waterui-layout 0.5.1

//! Horizontal stack layout.

use alloc::{vec, vec::Vec};
use nami::{Computed, Signal, SignalExt, collection::Collection};
use waterui_core::{
    AnyView, IntoSignalF32, View, env::with, id::Identifiable, layout::LayoutInvalidationCallback,
    view::TupleViews, views::ForEach,
};

use crate::{
    Layout, LazyContainer, PlacedSubview, Point, ProposalSize, Rect, Size, StretchAxis, SubView,
    SubviewPlacement,
    container::FixedContainer,
    stack::{
        Axis, VerticalAlignment,
        distribute::{
            ChildMeasurement, LineAnchor, container_line, cross_envelope, measure_stack,
            place_cross_extent, stack_spacing,
        },
        stack_stretch_axis,
    },
};

/// A view that arranges its children in a horizontal line.
///
/// Use an `HStack` to arrange views side-by-side. The stack sizes itself to fit
/// its contents, distributing available space among its children.
///
/// ```rust
/// # use waterui::prelude::*;
/// # fn greeting() -> impl View {
/// hstack((
///     text("Hello"),
///     text("World"),
/// ))
/// # }
/// ```
///
/// You can customize the spacing between children and their vertical alignment:
///
/// ```rust
/// # use waterui::prelude::*;
/// # fn spaced() -> impl View {
/// HStack::new(VerticalAlignment::Top, 20.0, (
///     text("First"),
///     text("Second"),
/// ))
/// # }
/// ```
///
/// Use [`spacer()`](crate::spacer()) to push content to the sides:
///
/// ```rust
/// # use waterui::prelude::*;
/// # fn toolbar() -> impl View {
/// hstack((
///     text("Leading"),
///     spacer(),
///     text("Trailing"),
/// ))
/// # }
/// ```
#[derive(Debug, Clone)]
pub struct HStack<C> {
    layout: HStackLayout,
    contents: C,
}

/// Layout engine shared by the public [`HStack`] view.
#[derive(Debug, Clone)]
pub struct HStackLayout {
    /// The vertical alignment of children within the stack.
    pub alignment: VerticalAlignment,
    /// The spacing between children in the stack.
    pub spacing: Computed<f32>,
}

impl Default for HStackLayout {
    fn default() -> Self {
        Self {
            alignment: VerticalAlignment::Center,
            spacing: Computed::constant(10.0),
        }
    }
}

/// The tallest child above and below the alignment guide.
///
/// Every child that reports a height counts, the ones that fill the cross axis
/// included. Filling means "at least what I measure, and more if you have it",
/// not "nothing": leaving a filler out of this makes a row of nothing-but-
/// fillers report zero height, and its parent then hands it zero height to
/// fill. A child that answers an unbounded height is answering "as much as you
/// have" rather than naming a size, so it sets no floor here — the fill pass in
/// [`Layout::place`] is what gives it the row's height.
/// The vertical envelope of the row's children lined up on `alignment`.
fn hstack_intrinsic_cross_metrics(
    measurements: &[ChildMeasurement],
    alignment: VerticalAlignment,
) -> (f32, f32) {
    cross_envelope(measurements.iter().map(|measurement| {
        (
            measurement.size().height,
            measurement.vertical_guide(alignment),
        )
    }))
}

impl Layout for HStackLayout {
    /// An `HStack` claims nothing of its own — a row of labels is content-sized,
    /// like `SwiftUI`'s, and a parent placing an undersized row centers it per
    /// its alignment. What it does claim is whatever its children claim: filling
    /// comes from children that ask for it (`Spacer`, greedy frames, `Color`),
    /// and the ask has to survive the trip up through every container between
    /// that child and whoever owns the space.
    fn stretch_axis(&self, children: &[StretchAxis]) -> StretchAxis {
        stack_stretch_axis(Axis::Horizontal, children)
    }

    fn size_that_fits(&self, proposal: ProposalSize, children: &[&dyn SubView]) -> Size {
        if children.is_empty() {
            return Size::zero();
        }

        let spacing = self.spacing.get();
        let measurements = measure_stack(Axis::Horizontal, proposal, spacing, children);
        let width = measurements.iter().map(|m| m.size().width).sum::<f32>()
            + stack_spacing(spacing, children.len());
        let (above, below) = hstack_intrinsic_cross_metrics(&measurements, self.alignment);
        let height = if measurements.iter().any(|m| m.size().height.is_infinite()) {
            f32::INFINITY
        } else {
            above + below
        };
        Size::new(width, height)
    }

    fn place(
        &self,
        bounds: Rect,
        _proposal: ProposalSize,
        children: &[&dyn SubView],
    ) -> Vec<SubviewPlacement> {
        if children.is_empty() {
            return vec![];
        }

        let spacing = self.spacing.get();
        // Placement is a fresh negotiation against the bounds the row was
        // placed in: every child is allocated from the row's resolved width
        // and proposed the row's resolved height, so what a child lays out
        // under is the extent it actually has, never the offer the row was
        // measured with.
        let placement = ProposalSize::new(Some(bounds.width()), Some(bounds.height()));
        let measurements = measure_stack(Axis::Horizontal, placement, spacing, children);

        let (above, below) = hstack_intrinsic_cross_metrics(&measurements, self.alignment);
        let guide_line = bounds.y()
            + container_line(
                bounds.height(),
                LineAnchor::vertical(self.alignment),
                above,
                below,
            );

        // Place children
        let mut placements = Vec::with_capacity(children.len());
        let mut current_x = bounds.x();

        for (i, measurement) in measurements.iter().enumerate() {
            if i > 0 {
                current_x += spacing;
            }

            let child_height = place_cross_extent(
                measurement.size().height,
                bounds.height(),
                measurement.stretches_cross_axis(),
            );

            let child_width = measurement.size().width;

            let mut adjusted_dimensions = measurement.dimensions.clone();
            adjusted_dimensions.size = Size::new(child_width, child_height);

            // A child that fills the cross axis spans the bounds; every other
            // child sits with its guide on the row's line, wherever that
            // guide lies.
            let y = if measurement.stretches_cross_axis() {
                bounds.y()
            } else {
                guide_line - adjusted_dimensions.vertical(self.alignment)
            };

            let rect = Rect::new(
                Point::new(current_x, y),
                Size::new(child_width, child_height),
            );
            placements.push(SubviewPlacement::new(rect, measurement.proposal));

            current_x += child_width;
        }

        placements
    }

    fn explicit_vertical(
        &self,
        alignment: VerticalAlignment,
        _bounds: Rect,
        children: &[PlacedSubview<'_>],
    ) -> Option<f32> {
        if alignment == VerticalAlignment::LastBaseline {
            return children
                .iter()
                .filter_map(|child| child.explicit_vertical(alignment))
                .max_by(f32::total_cmp);
        }

        if alignment == VerticalAlignment::FirstBaseline || alignment == self.alignment {
            return children
                .iter()
                .filter_map(|child| child.explicit_vertical(alignment))
                .min_by(f32::total_cmp);
        }

        None
    }

    fn watch_invalidation(
        &self,
        invalidate: LayoutInvalidationCallback,
    ) -> Vec<nami::watcher::BoxWatcherGuard> {
        vec![self.spacing.watch(move |_| invalidate())]
    }
}

impl<C: TupleViews> HStack<(C,)> {
    /// Creates a horizontal stack with the provided alignment, spacing, and
    /// children.
    pub fn new(alignment: VerticalAlignment, spacing: f32, contents: C) -> Self {
        Self {
            layout: HStackLayout {
                alignment,
                spacing: Computed::constant(spacing),
            },
            contents: (contents,),
        }
    }
}

impl<C> HStack<C> {
    /// Sets the vertical alignment for children in the stack — a
    /// [`VerticalAlignment`] or one of the tokens [`Top`], [`Center`],
    /// [`Bottom`], [`FirstBaseline`], [`LastBaseline`].
    ///
    /// [`Top`]: crate::Top
    /// [`Center`]: crate::Center
    /// [`Bottom`]: crate::Bottom
    /// [`FirstBaseline`]: crate::FirstBaseline
    /// [`LastBaseline`]: crate::LastBaseline
    #[must_use]
    pub fn alignment(mut self, alignment: impl Into<VerticalAlignment>) -> Self {
        self.layout.alignment = alignment.into();
        self
    }

    crate::alignment::vertical_alignment_methods!();

    /// Sets the spacing between children in the stack.
    ///
    /// Accepts any numeric literal or signal of f32. Signal changes invalidate
    /// only this stack's native layout.
    #[must_use]
    pub fn spacing(mut self, spacing: impl IntoSignalF32 + 'static) -> Self {
        self.layout.spacing = spacing.into_signal_f32().computed();
        self
    }
}

crate::stack::impl_stack_for_each!(HStack, HStackLayout);

impl<V> FromIterator<V> for HStack<(Vec<AnyView>,)>
where
    V: View,
{
    fn from_iter<T: IntoIterator<Item = V>>(iter: T) -> Self {
        let contents = iter.into_iter().map(AnyView::new).collect();
        Self::new(VerticalAlignment::default(), 10.0, contents)
    }
}

/// Convenience constructor that centres children and uses the default spacing.
pub fn hstack<C: TupleViews>(contents: C) -> HStack<(C,)> {
    HStack::new(VerticalAlignment::Center, 10.0, contents)
}

impl<C, F, V> View for HStack<ForEach<C, F, V>>
where
    C: Collection + Clone,
    C::Item: Identifiable,
    F: 'static + Fn(C::Item) -> V,
    V: View,
{
    fn body(self, _env: &waterui_core::Environment) -> impl View {
        // Inject the horizontal axis into the container
        with(
            LazyContainer::new(self.layout, self.contents),
            Axis::Horizontal,
        )
    }

    /// Resolves to `LazyContainer`, which cannot enumerate children without
    /// materializing them and answers its layout's axis over an empty child
    /// set — matching `LazyContainer::stretch_axis`.
    fn stretch_axis(&self) -> StretchAxis {
        self.layout.stretch_axis(&[])
    }
}

impl<C: TupleViews + 'static> View for HStack<(C,)> {
    fn body(self, _env: &waterui_core::Environment) -> impl View {
        // Inject the horizontal axis into the container
        with(
            FixedContainer::new(self.layout, self.contents.0),
            Axis::Horizontal,
        )
    }

    /// Resolves to `FixedContainer` over the same layout and children;
    /// reports what that container would — matching `FixedContainer`'s
    /// `View::stretch_axis`.
    fn stretch_axis(&self) -> StretchAxis {
        self.layout.stretch_axis(&self.contents.0.stretch_axes())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::ViewDimensions;
    use crate::tests::CompressibleView;

    struct MockSubView {
        size: Size,
        stretch_axis: StretchAxis,
    }

    impl SubView for MockSubView {
        fn measure(&self, _proposal: ProposalSize) -> ViewDimensions {
            ViewDimensions::new(self.size)
        }
        fn stretch_axis(&self) -> StretchAxis {
            self.stretch_axis
        }
        fn priority(&self) -> i32 {
            0
        }
    }

    struct ResponsiveSubView {
        intrinsic: Size,
        wrapped_height: f32,
        wrap_at_or_below: f32,
        stretch_axis: StretchAxis,
    }

    impl SubView for ResponsiveSubView {
        fn measure(&self, proposal: ProposalSize) -> ViewDimensions {
            ViewDimensions::new(match proposal.width {
                Some(width) if width <= self.wrap_at_or_below => {
                    Size::new(width, self.wrapped_height)
                }
                Some(width) => Size::new(width, self.intrinsic.height),
                None => self.intrinsic,
            })
        }

        fn stretch_axis(&self) -> StretchAxis {
            self.stretch_axis
        }

        fn priority(&self) -> i32 {
            0
        }
    }

    #[test]
    fn test_hstack_size_two_children() {
        let layout = HStackLayout {
            alignment: VerticalAlignment::Center,
            spacing: Computed::constant(10.0),
        };

        let mut child1 = MockSubView {
            size: Size::new(50.0, 30.0),
            stretch_axis: StretchAxis::None,
        };
        let mut child2 = MockSubView {
            size: Size::new(60.0, 40.0),
            stretch_axis: StretchAxis::None,
        };

        let children: Vec<&dyn SubView> = vec![&mut child1, &mut child2];

        let size = layout.size_that_fits(ProposalSize::UNSPECIFIED, &children);

        assert!((size.width - 120.0).abs() < f32::EPSILON); // 50 + 10 + 60
        assert!((size.height - 40.0).abs() < f32::EPSILON); // max height
    }

    #[test]
    fn test_hstack_with_spacer() {
        let layout = HStackLayout {
            alignment: VerticalAlignment::Center,
            spacing: Computed::constant(0.0),
        };

        let mut child1 = MockSubView {
            size: Size::new(30.0, 40.0),
            stretch_axis: StretchAxis::None,
        };
        let mut spacer = MockSubView {
            size: Size::zero(),
            stretch_axis: StretchAxis::Both, // Spacer stretches in both directions
        };
        let mut child2 = MockSubView {
            size: Size::new(30.0, 40.0),
            stretch_axis: StretchAxis::None,
        };

        let children: Vec<&dyn SubView> = vec![&mut child1, &mut spacer, &mut child2];

        // With specified width, spacer should expand
        let size = layout.size_that_fits(ProposalSize::new(Some(200.0), None), &children);

        assert!((size.width - 200.0).abs() < f32::EPSILON);

        // Place should distribute remaining space to spacer
        let bounds = Rect::new(Point::zero(), Size::new(200.0, 40.0));

        let mut child1 = MockSubView {
            size: Size::new(30.0, 40.0),
            stretch_axis: StretchAxis::None,
        };
        let mut spacer = MockSubView {
            size: Size::zero(),
            stretch_axis: StretchAxis::Both,
        };
        let mut child2 = MockSubView {
            size: Size::new(30.0, 40.0),
            stretch_axis: StretchAxis::None,
        };
        let children: Vec<&dyn SubView> = vec![&mut child1, &mut spacer, &mut child2];

        let placements = layout.place(bounds, ProposalSize::new(Some(200.0), None), &children);

        assert!((placements[0].frame.width() - 30.0).abs() < f32::EPSILON);
        assert!((placements[1].frame.width() - 140.0).abs() < f32::EPSILON); // 200 - 30 - 30
        assert!((placements[2].frame.width() - 30.0).abs() < f32::EPSILON);
        assert!((placements[2].frame.x() - 170.0).abs() < f32::EPSILON); // 30 + 140
    }

    /// A child that fills the cross axis still contributes the height it
    /// measures. Filling means "at least this, and more if you have it": a row
    /// that reported less than its tallest child would be handed less, and the
    /// child would fill a box too small for it.
    #[test]
    fn a_cross_filling_child_still_sets_the_row_height() {
        // Vertical stretch component in HStack: stretches HEIGHT but has fixed WIDTH
        // This is like a Slider/TextField rotated for use in HStack context
        let layout = HStackLayout {
            alignment: VerticalAlignment::Center,
            spacing: Computed::constant(10.0),
        };

        let mut label = MockSubView {
            size: Size::new(50.0, 20.0),
            stretch_axis: StretchAxis::None,
        };
        // A vertically-stretching component: fixed width, wants to fill height
        let mut vertical_stretch = MockSubView {
            size: Size::new(40.0, 100.0), // reports minimum width, tall height
            stretch_axis: StretchAxis::Vertical, // stretches height only
        };
        let mut button = MockSubView {
            size: Size::new(80.0, 44.0),
            stretch_axis: StretchAxis::None,
        };

        let children: Vec<&dyn SubView> = vec![&mut label, &mut vertical_stretch, &mut button];

        let size = layout.size_that_fits(ProposalSize::UNSPECIFIED, &children);

        // Width: all children contribute (vertical_stretch doesn't stretch horizontally)
        // = 50 + 10 + 40 + 10 + 80 = 190
        assert!((size.width - 190.0).abs() < f32::EPSILON);
        // Height: max of every child = max(20, 100, 44) = 100
        assert!(
            (size.height - 100.0).abs() < f32::EPSILON,
            "the stretching child's own height has to reach the row, got {}",
            size.height
        );
    }

    #[test]
    fn test_hstack_compresses_equal_children_evenly_bounded_proposal() {
        // Seven equal 40pt columns with 8pt spacing (a calendar's day row) in
        // a 272pt bound: the 56pt deficit must be shared equally — every
        // column shrinks to 32 at a uniform 40pt pitch — never taken
        // order-dependently from the leading children.
        let layout = HStackLayout {
            alignment: VerticalAlignment::Center,
            spacing: Computed::constant(8.0),
        };

        let mut columns: Vec<CompressibleView> = (0..7)
            .map(|_| CompressibleView {
                ideal: Size::new(40.0, 40.0),
                floor: 0.0,
            })
            .collect();
        let children: Vec<&dyn SubView> = columns
            .iter_mut()
            .map(|child| child as &dyn SubView)
            .collect();

        let bounds = Rect::new(Point::zero(), Size::new(272.0, 40.0));
        let proposal = ProposalSize::new(Some(bounds.width()), Some(bounds.height()));
        let placements = layout.place(bounds, proposal, &children);

        for placement in &placements {
            assert!(
                (placement.frame.width() - 32.0).abs() < 0.001,
                "expected even 32pt columns, got {}",
                placement.frame.width()
            );
        }
        for pair in placements.windows(2) {
            assert!(
                ((pair[1].frame.x() - pair[0].frame.x()) - 40.0).abs() < 0.001,
                "expected uniform 40pt pitch, got {}",
                pair[1].frame.x() - pair[0].frame.x()
            );
        }
    }

    #[test]
    fn test_hstack_compression_keeps_small_children_intrinsic_bounded_proposal() {
        // A 50pt label next to a 200pt text in 140pt of space: the text alone
        // absorbs the deficit (clamped to 90) while the label keeps its
        // intrinsic width.
        let layout = HStackLayout {
            alignment: VerticalAlignment::Center,
            spacing: Computed::constant(10.0),
        };

        let mut label = MockSubView {
            size: Size::new(50.0, 20.0),
            stretch_axis: StretchAxis::None,
        };
        let mut long_text = ResponsiveSubView {
            intrinsic: Size::new(200.0, 20.0),
            wrapped_height: 40.0,
            wrap_at_or_below: 60.0,
            stretch_axis: StretchAxis::None,
        };
        let children: Vec<&dyn SubView> = vec![&mut label, &mut long_text];

        let bounds = Rect::new(Point::zero(), Size::new(150.0, 40.0));
        let proposal = ProposalSize::new(Some(bounds.width()), Some(bounds.height()));
        let placements = layout.place(bounds, proposal, &children);

        assert!((placements[0].frame.width() - 50.0).abs() < 0.001);
        assert!((placements[1].frame.width() - 90.0).abs() < 0.001);
    }

    #[test]
    fn test_hstack_compression_never_goes_below_a_reported_minimum_bounded_proposal() {
        // Two children that will not go below 20pt, in 10pt of space: the row
        // overflows rather than squeezing them past what they said they need.
        // The floor is each child's own answer, not a constant the stack picked.
        let layout = HStackLayout {
            alignment: VerticalAlignment::Center,
            spacing: Computed::constant(0.0),
        };

        let mut first = CompressibleView {
            ideal: Size::new(60.0, 20.0),
            floor: 20.0,
        };
        let mut second = CompressibleView {
            ideal: Size::new(60.0, 20.0),
            floor: 20.0,
        };
        let children: Vec<&dyn SubView> = vec![&mut first, &mut second];

        let bounds = Rect::new(Point::zero(), Size::new(10.0, 20.0));
        let proposal = ProposalSize::new(Some(bounds.width()), Some(bounds.height()));
        let placements = layout.place(bounds, proposal, &children);

        assert!((placements[0].frame.width() - 20.0).abs() < 0.001);
        assert!((placements[1].frame.width() - 20.0).abs() < 0.001);
    }

    #[test]
    fn test_hstack_measures_stretch_child_with_allocated_width_for_height() {
        let layout = HStackLayout {
            alignment: VerticalAlignment::Center,
            spacing: Computed::constant(0.0),
        };

        let mut fixed = MockSubView {
            size: Size::new(4.0, 10.0),
            stretch_axis: StretchAxis::None,
        };

        // Simulate a content-bearing stretch child whose height increases when width is constrained.
        let mut stretch = ResponsiveSubView {
            intrinsic: Size::new(100.0, 20.0),
            wrapped_height: 40.0,
            wrap_at_or_below: 60.0,
            stretch_axis: StretchAxis::Horizontal,
        };

        let children: Vec<&dyn SubView> = vec![&mut fixed, &mut stretch];

        let size = layout.size_that_fits(ProposalSize::new(Some(40.0), None), &children);

        assert!((size.width - 40.0).abs() < f32::EPSILON);
        assert!((size.height - 40.0).abs() < f32::EPSILON);
    }

    #[test]
    fn test_hstack_place_uses_stretch_child_wrapped_height_bounded_proposal() {
        let layout = HStackLayout {
            alignment: VerticalAlignment::Center,
            spacing: Computed::constant(0.0),
        };

        let bounds = Rect::new(Point::zero(), Size::new(40.0, 40.0));

        let mut fixed = MockSubView {
            size: Size::new(4.0, 10.0),
            stretch_axis: StretchAxis::None,
        };

        let mut stretch = ResponsiveSubView {
            intrinsic: Size::new(100.0, 20.0),
            wrapped_height: 40.0,
            wrap_at_or_below: 60.0,
            stretch_axis: StretchAxis::Horizontal,
        };

        let children: Vec<&dyn SubView> = vec![&mut fixed, &mut stretch];

        let proposal = ProposalSize::new(Some(bounds.width()), Some(bounds.height()));
        let placements = layout.place(bounds, proposal, &children);

        assert!((placements[0].frame.width() - 4.0).abs() < f32::EPSILON);
        assert!((placements[1].frame.width() - 36.0).abs() < f32::EPSILON);
        assert!((placements[1].frame.height() - 40.0).abs() < f32::EPSILON);
    }

    #[test]
    fn test_hstack_min_size_query_correctly_sums_children() {
        // When ProposalSize::ZERO is used (min size query), ALL children's widths
        // should be summed to ensure window minimum width calculation is correct.
        // Previous bug: if spacer (stretch) existed, it would return 0 width for min size query.
        let layout = HStackLayout {
            alignment: VerticalAlignment::Center,
            spacing: Computed::constant(10.0),
        };

        let mut label = MockSubView {
            size: Size::new(50.0, 20.0),
            stretch_axis: StretchAxis::None,
        };
        let mut spacer = MockSubView {
            size: Size::zero(),
            stretch_axis: StretchAxis::Both,
        };
        let mut button = MockSubView {
            size: Size::new(80.0, 44.0),
            stretch_axis: StretchAxis::None,
        };

        let children: Vec<&dyn SubView> = vec![&mut label, &mut spacer, &mut button];

        // With ZERO proposal (min size query)
        let min_size = layout.size_that_fits(ProposalSize::ZERO, &children);

        // Width: 50 + 10 + 0 + 10 + 80 = 150
        assert!(
            (min_size.width - 150.0).abs() < f32::EPSILON,
            "Min size query should return sum of child min widths (150.0), got {}",
            min_size.width
        );

        // Verify regular behavior (Unspecified) still works
        let intrinsic_size = layout.size_that_fits(ProposalSize::UNSPECIFIED, &children);
        // Should also be 150 because spacer has 0 intrinsic width
        assert!((intrinsic_size.width - 150.0).abs() < f32::EPSILON);
    }
}