from __future__ import annotations

from fractions import Fraction
from typing import cast

from textual.geometry import Size, Region
from textual._layout import ArrangeResult, Layout, WidgetPlacement

from textual.widget import Widget


class HorizontalLayout(Layout):
    """Used to layout Widgets horizontally on screen, from left to right. Since Widgets naturally
    fill the space of their parent container, all widgets used in a horizontal layout should have a specified.
    """

    name = "horizontal"

    def arrange(
        self, parent: Widget, children: list[Widget], size: Size
    ) -> ArrangeResult:

        placements: list[WidgetPlacement] = []
        add_placement = placements.append

        x = max_height = Fraction(0)
        parent_size = parent.outer_size

        styles = [child.styles for child in children if child.styles.width is not None]
        total_fraction = sum(
            [int(style.width.value) for style in styles if style.width.is_fraction]
        )
        fraction_unit = Fraction(size.width, total_fraction or 1)

        box_models = [
            widget._get_box_model(size, parent_size, fraction_unit)
            for widget in cast("list[Widget]", children)
        ]

        margins = [
            max((box1.margin.right, box2.margin.left))
            for box1, box2 in zip(box_models, box_models[1:])
        ]
        if box_models:
            margins.append(box_models[-1].margin.right)

        x = Fraction(box_models[0].margin.left if box_models else 0)

        displayed_children = [child for child in children if child.display]

        _Region = Region
        _WidgetPlacement = WidgetPlacement
        for widget, box_model, margin in zip(children, box_models, margins):
            content_width, content_height, box_margin = box_model
            offset_y = box_margin.top
            next_x = x + content_width
            region = _Region(
                int(x), offset_y, int(next_x - int(x)), int(content_height)
            )
            max_height = max(
                max_height, content_height + offset_y + box_model.margin.bottom
            )
            add_placement(_WidgetPlacement(region, box_model.margin, widget, 0))
            x = next_x + margin

        return placements, set(displayed_children)