frus-widgets 0.2.1

//! [`Checkbox`]: a **controlled** checkbox, its state coming from the application.

use frus_core::{Color, Point, Rect, ResolvedTextStyle, Scene, TextStyle};
use frus_layout::{Dimension, Style};

use crate::disabled::{disabled_content, disabled_mark};
use crate::interaction::{Interaction, Status};
use crate::theme::{TapTarget, Theme};
use crate::widget::Widget;

const BOX: f32 = 20.0;
/// The partly-ticked bar: its inset from either side of the box, and its thickness.
const MIXED_INSET: f32 = 4.0;
const MIXED_THICKNESS: f32 = 2.0;
const GAP: f32 = 10.0;

/// A checkbox, with an optional label.
pub struct Checkbox<Msg = crate::callback::Callback> {
    /// On, off, or **partly** on; see [`Checkbox::maybe`].
    value: Option<bool>,
    /// Whether a click may land on the partly-on answer.
    tristate: bool,
    label: Option<String>,
    size: f32,
    enabled: bool,
    fill_color: Option<Color>,
    check_color: Option<Color>,
    border_color: Option<Color>,
    active_border_color: Option<Color>,
    tap_target: Option<TapTarget>,
    radius: Option<f32>,
    label_color: Option<Color>,
    on_toggle: Option<Box<dyn Fn(bool) -> Msg>>,
    on_change: Option<Box<dyn Fn(Option<bool>) -> Msg>>,
}

impl<Msg> Checkbox<Msg> {
    /// Creates a checkbox whose checked state is supplied.
    pub fn new(checked: bool) -> Self {
        Self {
            value: Some(checked),
            tristate: false,
            label: None,
            size: 18.0,
            enabled: true,
            fill_color: None,
            check_color: None,
            border_color: None,
            active_border_color: None,
            tap_target: None,
            radius: None,
            label_color: None,
            on_toggle: None,
            on_change: None,
        }
    }

    /// A checkbox with **three** answers: on, off, and partly on.
    ///
    /// `None` is the third, and it is an answer rather than a missing one. A "select
    /// all" above five rows of which three are ticked is not unchecked — saying so tells
    /// the reader something false, and a screen reader is told `mixed` for the same
    /// reason.
    ///
    /// A click cycles off → on → partly on → off, which is the reference's order. Pair it
    /// with [`on_change`](Checkbox::on_change), since [`on_toggle`](Checkbox::on_toggle)
    /// has no way to say the third answer.
    ///
    /// ```
    /// # use frus_widgets::Checkbox;
    /// # #[derive(Clone)] enum Msg { All(Option<bool>) }
    /// # let (done, total) = (3usize, 5usize);
    /// let all = match done {
    ///     0 => Some(false),
    ///     n if n == total => Some(true),
    ///     _ => None,
    /// };
    /// Checkbox::maybe(all).label("Select all").on_change(Msg::All);
    /// ```
    pub fn maybe(value: Option<bool>) -> Self {
        let mut checkbox = Self::new(false);
        checkbox.value = value;
        checkbox.tristate = true;
        checkbox
    }

    /// The box's fill when it is **ticked**; the theme's `primary` otherwise.
    pub fn fill_color(mut self, color: Color) -> Self {
        self.fill_color = Some(color);
        self
    }

    /// The tick drawn on that fill; the theme's `on_primary` otherwise.
    pub fn check_color(mut self, color: Color) -> Self {
        self.check_color = Some(color);
        self
    }

    /// The outline when the box is **not** ticked and at rest.
    ///
    /// Set on its own it also becomes the colour under a pointer or focus, unless
    /// [`active_border_color`](Checkbox::active_border_color) says otherwise: a caller
    /// who names one outline colour means the outline, not half of it.
    pub fn border_color(mut self, color: Color) -> Self {
        self.border_color = Some(color);
        self
    }

    /// The outline under a pointer, a finger or focus. The reference resolves this side
    /// per state, and an outline that did not answer at all would look inert.
    pub fn active_border_color(mut self, color: Color) -> Self {
        self.active_border_color = Some(color);
        self
    }

    /// The box's corner radius.
    pub fn radius(mut self, radius: f32) -> Self {
        self.radius = Some(radius);
        self
    }

    /// The label's colour; the theme's `on_surface` otherwise.
    pub fn label_color(mut self, color: Color) -> Self {
        self.label_color = Some(color);
        self
    }

    /// The corner radius actually used.
    fn corner(&self, theme: &Theme) -> f32 {
        self.radius.or(theme.widgets.checkbox.radius).unwrap_or(5.0)
    }

    /// Adds a label on the right.
    pub fn label(mut self, label: impl Into<String>) -> Self {
        self.label = Some(label.into());
        self
    }

    /// Whether the box can be ticked. Disabled it is **inert** — no message, out of the
    /// tab order, announced as unavailable — and it still shows whether it is ticked,
    /// because read-only is not invisible.
    ///
    /// See [`crate::disabled`] for the whole contract.
    pub fn enabled(mut self, enabled: bool) -> Self {
        self.enabled = enabled;
        self
    }

    /// A closure producing a message from the new state, checked or not.
    pub fn on_toggle<R: crate::callback::IntoMsg<Msg>>(
        mut self,
        on_toggle: impl Fn(bool) -> R + 'static,
    ) -> Self {
        self.on_toggle = Some(Box::new(crate::callback::handler1(on_toggle)));
        self
    }

    /// A closure producing a message from the new state, **including** the partly-on
    /// one. What [`Checkbox::maybe`] wants; it wins over
    /// [`on_toggle`](Checkbox::on_toggle) when both are given.
    pub fn on_change<R: crate::callback::IntoMsg<Msg>>(
        mut self,
        on_change: impl Fn(Option<bool>) -> R + 'static,
    ) -> Self {
        self.on_change = Some(Box::new(crate::callback::handler1(on_change)));
        self
    }

    /// Is the box filled? Both **on** and **partly on** are: the mark differs, the
    /// surface under it does not, which is what says "this is not simply off".
    fn filled(&self) -> bool {
        self.value != Some(false)
    }

    /// The state a click moves to. Three-way it is the reference's cycle; otherwise the
    /// old one, unchanged.
    fn next(&self) -> Option<bool> {
        if self.tristate {
            match self.value {
                Some(false) => Some(true),
                Some(true) => None,
                None => Some(false),
            }
        } else {
            Some(self.value != Some(true))
        }
    }

    fn label_width(&self) -> f32 {
        match &self.label {
            Some(text) => GAP + frus_text::measure(text, self.size).width,
            None => 0.0,
        }
    }
}

impl<Msg> Checkbox<Msg> {
    /// **How much room it reserves for a finger** ([`TapTarget`]). Unset, the theme's
    /// answer, which is [`Padded`](TapTarget::Padded) — at least 48 pixels either way,
    /// whatever this control paints in the middle of it.
    pub fn tap_target(mut self, target: TapTarget) -> Self {
        self.tap_target = Some(target);
        self
    }

    /// The label's style, **resolved once** so that the number the box is measured with is
    /// the number the glyphs are drawn at. Resolving is the single place the reader's font
    /// setting is applied (milestone 403).
    fn label_style(&self) -> ResolvedTextStyle {
        TextStyle::new(self.size).resolved()
    }

    /// The room this checkbox reserves, resolved as `caller ?? theme ?? framework`
    /// (`checkbox.dart:510`).
    fn reserved(&self, theme: &Theme) -> f32 {
        self.tap_target
            .or(theme.widgets.checkbox.tap_target)
            .unwrap_or(theme.tap_target)
            .min_side()
    }
}

impl<Msg> Widget<Msg> for Checkbox<Msg> {
    fn style(&self) -> Style {
        Widget::<Msg>::style_themed(self, &Theme::default())
    }

    /// **A 20-pixel box is not something a finger can be asked to hit** — the reference
    /// lays a checkbox out inside a 48-pixel square whatever it paints in the middle
    /// (`checkbox.dart:516`).
    ///
    /// The target here is the **whole control**, label included, rather than a square
    /// around the box: the reference's checkbox carries no label, so it reaches the same
    /// guarantee by being a square with the words outside it. A labelled one is already
    /// wider than the minimum, so the width floor only ever binds on a bare box — and
    /// then the box is centred in what it was given.
    fn style_themed(&self, theme: &Theme) -> Style {
        let least = self.reserved(theme);
        let line = self.label_style().line_height().max(BOX);
        Style {
            width: Dimension::Length((BOX + self.label_width()).max(least).ceil()),
            height: Dimension::Length(line.max(least).ceil()),
            ..Default::default()
        }
    }

    fn children(&self) -> &[Box<dyn Widget<Msg>>] {
        &[]
    }

    fn paint(&self, bounds: Rect, status: Status, theme: &Theme, scene: &mut Scene) {
        let o = status.opacity;
        let box_y = bounds.y + (bounds.height - BOX) * 0.5;
        // Centred across as well when there is nothing beside it, since the box is then
        // the only thing in a square wider than itself. With a label it stays at the
        // leading edge and the words follow it.
        let box_x = bounds.x
            + if self.label.is_none() {
                (bounds.width - BOX) * 0.5
            } else {
                0.0
            };
        let box_rect = Rect::new(box_x, box_y, BOX, BOX);

        if self.filled() {
            // Disabled and ticked: the box flattens to `on_surface` at 38 % and the tick
            // punches through in `surface`. A translucent tick on a translucent box would
            // land within a few percent of it and vanish.
            let (fill, tick) = if self.enabled {
                (
                    self.fill_color
                        .or(theme.widgets.checkbox.fill_color)
                        .unwrap_or(theme.primary),
                    self.check_color
                        .or(theme.widgets.checkbox.check_color)
                        .unwrap_or(theme.on_primary),
                )
            } else {
                (disabled_content(theme), disabled_mark(theme))
            };
            scene.draw_rect(
                box_rect,
                fill.fade(o),
                self.corner(theme),
                0.0,
                Color::TRANSPARENT,
            );
            match self.value {
                // Ticked.
                // `exact`: the tick is an icon drawn as a glyph and it lives inside a
                // `BOX` that does not move, so it must not follow the reader's type.
                Some(_) => scene.text(
                    Point::new(box_rect.x + 3.0, box_rect.y + 1.0),
                    "✓".to_string(),
                    &ResolvedTextStyle::exact(self.size),
                    tick.fade(o),
                ),
                // Partly ticked: a bar, and a **drawn** one rather than a dash of text.
                // The tick above is a glyph and pays for it — a font's own width and
                // weight — but the reference draws this mark, and a bar is two numbers
                // rather than a code point some font may not carry.
                None => scene.draw_rect(
                    Rect::new(
                        box_rect.x + MIXED_INSET,
                        box_rect.y + (BOX - MIXED_THICKNESS) * 0.5,
                        BOX - MIXED_INSET * 2.0,
                        MIXED_THICKNESS,
                    ),
                    tick.fade(o),
                    MIXED_THICKNESS * 0.5,
                    0.0,
                    Color::TRANSPARENT,
                ),
            }
        } else {
            // Unticked, the outline *is* the control — the mark rather than a container —
            // so it takes the content opacity, as the reference's does.
            //
            // And it is **not** `outline`. The reference resolves this side per state:
            // `on_surface_variant` at rest, the full `on_surface` under a finger, a
            // pointer or focus, and `on_surface` at 38 % when disabled. An unselected
            // checkbox is a mark, and a mark is drawn in an *on* colour; `outline` is for
            // the edge of a container, which this is not. Milestone 332.
            //
            // A caller who names one outline colour means the outline, so the pointer
            // state falls back to the resting override before it falls back to the
            // scheme -- otherwise a green checkbox would turn grey under a finger.
            let resting = self.border_color.or(theme.widgets.checkbox.border_color);
            let border = if !self.enabled {
                disabled_content(theme)
            } else if status.interaction != Interaction::None || status.focused {
                self.active_border_color
                    .or(theme.widgets.checkbox.active_border_color)
                    .or(resting)
                    .unwrap_or(theme.scheme.on_surface)
            } else {
                resting.unwrap_or(theme.scheme.on_surface_variant)
            };
            scene.draw_rect(
                box_rect,
                theme.surface.fade(o),
                self.corner(theme),
                2.0,
                border.fade(o),
            );
        }

        if let Some(label) = &self.label {
            let color = if self.enabled {
                self.label_color
                    .or(theme.widgets.checkbox.label_color)
                    .unwrap_or(theme.on_surface)
            } else {
                disabled_content(theme)
            };
            // Centred down the box's own height. It used to be drawn at the top of the
            // bounds, which was the same sentence while the bounds *were* the line; a
            // floor under the height makes the two different.
            let style = self.label_style();
            scene.text(
                Point::new(
                    bounds.x + BOX + GAP,
                    bounds.y + (bounds.height - style.line_height()) * 0.5,
                ),
                label.clone(),
                &style,
                color.fade(o),
            );
        }
    }

    fn on_click(&self) -> Option<Msg> {
        if !self.enabled {
            return None;
        }
        let next = self.next();
        if let Some(make) = self.on_change.as_ref() {
            return Some(make(next));
        }
        // `on_toggle` cannot say the third answer, so a tristate box wired only to it
        // reports the two it can: partly on reads as on, which is what a click on it
        // moves away from.
        self.on_toggle
            .as_ref()
            .map(|make| make(next.unwrap_or(true)))
    }

    fn focusable(&self) -> bool {
        self.enabled
    }

    fn semantics(&self) -> Option<frus_core::SemanticsProperties> {
        // Still ticked or not, still announced: a reader who cannot change the answer is
        // still owed it.
        let mut s = frus_core::SemanticsProperties::new(frus_core::Role::CheckBox)
            .maybe_toggled(self.value);
        s = if self.enabled {
            s.clickable()
        } else {
            s.disabled(true)
        };
        if let Some(label) = &self.label {
            s = s.label(label.clone());
        }
        Some(s)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::theme::{MIN_TAP_TARGET, SHRUNK_TAP_TARGET};

    #[derive(Clone, Debug, PartialEq)]
    enum Msg {
        Set(bool),
        Maybe(Option<bool>),
    }

    /// **A 20-pixel box is not something a finger can be asked to hit** (milestone 442).
    ///
    /// The reference lays a checkbox out inside a 48-pixel square whatever it paints in
    /// the middle (`checkbox.dart:516`). This asked for the box and the label's line, so
    /// a bare checkbox was a 20-pixel target and a labelled one was as tall as its type.
    #[test]
    fn a_checkbox_reserves_room_for_a_finger() {
        let theme = Theme::dark();
        let bare: Checkbox<Msg> = Checkbox::new(false);
        let square = Widget::<Msg>::style_themed(&bare, &theme);
        assert_eq!(square.width, Dimension::Length(MIN_TAP_TARGET));
        assert_eq!(square.height, Dimension::Length(MIN_TAP_TARGET));

        // With a label the control is already wider than the minimum, so only the height
        // floor binds — the target is the whole control, words included.
        let labelled: Checkbox<Msg> = Checkbox::new(false).label("Remember me");
        let row = Widget::<Msg>::style_themed(&labelled, &theme);
        assert_eq!(row.height, Dimension::Length(MIN_TAP_TARGET));
        match row.width {
            Dimension::Length(w) => assert!(w > MIN_TAP_TARGET, "width = {w}"),
            other => panic!("{other:?}"),
        }

        let dense: Checkbox<Msg> = Checkbox::new(false).tap_target(TapTarget::ShrinkWrap);
        assert_eq!(
            Widget::<Msg>::style_themed(&dense, &theme).height,
            Dimension::Length(SHRUNK_TAP_TARGET)
        );
    }

    /// And **the click lands in the room**, which is the whole point of reserving it: a
    /// point below the box, inside the square, reaches the checkbox.
    #[test]
    fn a_click_below_the_box_still_lands() {
        use frus_core::Size;
        let ui = crate::ui::build_ui(
            &Checkbox::new(false).on_toggle(Msg::Set),
            Size::new(200.0, 200.0),
            &crate::runtime::Runtime::default(),
            &Theme::dark(),
        );
        // The box occupies 14..34 in both axes of the 48-pixel square; this is under it.
        let below = Point::new(24.0, 42.0);
        let landed = ui.hit(below).and_then(|id| ui.msg_for(id));
        assert_eq!(landed, Some(Msg::Set(true)), "a finger just low of the box");
    }

    /// The box is centred in that square when nothing stands beside it, and stays at the
    /// leading edge when a label does.
    #[test]
    fn a_bare_box_is_centred_in_its_room() {
        let theme = Theme::dark();
        let box_of = |checkbox: &Checkbox<Msg>, width: f32| {
            let mut scene = Scene::new();
            Widget::<Msg>::paint(
                checkbox,
                Rect::new(0.0, 0.0, width, MIN_TAP_TARGET),
                Status::default(),
                &theme,
                &mut scene,
            );
            scene
                .primitives()
                .iter()
                .find_map(|p| match p {
                    frus_core::Primitive::Rect { rect, .. } => Some(*rect),
                    _ => None,
                })
                .expect("a checkbox paints its box")
        };

        let bare = box_of(&Checkbox::new(true), MIN_TAP_TARGET);
        assert!(
            (bare.x - (MIN_TAP_TARGET - BOX) * 0.5).abs() < 0.01,
            "centred across: {bare:?}"
        );
        assert!(
            (bare.y - (MIN_TAP_TARGET - BOX) * 0.5).abs() < 0.01,
            "and down: {bare:?}"
        );

        let labelled = box_of(&Checkbox::new(true).label("Remember me"), 200.0);
        assert_eq!(
            labelled.x, 0.0,
            "the words follow the box, not the other way"
        );
    }

    #[test]
    fn click_toggles() {
        let unchecked = Checkbox::new(false).on_toggle(Msg::Set);
        assert_eq!(Widget::on_click(&unchecked), Some(Msg::Set(true)));
        let checked = Checkbox::new(true).on_toggle(Msg::Set);
        assert_eq!(Widget::on_click(&checked), Some(Msg::Set(false)));
    }

    #[test]
    fn a_disabled_box_is_inert_but_still_says_whether_it_is_ticked() {
        let dead = Checkbox::new(true).on_toggle(Msg::Set).enabled(false);
        assert_eq!(Widget::on_click(&dead), None, "the press goes nowhere");
        assert!(!Widget::<Msg>::focusable(&dead), "out of the tab order");
        let semantics = Widget::<Msg>::semantics(&dead).expect("still announced");
        assert!(semantics.disabled, "and announced as unavailable");
        // The answer survives: read-only is not invisible.
        assert_eq!(semantics.toggled, frus_core::Toggled::True);
    }

    /// An unselected box's side, state by state. The reference resolves it as
    /// `on_surface_variant` at rest and the full `on_surface` under a finger, a pointer or
    /// focus — an unselected checkbox is a **mark**, so it takes an *on* colour. Ours was
    /// `outline`, the role for the edge of a container, since it was written.
    #[test]
    fn an_unticked_box_is_a_mark_not_a_container_edge() {
        let theme = Theme::dark();
        let side = |status: Status| {
            let mut scene = Scene::new();
            Widget::<Msg>::paint(
                &Checkbox::<Msg>::new(false),
                Rect::new(0.0, 0.0, 20.0, 20.0),
                status,
                &theme,
                &mut scene,
            );
            scene
                .primitives()
                .iter()
                .find_map(|p| match p {
                    frus_core::Primitive::Rect { border_color, .. } => Some(*border_color),
                    _ => None,
                })
                .expect("the box")
        };
        let at = |interaction, focused| Status {
            opacity: 1.0,
            interaction,
            focused,
            ..Default::default()
        };
        assert_eq!(
            side(at(Interaction::None, false)),
            theme.scheme.on_surface_variant,
            "at rest"
        );
        for (name, status) in [
            ("hovered", at(Interaction::Hovered, false)),
            ("pressed", at(Interaction::Pressed, false)),
            ("focused", at(Interaction::None, true)),
        ] {
            assert_eq!(side(status), theme.scheme.on_surface, "{name}");
        }
        // And it is no longer the container-edge role, which is what it used to be.
        assert_ne!(
            side(at(Interaction::None, false)),
            theme.scheme.outline,
            "an unselected box is a mark, not a container's edge"
        );
    }

    #[test]
    fn a_disabled_tick_does_not_disappear_into_its_box() {
        // Both are drawn from `on_surface`; if the tick took the content opacity too it
        // would land within a few percent of the 38 % box behind it and vanish. It punches
        // through in `surface` instead, and this is the assertion that says so.
        for theme in [Theme::dark(), Theme::light()] {
            let mut scene = Scene::new();
            Widget::<Msg>::paint(
                &Checkbox::<Msg>::new(true).enabled(false),
                Rect::new(0.0, 0.0, 20.0, 20.0),
                Status {
                    opacity: 1.0,
                    ..Default::default()
                },
                &theme,
                &mut scene,
            );
            let box_fill = scene
                .primitives()
                .iter()
                .find_map(|p| match p {
                    frus_core::Primitive::Rect { color, .. } => Some(*color),
                    _ => None,
                })
                .expect("the box");
            let tick = scene
                .primitives()
                .iter()
                .find_map(|p| match p {
                    frus_core::Primitive::Text { color, .. } => Some(*color),
                    _ => None,
                })
                .expect("the tick");
            let against = |c: frus_core::Color| {
                (c.r - theme.scheme.surface.r).abs()
                    + (c.g - theme.scheme.surface.g).abs()
                    + (c.b - theme.scheme.surface.b).abs()
            };
            // The tick is the surface punching through, so it is *at* the surface while
            // the fill it sits on is a measurable way off it. Since milestone 329 the
            // disabled tokens resolve to opaque colours, so the two are told apart by
            // where they sit rather than by an alpha.
            assert!(
                against(tick) < 0.01,
                "the tick is the surface punching through: {tick:?}"
            );
            assert!(
                against(box_fill) > 0.1,
                "and the box it is inside is not: {box_fill:?}"
            );
        }
    }

    /// The third answer is an answer, and the cycle is the reference's.
    ///
    /// A "select all" above five rows of which three are ticked is not unchecked. Drawn
    /// that way it says *nothing here is selected*, which is false; drawn ticked it says
    /// *everything is*, which is also false. So the control has a third state, and a
    /// click walks off → on → partly on → off.
    #[test]
    fn a_tristate_box_cycles_through_the_third_answer() {
        let seen = |value| Widget::on_click(&Checkbox::maybe(value).on_change(Msg::Maybe));
        assert_eq!(seen(Some(false)), Some(Msg::Maybe(Some(true))));
        assert_eq!(seen(Some(true)), Some(Msg::Maybe(None)));
        assert_eq!(seen(None), Some(Msg::Maybe(Some(false))));
    }

    /// A two-state box is untouched by any of it: `new` is not `maybe`, so the cycle it
    /// walks is still the old one and `on_toggle` still says what it always said.
    #[test]
    fn a_two_state_box_never_reaches_the_third() {
        assert_eq!(
            Widget::on_click(&Checkbox::new(true).on_change(Msg::Maybe)),
            Some(Msg::Maybe(Some(false))),
            "no `None` in the middle"
        );
    }

    /// `on_toggle` takes a `bool` and there is no value of `bool` that means *partly*, so
    /// a tristate box wired only to it reports the two answers that type can carry —
    /// partly-on reading as on, which is what a click on it moves away from. Making the
    /// case emit nothing would be a widget that looks live and is not.
    #[test]
    fn a_tristate_box_on_the_old_callback_is_not_left_silent() {
        assert_eq!(
            Widget::on_click(&Checkbox::maybe(None).on_toggle(Msg::Set)),
            Some(Msg::Set(false)),
            "partly on moves to off, and `bool` can say that"
        );
        assert_eq!(
            Widget::on_click(&Checkbox::maybe(Some(true)).on_toggle(Msg::Set)),
            Some(Msg::Set(true)),
            "on moves to partly on, which reads as on"
        );
    }

    /// `on_change` wins when both are given: it is the one that can say all three.
    #[test]
    fn the_three_state_callback_wins_over_the_two_state_one() {
        let both = Checkbox::maybe(Some(true))
            .on_toggle(|_| Msg::Set(false))
            .on_change(Msg::Maybe);
        assert_eq!(Widget::on_click(&both), Some(Msg::Maybe(None)));
    }

    /// The screen reader is told `mixed` rather than handed a lie in one of the two
    /// directions.
    #[test]
    fn partly_ticked_is_announced_as_mixed() {
        let announced = |value| {
            Widget::<Msg>::semantics(&Checkbox::<Msg>::maybe(value))
                .expect("announced")
                .toggled
        };
        assert_eq!(announced(None), frus_core::Toggled::Mixed);
        assert_eq!(announced(Some(true)), frus_core::Toggled::True);
        assert_eq!(announced(Some(false)), frus_core::Toggled::False);
    }

    /// Both **on** and **partly on** fill the box; only the mark differs. The filled
    /// surface is what says *this is not simply off*, and the mark says which of the two
    /// it is — which is the reference's drawing.
    #[test]
    fn both_answers_that_are_not_off_fill_the_box() {
        let theme = Theme::default();
        let painted = |value| {
            let mut scene = Scene::new();
            Widget::<Msg>::paint(
                &Checkbox::<Msg>::maybe(value),
                Rect::new(0.0, 0.0, 20.0, 20.0),
                Status {
                    opacity: 1.0,
                    ..Default::default()
                },
                &theme,
                &mut scene,
            );
            scene.primitives().to_vec()
        };
        let filled = |primitives: &[frus_core::Primitive]| {
            primitives.iter().any(|p| {
                matches!(p, frus_core::Primitive::Rect { color, .. } if *color == theme.primary)
            })
        };
        assert!(filled(&painted(Some(true))), "ticked fills");
        assert!(filled(&painted(None)), "partly ticked fills too");
        assert!(!filled(&painted(Some(false))), "off does not");
    }

    /// The partly-on mark is **drawn** rather than a glyph — a bar, two numbers — so no
    /// font gets to decide whether it exists. The tick above it is text and pays for it;
    /// there was no reason to add a second one.
    #[test]
    fn the_partly_ticked_mark_is_drawn_and_the_tick_is_not() {
        let has_text = |value| {
            let mut scene = Scene::new();
            Widget::<Msg>::paint(
                &Checkbox::<Msg>::maybe(value),
                Rect::new(0.0, 0.0, 20.0, 20.0),
                Status {
                    opacity: 1.0,
                    ..Default::default()
                },
                &Theme::default(),
                &mut scene,
            );
            scene
                .primitives()
                .iter()
                .any(|p| matches!(p, frus_core::Primitive::Text { .. }))
        };
        assert!(has_text(Some(true)), "the tick is a glyph");
        assert!(!has_text(None), "the bar is not");
    }
}

#[cfg(test)]
mod color_tests {
    use super::*;
    use crate::widget::Widget;
    use frus_core::Primitive;

    const BRAND: Color = Color::rgb(0.0, 0.6, 0.3);
    const MARK: Color = Color::rgb(0.9, 0.9, 0.2);

    /// The box: its fill, its border colour and its radius.
    fn box_of(cb: &Checkbox<()>, status: Status, theme: &Theme) -> (Color, Color, f32) {
        let mut scene = Scene::new();
        Widget::<()>::paint(
            cb,
            Rect::new(0.0, 0.0, 200.0, BOX),
            status,
            theme,
            &mut scene,
        );
        scene
            .primitives()
            .iter()
            .find_map(|p| match p {
                Primitive::Rect {
                    color,
                    border_color,
                    radius,
                    ..
                } => Some((*color, *border_color, radius.top_left)),
                _ => None,
            })
            .expect("the box is painted")
    }

    /// The tick's colour, or the label's — whichever text came out.
    fn text_color(cb: &Checkbox<()>, theme: &Theme) -> Vec<Color> {
        let mut scene = Scene::new();
        Widget::<()>::paint(
            cb,
            Rect::new(0.0, 0.0, 200.0, BOX),
            Status {
                opacity: 1.0,
                ..Default::default()
            },
            theme,
            &mut scene,
        );
        scene
            .primitives()
            .iter()
            .filter_map(|p| match p {
                Primitive::Text { color, .. } => Some(*color),
                _ => None,
            })
            .collect()
    }

    fn rest() -> Status {
        Status {
            opacity: 1.0,
            ..Default::default()
        }
    }

    /// Nothing said: what it always painted.
    #[test]
    fn the_defaults_are_what_they_were() {
        let theme = Theme::default();
        let (fill, _, radius) = box_of(&Checkbox::<()>::new(true), rest(), &theme);
        assert_eq!(fill, theme.primary);
        assert_eq!(radius, 5.0);
        let (_, border, _) = box_of(&Checkbox::<()>::new(false), rest(), &theme);
        assert_eq!(border, theme.scheme.on_surface_variant);
    }

    /// A ticked box takes its fill and its tick; the corner takes its radius.
    #[test]
    fn a_ticked_box_takes_its_colours() {
        let theme = Theme::default();
        let cb = Checkbox::<()>::new(true)
            .fill_color(BRAND)
            .check_color(MARK)
            .radius(2.0);
        let (fill, _, radius) = box_of(&cb, rest(), &theme);
        assert_eq!((fill, radius), (BRAND, 2.0));
        assert_eq!(text_color(&cb, &theme), vec![MARK]);
    }

    /// A caller who names one outline colour means the outline: the pointer state falls
    /// back to it before it falls back to the scheme. Otherwise a green checkbox would
    /// turn grey the moment a finger came near it.
    #[test]
    fn one_outline_colour_covers_both_states() {
        let theme = Theme::default();
        let hovered = Status {
            opacity: 1.0,
            interaction: Interaction::Hovered,
            ..Default::default()
        };
        let cb = Checkbox::<()>::new(false).border_color(BRAND);
        assert_eq!(box_of(&cb, rest(), &theme).1, BRAND);
        assert_eq!(box_of(&cb, hovered, &theme).1, BRAND, "and under a finger");

        let both = Checkbox::<()>::new(false)
            .border_color(BRAND)
            .active_border_color(MARK);
        assert_eq!(box_of(&both, rest(), &theme).1, BRAND);
        assert_eq!(box_of(&both, hovered, &theme).1, MARK, "unless it is named");
    }

    /// The theme answers when the instance does not, and loses when it does.
    #[test]
    fn the_theme_answers_and_the_instance_overrules_it() {
        let mut theme = Theme::default();
        theme.widgets.checkbox.fill_color = Some(MARK);
        assert_eq!(box_of(&Checkbox::<()>::new(true), rest(), &theme).0, MARK);
        assert_eq!(
            box_of(&Checkbox::<()>::new(true).fill_color(BRAND), rest(), &theme).0,
            BRAND
        );
    }

    /// The label answers too.
    #[test]
    fn the_label_takes_its_colour() {
        let theme = Theme::default();
        let cb = Checkbox::<()>::new(false).label("Ready").label_color(BRAND);
        assert_eq!(text_color(&cb, &theme), vec![BRAND]);
    }
}