use core::f32;

use crate::algo::Number::{Defined, Undefined};
use crate::forest::{Forest, NodeData};
use crate::geometry::{Point, Rect, Size};
use crate::id::NodeId;
use crate::node::MeasureFunc;
use crate::number::{MinMax, OrElse};
use crate::prelude::Number;
use crate::result;
use crate::style::{AlignContent, AlignSelf, Dimension, Display, FlexWrap, JustifyContent, PositionType};
use crate::sys;

#[derive(Debug, Clone)]
pub struct ComputeResult {
    pub size: Size<f32>,
}

struct FlexItem {
    node: NodeId,

    size: Size<Number>,
    min_size: Size<Number>,
    max_size: Size<Number>,

    position: Rect<Number>,
    margin: Rect<f32>,
    padding: Rect<f32>,
    border: Rect<f32>,

    flex_basis: f32,
    inner_flex_basis: f32,
    violation: f32,
    frozen: bool,

    hypothetical_inner_size: Size<f32>,
    hypothetical_outer_size: Size<f32>,
    target_size: Size<f32>,
    outer_target_size: Size<f32>,

    baseline: f32,

    // temporary values for holding offset in the main / cross direction.
    // offset is the relative position from the item's natural flow position based on
    // relative position values, alignment, and justification. Does not include margin/padding/border.
    offset_main: f32,
    offset_cross: f32,
}

struct FlexLine<'a> {
    items: &'a mut [FlexItem],
    cross_size: f32,
    offset_cross: f32,
}

impl Forest {
    pub(crate) fn compute(&mut self, root: NodeId, size: Size<Number>) {
        let style = self.nodes[root].style;
        let has_root_min_max = style.min_size.width.is_defined()
            || style.min_size.height.is_defined()
            || style.max_size.width.is_defined()
            || style.max_size.height.is_defined();

        let result = if has_root_min_max {
            let first_pass = self.compute_internal(root, style.size.resolve(size), size, false, true);

            self.compute_internal(
                root,
                Size {
                    width: first_pass
                        .size
                        .width
                        .maybe_max(style.min_size.width.resolve(size.width))
                        .maybe_min(style.max_size.width.resolve(size.width))
                        .into(),
                    height: first_pass
                        .size
                        .height
                        .maybe_max(style.min_size.height.resolve(size.height))
                        .maybe_min(style.max_size.height.resolve(size.height))
                        .into(),
                },
                size,
                true,
                true,
            )
        } else {
            self.compute_internal(root, style.size.resolve(size), size, true, true)
        };

        self.nodes[root].layout = result::Layout { order: 0, size: result.size, location: Point::zero() };

        Self::round_layout(&mut self.nodes, &self.children, root, 0.0, 0.0);
    }

    fn round_layout(
        nodes: &mut [NodeData],
        children: &[sys::ChildrenVec<NodeId>],
        root: NodeId,
        abs_x: f32,
        abs_y: f32,
    ) {
        let layout = &mut nodes[root].layout;
        let abs_x = abs_x + layout.location.x;
        let abs_y = abs_y + layout.location.y;

        layout.location.x = sys::round(layout.location.x);
        layout.location.y = sys::round(layout.location.y);

        layout.size.width = sys::round(abs_x + layout.size.width) - sys::round(abs_x);
        layout.size.height = sys::round(abs_y + layout.size.height) - sys::round(abs_y);

        for child in &children[root] {
            Self::round_layout(nodes, children, *child, abs_x, abs_y);
        }
    }

    fn cache(&mut self, node: NodeId, main_size: bool) -> &mut Option<result::Cache> {
        if main_size {
            &mut self.nodes[node].main_size_layout_cache
        } else {
            &mut self.nodes[node].other_layout_cache
        }
    }

    #[allow(clippy::cognitive_complexity)]
    fn compute_internal(
        &mut self,
        node: NodeId,
        node_size: Size<Number>,
        parent_size: Size<Number>,
        perform_layout: bool,
        main_size: bool,
    ) -> ComputeResult {
        self.nodes[node].is_dirty = false;

        // First we check if we have a result for the given input
        if let Some(ref cache) = self.cache(node, main_size) {
            if cache.perform_layout || !perform_layout {
                let width_compatible = if let Number::Defined(width) = node_size.width {
                    sys::abs(width - cache.result.size.width) < f32::EPSILON
                } else {
                    cache.node_size.width.is_undefined()
                };

                let height_compatible = if let Number::Defined(height) = node_size.height {
                    sys::abs(height - cache.result.size.height) < f32::EPSILON
                } else {
                    cache.node_size.height.is_undefined()
                };

                if width_compatible && height_compatible {
                    return cache.result.clone();
                }

                if cache.node_size == node_size && cache.parent_size == parent_size {
                    return cache.result.clone();
                }
            }
        }

        // Define some general constants we will need for the remainder
        // of the algorithm.

        let dir = self.nodes[node].style.flex_direction;
        let is_row = dir.is_row();
        let is_column = dir.is_column();
        let is_wrap_reverse = self.nodes[node].style.flex_wrap == FlexWrap::WrapReverse;

        let margin = self.nodes[node].style.margin.map(|n| n.resolve(parent_size.width).or_else(0.0));
        let padding = self.nodes[node].style.padding.map(|n| n.resolve(parent_size.width).or_else(0.0));
        let border = self.nodes[node].style.border.map(|n| n.resolve(parent_size.width).or_else(0.0));

        let padding_border = Rect {
            start: padding.start + border.start,
            end: padding.end + border.end,
            top: padding.top + border.top,
            bottom: padding.bottom + border.bottom,
        };

        let node_inner_size = Size {
            width: node_size.width - padding_border.horizontal(),
            height: node_size.height - padding_border.vertical(),
        };

        let mut container_size = Size::zero();
        let mut inner_container_size = Size::zero();

        // If this is a leaf node we can skip a lot of this function in some cases
        if self.children[node].is_empty() {
            if node_size.width.is_defined() && node_size.height.is_defined() {
                return ComputeResult { size: node_size.map(|s| s.or_else(0.0)) };
            }

            if let Some(ref measure) = self.nodes[node].measure {
                let result = match measure {
                    MeasureFunc::Raw(measure) => ComputeResult { size: measure(node_size) },
                    #[cfg(any(feature = "std", feature = "alloc"))]
                    MeasureFunc::Boxed(measure) => ComputeResult { size: measure(node_size) },
                };
                *self.cache(node, main_size) =
                    Some(result::Cache { node_size, parent_size, perform_layout, result: result.clone() });
                return result;
            }

            return ComputeResult {
                size: Size {
                    width: node_size.width.or_else(0.0) + padding_border.horizontal(),
                    height: node_size.height.or_else(0.0) + padding_border.vertical(),
                },
            };
        }

        // 9.2. Line Length Determination

        // 1. Generate anonymous flex items as described in §4 Flex Items.

        // 2. Determine the available main and cross space for the flex items.
        //    For each dimension, if that dimension of the flex container’s content box
        //    is a definite size, use that; if that dimension of the flex container is
        //    being sized under a min or max-content constraint, the available space in
        //    that dimension is that constraint; otherwise, subtract the flex container’s
        //    margin, border, and padding from the space available to the flex container
        //    in that dimension and use that value. This might result in an infinite value.

        let available_space = Size {
            width: node_size.width.or_else(parent_size.width - margin.horizontal()) - padding_border.horizontal(),
            height: node_size.height.or_else(parent_size.height - margin.vertical()) - padding_border.vertical(),
        };

        let mut flex_items: sys::Vec<FlexItem> = self.children[node]
            .iter()
            .map(|child| (child, &self.nodes[*child].style))
            .filter(|(_, style)| style.position_type != PositionType::Absolute)
            .filter(|(_, style)| style.display != Display::None)
            .map(|(child, child_style)| FlexItem {
                node: *child,
                size: child_style.size.resolve(node_inner_size),
                min_size: child_style.min_size.resolve(node_inner_size),
                max_size: child_style.max_size.resolve(node_inner_size),

                position: child_style.position.zip_size(node_inner_size, |p, s| p.resolve(s)),
                margin: child_style.margin.map(|m| m.resolve(node_inner_size.width).or_else(0.0)),
                padding: child_style.padding.map(|p| p.resolve(node_inner_size.width).or_else(0.0)),
                border: child_style.border.map(|b| b.resolve(node_inner_size.width).or_else(0.0)),

                flex_basis: 0.0,
                inner_flex_basis: 0.0,
                violation: 0.0,
                frozen: false,

                hypothetical_inner_size: Size::zero(),
                hypothetical_outer_size: Size::zero(),
                target_size: Size::zero(),
                outer_target_size: Size::zero(),

                baseline: 0.0,

                offset_main: 0.0,
                offset_cross: 0.0,
            })
            .collect();

        let has_baseline_child = flex_items
            .iter()
            .any(|child| self.nodes[child.node].style.align_self(&self.nodes[node].style) == AlignSelf::Baseline);

        // TODO - this does not follow spec. See commented out code below
        // 3. Determine the flex base size and hypothetical main size of each item:
        for child in &mut flex_items {
            let child_style = self.nodes[child.node].style;

            // A. If the item has a definite used flex basis, that’s the flex base size.

            let flex_basis = child_style.flex_basis.resolve(node_inner_size.main(dir));
            if flex_basis.is_defined() {
                child.flex_basis = flex_basis.or_else(0.0);
                continue;
            };

            // B. If the flex item has an intrinsic aspect ratio,
            //    a used flex basis of content, and a definite cross size,
            //    then the flex base size is calculated from its inner
            //    cross size and the flex item’s intrinsic aspect ratio.

            if let Defined(ratio) = child_style.aspect_ratio {
                if let Defined(cross) = node_size.cross(dir) {
                    if child_style.flex_basis == Dimension::Auto {
                        child.flex_basis = cross * ratio;
                        continue;
                    }
                }
            }

            // C. If the used flex basis is content or depends on its available space,
            //    and the flex container is being sized under a min-content or max-content
            //    constraint (e.g. when performing automatic table layout [CSS21]),
            //    size the item under that constraint. The flex base size is the item’s
            //    resulting main size.

            // TODO - Probably need to cover this case in future

            // D. Otherwise, if the used flex basis is content or depends on its
            //    available space, the available main size is infinite, and the flex item’s
            //    inline axis is parallel to the main axis, lay the item out using the rules
            //    for a box in an orthogonal flow [CSS3-WRITING-MODES]. The flex base size
            //    is the item’s max-content main size.

            // TODO - Probably need to cover this case in future

            // E. Otherwise, size the item into the available space using its used flex basis
            //    in place of its main size, treating a value of content as max-content.
            //    If a cross size is needed to determine the main size (e.g. when the
            //    flex item’s main size is in its block axis) and the flex item’s cross size
            //    is auto and not definite, in this calculation use fit-content as the
            //    flex item’s cross size. The flex base size is the item’s resulting main size.

            let width: Number = if !child.size.width.is_defined()
                && child_style.align_self(&self.nodes[node].style) == AlignSelf::Stretch
                && is_column
            {
                available_space.width
            } else {
                child.size.width
            };

            let height: Number = if !child.size.height.is_defined()
                && child_style.align_self(&self.nodes[node].style) == AlignSelf::Stretch
                && is_row
            {
                available_space.height
            } else {
                child.size.height
            };

            child.flex_basis = self
                .compute_internal(
                    child.node,
                    Size {
                        width: width.maybe_max(child.min_size.width).maybe_min(child.max_size.width),
                        height: height.maybe_max(child.min_size.height).maybe_min(child.max_size.height),
                    },
                    available_space,
                    false,
                    true,
                )
                .size
                .main(dir)
                .maybe_max(child.min_size.main(dir))
                .maybe_min(child.max_size.main(dir));
        }

        // The hypothetical main size is the item’s flex base size clamped according to its
        // used min and max main sizes (and flooring the content box size at zero).

        for child in &mut flex_items {
            child.inner_flex_basis = child.flex_basis - child.padding.main(dir) - child.border.main(dir);

            // TODO - not really spec abiding but needs to be done somewhere. probably somewhere else though.
            // The following logic was developed not from the spec but by trail and error looking into how
            // webkit handled various scenarios. Can probably be solved better by passing in
            // min-content max-content constraints from the top
            let min_main = self
                .compute_internal(child.node, Size::undefined(), available_space, false, false)
                .size
                .main(dir)
                .maybe_max(child.min_size.main(dir))
                .maybe_min(child.size.main(dir))
                .into();

            child
                .hypothetical_inner_size
                .set_main(dir, child.flex_basis.maybe_max(min_main).maybe_min(child.max_size.main(dir)));

            child
                .hypothetical_outer_size
                .set_main(dir, child.hypothetical_inner_size.main(dir) + child.margin.main(dir));
        }

        // 9.3. Main Size Determination

        // 5. Collect flex items into flex lines:
        //    - If the flex container is single-line, collect all the flex items into
        //      a single flex line.
        //    - Otherwise, starting from the first uncollected item, collect consecutive
        //      items one by one until the first time that the next collected item would
        //      not fit into the flex container’s inner main size (or until a forced break
        //      is encountered, see §10 Fragmenting Flex Layout). If the very first
        //      uncollected item wouldn’t fit, collect just it into the line.
        //
        //      For this step, the size of a flex item is its outer hypothetical main size. (Note: This can be negative.)
        //      Repeat until all flex items have been collected into flex lines
        //
        //      Note that the "collect as many" line will collect zero-sized flex items onto
        //      the end of the previous line even if the last non-zero item exactly "filled up" the line.

        let mut flex_lines: sys::Vec<_> = {
            let mut lines = sys::new_vec_with_capacity(1);

            if self.nodes[node].style.flex_wrap == FlexWrap::NoWrap {
                lines.push(FlexLine { items: flex_items.as_mut_slice(), cross_size: 0.0, offset_cross: 0.0 });
            } else {
                let mut flex_items = &mut flex_items[..];

                while !flex_items.is_empty() {
                    let mut line_length = 0.0;
                    let index = flex_items
                        .iter()
                        .enumerate()
                        .find(|&(idx, child)| {
                            line_length += child.hypothetical_outer_size.main(dir);
                            if let Defined(main) = available_space.main(dir) {
                                line_length > main && idx != 0
                            } else {
                                false
                            }
                        })
                        .map(|(idx, _)| idx)
                        .unwrap_or(flex_items.len());

                    let (items, rest) = flex_items.split_at_mut(index);
                    lines.push(FlexLine { items, cross_size: 0.0, offset_cross: 0.0 });
                    flex_items = rest;
                }
            }

            lines
        };

        // 6. Resolve the flexible lengths of all the flex items to find their used main size.
        //    See §9.7 Resolving Flexible Lengths.
        //
        // 9.7. Resolving Flexible Lengths

        for line in &mut flex_lines {
            // 1. Determine the used flex factor. Sum the outer hypothetical main sizes of all
            //    items on the line. If the sum is less than the flex container’s inner main size,
            //    use the flex grow factor for the rest of this algorithm; otherwise, use the
            //    flex shrink factor.

            let used_flex_factor: f32 = line.items.iter().map(|child| child.hypothetical_outer_size.main(dir)).sum();
            let growing = used_flex_factor < node_inner_size.main(dir).or_else(0.0);
            let shrinking = !growing;

            // 2. Size inflexible items. Freeze, setting its target main size to its hypothetical main size
            //    - Any item that has a flex factor of zero
            //    - If using the flex grow factor: any item that has a flex base size
            //      greater than its hypothetical main size
            //    - If using the flex shrink factor: any item that has a flex base size
            //      smaller than its hypothetical main size

            for child in line.items.iter_mut() {
                // TODO - This is not found by reading the spec. Maybe this can be done in some other place
                // instead. This was found by trail and error fixing tests to align with webkit output.
                if node_inner_size.main(dir).is_undefined() && is_row {
                    child.target_size.set_main(
                        dir,
                        self.compute_internal(
                            child.node,
                            Size {
                                width: child.size.width.maybe_max(child.min_size.width).maybe_min(child.max_size.width),
                                height: child
                                    .size
                                    .height
                                    .maybe_max(child.min_size.height)
                                    .maybe_min(child.max_size.height),
                            },
                            available_space,
                            false,
                            false,
                        )
                        .size
                        .main(dir)
                        .maybe_max(child.min_size.main(dir))
                        .maybe_min(child.max_size.main(dir)),
                    );
                } else {
                    child.target_size.set_main(dir, child.hypothetical_inner_size.main(dir));
                }

                // TODO this should really only be set inside the if-statement below but
                // that causes the target_main_size to never be set for some items

                child.outer_target_size.set_main(dir, child.target_size.main(dir) + child.margin.main(dir));

                let child_style = &self.nodes[child.node].style;
                if (child_style.flex_grow == 0.0 && child_style.flex_shrink == 0.0)
                    || (growing && child.flex_basis > child.hypothetical_inner_size.main(dir))
                    || (shrinking && child.flex_basis < child.hypothetical_inner_size.main(dir))
                {
                    child.frozen = true;
                }
            }

            // 3. Calculate initial free space. Sum the outer sizes of all items on the line,
            //    and subtract this from the flex container’s inner main size. For frozen items,
            //    use their outer target main size; for other items, use their outer flex base size.

            let used_space: f32 = line
                .items
                .iter()
                .map(|child| {
                    child.margin.main(dir) + if child.frozen { child.target_size.main(dir) } else { child.flex_basis }
                })
                .sum();

            let initial_free_space = (node_inner_size.main(dir) - used_space).or_else(0.0);

            // 4. Loop

            loop {
                // a. Check for flexible items. If all the flex items on the line are frozen,
                //    free space has been distributed; exit this loop.

                if line.items.iter().all(|child| child.frozen) {
                    break;
                }

                // b. Calculate the remaining free space as for initial free space, above.
                //    If the sum of the unfrozen flex items’ flex factors is less than one,
                //    multiply the initial free space by this sum. If the magnitude of this
                //    value is less than the magnitude of the remaining free space, use this
                //    as the remaining free space.

                let used_space: f32 = line
                    .items
                    .iter()
                    .map(|child| {
                        child.margin.main(dir)
                            + if child.frozen { child.target_size.main(dir) } else { child.flex_basis }
                    })
                    .sum();

                let mut unfrozen: sys::Vec<&mut FlexItem> =
                    line.items.iter_mut().filter(|child| !child.frozen).collect();

                let (sum_flex_grow, sum_flex_shrink): (f32, f32) =
                    unfrozen.iter().fold((0.0, 0.0), |(flex_grow, flex_shrink), item| {
                        let style = &self.nodes[item.node].style;
                        (flex_grow + style.flex_grow, flex_shrink + style.flex_shrink)
                    });

                let free_space = if growing && sum_flex_grow < 1.0 {
                    (initial_free_space * sum_flex_grow).maybe_min(node_inner_size.main(dir) - used_space)
                } else if shrinking && sum_flex_shrink < 1.0 {
                    (initial_free_space * sum_flex_shrink).maybe_max(node_inner_size.main(dir) - used_space)
                } else {
                    (node_inner_size.main(dir) - used_space).or_else(0.0)
                };

                // c. Distribute free space proportional to the flex factors.
                //    - If the remaining free space is zero
                //        Do Nothing
                //    - If using the flex grow factor
                //        Find the ratio of the item’s flex grow factor to the sum of the
                //        flex grow factors of all unfrozen items on the line. Set the item’s
                //        target main size to its flex base size plus a fraction of the remaining
                //        free space proportional to the ratio.
                //    - If using the flex shrink factor
                //        For every unfrozen item on the line, multiply its flex shrink factor by
                //        its inner flex base size, and note this as its scaled flex shrink factor.
                //        Find the ratio of the item’s scaled flex shrink factor to the sum of the
                //        scaled flex shrink factors of all unfrozen items on the line. Set the item’s
                //        target main size to its flex base size minus a fraction of the absolute value
                //        of the remaining free space proportional to the ratio. Note this may result
                //        in a negative inner main size; it will be corrected in the next step.
                //    - Otherwise
                //        Do Nothing

                if free_space.is_normal() {
                    if growing && sum_flex_grow > 0.0 {
                        for child in &mut unfrozen {
                            child.target_size.set_main(
                                dir,
                                child.flex_basis
                                    + free_space * (self.nodes[child.node].style.flex_grow / sum_flex_grow),
                            );
                        }
                    } else if shrinking && sum_flex_shrink > 0.0 {
                        let sum_scaled_shrink_factor: f32 = unfrozen
                            .iter()
                            .map(|child| child.inner_flex_basis * self.nodes[child.node].style.flex_shrink)
                            .sum();

                        if sum_scaled_shrink_factor > 0.0 {
                            for child in &mut unfrozen {
                                let scaled_shrink_factor =
                                    child.inner_flex_basis * self.nodes[child.node].style.flex_shrink;
                                child.target_size.set_main(
                                    dir,
                                    child.flex_basis + free_space * (scaled_shrink_factor / sum_scaled_shrink_factor),
                                )
                            }
                        }
                    }
                }

                // d. Fix min/max violations. Clamp each non-frozen item’s target main size by its
                //    used min and max main sizes and floor its content-box size at zero. If the
                //    item’s target main size was made smaller by this, it’s a max violation.
                //    If the item’s target main size was made larger by this, it’s a min violation.

                let total_violation = unfrozen.iter_mut().fold(0.0, |acc, child| -> f32 {
                    // TODO - not really spec abiding but needs to be done somewhere. probably somewhere else though.
                    // The following logic was developed not from the spec but by trail and error looking into how
                    // webkit handled various scenarios. Can probably be solved better by passing in
                    // min-content max-content constraints from the top. Need to figure out correct thing to do here as
                    // just piling on more conditionals.
                    let min_main = if is_row && self.nodes[child.node].measure.is_none() {
                        self.compute_internal(child.node, Size::undefined(), available_space, false, false)
                            .size
                            .width
                            .maybe_min(child.size.width)
                            .maybe_max(child.min_size.width)
                            .into()
                    } else {
                        child.min_size.main(dir)
                    };

                    let max_main = child.max_size.main(dir);
                    let clamped = child.target_size.main(dir).maybe_min(max_main).maybe_max(min_main).max(0.0);
                    child.violation = clamped - child.target_size.main(dir);
                    child.target_size.set_main(dir, clamped);
                    child.outer_target_size.set_main(dir, child.target_size.main(dir) + child.margin.main(dir));

                    acc + child.violation
                });

                // e. Freeze over-flexed items. The total violation is the sum of the adjustments
                //    from the previous step ∑(clamped size - unclamped size). If the total violation is:
                //    - Zero
                //        Freeze all items.
                //    - Positive
                //        Freeze all the items with min violations.
                //    - Negative
                //        Freeze all the items with max violations.

                for child in &mut unfrozen {
                    match total_violation {
                        v if v > 0.0 => child.frozen = child.violation > 0.0,
                        v if v < 0.0 => child.frozen = child.violation < 0.0,
                        _ => child.frozen = true,
                    }
                }

                // f. Return to the start of this loop.
            }
        }

        // Not part of the spec from what i can see but seems correct
        container_size.set_main(
            dir,
            node_size.main(dir).or_else({
                let longest_line = flex_lines.iter().fold(f32::MIN, |acc, line| {
                    let length: f32 = line.items.iter().map(|item| item.outer_target_size.main(dir)).sum();
                    acc.max(length)
                });

                let size = longest_line + padding_border.main(dir);
                match available_space.main(dir) {
                    Defined(val) if flex_lines.len() > 1 && size < val => val,
                    _ => size,
                }
            }),
        );

        inner_container_size.set_main(dir, container_size.main(dir) - padding_border.main(dir));

        // 9.4. Cross Size Determination

        // 7. Determine the hypothetical cross size of each item by performing layout with the
        //    used main size and the available space, treating auto as fit-content.

        for line in &mut flex_lines {
            for child in line.items.iter_mut() {
                let child_cross =
                    child.size.cross(dir).maybe_max(child.min_size.cross(dir)).maybe_min(child.max_size.cross(dir));

                child.hypothetical_inner_size.set_cross(
                    dir,
                    self.compute_internal(
                        child.node,
                        Size {
                            width: if is_row { child.target_size.width.into() } else { child_cross },
                            height: if is_row { child_cross } else { child.target_size.height.into() },
                        },
                        Size {
                            width: if is_row { container_size.main(dir).into() } else { available_space.width },
                            height: if is_row { available_space.height } else { container_size.main(dir).into() },
                        },
                        false,
                        false,
                    )
                    .size
                    .cross(dir)
                    .maybe_max(child.min_size.cross(dir))
                    .maybe_min(child.max_size.cross(dir)),
                );

                child
                    .hypothetical_outer_size
                    .set_cross(dir, child.hypothetical_inner_size.cross(dir) + child.margin.cross(dir));
            }
        }

        // TODO - probably should move this somewhere else as it doesn't make a ton of sense here but we need it below
        // TODO - This is expensive and should only be done if we really require a baseline. aka, make it lazy

        fn calc_baseline(db: &Forest, node: NodeId, layout: &result::Layout) -> f32 {
            if db.children[node].is_empty() {
                layout.size.height
            } else {
                let child = db.children[node][0];
                calc_baseline(db, child, &db.nodes[child].layout)
            }
        }

        if has_baseline_child {
            for line in &mut flex_lines {
                for child in line.items.iter_mut() {
                    let result = self.compute_internal(
                        child.node,
                        Size {
                            width: if is_row {
                                child.target_size.width.into()
                            } else {
                                child.hypothetical_inner_size.width.into()
                            },
                            height: if is_row {
                                child.hypothetical_inner_size.height.into()
                            } else {
                                child.target_size.height.into()
                            },
                        },
                        Size {
                            width: if is_row { container_size.width.into() } else { node_size.width },
                            height: if is_row { node_size.height } else { container_size.height.into() },
                        },
                        true,
                        false,
                    );

                    child.baseline = calc_baseline(
                        self,
                        child.node,
                        &result::Layout {
                            order: self.children[node].iter().position(|n| *n == child.node).unwrap() as u32,
                            size: result.size,
                            location: Point::zero(),
                        },
                    );
                }
            }
        }

        // 8. Calculate the cross size of each flex line.
        //    If the flex container is single-line and has a definite cross size, the cross size
        //    of the flex line is the flex container’s inner cross size. Otherwise, for each flex line:
        //
        //    If the flex container is single-line, then clamp the line’s cross-size to be within
        //    the container’s computed min and max cross sizes. Note that if CSS 2.1’s definition
        //    of min/max-width/height applied more generally, this behavior would fall out automatically.

        if flex_lines.len() == 1 && node_size.cross(dir).is_defined() {
            flex_lines[0].cross_size = (node_size.cross(dir) - padding_border.cross(dir)).or_else(0.0);
        } else {
            for line in &mut flex_lines {
                //    1. Collect all the flex items whose inline-axis is parallel to the main-axis, whose
                //       align-self is baseline, and whose cross-axis margins are both non-auto. Find the
                //       largest of the distances between each item’s baseline and its hypothetical outer
                //       cross-start edge, and the largest of the distances between each item’s baseline
                //       and its hypothetical outer cross-end edge, and sum these two values.

                //    2. Among all the items not collected by the previous step, find the largest
                //       outer hypothetical cross size.

                //    3. The used cross-size of the flex line is the largest of the numbers found in the
                //       previous two steps and zero.

                let max_baseline: f32 = line.items.iter().map(|child| child.baseline).fold(0.0, |acc, x| acc.max(x));
                line.cross_size = line
                    .items
                    .iter()
                    .map(|child| {
                        let child_style = &self.nodes[child.node].style;
                        if child_style.align_self(&self.nodes[node].style) == AlignSelf::Baseline
                            && child_style.cross_margin_start(dir) != Dimension::Auto
                            && child_style.cross_margin_end(dir) != Dimension::Auto
                            && child_style.cross_size(dir) == Dimension::Auto
                        {
                            max_baseline - child.baseline + child.hypothetical_outer_size.cross(dir)
                        } else {
                            child.hypothetical_outer_size.cross(dir)
                        }
                    })
                    .fold(0.0, |acc, x| acc.max(x));
            }
        }

        // 9. Handle 'align-content: stretch'. If the flex container has a definite cross size,
        //    align-content is stretch, and the sum of the flex lines' cross sizes is less than
        //    the flex container’s inner cross size, increase the cross size of each flex line
        //    by equal amounts such that the sum of their cross sizes exactly equals the
        //    flex container’s inner cross size.

        if self.nodes[node].style.align_content == AlignContent::Stretch && node_size.cross(dir).is_defined() {
            let total_cross: f32 = flex_lines.iter().map(|line| line.cross_size).sum();
            let inner_cross = (node_size.cross(dir) - padding_border.cross(dir)).or_else(0.0);

            if total_cross < inner_cross {
                let remaining = inner_cross - total_cross;
                let addition = remaining / flex_lines.len() as f32;
                flex_lines.iter_mut().for_each(|line| line.cross_size += addition);
            }
        }

        // 10. Collapse visibility:collapse items. If any flex items have visibility: collapse,
        //     note the cross size of the line they’re in as the item’s strut size, and restart
        //     layout from the beginning.
        //
        //     In this second layout round, when collecting items into lines, treat the collapsed
        //     items as having zero main size. For the rest of the algorithm following that step,
        //     ignore the collapsed items entirely (as if they were display:none) except that after
        //     calculating the cross size of the lines, if any line’s cross size is less than the
        //     largest strut size among all the collapsed items in the line, set its cross size to
        //     that strut size.
        //
        //     Skip this step in the second layout round.

        // TODO implement once (if ever) we support visibility:collapse

        // 11. Determine the used cross size of each flex item. If a flex item has align-self: stretch,
        //     its computed cross size property is auto, and neither of its cross-axis margins are auto,
        //     the used outer cross size is the used cross size of its flex line, clamped according to
        //     the item’s used min and max cross sizes. Otherwise, the used cross size is the item’s
        //     hypothetical cross size.
        //
        //     If the flex item has align-self: stretch, redo layout for its contents, treating this
        //     used size as its definite cross size so that percentage-sized children can be resolved.
        //
        //     Note that this step does not affect the main size of the flex item, even if it has an
        //     intrinsic aspect ratio.

        for line in &mut flex_lines {
            let line_cross_size = line.cross_size;

            for child in line.items.iter_mut() {
                let child_style = &self.nodes[child.node].style;
                child.target_size.set_cross(
                    dir,
                    if child_style.align_self(&self.nodes[node].style) == AlignSelf::Stretch
                        && child_style.cross_margin_start(dir) != Dimension::Auto
                        && child_style.cross_margin_end(dir) != Dimension::Auto
                        && child_style.cross_size(dir) == Dimension::Auto
                    {
                        (line_cross_size - child.margin.cross(dir))
                            .maybe_max(child.min_size.cross(dir))
                            .maybe_min(child.max_size.cross(dir))
                    } else {
                        child.hypothetical_inner_size.cross(dir)
                    },
                );

                child.outer_target_size.set_cross(dir, child.target_size.cross(dir) + child.margin.cross(dir));
            }
        }

        // 9.5. Main-Axis Alignment

        // 12. Distribute any remaining free space. For each flex line:
        //     1. If the remaining free space is positive and at least one main-axis margin on this
        //        line is auto, distribute the free space equally among these margins. Otherwise,
        //        set all auto margins to zero.
        //     2. Align the items along the main-axis per justify-content.

        for line in &mut flex_lines {
            let used_space: f32 = line.items.iter().map(|child| child.outer_target_size.main(dir)).sum();
            let free_space = inner_container_size.main(dir) - used_space;
            let mut num_auto_margins = 0;

            for child in line.items.iter_mut() {
                let child_style = &self.nodes[child.node].style;
                if child_style.main_margin_start(dir) == Dimension::Auto {
                    num_auto_margins += 1;
                }
                if child_style.main_margin_end(dir) == Dimension::Auto {
                    num_auto_margins += 1;
                }
            }

            if free_space > 0.0 && num_auto_margins > 0 {
                let margin = free_space / num_auto_margins as f32;

                for child in line.items.iter_mut() {
                    let child_style = &self.nodes[child.node].style;
                    if child_style.main_margin_start(dir) == Dimension::Auto {
                        if is_row {
                            child.margin.start = margin;
                        } else {
                            child.margin.top = margin;
                        }
                    }
                    if child_style.main_margin_end(dir) == Dimension::Auto {
                        if is_row {
                            child.margin.end = margin;
                        } else {
                            child.margin.bottom = margin;
                        }
                    }
                }
            } else {
                let num_items = line.items.len();
                let layout_reverse = dir.is_reverse();

                let justify_item = |(i, child): (usize, &mut FlexItem)| {
                    let is_first = i == 0;

                    child.offset_main = match self.nodes[node].style.justify_content {
                        JustifyContent::FlexStart => {
                            if layout_reverse && is_first {
                                free_space
                            } else {
                                0.0
                            }
                        }
                        JustifyContent::Center => {
                            if is_first {
                                free_space / 2.0
                            } else {
                                0.0
                            }
                        }
                        JustifyContent::FlexEnd => {
                            if is_first && !layout_reverse {
                                free_space
                            } else {
                                0.0
                            }
                        }
                        JustifyContent::SpaceBetween => {
                            if is_first {
                                0.0
                            } else {
                                free_space / (num_items - 1) as f32
                            }
                        }
                        JustifyContent::SpaceAround => {
                            if is_first {
                                (free_space / num_items as f32) / 2.0
                            } else {
                                free_space / num_items as f32
                            }
                        }
                        JustifyContent::SpaceEvenly => free_space / (num_items + 1) as f32,
                    };
                };

                if layout_reverse {
                    line.items.iter_mut().rev().enumerate().for_each(justify_item);
                } else {
                    line.items.iter_mut().enumerate().for_each(justify_item);
                }
            }
        }

        // 9.6. Cross-Axis Alignment

        // 13. Resolve cross-axis auto margins. If a flex item has auto cross-axis margins:
        //     - If its outer cross size (treating those auto margins as zero) is less than the
        //       cross size of its flex line, distribute the difference in those sizes equally
        //       to the auto margins.
        //     - Otherwise, if the block-start or inline-start margin (whichever is in the cross axis)
        //       is auto, set it to zero. Set the opposite margin so that the outer cross size of the
        //       item equals the cross size of its flex line.

        for line in &mut flex_lines {
            let line_cross_size = line.cross_size;
            let max_baseline: f32 = line.items.iter_mut().map(|child| child.baseline).fold(0.0, |acc, x| acc.max(x));

            for child in line.items.iter_mut() {
                let free_space = line_cross_size - child.outer_target_size.cross(dir);
                let child_style = &self.nodes[child.node].style;

                if child_style.cross_margin_start(dir) == Dimension::Auto
                    && child_style.cross_margin_end(dir) == Dimension::Auto
                {
                    if is_row {
                        child.margin.top = free_space / 2.0;
                        child.margin.bottom = free_space / 2.0;
                    } else {
                        child.margin.start = free_space / 2.0;
                        child.margin.end = free_space / 2.0;
                    }
                } else if child_style.cross_margin_start(dir) == Dimension::Auto {
                    if is_row {
                        child.margin.top = free_space;
                    } else {
                        child.margin.start = free_space;
                    }
                } else if child_style.cross_margin_end(dir) == Dimension::Auto {
                    if is_row {
                        child.margin.bottom = free_space;
                    } else {
                        child.margin.end = free_space;
                    }
                } else {
                    // 14. Align all flex items along the cross-axis per align-self, if neither of the item’s
                    //     cross-axis margins are auto.

                    child.offset_cross = match child_style.align_self(&self.nodes[node].style) {
                        AlignSelf::Auto => 0.0, // Should never happen
                        AlignSelf::FlexStart => {
                            if is_wrap_reverse {
                                free_space
                            } else {
                                0.0
                            }
                        }
                        AlignSelf::FlexEnd => {
                            if is_wrap_reverse {
                                0.0
                            } else {
                                free_space
                            }
                        }
                        AlignSelf::Center => free_space / 2.0,
                        AlignSelf::Baseline => {
                            if is_row {
                                max_baseline - child.baseline
                            } else {
                                // baseline alignment only makes sense if the direction is row
                                // we treat it as flex-start alignment in columns.
                                if is_wrap_reverse {
                                    free_space
                                } else {
                                    0.0
                                }
                            }
                        }
                        AlignSelf::Stretch => {
                            if is_wrap_reverse {
                                free_space
                            } else {
                                0.0
                            }
                        }
                    };
                }
            }
        }

        // 15. Determine the flex container’s used cross size:
        //     - If the cross size property is a definite size, use that, clamped by the used
        //       min and max cross sizes of the flex container.
        //     - Otherwise, use the sum of the flex lines' cross sizes, clamped by the used
        //       min and max cross sizes of the flex container.

        let total_cross_size: f32 = flex_lines.iter().map(|line| line.cross_size).sum();
        container_size.set_cross(dir, node_size.cross(dir).or_else(total_cross_size + padding_border.cross(dir)));
        inner_container_size.set_cross(dir, container_size.cross(dir) - padding_border.cross(dir));

        // We have the container size. If our caller does not care about performing
        // layout we are done now.
        if !perform_layout {
            let result = ComputeResult { size: container_size };
            *self.cache(node, main_size) =
                Some(result::Cache { node_size, parent_size, perform_layout, result: result.clone() });
            return result;
        }

        // 16. Align all flex lines per align-content.

        let free_space = inner_container_size.cross(dir) - total_cross_size;
        let num_lines = flex_lines.len();

        let align_line = |(i, line): (usize, &mut FlexLine)| {
            let is_first = i == 0;

            line.offset_cross = match self.nodes[node].style.align_content {
                AlignContent::FlexStart => {
                    if is_first && is_wrap_reverse {
                        free_space
                    } else {
                        0.0
                    }
                }
                AlignContent::FlexEnd => {
                    if is_first && !is_wrap_reverse {
                        free_space
                    } else {
                        0.0
                    }
                }
                AlignContent::Center => {
                    if is_first {
                        free_space / 2.0
                    } else {
                        0.0
                    }
                }
                AlignContent::Stretch => 0.0,
                AlignContent::SpaceBetween => {
                    if is_first {
                        0.0
                    } else {
                        free_space / (num_lines - 1) as f32
                    }
                }
                AlignContent::SpaceAround => {
                    if is_first {
                        (free_space / num_lines as f32) / 2.0
                    } else {
                        free_space / num_lines as f32
                    }
                }
            };
        };

        if is_wrap_reverse {
            flex_lines.iter_mut().rev().enumerate().for_each(align_line);
        } else {
            flex_lines.iter_mut().enumerate().for_each(align_line);
        }

        // Do a final layout pass and gather the resulting layouts
        {
            let mut total_offset_cross = padding_border.cross_start(dir);

            let layout_line = |line: &mut FlexLine| {
                let mut total_offset_main = padding_border.main_start(dir);
                let line_offset_cross = line.offset_cross;

                let layout_item = |child: &mut FlexItem| {
                    let result = self.compute_internal(
                        child.node,
                        child.target_size.map(|s| s.into()),
                        container_size.map(|s| s.into()),
                        true,
                        false,
                    );

                    let offset_main = total_offset_main
                        + child.offset_main
                        + child.margin.main_start(dir)
                        + (child.position.main_start(dir).or_else(0.0) - child.position.main_end(dir).or_else(0.0));

                    let offset_cross = total_offset_cross
                        + child.offset_cross
                        + line_offset_cross
                        + child.margin.cross_start(dir)
                        + (child.position.cross_start(dir).or_else(0.0) - child.position.cross_end(dir).or_else(0.0));

                    self.nodes[child.node].layout = result::Layout {
                        order: self.children[node].iter().position(|n| *n == child.node).unwrap() as u32,
                        size: result.size,
                        location: Point {
                            x: if is_row { offset_main } else { offset_cross },
                            y: if is_column { offset_main } else { offset_cross },
                        },
                    };

                    total_offset_main += child.offset_main + child.margin.main(dir) + result.size.main(dir);
                };

                if dir.is_reverse() {
                    line.items.iter_mut().rev().for_each(layout_item);
                } else {
                    line.items.iter_mut().for_each(layout_item);
                }

                total_offset_cross += line_offset_cross + line.cross_size;
            };

            if is_wrap_reverse {
                flex_lines.iter_mut().rev().for_each(layout_line);
            } else {
                flex_lines.iter_mut().for_each(layout_line);
            }
        }

        // Before returning we perform absolute layout on all absolutely positioned children
        {
            // TODO: remove number of Vec<_> generated
            let candidates = self.children[node]
                .iter()
                .cloned()
                .enumerate()
                .filter(|(_, child)| self.nodes[*child].style.position_type == PositionType::Absolute)
                .collect::<sys::Vec<_>>();

            for (order, child) in candidates {
                let container_width = container_size.width.into();
                let container_height = container_size.height.into();

                let child_style = self.nodes[child].style;

                let start = child_style.position.start.resolve(container_width)
                    + child_style.margin.start.resolve(container_width);
                let end =
                    child_style.position.end.resolve(container_width) + child_style.margin.end.resolve(container_width);
                let top = child_style.position.top.resolve(container_height)
                    + child_style.margin.top.resolve(container_height);
                let bottom = child_style.position.bottom.resolve(container_height)
                    + child_style.margin.bottom.resolve(container_height);

                let (start_main, end_main) = if is_row { (start, end) } else { (top, bottom) };
                let (start_cross, end_cross) = if is_row { (top, bottom) } else { (start, end) };

                let width = child_style
                    .size
                    .width
                    .resolve(container_width)
                    .maybe_max(child_style.min_size.width.resolve(container_width))
                    .maybe_min(child_style.max_size.width.resolve(container_width))
                    .or_else(if start.is_defined() && end.is_defined() {
                        container_width - start - end
                    } else {
                        Undefined
                    });

                let height = child_style
                    .size
                    .height
                    .resolve(container_height)
                    .maybe_max(child_style.min_size.height.resolve(container_height))
                    .maybe_min(child_style.max_size.height.resolve(container_height))
                    .or_else(if top.is_defined() && bottom.is_defined() {
                        container_height - top - bottom
                    } else {
                        Undefined
                    });

                let result = self.compute_internal(
                    child,
                    Size { width, height },
                    Size { width: container_width, height: container_height },
                    true,
                    false,
                );

                let free_main_space = container_size.main(dir)
                    - result
                        .size
                        .main(dir)
                        .maybe_max(child_style.min_main_size(dir).resolve(node_inner_size.main(dir)))
                        .maybe_min(child_style.max_main_size(dir).resolve(node_inner_size.main(dir)));

                let free_cross_space = container_size.cross(dir)
                    - result
                        .size
                        .cross(dir)
                        .maybe_max(child_style.min_cross_size(dir).resolve(node_inner_size.cross(dir)))
                        .maybe_min(child_style.max_cross_size(dir).resolve(node_inner_size.cross(dir)));

                let offset_main = if start_main.is_defined() {
                    start_main.or_else(0.0) + border.main_start(dir)
                } else if end_main.is_defined() {
                    free_main_space - end_main.or_else(0.0) - border.main_end(dir)
                } else {
                    match self.nodes[node].style.justify_content {
                        JustifyContent::SpaceBetween | JustifyContent::FlexStart => padding_border.main_start(dir),
                        JustifyContent::FlexEnd => free_main_space - padding_border.main_end(dir),
                        JustifyContent::SpaceEvenly | JustifyContent::SpaceAround | JustifyContent::Center => {
                            free_main_space / 2.0
                        }
                    }
                };

                let offset_cross = if start_cross.is_defined() {
                    start_cross.or_else(0.0) + border.cross_start(dir)
                } else if end_cross.is_defined() {
                    free_cross_space - end_cross.or_else(0.0) - border.cross_end(dir)
                } else {
                    match child_style.align_self(&self.nodes[node].style) {
                        AlignSelf::Auto => 0.0, // Should never happen
                        AlignSelf::FlexStart => {
                            if is_wrap_reverse {
                                free_cross_space - padding_border.cross_end(dir)
                            } else {
                                padding_border.cross_start(dir)
                            }
                        }
                        AlignSelf::FlexEnd => {
                            if is_wrap_reverse {
                                padding_border.cross_start(dir)
                            } else {
                                free_cross_space - padding_border.cross_end(dir)
                            }
                        }
                        AlignSelf::Center => free_cross_space / 2.0,
                        AlignSelf::Baseline => free_cross_space / 2.0, // Treat as center for now until we have baseline support
                        AlignSelf::Stretch => {
                            if is_wrap_reverse {
                                free_cross_space - padding_border.cross_end(dir)
                            } else {
                                padding_border.cross_start(dir)
                            }
                        }
                    }
                };

                self.nodes[child].layout = result::Layout {
                    order: order as u32,
                    size: result.size,
                    location: Point {
                        x: if is_row { offset_main } else { offset_cross },
                        y: if is_column { offset_main } else { offset_cross },
                    },
                };
            }
        }

        fn hidden_layout(nodes: &mut [NodeData], children: &[sys::ChildrenVec<NodeId>], node: NodeId, order: u32) {
            nodes[node].layout = result::Layout { order, size: Size::zero(), location: Point::zero() };

            for (order, child) in children[node].iter().enumerate() {
                hidden_layout(nodes, children, *child, order as _);
            }
        }

        for (order, child) in self.children[node].iter().enumerate() {
            if self.nodes[*child].style.display == Display::None {
                hidden_layout(&mut self.nodes, &self.children, *child, order as _);
            }
        }

        let result = ComputeResult { size: container_size };
        *self.cache(node, main_size) =
            Some(result::Cache { node_size, parent_size, perform_layout, result: result.clone() });

        result
    }
}