WeasyPrint/weasy/layout/tables.py

# coding: utf8

#  WeasyPrint converts web documents (HTML, CSS, ...) to PDF.
#  Copyright (C) 2011  Simon Sapin
#
#  This program is free software: you can redistribute it and/or modify
#  it under the terms of the GNU Affero General Public License as
#  published by the Free Software Foundation, either version 3 of the
#  License, or (at your option) any later version.
#
#  This program 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 Affero General Public License for more details.
#
#  You should have received a copy of the GNU Affero General Public License
#  along with this program.  If not, see <http://www.gnu.org/licenses/>.

"""
Functions laying out tables.

"""

from __future__ import division

from ..formatting_structure import boxes
from .percentages import resolve_percentages, resolve_one_percentage


def table_layout(table, max_position_y, containing_block, device_size,
                 page_is_empty):
    """Layout for a table box.

    For now only the fixed layout and separate border model are supported.

    """
    # Avoid a circular import
    from .blocks import block_level_height

    column_widths = fixed_table_layout(table)

    border_spacing_x, border_spacing_y = table.style.border_spacing
    # TODO: revert this for direction: rtl
    column_positions = []
    position_x = table.content_box_x()
    rows_x = position_x + border_spacing_x
    for width in column_widths:
        position_x += border_spacing_x
        column_positions.append(position_x)
        position_x += width
    rows_width = position_x - rows_x

    # Layout for row groups, rows and cells
    position_y = table.content_box_y() + border_spacing_y
    initial_position_y = position_y
    new_table_children = []
    for group in table.children:
        resolve_percentages(group, containing_block=table)
        group.position_x = rows_x
        group.position_y = position_y
        group.width = rows_width
        new_group_children = []
        # For each rows, cells for which this is the last row (with rowspan)
        ending_cells_by_row = [[] for row in group.children]
        for row in group.children:
            resolve_percentages(row, containing_block=table)
            row.position_x = rows_x
            row.position_y = position_y
            row.width = rows_width
            # Place cells at the top of the row and layout their content
            new_row_children = []
            for cell in row.children:
                resolve_percentages(cell, containing_block=table)
                cell.position_x = column_positions[cell.grid_x]
                cell.position_y = row.position_y
                cell.margin_top = 0
                cell.margin_left = 0
                cell.width = 0
                borders_plus_padding = cell.border_width()  # with width==0
                cell.width = (
                    sum(column_widths[cell.grid_x:cell.grid_x + cell.colspan])
                    + border_spacing_x * (cell.colspan - 1)
                    - borders_plus_padding)
                # The computed height is a minimum
                computed_cell_height = cell.height
                cell.height = 'auto'
                cell, _ = block_level_height(cell,
                    max_position_y=float('inf'),
                    skip_stack=None,
                    device_size=device_size,
                    page_is_empty=True)
                if computed_cell_height != 'auto':
                    cell.height = max(cell.height, computed_cell_height)
                new_row_children.append(cell)

            row = row.copy_with_children(new_row_children)
            new_group_children.append(row)

            # Table height algorithm
            # http://www.w3.org/TR/CSS21/tables.html#height-layout

            # cells with vertical-align: baseline
            baseline_cells = []
            for cell in row.children:
                vertical_align = cell.style.vertical_align
                if vertical_align in ('top', 'middle', 'bottom'):
                    cell.vertical_align = vertical_align
                else:
                    # Assume 'baseline' for any other value
                    cell.vertical_align = 'baseline'
                    cell.baseline = cell_baseline(cell)
                    baseline_cells.append(cell)
            if baseline_cells:
                row.baseline = max(cell.baseline for cell in baseline_cells)
                for cell in baseline_cells:
                    if cell.baseline != row.baseline:
                        add_top_padding(cell, row.baseline - cell.baseline)
            else:
                row.baseline = None

            # row height
            for cell in row.children:
                ending_cells_by_row[cell.rowspan - 1].append(cell)
            ending_cells = ending_cells_by_row.pop(0)
            if ending_cells:  # in this row
                row_bottom_y = max(
                    cell.position_y + cell.border_height()
                    for cell in ending_cells)
                row.height = row_bottom_y - row.position_y
            else:
                row_bottom_y = row.position_y
                row.height = 0

            # Add extra padding to make the cells the same height as the row
            for cell in ending_cells:
                cell_bottom_y = cell.position_y + cell.border_height()
                extra = row_bottom_y - cell_bottom_y
                if cell.vertical_align == 'bottom':
                    add_top_padding(cell, extra)
                elif cell.vertical_align == 'middle':
                    extra /= 2.
                    add_top_padding(cell, extra)
                    cell.padding_bottom += extra
                else:
                    cell.padding_bottom += extra

            position_y += row.height + border_spacing_y

        group = group.copy_with_children(new_group_children)
        new_table_children.append(group)

        # Set missing baselines in a second loop because of rowspan
        for row in group.children:
            if row.baseline is None:
                if row.children:
                    # lowest bottom content edge
                    row.baseline = row.position_y - max(
                        cell.content_box_y() + cell.height
                        for cell in row.children)
                else:
                    row.baseline = 0
        group.height = position_y - group.position_y
        if group.children:
            # The last border spacing is outside of the group.
            group.height -= border_spacing_y
    table = table.copy_with_children(new_table_children)

    # If the height property has a bigger value, just add blank space
    # below the last row group.
    table.height = max(
        table.height if table.height != 'auto' else 0,
        position_y - table.content_box_y())

    # Layout for column groups and columns
    columns_height = position_y - initial_position_y
    if table.children:
        # The last border spacing is below the columns.
        columns_height -= border_spacing_y
    for group in table.column_groups:
        for column in group.children:
            column.position_x = column_positions[column.grid_x]
            column.position_y = initial_position_y
            column.width = column_widths[column.grid_x]
            column.height = columns_height
        first = group.children[0]
        last = group.children[-1]
        group.position_x = first.position_x
        group.position_y = initial_position_y
        group.width = last.position_x + last.width - first.position_x
        group.height = columns_height

    if ((table.position_y + table.margin_height()) > max_position_y
            and not page_is_empty):
        # If the table does not fit, put it on the next page.
        # (No page break inside tables yet.)
        return None, None
    else:
        return table, None


def add_top_padding(box, extra_padding):
    """Increase the top padding of a box. This also translates the children.
    """
    box.padding_top += extra_padding
    for child in box.children:
        child.translate(dy=extra_padding)


def fixed_table_layout(table):
    """Run the fixed table layout and return a list of column widths

    http://www.w3.org/TR/CSS21/tables.html#fixed-table-layout

    """
    assert table.width != 'auto'

    all_columns = [column for column_group in table.column_groups
                          for column in column_group.children]
    if table.children and table.children[0].children:
        first_rowgroup = table.children[0]
        first_row_cells = first_rowgroup.children[0].children
    else:
        first_row_cells = []
    num_columns = max(
        len(all_columns),
        sum(cell.colspan for cell in first_row_cells)
    )
    # ``None`` means not know yet.
    column_widths = [None] * num_columns

    # `width` on column boxes
    for i, column in enumerate(all_columns):
        resolve_one_percentage(column, 'width', table.width, ['auto'])
        if column.width != 'auto':
            column_widths[i] = column.width

    # `width` on cells of the first row.
    border_spacing_x, border_spacing_y = table.style.border_spacing
    i = 0
    for cell in first_row_cells:
        resolve_percentages(cell, table)
        if cell.width != 'auto':
            width = cell.border_width()
            width -= border_spacing_x * (cell.colspan - 1)
            # In the general case, this width affects several columns (through
            # colspan) some of which already have a width. Subscract these
            # known widths and divide among remaining columns.
            columns_without_width = []  # and occupied by this cell
            for j in xrange(i, i + cell.colspan):
                if column_widths[j] is None:
                    columns_without_width.append(j)
                else:
                    width -= column_widths[j]
            width_per_column = width / len(columns_without_width)
            for j in columns_without_width:
                column_widths[j] = width_per_column
        i += cell.colspan

    # Distribute the remaining space equally on columns that do not have
    # a width yet.
    all_border_spacing = border_spacing_x * (num_columns + 1)
    min_table_width = (sum(w for w in column_widths if w is not None)
                       + all_border_spacing)
    columns_without_width = [i for i, width in enumerate(column_widths)
                               if width is None]
    if columns_without_width and table.width >= min_table_width:
        remaining_width = table.width - min_table_width
        width_per_column = remaining_width / len(columns_without_width)
        for i in columns_without_width:
            column_widths[i] = width_per_column
    else:
        # XXX this is bad, but we were given a broken table to work with...
        for i in columns_without_width:
            column_widths[i] = 0

    # If the sum is less than the table width,
    # distribute the remaining space equally
    extra_width = table.width - sum(column_widths) - all_border_spacing
    if extra_width <= 0:
        # substract a negative: widen the table
        table.width -= extra_width
    elif num_columns:
        extra_per_column = extra_width / num_columns
        column_widths = [w + extra_per_column for w in column_widths]

    # Now we have table.width == sum(column_widths) + all_border_spacing
    # with possible floating point rounding errors.
    # (unless there is zero column)
    return column_widths


def cell_baseline(cell):
    """
    Return the y position of a cell’s baseline from the top of its border box.

    See http://www.w3.org/TR/CSS21/tables.html#height-layout

    """
    # Do not use cell.descendants() as we do not want to recurse into
    # out-of-flow children.
    stack = [iter(cell.children)]  # DIY recursion
    while stack:
        child = next(stack[-1], None)
        if child is None:
            stack.pop()
            continue
        if not child.is_in_normal_flow():
            continue
        if isinstance(child, (boxes.LineBox, boxes.TableRowBox)):
            # First in-flow line or row.
            return child.baseline + child.position_y - cell.position_y
        if isinstance(child, boxes.ParentBox):
            stack.append(iter(child.children))
    # Default to the bottom of the content area.
    return cell.border_top_width + cell.padding_top + cell.height