"""Resolve percentages into fixed values."""

from math import inf

from ..formatting_structure import boxes


def percentage(value, refer_to):
    """Return the percentage of the reference value, or the value unchanged.

    ``refer_to`` is the length for 100%. If ``refer_to`` is not a number, it
    just replaces percentages.

    """
    if value is None or value == 'auto':
        return value
    elif value.unit == 'px':
        return value.value
    else:
        assert value.unit == '%'
        return refer_to * value.value / 100.


def resolve_one_percentage(box, property_name, refer_to,
                           main_flex_direction=None):
    """Set a used length value from a computed length value.

    ``refer_to`` is the length for 100%. If ``refer_to`` is not a number, it
    just replaces percentages.

    """
    # box.style has computed values
    value = box.style[property_name]
    # box attributes are used values
    percent = percentage(value, refer_to)
    setattr(box, property_name, percent)
    if property_name in ('min_width', 'min_height') and percent == 'auto':
        if (main_flex_direction is None or
                property_name != (f'min_{main_flex_direction}')):
            setattr(box, property_name, 0)


def resolve_position_percentages(box, containing_block):
    cb_width, cb_height = containing_block
    resolve_one_percentage(box, 'left', cb_width)
    resolve_one_percentage(box, 'right', cb_width)
    resolve_one_percentage(box, 'top', cb_height)
    resolve_one_percentage(box, 'bottom', cb_height)


def resolve_percentages(box, containing_block, main_flex_direction=None):
    """Set used values as attributes of the box object."""
    if isinstance(containing_block, boxes.Box):
        # cb is short for containing block
        cb_width = containing_block.width
        cb_height = containing_block.height
    else:
        cb_width, cb_height = containing_block
    if isinstance(box, boxes.PageBox):
        maybe_height = cb_height
    else:
        maybe_height = cb_width
    resolve_one_percentage(box, 'margin_left', cb_width)
    resolve_one_percentage(box, 'margin_right', cb_width)
    resolve_one_percentage(box, 'margin_top', maybe_height)
    resolve_one_percentage(box, 'margin_bottom', maybe_height)
    resolve_one_percentage(box, 'padding_left', cb_width)
    resolve_one_percentage(box, 'padding_right', cb_width)
    resolve_one_percentage(box, 'padding_top', maybe_height)
    resolve_one_percentage(box, 'padding_bottom', maybe_height)
    resolve_one_percentage(box, 'width', cb_width)
    resolve_one_percentage(box, 'min_width', cb_width, main_flex_direction)
    resolve_one_percentage(box, 'max_width', cb_width, main_flex_direction)

    # XXX later: top, bottom, left and right on positioned elements

    if cb_height == 'auto':
        # Special handling when the height of the containing block
        # depends on its content.
        height = box.style['height']
        if height == 'auto' or height.unit == '%':
            box.height = 'auto'
        else:
            assert height.unit == 'px'
            box.height = height.value
        resolve_one_percentage(box, 'min_height', 0, main_flex_direction)
        resolve_one_percentage(box, 'max_height', inf, main_flex_direction)
    else:
        resolve_one_percentage(box, 'height', cb_height)
        resolve_one_percentage(
            box, 'min_height', cb_height, main_flex_direction)
        resolve_one_percentage(
            box, 'max_height', cb_height, main_flex_direction)

    # Used value == computed value
    for side in ['top', 'right', 'bottom', 'left']:
        prop = f'border_{side}_width'
        setattr(box, prop, box.style[prop])

    # Shrink *content* widths and heights according to box-sizing
    # Thanks heavens and the spec: Our validator rejects negative values
    # for padding and border-width
    if box.style['box_sizing'] == 'border-box':
        horizontal_delta = (
            box.padding_left + box.padding_right +
            box.border_left_width + box.border_right_width)
        vertical_delta = (
            box.padding_top + box.padding_bottom +
            box.border_top_width + box.border_bottom_width)
    elif box.style['box_sizing'] == 'padding-box':
        horizontal_delta = box.padding_left + box.padding_right
        vertical_delta = box.padding_top + box.padding_bottom
    else:
        assert box.style['box_sizing'] == 'content-box'
        horizontal_delta = 0
        vertical_delta = 0

    # Keep at least min_* >= 0 to prevent funny output in case box.width or
    # box.height become negative.
    # Restricting max_* seems reasonable, too.
    if horizontal_delta > 0:
        if box.width != 'auto':
            box.width = max(0, box.width - horizontal_delta)
        box.max_width = max(0, box.max_width - horizontal_delta)
        if box.min_width != 'auto':
            box.min_width = max(0, box.min_width - horizontal_delta)
    if vertical_delta > 0:
        if box.height != 'auto':
            box.height = max(0, box.height - vertical_delta)
        box.max_height = max(0, box.max_height - vertical_delta)
        if box.min_height != 'auto':
            box.min_height = max(0, box.min_height - vertical_delta)


def resolve_radii_percentages(box):
    corners = ('top_left', 'top_right', 'bottom_right', 'bottom_left')
    for corner in corners:
        property_name = f'border_{corner}_radius'
        for side in corner.split('_'):
            if side in box.remove_decoration_sides:
                setattr(box, property_name, (0, 0))
                break
        else:
            rx, ry = box.style[property_name]
            rx = percentage(rx, box.border_width())
            ry = percentage(ry, box.border_height())
            setattr(box, property_name, (rx, ry))