"""Stacking contexts management."""

import operator

from .formatting_structure import boxes
from .layout.absolute import AbsolutePlaceholder

_Z_INDEX_GETTER = operator.attrgetter('z_index')


class StackingContext:
    """Stacking contexts define the paint order of all pieces of a document.

    http://www.w3.org/TR/CSS21/visuren.html#x43
    http://www.w3.org/TR/CSS21/zindex.html

    """
    def __init__(self, box, child_contexts, blocks, floats, blocks_and_cells,
                 page):
        self.box = box
        self.page = page
        self.block_level_boxes = blocks  # 4: In flow, non positioned
        self.float_contexts = floats  # 5: Non positioned
        self.negative_z_contexts = []  # 3: Child contexts, z-index < 0
        self.zero_z_contexts = []  # 8: Child contexts, z-index = 0
        self.positive_z_contexts = []  # 9: Child contexts, z-index > 0
        self.blocks_and_cells = blocks_and_cells  # 7: Non positioned

        for context in child_contexts:
            if context.z_index < 0:
                self.negative_z_contexts.append(context)
            elif context.z_index == 0:
                self.zero_z_contexts.append(context)
            else:  # context.z_index > 0
                self.positive_z_contexts.append(context)
        self.negative_z_contexts.sort(key=_Z_INDEX_GETTER)
        self.positive_z_contexts.sort(key=_Z_INDEX_GETTER)
        # sort() is stable, so the lists are now storted
        # by z-index, then tree order.

        self.z_index = box.style['z_index']
        if self.z_index == 'auto':
            self.z_index = 0

    @classmethod
    def from_page(cls, page):
        # Page children (the box for the root element and margin boxes)
        # as well as the page box itself are unconditionally stacking contexts.
        child_contexts = [cls.from_box(child, page) for child in page.children]
        # Children are sub-contexts, remove them from the "normal" tree.
        page = page.copy_with_children([])
        return cls(page, child_contexts, [], [], [], page)

    @classmethod
    def from_box(cls, box, page, child_contexts=None):
        children = []  # What will be passed to this box
        if child_contexts is None:
            child_contexts = children
        # child_contexts: where to put sub-contexts that we find here.
        # May not be the same as children for:
        #   "treat the element as if it created a new stacking context,
        #    but any positioned descendants and descendants which actually
        #    create a new stacking context should be considered part of the
        #    parent stacking context, not this new one."
        blocks = []
        floats = []
        blocks_and_cells = []

        def dispatch(box):
            if isinstance(box, AbsolutePlaceholder):
                box = box._box
            style = box.style
            absolute_and_z_index = (
                style['position'] != 'static' and style['z_index'] != 'auto')
            if (absolute_and_z_index or
                    style['opacity'] < 1 or
                    # 'transform: none' gives a "falsy" empty list here
                    style['transform'] or
                    style['overflow'] != 'visible'):
                # This box defines a new stacking context, remove it
                # from the "normal" children list.
                child_contexts.append(
                    StackingContext.from_box(box, page))
            else:
                if style['position'] != 'static':
                    assert style['z_index'] == 'auto'
                    # "Fake" context: sub-contexts will go in this
                    # `child_contexts` list.
                    # Insert at the position before creating the sub-context.
                    index = len(child_contexts)
                    child_contexts.insert(
                        index,
                        StackingContext.from_box(box, page, child_contexts))
                elif box.is_floated():
                    floats.append(StackingContext.from_box(
                        box, page, child_contexts))
                elif isinstance(
                        box, (boxes.InlineBlockBox, boxes.InlineFlexBox)):
                    # Have this fake stacking context be part of the "normal"
                    # box tree, because we need its position in the middle
                    # of a tree of inline boxes.
                    return StackingContext.from_box(box, page, child_contexts)
                else:
                    if isinstance(box, boxes.BlockLevelBox):
                        blocks_index = len(blocks)
                        blocks_and_cells_index = len(blocks_and_cells)
                    elif isinstance(box, boxes.TableCellBox):
                        blocks_index = None
                        blocks_and_cells_index = len(blocks_and_cells)
                    else:
                        blocks_index = None
                        blocks_and_cells_index = None

                    box = dispatch_children(box)

                    # Insert at the positions before dispatch the children.
                    if blocks_index is not None:
                        blocks.insert(blocks_index, box)
                    if blocks_and_cells_index is not None:
                        blocks_and_cells.insert(blocks_and_cells_index, box)

                    return box

        def dispatch_children(box):
            if not isinstance(box, boxes.ParentBox):
                return box

            new_children = []
            for child in box.children:
                result = dispatch(child)
                if result is not None:
                    new_children.append(result)
            box = box.copy_with_children(new_children)
            return box

        box = dispatch_children(box)

        return cls(box, children, blocks, floats, blocks_and_cells, page)
