margins=None, scroll_offsets=None,
                 allow_scroll_beyond_bottom=False, wrap_lines=False,
                 get_vertical_scroll=None, get_horizontal_scroll=None, always_hide_cursor=False,
                 cursorline=False, cursorcolumn=False, get_colorcolumns=None,
                 cursorline_token=Token.CursorLine, cursorcolumn_token=Token.CursorColumn):
        assert isinstance(content, UIControl)
        assert width is None or isinstance(width, LayoutDimension)
        assert height is None or isinstance(height, LayoutDimension)
        assert get_width is None or callable(get_width)
        assert get_height is None or callable(get_height)
        assert width is None or get_width is None
        assert height is None or get_height is None
        assert scroll_offsets is None or isinstance(scroll_offsets, ScrollOffsets)
        assert left_margins is None or all(isinstance(m, Margin) for m in left_margins)
        assert right_margins is None or all(isinstance(m, Margin) for m in right_margins)
        assert get_vertical_scroll is None or callable(get_vertical_scroll)
        assert get_horizontal_scroll is None or callable(get_horizontal_scroll)
        assert get_colorcolumns is None or callable(get_colorcolumns)

        self.allow_scroll_beyond_bottom = to_cli_filter(allow_scroll_beyond_bottom)
        self.always_hide_cursor = to_cli_filter(always_hide_cursor)
        self.wrap_lines = to_cli_filter(wrap_lines)
        self.cursorline = to_cli_filter(cursorline)
        self.cursorcolumn = to_cli_filter(cursorcolumn)

        self.content = content
        self.dont_extend_width = dont_extend_width
        self.dont_extend_height = dont_extend_height
        self.left_margins = left_margins or []
        self.right_margins = right_margins or []
        self.scroll_offsets = scroll_offsets or ScrollOffsets()
        self.get_vertical_scroll = get_vertical_scroll
        self.get_horizontal_scroll = get_horizontal_scroll
        self._width = get_width or (lambda cli: width)
        self._height = get_height or (lambda cli: height)
        self.get_colorcolumns = get_colorcolumns or (lambda cli: [])
        self.cursorline_token = cursorline_token
        self.cursorcolumn_token = cursorcolumn_token

        # Cache for the screens generated by the margin.
        self._ui_content_cache = SimpleCache(maxsize=8)
        self._margin_width_cache = SimpleCache(maxsize=1)

        self.reset()

    def __repr__(self):
        return 'Window(content=%r)' % self.content

    def reset(self):
        self.content.reset()

        #: Scrolling position of the main content.
        self.vertical_scroll = 0
        self.horizontal_scroll = 0

        # Vertical scroll 2: this is the vertical offset that a line is
        # scrolled if a single line (the one that contains the cursor) consumes
        # all of the vertical space.
        self.vertical_scroll_2 = 0

        #: Keep render information (mappings between buffer input and render
        #: output.)
        self.render_info = None

    def _get_margin_width(self, cli, margin):
        """
        Return the width for this margin.
        (Calculate only once per render time.)
        """
        # Margin.get_width, needs to have a UIContent instance.
        def get_ui_content():
            return self._get_ui_content(cli, width=0, height=0)

        def get_width():
            return margin.get_width(cli, get_ui_content)

        key = (margin, cli.render_counter)
        return self._margin_width_cache.get(key, get_width)

    def preferred_width(self, cli, max_available_width):
        # Calculate the width of the margin.
        total_margin_width = sum(self._get_margin_width(cli, m) for m in
                                 self.left_margins + self.right_margins)

        # Window of the content. (Can be `None`.)
        preferred_width = self.content.preferred_width(
            cli, max_available_width - total_margin_width)

        if preferred_width is not None:
            # Include width of the margins.
            preferred_width += total_margin_width

        # Merge.
        return self._merge_dimensions(
            dimension=self._width(cli),
            preferred=preferred_width,
            dont_extend=self.dont_extend_width)

    def preferred_height(self, cli, width, max_available_height):
        total_margin_width = sum(self._get_margin_width(cli, m) for m in
                                 self.left_margins + self.right_margins)
        wrap_lines = self.wrap_lines(cli)

        return self._merge_dimensions(
            dimension=self._height(cli),
            preferred=self.content.preferred_height(
                cli, width - total_margin_width, max_available_height, wrap_lines),
            dont_extend=self.dont_extend_height)

    @staticmethod
    def _merge_dimensions(dimension, preferred=None, dont_extend=False):
        """
        Take the LayoutDimension from this `Window` class and the received
        preferred size from the `UIControl` and return a `LayoutDimension` to
        report to the parent container.
        """
        dimension = dimension or LayoutDimension()

        # When a preferred dimension was explicitly given to the Window,
        # ignore the UIControl.
        if dimension.preferred_specified:
            preferred = dimension.preferred

        # When a 'preferred' dimension is given by the UIControl, make sure
        # that it stays within the bounds of the Window.
        if preferred is not None:
            if dimension.max:
                preferred = min(preferred, dimension.max)

            if dimension.min:
                preferred = max(preferred, dimension.min)

        # When a `dont_extend` flag has been given, use the preferred dimension
        # also as the max dimension.
        if dont_extend and preferred is not None:
            max_ = min(dimension.max, preferred)
        else:
            max_ = dimension.max

        return LayoutDimension(
            min=dimension.min, max=max_,
            preferred=preferred, weight=dimension.weight)

    def _get_ui_content(self, cli, width, height):
        """
        Create a `UIContent` instance.
        """
        def get_content():
            return self.content.create_content(cli, width=width, height=height)

        key = (cli.render_counter, width, height)
        return self._ui_content_cache.get(key, get_content)

    def _get_digraph_char(self, cli):
        " Return `False`, or the Digraph symbol to be used. "
        if cli.quoted_insert:
            return '^'
        if cli.vi_state.waiting_for_digraph:
            if cli.vi_state.digraph_symbol1:
                return cli.vi_state.digraph_symbol1
            return '?'
        return False

    def write_to_screen(self, cli, screen, mouse_handlers, write_position):
        """
        Write window to screen. This renders the user control, the margins and
        copies everything over to the absolute position at the given screen.
        """
        # Calculate margin sizes.
        left_margin_widths = [self._get_margin_width(cli, m) for m in self.left_margins]
        right_margin_widths = [self._get_margin_width(cli, m) for m in self.right_margins]
        total_margin_width = sum(left_margin_widths + right_margin_widths)

        # Render UserControl.
        ui_content = self.content.create_content(
            cli, write_position.width - total_margin_width, write_position.height)
        assert isinstance(ui_content, UIContent)

        # Scroll content.
        wrap_lines = self.wrap_lines(cli)
        scroll_func = self._scroll_when_linewrapping if wrap_lines else self._scroll_without_linewrapping

        scroll_func(
            ui_content, write_position.width - total_margin_width, write_position.height, cli)

        # Write body
        visible_line_to_row_col, rowcol_to_yx = self._copy_body(
            cli, ui_content, screen, write_position,
            sum(left_margin_widths), write_position.width - total_margin_width,
            self.vertical_scroll, self.horizontal_scroll,
            has_focus=self.content.has_focus(cli),
            wrap_lines=wrap_lines, highlight_lines=True,
            vertical_scroll_2=self.vertical_scroll_2,
            always_hide_cursor=self.always_hide_cursor(cli))

        # Remember render info. (Set before generating the margins. They need this.)
        x_offset=write_position.xpos + sum(left_margin_widths)
        y_offset=write_position.ypos

        self.render_info = WindowRenderInfo(
            ui_content=ui_content,
            horizontal_scroll=self.horizontal_scroll,
            vertical_scroll=self.vertical_scroll,
            window_width=write_position.width - total_margin_width,
            window_height=write_position.height,
            configured_scroll_offsets=self.scroll_offsets,
            visible_line_to_row_col=visible_line_to_row_col,
            rowcol_to_yx=rowcol_to_yx,
            x_offset=x_offset,
            y_offset=y_offset,
            wrap_lines=wrap_lines)

        # Set mouse handlers.
        def mouse_handler(cli, mouse_event):
            """ Wrapper around the mouse_handler of the `UIControl` that turns
            screen coordinates into line coordinates. """
            # Find row/col position first.
            yx_to_rowcol = dict((v, k) for k, v in rowcol_to_yx.items())
            y = mouse_event.position.y
            x = mouse_event.position.x

            # If clicked below the content area, look for a position in the
            # last line instead.
            max_y = write_position.ypos + len(visible_line_to_row_col) - 1
            y = min(max_y, y)

            while x >= 0:
                try:
                    row, col = yx_to_rowcol[y, x]
                except KeyError:
                    # Try again. (When clicking on the right side of double
                    # width characters, or on the right side of the input.)
                    x -= 1
                else:
                    # Found position, call handler of UIControl.
                    result = self.content.mouse_handler(
                        cli, MouseEvent(position=Point(x=col, y=row),
                                        event_type=mouse_event.event_type))
                    break
            else:
                # nobreak.
                # (No x/y coordinate found for the content. This happens in
                # case of a FillControl, that only specifies a background, but
                # doesn't have a content. Report (0,0) instead.)
                result = self.content.mouse_handler(
                    cli, MouseEvent(position=Point(x=0, y=0),
                                    event_type=mouse_event.event_type))

            # If it returns NotImplemented, handle it here.
            if result == NotImplemented:
                return self._mouse_handler(cli, mouse_event)

            return result

        mouse_handlers.set_mouse_handler_for_range(
            x_min=write_position.xpos + sum(left_margin_widths),
            x_max=write_position.xpos + write_position.width - total_margin_width,
            y_min=write_position.ypos,
            y_max=write_position.ypos + write_position.height,
            handler=mouse_handler)

        # Render and copy margins.
        move_x = 0

        def render_margin(m, width):
            " Render margin. Return `Screen`. "
            # Retrieve margin tokens.
            tokens = m.create_margin(cli, self.render_info, width, write_position.height)

            # Turn it into a UIContent object.
            # already rendered those tokens using this size.)
            return TokenListControl.static(tokens).create_content(
                cli, width + 1, write_position.height)

        for m, width in zip(self.left_margins, left_margin_widths):
            # Create screen for margin.
            margin_screen = render_margin(m, width)

            # Copy and shift X.
            self._copy_margin(cli, margin_screen, screen, write_position, move_x, width)
            move_x += width

        move_x = write_position.width - sum(right_margin_widths)

        for m, width in zip(self.right_margins, right_margin_widths):
            # Create screen for margin.
            margin_screen = render_margin(m, width)

            # Copy and shift X.
            self._copy_margin(cli, margin_screen, screen, write_position, move_x, width)
            move_x += width

    def _copy_body(self, cli, ui_content, new_screen, write_position, move_x,
                   width, vertical_scroll=0, horizontal_scroll=0,
                   has_focus=False, wrap_lines=False, highlight_lines=False,
                   vertical_scroll_2=0, always_hide_cursor=False):
        """
        Copy the UIContent into the output screen.
        """
        xpos = write_position.xpos + move_x
        ypos = write_position.ypos
        line_count = ui_content.line_count
        new_buffer = new_screen.data_buffer
        empty_char = _CHAR_CACHE['', Token]
        ZeroWidthEscape = Token.ZeroWidthEscape

        # Map visible line number to (row, col) of input.
        # 'col' will always be zero if line wrapping is off.
        visible_line_to_row_col = {}
        rowcol_to_yx = {}  # Maps (row, col) from the input to (y, x) screen coordinates.

        # Fill background with default_char first.
        default_char = ui_content.default_char

        if default_char:
            for y in range(ypos, ypos + write_position.height):
                new_buffer_row = new_buffer[y]
                for x in range(xpos, xpos + width):
                    new_buffer_row[x] = default_char

        # Copy content.
        def copy():
            y = - vertical_scroll_2
            lineno = vertical_scroll

            while y < write_position.height and lineno < line_count:
                # Take the next line and copy it in the real screen.
                line = ui_content.get_line(lineno)

                col = 0
                x = -horizontal_scroll

                visible_line_to_row_col[y] = (lineno, horizontal_scroll)
                new_buffer_row = new_buffer[y + ypos]

                for token, text in line:
                    # Remember raw VT escape sequences. (E.g. FinalTerm's
                    # escape sequences.)
                    if token == ZeroWidthEscape:
                        new_screen.zero_width_escapes[y + ypos][x + xpos] += text
                        continue

                    for c in text:
                        char = _CHAR_CACHE[c, token]
                        char_width = char.width

                        # Wrap when the line width is exceeded.
                        if wrap_lines and x + char_width > width:
                            visible_line_to_row_col[y + 1] = (
                                lineno, visible_line_to_row_col[y][1] + x)
                            y += 1
                            x = -horizontal_scroll  # This would be equal to zero.
                                                    # (horizontal_scroll=0 when wrap_lines.)
                            new_buffer_row = new_buffer[y + ypos]

                            if y >= write_position.height:
                                return y  # Break out of all for loops.

                        # Set character in screen and shift 'x'.
                        if x >= 0 and y >= 0 and x < write_position.width:
                            new_buffer_row[x + xpos] = char

                            # When we print a multi width character, make sure
                            # to erase the neighbous positions in the screen.
                            # (The empty string if different from everything,
                            # so next redraw this cell will repaint anyway.)
                            if char_width > 1:
                                for i in range(1, char_width):
                                    new_buffer_row[x + xpos + i] = empty_char

                            # If this is a zero width characters, then it's
                            # probably part of a decomposed unicode character.
                            # See: https://en.wikipedia.org/wiki/Unicode_equivalence
                            # Merge it in the previous cell.
                            elif char_width == 0 and x - 1 >= 0:
                                prev_char = new_buffer_row[x + xpos - 1]
                                char2 = _CHAR_CACHE[prev_char.char + c, prev_char.token]
                                new_buffer_row[x + xpos - 1] = char2

                            # Keep track of write position for each character.
                            rowcol_to_yx[lineno, col] = (y + ypos, x + xpos)

                        col += 1
                        x += char_width

                lineno += 1
                y += 1
            return y

        y = copy()

        def cursor_pos_to_screen_pos(row, col):
            " Translate row/col from UIContent to real Screen coordinates. "
            try:
                y, x = rowcol_to_yx[row, col]
            except KeyError:
                # Normally this should never happen. (It is a bug, if it happens.)
                # But to be sure, return (0, 0)
                return Point(y=0, x=0)

                # raise ValueError(
                #     'Invalid position. row=%r col=%r, vertical_scroll=%r, '
                #     'horizontal_scroll=%r, height=%r' %
                #     (row, col, vertical_scroll, horizontal_scroll, write_position.height))
            else:
                return Point(y=y, x=x)

        # Set cursor and menu positions.
        if ui_content.cursor_position:
            screen_cursor_position = cursor_pos_to_screen_pos(
                    ui_content.cursor_position.y, ui_content.cursor_position.x)

            if has_focus:
                new_screen.cursor_position = screen_cursor_position

                if always_hide_cursor:
                    new_screen.show_cursor = False
                else:
                    new_screen.show_cursor = ui_content.show_cursor

                self._highlight_digraph(cli, new_screen)

            if highlight_lines:
                self._highlight_cursorlines(
                    cli, new_screen, screen_cursor_position, xpos, ypos, width,
                    write_position.height)

        # Draw input characters from the input processor queue.
        if has_focus and ui_content.cursor_position:
            self._show_input_processor_key_buffer(cli, new_screen)

        # Set menu position.
        if not new_screen.menu_position and ui_content.menu_position:
            new_screen.menu_position = cursor_pos_to_screen_pos(
                    ui_content.menu_position.y, ui_content.menu_position.x)

        # Update output screne height.
        new_screen.height = max(new_screen.height, ypos + write_position.height)

        return visible_line_to_row_col, rowcol_to_yx

    def _highlight_digraph(self, cli, new_screen):
        """
        When we are in Vi digraph mode, put a question mark underneath the
        cursor.
        """
        digraph_char = self._get_digraph_char(cli)
        if digraph_char:
            cpos = new_screen.cursor_position
            new_screen.data_buffer[cpos.y][cpos.x] = \
                _CHAR_CACHE[digraph_char, Token.Digraph]

    def _show_input_processor_key_buffer(self, cli, new_screen):
        """
        When the user is typing a key binding that consists of several keys,
        display the last pressed key if the user is in insert mode and the key
        is meaningful to be displayed.
        E.g. Some people want to bind 'jj' to escape in Vi insert mode. But the
             first 'j' needs to be displayed in order to get some feedback.
        """
        key_buffer = cli.input_processor.key_buffer

        if key_buffer and _in_insert_mode(cli) and not cli.is_done:
            # The textual data for the given key. (Can be a VT100 escape
            # sequence.)
            data = key_buffer[-1].data

            # Display only if this is a 1 cell width character.
            if get_cwidth(data) == 1:
                cpos = new_screen.cursor_position
                new_screen.data_buffer[cpos.y][cpos.x] = \
                    _CHAR_CACHE[data, Token.PartialKeyBinding]

    def _highlight_cursorlines(self, cli, new_screen, cpos, x, y, width, height):
        """
        Highlight cursor row/column.
        """
        cursor_line_token = (':', ) + self.cursorline_token
        cursor_column_token = (':', ) + self.cursorcolumn_token

        data_buffer = new_screen.data_buffer

        # Highlight cursor line.
        if self.cursorline(cli):
            row = data_buffer[cpos.y]
            for x in range(x, x + width):
                original_char = row[x]
                row[x] = _CHAR_CACHE[
                    original_char.char, original_char.token + cursor_line_token]

        # Highlight cursor column.
        if self.cursorcolumn(cli):
            for y2 in range(y, y + height):
                row = data_buffer[y2]
                original_char = row[cpos.x]
                row[cpos.x] = _CHAR_CACHE[
                   original_char.char, original_char.token + cursor_column_token]

        # Highlight color columns
        for cc in self.get_colorcolumns(cli):
            assert isinstance(cc, ColorColumn)
            color_column_token = (':', ) + cc.token
            column = cc.position

            for y2 in range(y, y + height):
                row = data_buffer[y2]
                original_char = row[column]
                row[column] = _CHAR_CACHE[
                   original_char.char, original_char.token + color_column_token]

    def _copy_margin(self, cli, lazy_screen, new_screen, write_position, move_x, width):
        """
        Copy characters from the margin screen to the real screen.
        """
        xpos = write_position.xpos + move_x
        ypos = write_position.ypos

        margin_write_position = WritePosition(xpos, ypos, width, write_position.height)
        self._copy_body(cli, lazy_screen, new_screen, margin_write_position, 0, width)

    def _scroll_when_linewrapping(self, ui_content, width, height, cli):
        """
        Scroll to make sure the cursor position is visible and that we maintain
        the requested scroll offset.

        Set `self.horizontal_scroll/vertical_scroll`.
        """
        scroll_offsets_bottom = self.scroll_offsets.bottom
        scroll_offsets_top = self.scroll_offsets.top

        # We don't have horizontal scrolling.
        self.horizontal_scroll = 0

        # If the current line consumes more than the whole window height,
        # then we have to scroll vertically inside this line. (We don't take
        # the scroll offsets into account for this.)
        # Also, ignore the scroll offsets in this case. Just set the vertical
        # scroll to this line.
        if ui_content.get_height_for_line(ui_content.cursor_position.y, width) > height - scroll_offsets_top:
            # Calculate the height of the text before the cursor, with the line
            # containing the cursor included, and the character belowe the
            # cursor included as well.
            line = explode_tokens(ui_content.get_line(ui_content.cursor_position.y))
            text_before_cursor = token_list_to_text(line[:ui_content.cursor_position.x + 1])
            text_before_height = UIContent.get_height_for_text(text_before_cursor, width)

            # Adjust scroll offset.
            self.vertical_scroll = ui_content.cursor_position.y
            self.vertical_scroll_2 = min(text_before_height - 1, self.vertical_scroll_2)
            self.vertical_scroll_2 = max(0, text_before_height - height, self.vertical_scroll_2)
            return
        else:
            self.vertical_scroll_2 = 0

        # Current line doesn't consume the whole height. Take scroll offsets into account.
        def get_min_vertical_scroll():
            # Make sure that the cursor line is not below the bottom.
            # (Calculate how many lines can be shown between the cursor and the .)
            used_height = 0
            prev_lineno = ui_content.cursor_position.y

            for lineno in range(ui_content.cursor_position.y, -1, -1):
                used_height += ui_content.get_height_for_line(lineno, width)

                if used_height > height - scroll_offsets_bottom:
                    return prev_lineno
                else:
                    prev_lineno = lineno
            return 0

        def get_max_vertical_scroll():
            # Make sure that the cursor line is not above the top.
            prev_lineno = ui_content.cursor_position.y
            used_height = 0

            for lineno in range(ui_content.cursor_position.y - 1, -1, -1):
                used_height += ui_content.get_height_for_line(lineno, width)

                if used_height > scroll_offsets_top:
                    return prev_lineno
                else:
                    prev_lineno = lineno
            return prev_lineno

        def get_topmost_visible():
            """
            Calculate the upper most line that can be visible, while the bottom
            is still visible. We should not allow scroll more than this if
            `allow_scroll_beyond_bottom` is false.
            """
            prev_lineno = ui_content.line_count - 1
            used_height = 0
            for lineno in range(ui_content.line_count - 1, -1, -1):
                used_height += ui_content.get_height_for_line(lineno, width)
                if used_height > height:
                    return prev_lineno
                else:
                    prev_lineno = lineno
            return prev_lineno

        # Scroll vertically. (Make sure that the whole line which contains the
        # cursor is visible.
        topmost_visible = get_topmost_visible()

            # Note: the `min(topmost_visible, ...)` is to make sure that we
            # don't require scrolling up because of the bottom scroll offset,
            # when we are at the end of the document.
        self.vertical_scroll = max(self.vertical_scroll, min(topmost_visible, get_min_vertical_scroll()))
        self.vertical_scroll = min(self.vertical_scroll, get_max_vertical_scroll())

        # Disallow scrolling beyond bottom?
        if not self.allow_scroll_beyond_bottom(cli):
            self.vertical_scroll = min(self.vertical_scroll, topmost_visible)

    def _scroll_without_linewrapping(self, ui_content, width, height, cli):
        """
        Scroll to make sure the cursor position is visible and that we maintain
        the requested scroll offset.

        Set `self.horizontal_scroll/vertical_scroll`.
        """
        cursor_position = ui_content.cursor_position or Point(0, 0)

        # Without line wrapping, we will never have to scroll vertically inside
        # a single line.
        self.vertical_scroll_2 = 0

        if ui_content.line_count == 0:
            self.vertical_scroll = 0
            self.horizontal_scroll = 0
            return
        else:
            current_line_text = token_list_to_text(ui_content.get_line(cursor_position.y))

        def do_scroll(current_scroll, scroll_offset_start, scroll_offset_end,
                      cursor_pos, window_size, content_size):
            " Scrolling algorithm. Used for both horizontal and vertical scrolling. "
            # Calculate the scroll offset to apply.
            # This can obviously never be more than have the screen size. Also, when the
            # cursor appears at the top or bottom, we don't apply the offset.
            scroll_offset_start = int(min(scroll_offset_start, window_size / 2, cursor_pos))
            scroll_offset_end = int(min(scroll_offset_end, window_size / 2,
                                        content_size - 1 - cursor_pos))

            # Prevent negative scroll offsets.
            if current_scroll < 0:
                current_scroll = 0

            # Scroll back if we scrolled to much and there's still space to show more of the document.
            if (not self.allow_scroll_beyond_bottom(cli) and
                    current_scroll > content_size - window_size):
                current_scroll = max(0, content_size - window_size)

            # Scroll up if cursor is before visible part.
            if current_scroll > cursor_pos - scroll_offset_start:
                current_scroll = max(0, cursor_pos - scroll_offset_start)

            # Scroll down if cursor is after visible part.
            if current_scroll < (cursor_pos + 1) - window_size + scroll_offset_end:
                current_scroll = (cursor_pos + 1) - window_size + scroll_offset_end

            return current_scroll

        # When a preferred scroll is given, take that first into account.
        if self.get_vertical_scroll:
            self.vertical_scroll = self.get_vertical_scroll(self)
            assert isinstance(self.vertical_scroll, int)
        if self.get_horizontal_scroll:
            self.horizontal_scroll = self.get_horizontal_scroll(self)
            assert isinstance(self.horizontal_scroll, int)

        # Update horizontal/vertical scroll to make sure that the cursor
        # remains visible.
        offsets = self.scroll_offsets

        self.vertical_scroll = do_scroll(
            current_scroll=self.vertical_scroll,
            scroll_offset_start=offsets.top,
            scroll_offset_end=offsets.bottom,
            cursor_pos=ui_content.cursor_position.y,
            window_size=height,
            content_size=ui_content.line_count)

        self.horizontal_scroll = do_scroll(
            current_scroll=self.horizontal_scroll,
            scroll_offset_start=offsets.left,
            scroll_offset_end=offsets.right,
            cursor_pos=get_cwidth(current_line_text[:ui_content.cursor_position.x]),
            window_size=width,
            # We can only analyse the current line. Calculating the width off
            # all the lines is too expensive.
            content_size=max(get_cwidth(current_line_text), self.horizontal_scroll + width))

    def _mouse_handler(self, cli, mouse_event):
        """
        Mouse handler. Called when the UI control doesn't handle this
        particular event.
        """
        if mouse_event.event_type == MouseEventType.SCROLL_DOWN:
            self._scroll_down(cli)
        elif mouse_event.event_type == MouseEventType.SCROLL_UP:
            self._scroll_up(cli)

    def _scroll_down(self, cli):
        " Scroll window down. "
        info = self.render_info

        if self.vertical_scroll < info.content_height - info.window_height:
            if info.cursor_position.y <= info.configured_scroll_offsets.top:
                self.content.move_cursor_down(cli)

            self.vertical_scroll += 1

    def _scroll_up(self, cli):
        " Scroll window up. "
        info = self.render_info

        if info.vertical_scroll > 0:
            # TODO: not entirely correct yet in case of line wrapping and long lines.
            if info.cursor_position.y >= info.window_height - 1 - info.configured_scroll_offsets.bottom:
                self.content.move_cursor_up(cli)

            self.vertical_scroll -= 1

    def walk(self, cli):
        # Only yield self. A window doesn't have children.
        yield self


class ConditionalContainer(Container):
    """
    Wrapper around any other container that can change the visibility. The
    received `filter` determines whether the given container should be
    displayed or not.

    :param content: :class:`.Container` instance.
    :param filter: :class:`~prompt_toolkit.filters.CLIFilter` instance.
    """
    def __init__(self, content, filter):
        assert isinstance(content, Container)

        self.content = content
        self.filter = to_cli_filter(filter)

    def __repr__(self):
        return 'ConditionalContainer(%r, filter=%r)' % (self.content, self.filter)

    def reset(self):
        self.content.reset()

    def preferred_width(self, cli, max_available_width):
        if self.filter(cli):
            return self.content.preferred_width(cli, max_available_width)
        else:
            return LayoutDimension.exact(0)

    def preferred_height(self, cli, width, max_available_height):
        if self.filter(cli):
            return self.content.preferred_height(cli, width, max_available_height)
        else:
            return LayoutDimension.exact(0)

    def write_to_screen(self, cli, screen, mouse_handlers, write_position):
        if self.filter(cli):
            return self.content.write_to_screen(cli, screen, mouse_handlers, write_position)

    def walk(self, cli):
        return self.content.walk(cli)


# Deprecated alias for 'Container'.
Layout = Container