WeasyPrint/weasyprint/layout/preferred.py

# coding: utf8
"""
    weasyprint.layout.preferred
    ---------------------------

    Preferred and minimum preferred width, aka. the shrink-to-fit algorithm.

    :copyright: Copyright 2011-2012 Simon Sapin and contributors, see AUTHORS.
    :license: BSD, see LICENSE for details.

"""

from __future__ import division, unicode_literals

import cairo

from ..formatting_structure import boxes
from ..text import TextFragment


def shrink_to_fit(box, available_width):
    """Return the shrink-to-fit width of ``box``.

    http://www.w3.org/TR/CSS21/visudet.html#float-width

    """
    return min(
        max(preferred_minimum_width(box, outer=False), available_width),
        preferred_width(box, outer=False))


def preferred_minimum_width(box, outer=True):
    """Return the preferred minimum width for ``box``.

    This is the width by breaking at every line-break opportunity.

    """
    if isinstance(box, boxes.BlockContainerBox):
        if box.is_table_wrapper:
            return table_preferred_minimum_width(box, outer)
        else:
            return block_preferred_minimum_width(box, outer)
    elif isinstance(box, (boxes.InlineBox, boxes.LineBox)):
        return inline_preferred_minimum_width(box, outer)
    else:
        raise TypeError(
            'Preferred minimum width for %s not handled yet' %
            type(box).__name__)


def preferred_width(box, outer=True):
    """Return the preferred width for ``box``.

    This is the width by only breaking at forced line breaks.

    """
    if isinstance(box, boxes.BlockContainerBox):
        if box.is_table_wrapper:
            return table_preferred_width(box, outer)
        else:
            return block_preferred_width(box, outer)
    elif isinstance(box, (boxes.InlineBox, boxes.LineBox)):
        return inline_preferred_width(box, outer)
    else:
        raise TypeError(
            'Preferred width for %s not handled yet' % type(box).__name__)


def _block_preferred_width(box, function, outer):
    """Helper to create ``block_preferred_*_width.``"""
    width = box.style.width
    if width == 'auto' or width.unit == '%':
        # "percentages on the following properties are treated instead as
        #  though they were the following: width: auto"
        # http://dbaron.org/css/intrinsic/#outer-intrinsic
        if box.children:
            width = max(function(child, outer=True) for child in box.children)
        else:
            width = 0
    else:
        assert width.unit == 'px'
        width = width.value

    return adjust(box, outer, width)


def adjust(box, outer, width):
    """Add paddings, borders and margins to ``width`` when ``outer`` is set."""
    if not outer:
        return width

    min_width = box.style.min_width
    max_width = box.style.max_width
    min_width = min_width.value if min_width.unit != '%' else 0
    max_width = max_width.value if max_width.unit != '%' else float('inf')

    fixed = max(min_width, min(width, max_width))
    percentages = 0

    fixed += box.style.border_left_width + box.style.border_right_width
    for value in ('margin_left', 'margin_right',
                  'padding_left', 'padding_right'):
        style_value = box.style[value]
        if style_value != 'auto':
            if style_value.unit == 'px':
                fixed += style_value.value
            else:
                assert style_value.unit == '%'
                percentages += style_value.value

    if percentages < 1:
        return fixed / (1 - percentages / 100.)
    else:
        # Pathological case, ignore
        return 0


def block_preferred_minimum_width(box, outer=True):
    """Return the preferred minimum width for a ``BlockBox``."""
    return _block_preferred_width(box, preferred_minimum_width, outer)


def block_preferred_width(box, outer=True):
    """Return the preferred width for a ``BlockBox``."""
    return _block_preferred_width(box, preferred_width, outer)


def inline_preferred_minimum_width(box, outer=True):
    """Return the preferred minimum width for an ``InlineBox``."""
    widest_line = 0
    for child in box.children:
        if isinstance(child, boxes.InlineReplacedBox):
            # Images are on their own line
            current_line = replaced_preferred_width(child)
        elif isinstance(child, boxes.InlineBlockBox):
            current_line = block_preferred_minimum_width(child)
        elif isinstance(child, boxes.InlineBox):
            # TODO: handle forced line breaks
            current_line = inline_preferred_minimum_width(child)
        else:
            assert isinstance(child, boxes.TextBox)
            current_line = max(text_lines_width(child, width=0))
        widest_line = max(widest_line, current_line)
    return widest_line


def inline_preferred_width(box, outer=True):
    """Return the preferred width for an ``InlineBox``."""
    widest_line = 0
    current_line = 0
    for child in box.children:
        if isinstance(child, boxes.InlineReplacedBox):
            # No line break around images
            current_line += replaced_preferred_width(child)
        elif isinstance(child, boxes.InlineBlockBox):
            current_line += block_preferred_width(child)
        elif isinstance(child, boxes.InlineBox):
            # TODO: handle forced line breaks
            current_line += inline_preferred_width(child)
        else:
            assert isinstance(child, boxes.TextBox)
            lines = list(text_lines_width(child, width=None))
            assert lines
            # The first text line goes on the current line
            current_line += lines[0]
            if len(lines) > 1:
                # Forced line break
                widest_line = max(widest_line, current_line)
                if len(lines) > 2:
                    widest_line = max(widest_line, max(lines[1:-1]))
                current_line = lines[-1]
    widest_line = max(widest_line, current_line)

    return adjust(box, outer, widest_line)


def table_and_columns_preferred_widths(box, outer=True):
    """Return preferred widths for the table and its columns.

    The tuple returned is
    ``(table_preferred_minimum_width, table_preferred_width,
    column_preferred_minimum_widths, column_preferred_widths)``

    """
    table = box.get_wrapped_table()

    nb_columns = 0
    rows = []
    for i, row_group in enumerate(table.children):
        assert isinstance(row_group, boxes.TableRowGroupBox)
        for j, row in enumerate(row_group.children):
            assert isinstance(row, boxes.TableRowBox)
            rows.append(row)
            for k, cell in enumerate(row.children):
                assert isinstance(cell, boxes.TableCellBox)
                nb_columns = max(nb_columns, k + cell.colspan)
    nb_rows = len(rows)

    colspan_cells = []
    grid = [[None] * nb_columns for i in range(nb_rows)]
    for i, row in enumerate(rows):
        for cell in row.children:
            if cell.colspan == 1:
                grid[i][cell.grid_x] = cell
            else:
                cell.grid_y = i
                colspan_cells.append(cell)

    # Point #1
    column_preferred_widths = [[0] * nb_rows for i in range(nb_columns)]
    column_preferred_minimum_widths = [
        [0] * nb_rows for i in range(nb_columns)]
    for i, row in enumerate(grid):
        for j, cell in enumerate(row):
            if cell:
                # TODO: when border-collapse: collapse; set outer=False
                column_preferred_widths[j][i] = \
                    preferred_width(cell)
                column_preferred_minimum_widths[j][i] = \
                    preferred_minimum_width(cell)

    column_preferred_widths = [
        max(widths) for widths in column_preferred_widths]
    column_preferred_minimum_widths = [
        max(widths) for widths in column_preferred_minimum_widths]

    # Point #2
    column_groups_widths = []
    column_widths = [None] * nb_columns
    for column_group in table.column_groups:
        assert isinstance(column_group, boxes.TableColumnGroupBox)
        column_groups_widths.append((column_group, column_group.style.width))
        for column in column_group.children:
            assert isinstance(column, boxes.TableColumnBox)
            column_widths[column.grid_x] = column.style.width

    # TODO: handle percentages for column widths
    if column_widths:
        for widths in (column_preferred_widths,
                       column_preferred_minimum_widths):
            for i, width in enumerate(widths):
                column_width = column_widths[i]
                if (column_width and column_width != 'auto' and
                    column_width.unit != '%'):
                    widths[i] = max(column_width.value, widths[i])

    # Point #3
    for cell in colspan_cells:
        column_slice = slice(cell.grid_x, cell.grid_x + cell.colspan)

        # TODO: when border-collapse: collapse; set outer=False
        cell_width = preferred_width(cell)
        columns_width = sum(column_preferred_widths[column_slice])
        if cell_width > columns_width:
            added_space = (cell_width - columns_width) / cell.colspan
            for i in range(cell.grid_x, cell.grid_x + cell.colspan):
                column_preferred_widths[i] += added_space

        # TODO: when border-collapse: collapse; set outer=False
        cell_minimum_width = preferred_minimum_width(cell)
        columns_minimum_width = sum(
            column_preferred_minimum_widths[column_slice])
        if cell_minimum_width > columns_minimum_width:
            added_space = (
                (cell_minimum_width - columns_minimum_width) / cell.colspan)
            for i in range(cell.grid_x, cell.grid_x + cell.colspan):
                column_preferred_minimum_widths[i] += added_space

    # Point #4
    for column_group, column_group_width in column_groups_widths:
        # TODO: handle percentages for column group widths
        if (column_group_width and column_group_width != 'auto' and
            column_group_width.unit != '%'):
            column_indexes = [
                column.grid_x for column in column_group.children]
            columns_width = sum(
                column_preferred_minimum_widths[index]
                for index in column_indexes)
            column_group_width = column_group_width.value
            if column_group_width > columns_width:
                added_space = (
                    (column_group_width - columns_width) / len(column_indexes))
                for i in column_indexes:
                    column_preferred_minimum_widths[i] += added_space
                    # The spec seems to say that the colgroup's width is just a
                    # hint for column group's columns minimum width, but if the
                    # sum of the preferred maximum width of the colums is lower
                    # or greater than the colgroup's one, then the columns
                    # don't follow the hint. These lines make the preferred
                    # width equal or greater than the minimum preferred width.
                    if (column_preferred_widths[i] <
                        column_preferred_minimum_widths[i]):
                        column_preferred_widths[i] = \
                            column_preferred_minimum_widths[i]

    total_border_spacing = (nb_columns + 1) * table.style.border_spacing[0]
    table_preferred_minimum_width = (
        sum(column_preferred_minimum_widths) + total_border_spacing)
    table_preferred_width = sum(column_preferred_widths) + total_border_spacing

    return (
        table_preferred_minimum_width, table_preferred_width,
        column_preferred_minimum_widths, column_preferred_widths)


def table_preferred_minimum_width(box, outer=True):
    """Return the preferred minimum width for a ``TableBox``. wrapper"""
    minimum_width, _, _, _ = table_and_columns_preferred_widths(box)
    return adjust(box, outer, minimum_width)


def table_preferred_width(box, outer=True):
    """Return the preferred width for a ``TableBox`` wrapper."""
    _, width, _, _ = table_and_columns_preferred_widths(box)
    return adjust(box, outer, width)


def text_lines_width(box, width):
    """Return the list of line widths for a ``TextBox``."""
    # TODO: find the real surface, to have correct hinting
    context = cairo.Context(cairo.PDFSurface(None, 1, 1))
    fragment = TextFragment(box.text, box.style, context, width=width)
    return fragment.line_widths()


def replaced_preferred_width(box, outer=True):
    """Return the preferred minimum width for an ``InlineReplacedBox``."""
    width = box.style.width
    if width == 'auto' or width.unit == '%':
        # TODO: handle the images with no intinsic width
        _, width, _ = box.replacement
    else:
        assert width.unit == 'px'
        width = width.value
    return adjust(box, outer, width)