cotis-layout 0.1.0-alpha

use crate::layout_algorithm::axis_utils::Axis;
use crate::layout_struct::layout_states::{ChildWrapping, LayoutElement, LayoutElementInfo};
use crate::layout_struct::layout_tree::{LayoutTreeCursor, LayoutTreeNodeLocalMut};
use cotis_defaults::element_configs::style::types::{
    FloatingAttachPointType, LayoutAlignmentX, LayoutAlignmentY, LayoutDirection,
};

pub(crate) fn calculate_child_positions(local: &mut LayoutTreeCursor) {
    {
        let mut local = local.get_local_mut();
        if local.self_element.config.layout.layout_direction == LayoutDirection::LeftToRight {
            layout_ltr(&mut local);
        } else {
            layout_ttb(&mut local);
        }
    }
    for child in local.get_all_child_ids() {
        calculate_child_positions(&mut local.get_child_cursor(child).unwrap());
    }
}

fn layout_ltr(local: &mut LayoutTreeNodeLocalMut<'_>) {
    if local.self_element.config.layout.wrapping == ChildWrapping::Text {
        layout_ltr_wrapped(local);
        return;
    }

    let (px, py, pw, _ph) = parent_rect(local.self_element);
    let pad = local.self_element.config.layout.padding;
    let gap = local.self_element.config.layout.child_gap as f32;
    let x_off = clip_x_off(local.self_element);
    let y_off = clip_y_off(local.self_element);
    let parent_h = local
        .self_element
        .info
        .get_final_height()
        .expect("parent must have final height");

    match local.self_element.config.layout.child_alignment.x {
        LayoutAlignmentX::Left => {
            sequence_forward(
                &mut local.children_elements,
                PhysicalAxis::X,
                px,
                py,
                pw,
                parent_h,
                px + pad.left + x_off,
                gap,
            );
        }
        LayoutAlignmentX::Right => {
            sequence_backward(
                &mut local.children_elements,
                PhysicalAxis::X,
                px,
                py,
                pw,
                parent_h,
                px + pw - pad.right + x_off,
                gap,
            );
        }
        LayoutAlignmentX::Center => {
            let lead = local.free_space_axis(Axis::Width) / 2.0;
            sequence_forward(
                &mut local.children_elements,
                PhysicalAxis::X,
                px,
                py,
                pw,
                parent_h,
                px + lead + pad.left + x_off,
                gap,
            );
        }
    }

    match local.self_element.config.layout.child_alignment.y {
        LayoutAlignmentY::Top => {
            cross_fixed_start(
                &mut local.children_elements,
                PhysicalAxis::Y,
                px,
                py,
                pw,
                parent_h,
                py + pad.top + y_off,
            );
        }
        LayoutAlignmentY::Bottom => {
            cross_align_end(
                &mut local.children_elements,
                PhysicalAxis::Y,
                px,
                py,
                pw,
                parent_h,
                py + parent_h - pad.bottom + y_off,
            );
        }
        LayoutAlignmentY::Center => {
            let inner = parent_h - local.self_element.internal_space_height();
            cross_center_each(
                &mut local.children_elements,
                PhysicalAxis::Y,
                px,
                py,
                pw,
                parent_h,
                inner,
                py,
                pad.top,
                y_off,
            );
        }
    }
}

/// `ChildWrapping::Text` on an LTR row: break lines like [`crate::layout_algorithm::wrapping::wrap_elements_left_to_right`], then set child x/y.
fn layout_ltr_wrapped(local: &mut LayoutTreeNodeLocalMut<'_>) {
    let (px, py, pw, _) = parent_rect(local.self_element);
    let pad = local.self_element.config.layout.padding;
    let gap = local.self_element.config.layout.child_gap as f32;
    let x_off = clip_x_off(local.self_element);
    let y_off = clip_y_off(local.self_element);
    let parent_h = local
        .self_element
        .info
        .get_final_height()
        .expect("parent must have final height");

    let content_left = px + pad.left + x_off;
    let content_right = px + pw - pad.right + x_off;
    let content_width = (content_right - content_left).max(0.0);

    let children = &mut local.children_elements;

    for child in children.iter_mut() {
        if child.config.floating.config.is_some() {
            try_float_x(child, px, pw);
            try_float_y(child, py, parent_h);
        }
    }

    let in_flow: Vec<usize> = children
        .iter()
        .enumerate()
        .filter(|(_, c)| c.config.floating.config.is_none())
        .map(|(i, _)| i)
        .collect();

    let mut lines: Vec<Vec<usize>> = Vec::new();
    let mut current_line: Vec<usize> = Vec::new();
    let mut row_width = 0.0f32;

    for &i in &in_flow {
        let w = children[i].info.get_final_width().expect("child width");
        if current_line.is_empty() {
            current_line.push(i);
            row_width = w;
        } else if row_width + gap + w > content_width {
            lines.push(std::mem::take(&mut current_line));
            current_line.push(i);
            row_width = w;
        } else {
            current_line.push(i);
            row_width += gap + w;
        }
    }
    if !current_line.is_empty() {
        lines.push(current_line);
    }

    if lines.is_empty() {
        return;
    }

    let line_heights: Vec<f32> = lines
        .iter()
        .map(|line| wrapped_line_max_height(children.as_mut_slice(), line))
        .collect();

    let lines_inner_height: f32 =
        line_heights.iter().sum::<f32>() + gap * line_heights.len().saturating_sub(1) as f32;

    let inner_h = parent_h - pad.top - pad.bottom;
    let block_start_y = match local.self_element.config.layout.child_alignment.y {
        LayoutAlignmentY::Top => py + pad.top + y_off,
        LayoutAlignmentY::Bottom => py + parent_h - pad.bottom + y_off - lines_inner_height,
        LayoutAlignmentY::Center => py + pad.top + y_off + (inner_h - lines_inner_height) / 2.0,
    };

    let mut line_y = block_start_y;
    for (line_idx, line) in lines.iter().enumerate() {
        let row_h = line_heights[line_idx];
        let used_w = wrapped_line_used_width(children.as_mut_slice(), line, gap);

        let line_start_x = match local.self_element.config.layout.child_alignment.x {
            LayoutAlignmentX::Left => content_left,
            LayoutAlignmentX::Right => content_right - used_w,
            LayoutAlignmentX::Center => content_left + (content_width - used_w) / 2.0,
        };

        let mut cursor_x = line_start_x;
        for &i in line {
            let child = &mut children[i];
            let child_w = child.info.get_final_width().expect("child width");
            let child_h = child.info.get_final_height().expect("child height");
            let y = match local.self_element.config.layout.child_alignment.y {
                LayoutAlignmentY::Top => line_y,
                LayoutAlignmentY::Bottom => line_y + row_h - child_h,
                LayoutAlignmentY::Center => line_y + (row_h - child_h) / 2.0,
            };
            child.info.set_x(cursor_x);
            child.info.set_y(y);
            cursor_x += child_w + gap;
        }

        line_y += row_h + gap;
    }
}

fn wrapped_line_used_width(children: &mut [&mut LayoutElement], line: &[usize], gap: f32) -> f32 {
    if line.is_empty() {
        return 0.0;
    }
    let sum_w: f32 = line
        .iter()
        .map(|&i| children[i].info.get_final_width().expect("child width"))
        .sum();
    sum_w + gap * (line.len().saturating_sub(1) as f32)
}

fn wrapped_line_max_height(children: &mut [&mut LayoutElement], line: &[usize]) -> f32 {
    line.iter()
        .map(|&i| {
            children[i]
                .info
                .get_final_axis(Axis::Height)
                .expect("child min height for wrapped layout")
        })
        .fold(0.0f32, f32::max)
}

fn layout_ttb(local: &mut LayoutTreeNodeLocalMut<'_>) {
    let (px, py, pw, _ph) = parent_rect(local.self_element);
    let pad = local.self_element.config.layout.padding;
    let gap = local.self_element.config.layout.child_gap as f32;
    let x_off = clip_x_off(local.self_element);
    let y_off = clip_y_off(local.self_element);
    let parent_h = local
        .self_element
        .info
        .get_final_height()
        .expect("parent must have final height");

    match local.self_element.config.layout.child_alignment.y {
        LayoutAlignmentY::Top => {
            sequence_forward(
                &mut local.children_elements,
                PhysicalAxis::Y,
                px,
                py,
                pw,
                parent_h,
                py + pad.top + y_off,
                gap,
            );
        }
        LayoutAlignmentY::Bottom => {
            sequence_backward(
                &mut local.children_elements,
                PhysicalAxis::Y,
                px,
                py,
                pw,
                parent_h,
                py + parent_h - pad.bottom + y_off,
                gap,
            );
        }
        LayoutAlignmentY::Center => {
            let lead = local.free_space_axis(Axis::Height) / 2.0;
            sequence_forward(
                &mut local.children_elements,
                PhysicalAxis::Y,
                px,
                py,
                pw,
                parent_h,
                py + lead + pad.top + y_off,
                gap,
            );
        }
    }

    match local.self_element.config.layout.child_alignment.x {
        LayoutAlignmentX::Left => {
            cross_fixed_start(
                &mut local.children_elements,
                PhysicalAxis::X,
                px,
                py,
                pw,
                parent_h,
                px + pad.left + x_off,
            );
        }
        LayoutAlignmentX::Right => {
            cross_align_end(
                &mut local.children_elements,
                PhysicalAxis::X,
                px,
                py,
                pw,
                parent_h,
                px + pw - pad.right + x_off,
            );
        }
        LayoutAlignmentX::Center => {
            let inner = pw - local.self_element.internal_space_width();
            cross_center_each(
                &mut local.children_elements,
                PhysicalAxis::X,
                px,
                py,
                pw,
                parent_h,
                inner,
                px,
                pad.left,
                x_off,
            );
        }
    }
}

/// Horizontal vs vertical coordinate for child placement (distinct from flex [`Axis`]).
#[derive(Clone, Copy)]
enum PhysicalAxis {
    X,
    Y,
}

impl PhysicalAxis {
    fn try_float(
        self,
        child: &mut LayoutElement,
        px: f32,
        py: f32,
        parent_w: f32,
        parent_h: f32,
    ) -> bool {
        match self {
            PhysicalAxis::X => try_float_x(child, px, parent_w),
            PhysicalAxis::Y => try_float_y(child, py, parent_h),
        }
    }

    fn size(self, child: &LayoutElement) -> f32 {
        match self {
            PhysicalAxis::X => child.info.get_final_width().expect("child width"),
            PhysicalAxis::Y => child.info.get_final_height().expect("child height"),
        }
    }

    fn set(self, child: &mut LayoutElement, v: f32) {
        match self {
            PhysicalAxis::X => child.info.set_x(v),
            PhysicalAxis::Y => child.info.set_y(v),
        }
    }
}

fn with_children_order(
    children: &mut Vec<&mut LayoutElement>,
    reverse: bool,
    mut f: impl FnMut(&mut LayoutElement),
) {
    if reverse {
        for c in children.iter_mut().rev() {
            f(*c);
        }
    } else {
        for c in children.iter_mut() {
            f(*c);
        }
    }
}

/// In-flow children placed along the axis from `cursor`, advancing by size + gap (left/top main).
fn sequence_forward(
    children: &mut Vec<&mut LayoutElement>,
    axis: PhysicalAxis,
    px: f32,
    py: f32,
    parent_w: f32,
    parent_h: f32,
    mut cursor: f32,
    gap: f32,
) {
    with_children_order(children, false, |child| {
        if axis.try_float(child, px, py, parent_w, parent_h) {
            return;
        }
        let s = axis.size(child);
        axis.set(child, cursor);
        cursor += s + gap;
    });
}

/// In-flow children packed toward the end edge (right/bottom main), iterating children in reverse order.
fn sequence_backward(
    children: &mut Vec<&mut LayoutElement>,
    axis: PhysicalAxis,
    px: f32,
    py: f32,
    parent_w: f32,
    parent_h: f32,
    mut cursor: f32,
    gap: f32,
) {
    with_children_order(children, true, |child| {
        if axis.try_float(child, px, py, parent_w, parent_h) {
            return;
        }
        let s = axis.size(child);
        axis.set(child, cursor - s);
        cursor -= s + gap;
    });
}

/// Same coordinate for every in-flow child (e.g. top-aligned or left-aligned cross axis).
fn cross_fixed_start(
    children: &mut Vec<&mut LayoutElement>,
    axis: PhysicalAxis,
    px: f32,
    py: f32,
    parent_w: f32,
    parent_h: f32,
    coord: f32,
) {
    with_children_order(children, false, |child| {
        if axis.try_float(child, px, py, parent_w, parent_h) {
            return;
        }
        axis.set(child, coord);
    });
}

/// Align outer edge to `end` (bottom or right inner edge).
fn cross_align_end(
    children: &mut Vec<&mut LayoutElement>,
    axis: PhysicalAxis,
    px: f32,
    py: f32,
    parent_w: f32,
    parent_h: f32,
    end: f32,
) {
    with_children_order(children, true, |child| {
        if axis.try_float(child, px, py, parent_w, parent_h) {
            return;
        }
        let s = axis.size(child);
        axis.set(child, end - s);
    });
}

/// Center each child in the content box: `origin + (inner - size) / 2 + pad_start + clip_off`.
fn cross_center_each(
    children: &mut Vec<&mut LayoutElement>,
    axis: PhysicalAxis,
    px: f32,
    py: f32,
    parent_w: f32,
    parent_h: f32,
    inner: f32,
    origin: f32,
    pad_start: f32,
    clip_off: f32,
) {
    with_children_order(children, false, |child| {
        if axis.try_float(child, px, py, parent_w, parent_h) {
            return;
        }
        let s = axis.size(child);
        let half = (inner - s) / 2.0;
        axis.set(child, origin + half + pad_start + clip_off);
    });
}

fn parent_rect(parent: &LayoutElement) -> (f32, f32, f32, f32) {
    match &parent.info {
        LayoutElementInfo::TotalSizedAndPosition(p) => (p.x, p.y, p.width, p.height),
        _ => panic!("tried using parent without position"),
    }
}

fn clip_x_off(parent: &LayoutElement) -> f32 {
    if parent.config.clip.horizontal {
        parent.config.clip.offset.x
    } else {
        0.0
    }
}

fn clip_y_off(parent: &LayoutElement) -> f32 {
    if parent.config.clip.vertical {
        parent.config.clip.offset.y
    } else {
        0.0
    }
}

fn try_float_x(child: &mut LayoutElement, parent_x: f32, parent_w: f32) -> bool {
    if let Some(cfg) = &child.config.floating.config {
        let child_w = child.info.get_final_width().expect("child width");
        let anchor_x = floating_anchor_x(parent_x, parent_w, cfg.attach_point);
        let child_anchor_x = floating_child_anchor_x(child_w, cfg.attach_point);
        child.info.set_x(anchor_x - child_anchor_x + cfg.offset.x);
        true
    } else {
        false
    }
}

fn try_float_y(child: &mut LayoutElement, parent_y: f32, parent_h: f32) -> bool {
    if let Some(cfg) = &child.config.floating.config {
        let child_h = child.info.get_final_height().expect("child height");
        let anchor_y = floating_anchor_y(parent_y, parent_h, cfg.attach_point);
        let child_anchor_y = floating_child_anchor_y(child_h, cfg.attach_point);
        child.info.set_y(anchor_y - child_anchor_y + cfg.offset.y);
        true
    } else {
        false
    }
}

fn floating_anchor_x(parent_x: f32, parent_w: f32, attach: FloatingAttachPointType) -> f32 {
    match attach {
        FloatingAttachPointType::LeftTop
        | FloatingAttachPointType::LeftCenter
        | FloatingAttachPointType::LeftBottom => parent_x,
        FloatingAttachPointType::CenterTop
        | FloatingAttachPointType::CenterCenter
        | FloatingAttachPointType::CenterBottom => parent_x + parent_w / 2.0,
        FloatingAttachPointType::RightTop
        | FloatingAttachPointType::RightCenter
        | FloatingAttachPointType::RightBottom => parent_x + parent_w,
    }
}

fn floating_anchor_y(parent_y: f32, parent_h: f32, attach: FloatingAttachPointType) -> f32 {
    match attach {
        FloatingAttachPointType::LeftTop
        | FloatingAttachPointType::CenterTop
        | FloatingAttachPointType::RightTop => parent_y,
        FloatingAttachPointType::LeftCenter
        | FloatingAttachPointType::CenterCenter
        | FloatingAttachPointType::RightCenter => parent_y + parent_h / 2.0,
        FloatingAttachPointType::LeftBottom
        | FloatingAttachPointType::CenterBottom
        | FloatingAttachPointType::RightBottom => parent_y + parent_h,
    }
}

fn floating_child_anchor_x(child_w: f32, attach: FloatingAttachPointType) -> f32 {
    match attach {
        FloatingAttachPointType::LeftTop
        | FloatingAttachPointType::LeftCenter
        | FloatingAttachPointType::LeftBottom => 0.0,
        FloatingAttachPointType::CenterTop
        | FloatingAttachPointType::CenterCenter
        | FloatingAttachPointType::CenterBottom => child_w / 2.0,
        FloatingAttachPointType::RightTop
        | FloatingAttachPointType::RightCenter
        | FloatingAttachPointType::RightBottom => child_w,
    }
}

fn floating_child_anchor_y(child_h: f32, attach: FloatingAttachPointType) -> f32 {
    match attach {
        FloatingAttachPointType::LeftTop
        | FloatingAttachPointType::CenterTop
        | FloatingAttachPointType::RightTop => 0.0,
        FloatingAttachPointType::LeftCenter
        | FloatingAttachPointType::CenterCenter
        | FloatingAttachPointType::RightCenter => child_h / 2.0,
        FloatingAttachPointType::LeftBottom
        | FloatingAttachPointType::CenterBottom
        | FloatingAttachPointType::RightBottom => child_h,
    }
}