hephaestus 0.1.0

//! Axis rendering. Pre-shapes tick labels via [`crate::text::TextRun`],
//! reports their dimensions as a [`Measure`] for the composition solver,
//! and strokes the tick marks + labels at draw time.
//!
//! Conventions:
//!
//! - All tick labels are horizontal (no rotation). Wide labels on a
//!   vertical axis grow the axis chrome column.
//! - Tick mark length, label gap, and font size are pulled from the
//!   theme's resolved `AxisChromeStyle` — the same style the renderer
//!   uses at draw time, so the slot reservation matches the visible
//!   chrome.
//! - Tick labels use the scale's own [`Scale::format`], which renders
//!   numeric values via `{n}` Display and temporal values in calendar
//!   form (YYYY-MM-DD etc.).

use crate::geometry::{Point, Rect};
use crate::layout::{Measure, WidthHint};
use crate::plot::chrome::linear_axis::{draw_linear_axis_at, AxisChromeStyle};
use crate::plot::scale::Scale;
use crate::plot::theme::{HAlign, Theme};
use crate::scales::breaks::DEFAULT_BREAK_COUNT;
use crate::scales::value::Value;
use crate::scene::SceneBuilder;
use crate::text::TextRun;

use crate::scales::chrome::AxisSide;

// ─── Axis spec (high-level Plot surface) ─────────────────────────────────────

/// Stable identifier returned by [`crate::plot::Plot::add_axis`].
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct AxisId(u32);

impl AxisId {
    pub(crate) fn new(raw: u32) -> Self {
        Self(raw)
    }

    /// The raw handle value. Opaque — useful only as a key, and not
    /// comparable across plots.
    pub fn raw(self) -> u32 {
        self.0
    }
}

/// One axis attached to a [`Plot`](crate::plot::Plot). Built
/// manually by the caller — `Plot` doesn't infer any default axes
/// from its channel bindings.
///
/// Both the rail (`scale_name`) and the `title` are optional. A
/// title-only axis (rail = `None`, title = `Some`) reserves the
/// title slot for an axis whose rail has been suppressed.
#[derive(Clone, Debug)]
pub struct Axis {
    /// Scale that supplies the breaks + map for the rail. `None`
    /// means "no rail" — the title (if any) still renders.
    scale_name: Option<String>,
    placement: AxisPlacement,
    title: Option<String>,
}

/// Where an axis sits relative to its plot.
#[derive(Clone, Copy, Debug, PartialEq)]
pub enum AxisPlacement {
    /// Standard rectilinear axis along one of the panel's four
    /// edges. Wired into the corresponding patch slot via
    /// [`measure`] + [`draw`].
    Cartesian(AxisSide),
    /// Radius axis along a spoke at `theta_frac ∈ [0, 1]` on a
    /// polar projection. The spoke direction is computed via the
    /// projection's `unit_position` so it follows the polygon edge
    /// on chord-style projections.
    PolarRadius { theta_frac: f64 },
    /// Angular axis along the projection's outer or inner ring.
    /// The inner variant is silently skipped when the projection
    /// has `inner_radius_frac == 0` (no hole, no inner ring), so a
    /// single axis definition works for both disk and ring layouts.
    PolarAngular(PolarRing),
}

/// Which ring an angular axis runs along.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub enum PolarRing {
    Outer,
    Inner,
}

impl Axis {
    /// Axis with a rail driven by `scale_name`. Add a title via
    /// [`Self::title`].
    pub fn rail(scale_name: impl Into<String>, placement: AxisPlacement) -> Self {
        Self {
            scale_name: Some(scale_name.into()),
            placement,
            title: None,
        }
    }

    /// Title-only axis — reserves the matching title slot
    /// (cartesian) or renders an inline title (polar) without
    /// drawing a rail. Use when the rail would be visual noise but
    /// the slot still needs a label.
    pub fn title_only(title: impl Into<String>, placement: AxisPlacement) -> Self {
        Self {
            scale_name: None,
            placement,
            title: Some(title.into()),
        }
    }

    /// Attach a title to an existing axis. Cartesian axes draw the
    /// title into the matching patch
    /// [`Slot::AxisLeftTitle`](crate::composition::Slot) /
    /// `AxisBottomTitle` / etc.; polar axes render it inline.
    pub fn title(mut self, t: impl Into<String>) -> Self {
        self.title = Some(t.into());
        self
    }

    /// Name of the scale driving the rail, or `None` when the axis
    /// has no rail.
    pub fn scale_name(&self) -> Option<&str> {
        self.scale_name.as_deref()
    }

    /// Where the axis sits relative to its plot.
    pub fn placement(&self) -> AxisPlacement {
        self.placement
    }

    /// The axis title, or `None` when the axis carries no title.
    pub fn title_ref(&self) -> Option<&str> {
        self.title.as_deref()
    }
}

// ─── AxisMeasure ─────────────────────────────────────────────────────────────

/// Snapshot of an axis's chrome footprint. Holds shaped TextRuns for each
/// tick label so the layout solver can size the chrome track without
/// reshaping per query. The same labels are reshaped at draw time —
/// shaping is cheap, but a future per-channel cache (`Scale::generation`
/// hook) will eliminate the duplicate work.
pub(crate) struct AxisMeasure {
    side: AxisSide,
    /// (max label width across all ticks, in px at the dpi captured at
    /// construction). Computed once.
    max_label_w_px: f64,
    /// (max label height across all ticks, in px at the dpi captured at
    /// construction). Computed once.
    max_label_h_px: f64,
    /// Resolved tick length (px, absolute value — sign drives draw
    /// direction but not reservation magnitude).
    tick_length_px: f64,
    /// Resolved gap between tick end and label near-edge, px.
    gap_px: f64,
}

impl AxisMeasure {
    fn new(
        scale: &Scale,
        side: AxisSide,
        dpi: f64,
        chrome_style: &AxisChromeStyle,
        locale: &crate::scales::Locale,
    ) -> Self {
        let breaks = scale.breaks(DEFAULT_BREAK_COUNT);
        let mut max_w: f64 = 0.0;
        let mut max_h: f64 = 0.0;
        for v in &breaks {
            if matches!(v, Value::Null) {
                continue;
            }
            let label = scale.format(v, locale);
            let run = TextRun::new(&label, &chrome_style.text_style, dpi);
            // Lay out unconstrained to get the natural single-line width.
            let h = run.set_max_width(f32::INFINITY, HAlign::Start) as f64;
            // Tick labels render unwrapped — `natural_width` is the
            // actual draw width. `width_hint` returns the longest-
            // unbreakable-cluster bound (one word), which undershoots
            // multi-word labels and clips them at draw.
            let w = run.natural_width();
            max_w = max_w.max(w);
            max_h = max_h.max(h);
        }
        AxisMeasure {
            side,
            max_label_w_px: max_w,
            max_label_h_px: max_h,
            // Reservation uses the tick's magnitude — sign flips the
            // tick's draw direction but the slot still needs to fit
            // it either way.
            tick_length_px: chrome_style.tick_length_px.abs(),
            gap_px: chrome_style.gap_px,
        }
    }

    /// Total px contribution along the axis's perpendicular direction.
    /// For Left/Right axes this is the column width; for Bottom/Top it's
    /// the row height.
    fn chrome_thickness_px(&self) -> f64 {
        let label_dim = if self.side.is_vertical() {
            self.max_label_w_px
        } else {
            self.max_label_h_px
        };
        self.tick_length_px + self.gap_px + label_dim
    }
}

impl Measure for AxisMeasure {
    fn width_hint(&self, _dpi: f64) -> WidthHint {
        if self.side.is_vertical() {
            WidthHint::Min(self.chrome_thickness_px())
        } else {
            // Horizontal axes don't constrain column width.
            WidthHint::Min(0.0)
        }
    }

    fn height_at(&self, _width: f64, _dpi: f64) -> f64 {
        if self.side.is_horizontal() {
            self.chrome_thickness_px()
        } else {
            // Vertical axes inherit panel height; their cell doesn't
            // contribute to row sizing.
            0.0
        }
    }
}

// ─── Measure + draw ──────────────────────────────────────────────────────────

/// Pre-shape `scale`'s tick labels into a [`Measure`] cell suitable for
/// dropping into a [`composition::Patch`](crate::composition::Patch)
/// slot. The chrome style (label text style, tick / gap pixel sizes) is
/// resolved from `theme` against the channel + side derived from
/// `side`, so the slot reservation matches what [`draw`] emits.
pub fn measure(scale: &Scale, side: AxisSide, dpi: f64, theme: &Theme) -> Box<dyn Measure> {
    let (ch, side_idx) = axis_side_to_channel_side(side);
    let resolved = theme.resolved_axis(ch, side_idx);
    let chrome_style = AxisChromeStyle::from_resolved(
        &resolved,
        &theme.palette,
        dpi,
        crate::plot::chrome::root_text_pt(theme),
    );
    Box::new(AxisMeasure::new(
        scale,
        side,
        dpi,
        &chrome_style,
        &theme.locale,
    ))
}

/// Stroke tick marks and draw tick labels into `slot_rect`, mapping
/// the scale's breaks into panel-space pixels via `panel_rect`.
///
/// Conventions:
/// - For position scales (no output range), `scale.map_break(value)`
///   returns a `Value::Number` in `[0, 1]`; the geom-side convention
///   `px = panel.x0 + frac * panel_w` (and `panel.y1 - frac * panel_h`
///   for y, to flip pixels-grow-downward) applies here too.
/// - Tick marks stroke outward from the panel edge into `slot_rect`.
/// - Labels are anchored toward `slot_rect`'s far edge from the panel.
///
/// Silently does nothing if the scale has no input range, has empty
/// breaks, or the slot rect is degenerate.
#[allow(clippy::too_many_arguments)]
pub fn draw(
    scale: &Scale,
    scene: &mut dyn SceneBuilder,
    slot_rect: Rect,
    panel_rect: Rect,
    side: AxisSide,
    dpi: f64,
    theme: &Theme,
) {
    let breaks = scale.breaks(DEFAULT_BREAK_COUNT);
    if breaks.is_empty() {
        return;
    }
    let panel_w = panel_rect.x1 - panel_rect.x0;
    let panel_h = panel_rect.y1 - panel_rect.y0;
    if panel_w <= 0.0 || panel_h <= 0.0 {
        return;
    }

    // Translate the side + slot/panel layout into the linear-axis
    // primitives: baseline endpoints and the perpendicular tick
    // direction. `frac=0` corresponds to `start`; `frac=1` to
    // `end`. y axes flip so `frac=0` is at the panel BOTTOM.
    let (start, end, tick_direction) = match side {
        AxisSide::Bottom => (
            Point::new(panel_rect.x0, slot_rect.y0),
            Point::new(panel_rect.x1, slot_rect.y0),
            (0.0, 1.0),
        ),
        AxisSide::Top => (
            Point::new(panel_rect.x0, slot_rect.y1),
            Point::new(panel_rect.x1, slot_rect.y1),
            (0.0, -1.0),
        ),
        AxisSide::Left => (
            Point::new(slot_rect.x1, panel_rect.y1),
            Point::new(slot_rect.x1, panel_rect.y0),
            (-1.0, 0.0),
        ),
        AxisSide::Right => (
            Point::new(slot_rect.x0, panel_rect.y1),
            Point::new(slot_rect.x0, panel_rect.y0),
            (1.0, 0.0),
        ),
    };

    let majors: Vec<(f64, String)> = breaks
        .iter()
        .filter(|v| !matches!(v, Value::Null))
        .filter_map(|v| {
            scale
                .map_break(v)
                .as_number()
                .map(|f| (f, scale.format(v, &theme.locale)))
        })
        .filter(|(f, _)| f.is_finite())
        .collect();
    let minors: Vec<f64> = scale
        .minor_breaks(DEFAULT_BREAK_COUNT)
        .into_iter()
        .filter(|v| !matches!(v, Value::Null))
        .filter_map(|v| scale.map_break(&v).as_number())
        .filter(|f| f.is_finite())
        .collect();

    // Resolve the (channel, side) axis from the theme. Channel
    // is determined by which axis side this is — Bottom/Top
    // belong to channel 0 (x), Left/Right to channel 1 (y).
    // Side 0 / 1 within the channel selects between the two
    // possible axes for that channel.
    let (ch, side_idx) = axis_side_to_channel_side(side);
    let resolved = theme.resolved_axis(ch, side_idx);
    let style = AxisChromeStyle::from_resolved(
        &resolved,
        &theme.palette,
        dpi,
        crate::plot::chrome::root_text_pt(theme),
    );
    draw_linear_axis_at(
        scene,
        start,
        end,
        tick_direction,
        &majors,
        &minors,
        &style,
        dpi,
    );
}

/// Map an `AxisSide` to the projection-agnostic `(channel, side)`
/// indices the theme stores axis chrome under.
///
/// - `Bottom` → (0, 0): x-axis, primary side.
/// - `Top`    → (0, 1): x-axis, secondary side.
/// - `Left`   → (1, 0): y-axis, primary side.
/// - `Right`  → (1, 1): y-axis, secondary side.
pub(crate) fn axis_side_to_channel_side(side: AxisSide) -> (u8, u8) {
    match side {
        AxisSide::Bottom => (0, 0),
        AxisSide::Top => (0, 1),
        AxisSide::Left => (1, 0),
        AxisSide::Right => (1, 1),
    }
}

// ─── Tests ───────────────────────────────────────────────────────────────────

#[cfg(test)]
mod tests {
    use super::*;
    use crate::plot::scale;
    use crate::scales::value::Value;
    use crate::scene::recording::{Op, RecordingScene};

    fn dpi_96() -> f64 {
        96.0
    }

    fn panel_400_300() -> Rect {
        Rect::new(50.0, 20.0, 450.0, 320.0)
    }

    // ── Axis spec ──

    #[test]
    fn axis_builders_round_trip_through_the_accessors() {
        let rail = Axis::rail("x", AxisPlacement::Cartesian(AxisSide::Bottom)).title("Time");
        assert_eq!(rail.scale_name(), Some("x"));
        assert_eq!(rail.placement(), AxisPlacement::Cartesian(AxisSide::Bottom));
        assert_eq!(rail.title_ref(), Some("Time"));

        let title_only = Axis::title_only("Depth", AxisPlacement::PolarAngular(PolarRing::Outer));
        assert_eq!(title_only.scale_name(), None);
        assert_eq!(title_only.title_ref(), Some("Depth"));
    }

    // ── axis_measure ──

    #[test]
    fn bottom_axis_measure_reports_chrome_height() {
        let s = scale::continuous(0.0..=100.0);
        let theme = Theme::default();
        let m = measure(&s, AxisSide::Bottom, dpi_96(), &theme);
        // Bottom axis: width contribution = 0, height = tick + gap + label_h.
        assert_eq!(m.width_hint(dpi_96()), WidthHint::Min(0.0));
        let h = m.height_at(400.0, dpi_96());
        assert!(h > 0.0, "axis height should be positive");
        // Sanity: at least the tick length in px.
        assert!(h >= 1.0);
    }

    #[test]
    fn left_axis_measure_reports_chrome_width() {
        let s = scale::continuous(0.0..=100.0);
        let theme = Theme::default();
        let m = measure(&s, AxisSide::Left, dpi_96(), &theme);
        let w = match m.width_hint(dpi_96()) {
            WidthHint::Min(w) => w,
            WidthHint::NeedsHeight { seed } => seed,
        };
        assert!(w > 0.0, "axis width should be positive");
        // Left axis row contribution is zero (height is panel-driven).
        assert_eq!(m.height_at(w, dpi_96()), 0.0);
    }

    #[test]
    fn axis_chrome_grows_with_longer_labels() {
        // A scale whose labels are wider (8-digit numbers) should
        // produce a wider Left axis.
        let s_short = scale::continuous(0.0..=10.0);
        let s_long = scale::continuous(0.0..=100_000_000.0);
        let theme = Theme::default();
        let m_short = measure(&s_short, AxisSide::Left, dpi_96(), &theme);
        let m_long = measure(&s_long, AxisSide::Left, dpi_96(), &theme);
        let w_short = match m_short.width_hint(dpi_96()) {
            WidthHint::Min(w) => w,
            WidthHint::NeedsHeight { seed } => seed,
        };
        let w_long = match m_long.width_hint(dpi_96()) {
            WidthHint::Min(w) => w,
            WidthHint::NeedsHeight { seed } => seed,
        };
        assert!(
            w_long > w_short,
            "longer labels should grow the axis: short={w_short}, long={w_long}"
        );
    }

    // ── draw_axis op-emission ──

    fn count_strokes_and_glyph_runs(scene: &RecordingScene) -> (usize, usize) {
        let mut strokes = 0usize;
        let mut glyphs = 0usize;
        for op in &scene.ops {
            match op {
                Op::Stroke { .. } => strokes += 1,
                Op::DrawGlyphs(_) => glyphs += 1,
                _ => {}
            }
        }
        (strokes, glyphs)
    }

    #[test]
    fn bottom_axis_draws_ticks_and_labels() {
        let s = scale::continuous(0.0..=10.0);
        let panel = panel_400_300();
        // Place the slot directly below the panel — height = chrome.
        let theme = Theme::default();
        let m = measure(&s, AxisSide::Bottom, dpi_96(), &theme);
        let chrome_h = m.height_at(panel.x1 - panel.x0, dpi_96());
        let slot = Rect::new(panel.x0, panel.y1, panel.x1, panel.y1 + chrome_h);

        let mut scene = RecordingScene::default();
        draw(
            &s,
            &mut scene,
            slot,
            panel,
            AxisSide::Bottom,
            dpi_96(),
            &Theme::default(),
        );

        let (strokes, glyphs) = count_strokes_and_glyph_runs(&scene);
        let breaks = s.breaks(DEFAULT_BREAK_COUNT);
        let minors = s.minor_breaks(DEFAULT_BREAK_COUNT);
        let n_majors = breaks.iter().filter(|v| !matches!(v, Value::Null)).count();
        let n_minors = minors.iter().filter(|v| !matches!(v, Value::Null)).count();
        // Default theme has `axis.line = Blank` (ggplot2 theme_gray
        // style), so the baseline contributes no stroke — only ticks.
        let expected_strokes = n_majors + n_minors;
        assert_eq!(
            strokes, expected_strokes,
            "expected {expected_strokes} strokes ({n_majors} majors + {n_minors} minors, no baseline); got {strokes}"
        );
        assert!(
            glyphs >= n_majors,
            "expected at least one glyph-run per major label"
        );
    }

    #[test]
    fn left_axis_draws_ticks_and_labels() {
        let s = scale::continuous(0.0..=1.0);
        let panel = panel_400_300();
        let theme = Theme::default();
        let m = measure(&s, AxisSide::Left, dpi_96(), &theme);
        let chrome_w = match m.width_hint(dpi_96()) {
            WidthHint::Min(w) => w,
            WidthHint::NeedsHeight { seed } => seed,
        };
        let slot = Rect::new(panel.x0 - chrome_w, panel.y0, panel.x0, panel.y1);

        let mut scene = RecordingScene::default();
        draw(
            &s,
            &mut scene,
            slot,
            panel,
            AxisSide::Left,
            dpi_96(),
            &Theme::default(),
        );

        let (strokes, glyphs) = count_strokes_and_glyph_runs(&scene);
        let breaks = s.breaks(DEFAULT_BREAK_COUNT);
        let minors = s.minor_breaks(DEFAULT_BREAK_COUNT);
        let n_majors = breaks.iter().filter(|v| !matches!(v, Value::Null)).count();
        let n_minors = minors.iter().filter(|v| !matches!(v, Value::Null)).count();
        let expected_strokes = n_majors + n_minors;
        assert_eq!(strokes, expected_strokes);
        assert!(glyphs >= n_majors);
    }

    #[test]
    fn binned_axis_ticks_sit_on_their_own_bin_edges() {
        use crate::geometry::Shape as _;

        let edges = vec![2500.0, 3500.0, 4500.0, 5500.0, 6500.0];
        let s = scale::binned(2500.0..=6500.0, edges.clone());
        let panel = panel_400_300();
        let theme = Theme::default();
        let m = measure(&s, AxisSide::Bottom, dpi_96(), &theme);
        let chrome_h = m.height_at(panel.x1 - panel.x0, dpi_96());
        let slot = Rect::new(panel.x0, panel.y1, panel.x1, panel.y1 + chrome_h);

        let mut scene = RecordingScene::default();
        draw(
            &s,
            &mut scene,
            slot,
            panel,
            AxisSide::Bottom,
            dpi_96(),
            &theme,
        );

        let tick_xs: Vec<f64> = scene
            .ops
            .iter()
            .filter_map(|op| match op {
                Op::Stroke { path, .. } => Some(path.bounding_box().center().x),
                _ => None,
            })
            .collect();
        let panel_w = panel.x1 - panel.x0;
        let expected: Vec<f64> = edges
            .iter()
            .map(|e| panel.x0 + (e - 2500.0) / 4000.0 * panel_w)
            .collect();
        assert_eq!(tick_xs.len(), expected.len(), "one tick per bin edge");
        for (got, want) in tick_xs.iter().zip(&expected) {
            assert!(
                (got - want).abs() < 1e-6,
                "tick at {got}, expected {want} (ticks: {tick_xs:?})"
            );
        }
    }

    #[test]
    fn draw_axis_with_no_breaks_is_silent() {
        // Identity scale produces no breaks → no draws.
        let s = scale::identity();
        let panel = panel_400_300();
        let slot = Rect::new(panel.x0, panel.y1, panel.x1, panel.y1 + 30.0);

        let mut scene = RecordingScene::default();
        draw(
            &s,
            &mut scene,
            slot,
            panel,
            AxisSide::Bottom,
            dpi_96(),
            &Theme::default(),
        );
        assert!(
            scene.ops.is_empty(),
            "expected no ops for empty breaks; got {}",
            scene.ops.len()
        );
    }

    #[test]
    fn draw_axis_with_degenerate_panel_is_silent() {
        let s = scale::continuous(0.0..=10.0);
        // Zero-area panel.
        let panel = Rect::new(0.0, 0.0, 0.0, 0.0);
        let slot = Rect::new(0.0, 0.0, 10.0, 10.0);
        let mut scene = RecordingScene::default();
        draw(
            &s,
            &mut scene,
            slot,
            panel,
            AxisSide::Bottom,
            dpi_96(),
            &Theme::default(),
        );
        assert!(scene.ops.is_empty());
    }
}