//! On-canvas command input: while a feature dialog is open, its main value (extrude distance,
//! fillet radius…) gets a value box in the viewport next to the geometry, and an arrow
//! (extrude, fillet, shell, move) that can be dragged: values snap to round steps (hold Alt or
//! Ctrl for a free drag) and the dialog follows. The box takes the keyboard as soon as the
//! command has its geometry, so typing a number sets the value at once; Enter applies, Tab
//! moves on, Esc cancels.

use egui::{Color32, Pos2, Stroke, vec2};
use solidcraft_engine::Sel;
use solidcraft_engine::doc::expr::Kind as ValueKind;
use solidcraft_engine::geom::{Mesh, Vec2, Vec3};

use crate::SolveApp;
use crate::dialogs::{Dialog, Kind};
use crate::theme::Tokens;
use crate::viewport::{Proj, projected_polygon};

/// Where the dialog's geometry is: a base point and, for values that can be dragged, the
/// direction a growing value points.
pub fn anchor(app: &SolveApp, d: &Dialog) -> Option<(Vec3, Option<Vec3>)> {
    let st = app.session.world_state();
    let first = d.inputs.first()?.items.first()?;
    let (at, normal) = match first {
        Sel::Profile { sketch, index } => {
            let ss = st.sketch(*sketch)?;
            let plane = profile_plane(app, *sketch)?;
            let p = ss.profiles.get(*index)?;
            let centre = if matches!(d.kind, Kind::Extrude { .. }) {
                let regions: Vec<_> = d
                    .inputs
                    .first()?
                    .items
                    .iter()
                    .filter_map(|item| {
                        if let Sel::Profile { sketch: id, index } = item { (*id == *sketch).then(|| ss.profiles.get(*index)).flatten() } else { None }
                    })
                    .map(|p| p.region.clone())
                    .collect();
                let regions = solidcraft_engine::sketch::merge_regions(&regions);
                let points: Vec<_> = regions.iter().flat_map(|r| r.outer.polyline(1e-2)).collect();
                points.iter().fold(solidcraft_engine::geom::Vec2::default(), |sum, p| sum + *p) * (1.0 / points.len().max(1) as f64)
            } else {
                p.region.interior_point()
            };
            (plane.to_world(centre), Some(plane.normal()))
        }
        Sel::Face { body, index, point } => (*point, crate::dialogs::planar_face(&app.session, body, *index).map(|(_, n)| n)),
        Sel::Edge { body, index, point } => (*point, st.body(body).and_then(|b| edge_bisector(&b.mesh(), *index, *point))),
        Sel::Vertex { point, .. } => (*point, None),
        Sel::SketchCurve { id } => {
            let ss = st.sketches.iter().rev().find(|ss| ss.sketch.curve_index(id).is_some())?;
            let pts = ss.sketch.polyline(ss.sketch.curve_index(id)?);
            let (mid, tangent) = poly_mid(&pts)?;
            // An offset's drag arrow: the in-plane direction the distance grows along. The
            // command offsets a picked curve to its left, and the window's Flip row reverses it.
            // Symmetric hides Flip and offsets both ways, so the arrow keeps the left side.
            let dir = match &d.kind {
                Kind::SketchModify(crate::sketch_modify_ui::Mod::Offset { flip, mode, .. }) => {
                    let n = if *flip && !crate::sketch_modify_ui::offset_symmetric(*mode) { -tangent.perp() } else { tangent.perp() };
                    Some(ss.plane.to_world(mid + n) - ss.plane.to_world(mid))
                }
                // A thin extrude's curves extrude along their sketch's normal.
                Kind::Extrude { .. } => Some(ss.plane.normal()),
                _ => None,
            };
            (ss.plane.to_world(mid), dir)
        }
        // A corner picked into a sketch window ("<sketch id>:<point id>", or a bare id when it
        // was selected outside one): the value box sits on the corner itself.
        Sel::SketchPoint { id } => {
            let (sketch, point) = match id.split_once(':') {
                Some((sketch, point)) => (sketch.parse().ok()?, point),
                None => (app.session.active_sketch?, id.as_str()),
            };
            let ss = st.sketch(sketch)?;
            (ss.plane.to_world(ss.sketch.point(ss.sketch.resolve_point(point)?)?), None)
        }
        Sel::Body { name } => (st.body(name)?.mesh().bounds().center(), None),
        Sel::Plane { name } => {
            let pl = solidcraft_engine::geom::Plane::named(name).or_else(|| {
                solidcraft_engine::view::construction_planes(&app.session).into_iter().find(|(_, n, _)| n == name).map(|(_, _, pl)| pl)
            })?;
            (pl.origin, Some(pl.normal()))
        }
        _ => return None,
    };
    Some(match &d.kind {
        Kind::Extrude { start, .. } => {
            let n = normal?;
            let plane = solidcraft_engine::geom::Plane::from_normal(at, n)?;
            let from = reference_height(app, d, "From Object", &plane, at).unwrap_or(0.0);
            let offset = if start.trim().is_empty() { 0.0 } else { app.session.doc.eval(start, ValueKind::Length).ok()? };
            (at + n * (from + offset), Some(n))
        }
        // A hole on a curved face drills against the face's normal where it was picked.
        Kind::Hole { .. } if matches!(first, Sel::Face { .. }) => {
            (at, normal.or_else(|| solidcraft_engine::doc::hole_direction_at(&st, at).map(|d| -d)))
        }
        // Holes at sketch points go into the part the sketch touches (or away, flipped): the
        // arrow shows which way.
        Kind::Hole { .. } => {
            let mut by_sketch: Vec<(u64, Vec<String>)> = Vec::new();
            for x in &d.inputs.first()?.items {
                if let Sel::SketchPoint { id } = x
                    && let Some((sk, pid)) = id.split_once(':')
                    && let Ok(sk) = sk.parse::<u64>()
                {
                    match by_sketch.iter_mut().find(|(s, _)| *s == sk) {
                        Some((_, v)) => v.push(pid.to_string()),
                        None => by_sketch.push((sk, vec![pid.to_string()])),
                    }
                }
            }
            let flip = d.extra.get("flip").and_then(serde_json::Value::as_bool).unwrap_or(false);
            let dir = by_sketch.first().and_then(|(sk, ids)| solidcraft_engine::doc::sketch_hole_direction(&st, *sk, ids, flip));
            (at, normal.or(dir.map(|d| -d)))
        }
        Kind::Section { .. } | Kind::OffsetPlane { .. } | Kind::OffsetFaces { .. } => (at, normal),
        // Fillet radii, chamfer distances and shell thickness grow into the body.
        Kind::Fillet { .. } | Kind::Shell { .. } => (at, normal.map(|n| -n)),
        Kind::Sheet(_) => (at, crate::dialogs_sheet::arrow(app, d).or(normal)),
        Kind::Plastic(_) => (at, normal),
        Kind::PatternRect { .. } => (at, d.inputs.get(1).and_then(|i| i.items.first()).and_then(|x| crate::dialogs::axis_of(app, x)).map(|a| a.1)),
        // A sketch move's X Distance grows along the sketch's own x axis, so its drag arrow
        // lies in the sketch plane. Scale has no arrow: a factor is not a length, and the
        // square handle it wants is its own change.
        Kind::SketchModify(crate::sketch_modify_ui::Mod::Move { .. }) => {
            (at, app.session.active_sketch.and_then(|id| st.sketch(id)).and_then(|ss| ss.plane.x.normalized()))
        }
        // The rectangular pattern's spacing grows along the direction it was given, which the
        // module works out per variant. Offset's arrow is already computed above, per picked
        // curve, and `arrow` returns None for it so that one stands.
        Kind::SketchModify(_) => (at, crate::sketch_modify_ui::arrow(app, d).or(normal)),
        _ => (at, None),
    })
}

/// The point halfway along a polyline, with the unit tangent there. Indexing the middle sample
/// instead would land on a two-point line's far end, putting the value box and its arrow on a
/// corner. None for a polyline with no length.
fn poly_mid(poly: &[Vec2]) -> Option<(Vec2, Vec2)> {
    let total: f64 = poly.windows(2).map(|w| w[0].dist(w[1])).sum();
    if !total.is_finite() || total <= 0.0 {
        return None;
    }
    let half = total / 2.0;
    let mut walked = 0.0;
    let mut last = None;
    for w in poly.windows(2) {
        let (a, b) = (w[0], w[1]);
        let Some(dir) = (b - a).normalized() else { continue };
        let len = a.dist(b);
        if walked + len >= half {
            return Some((a + dir * (half - walked), dir));
        }
        walked += len;
        last = Some((b, dir));
    }
    last
}

fn profile_plane(app: &SolveApp, sketch: u64) -> Option<solidcraft_engine::geom::Plane> {
    let component = app.session.doc.feature(sketch)?.component;
    let state = app.session.model.state();
    let plane = state.sketch(sketch)?.plane;
    let frame = crate::dialogs::feature_frame(&app.session, component);
    solidcraft_engine::geom::Plane::new(
        solidcraft_engine::doc::apply_point(&frame, plane.origin),
        solidcraft_engine::doc::apply_vector(&frame, plane.x),
        solidcraft_engine::doc::apply_vector(&frame, plane.y),
    )
}

fn reference_height(app: &SolveApp, d: &Dialog, label: &str, plane: &solidcraft_engine::geom::Plane, centre: Vec3) -> Option<f64> {
    let point = crate::dialogs::object_point(&d.inputs, label)?;
    let p = point.as_array()?;
    let p = Vec3::new(p.first()?.as_f64()?, p.get(1)?.as_f64()?, p.get(2)?.as_f64()?);
    Some(solidcraft_engine::doc::object_height(&app.session.world_state(), plane, centre, p))
}

/// The outward direction between the two faces at an edge (a fillet's radius arrow points the
/// other way, into the body).
fn edge_bisector(m: &Mesh, index: usize, p: Vec3) -> Option<Vec3> {
    let faces = m.edge_faces.get(index)?;
    let mut sum = Vec3::ZERO;
    for f in faces {
        let n = m
            .triangles
            .iter()
            .zip(&m.tri_face)
            .filter(|(_, tf)| *tf == f)
            .filter_map(|(t, _)| m.tri(t))
            .min_by(|a, b| ((a[0] + a[1] + a[2]) / 3.0).dist(p).total_cmp(&((b[0] + b[1] + b[2]) / 3.0).dist(p)))
            .and_then(|[a, b, c]| (b - a).cross(c - a).normalized())?;
        sum += n;
    }
    sum.normalized()
}

/// Draw the manipulator and the value box (called by the viewport after the model is drawn).
pub fn show(app: &mut SolveApp, ui: &mut egui::Ui, painter: &egui::Painter, proj: &Proj) {
    let Some(mut d) = app.dialog.take() else { return };
    if matches!(d.kind, Kind::Assembly(_)) {
        crate::dialogs_assembly::overlay(app, painter, proj, &mut d);
        app.dialog = Some(d);
        return;
    }
    if crate::dialogs_sheet::overlay(app, painter, proj.rect, &d) {
        app.dialog = Some(d);
        return;
    }
    if let Kind::Measure { result: Some(r), .. } = &d.kind {
        measure_line(app, painter, proj, r);
        app.dialog = Some(d);
        return;
    }
    // Move: the triad at the pivot; dragging it sets the distances and angles. Its value box
    // sits beside it and reads the move's main value, so a drag shows its number and typing
    // one sets it. The triad is the manipulator here, so the box comes without the drag arrow
    // every other dialog's value gets (`dir` is None below).
    if matches!(d.kind, Kind::Move { .. }) {
        let mut dragging = false;
        if let Some(t) = crate::dialogs_move::triad(app, &d)
            && let Some(g) = crate::gizmo::show(ui, painter, proj, egui::Id::new("sc_move_triad"), &t, snap_step(app.cam.half_height()))
        {
            crate::dialogs_move::drag(app, &mut d, g);
            dragging = true;
        }
        // Read the triad again after the drag, so the box follows it in the same frame. Move
        // types with no triad (Rotate, Point to Point, Point to Position) put the box on the
        // picked bodies instead.
        let triad = crate::dialogs_move::triad(app, &d);
        let at = triad.map(|t| t.center).or_else(|| anchor(app, &d).map(|(base, _)| base));
        let focus = std::mem::take(&mut d.focus);
        if let Some(bs) = at.and_then(|base| proj.to_screen(base))
            && let Some((label, _, value)) = d.primary()
        {
            // Clear of the triad: its arrows reach LEN_PX and its rings RING of that, so a box
            // beside the centre would cover the handles the user is reaching for.
            let off = if triad.is_some() { vec2(crate::gizmo::LEN_PX as f32 + 16.0, -12.0) } else { vec2(16.0, -30.0) };
            value_box(ui, label, value, bs + off, focus || dragging);
        }
        app.dialog = Some(d);
        return;
    }
    if let Some((base, dir)) = anchor(app, &d)
        && let Some(bs) = proj.to_screen(base)
    {
        draw(app, ui, painter, proj, &mut d, base, bs, dir);
    }
    app.dialog = Some(d);
}

/// A round step for dragged values at this zoom (1, 2 or 5 times a power of ten).
pub fn snap_step(half_height: f64) -> f64 {
    let raw = (half_height / 40.0).max(1e-4);
    let p = 10f64.powf(raw.log10().floor());
    if raw / p < 2.0 {
        p
    } else if raw / p < 5.0 {
        2.0 * p
    } else {
        5.0 * p
    }
}

/// Parameter along the line `base + dir * t` closest to the view ray through `pos`.
fn along(proj: &Proj, pos: Pos2, base: Vec3, dir: Vec3) -> Option<f64> {
    let (o, r) = proj.ray(pos);
    let w0 = base - o;
    let (b, d, e) = (dir.dot(r), dir.dot(w0), r.dot(w0));
    let den = 1.0 - b * b;
    // Looking straight along the line: nothing to drag.
    if den.abs() < 1e-6 {
        return None;
    }
    Some((b * e - d) / den)
}

fn format_len(v: f64) -> String {
    let s = format!("{v:.3}");
    let s = s.trim_end_matches('0').trim_end_matches('.');
    format!("{} mm", if s == "-0" { "0" } else { s })
}

/// The offset plane preview: a square of half side `h` around `c`, square to `n`.
fn offset_plane_quad(proj: &Proj, c: Vec3, n: Vec3, h: f64) -> Option<Vec<Pos2>> {
    let u = n.cross(if n.z.abs() < 0.9 { Vec3::Z } else { Vec3::X }).normalized()?;
    let v = n.cross(u);
    [(-1.0, -1.0), (1.0, -1.0), (1.0, 1.0), (-1.0, 1.0)].iter().map(|(a, b)| proj.to_screen(c + u * (a * h) + v * (b * h))).collect()
}

#[allow(clippy::too_many_arguments)]
fn draw(app: &SolveApp, ui: &mut egui::Ui, painter: &egui::Painter, proj: &Proj, d: &mut Dialog, base: Vec3, bs: Pos2, dir: Option<Vec3>) {
    let t = Tokens::get();
    let to_span = dir.and_then(|n| {
        let plane = solidcraft_engine::geom::Plane::from_normal(base, n)?;
        reference_height(app, d, "To Object", &plane, base)
    });
    let all_span = if matches!(d.kind, Kind::Extrude { all: true, .. }) {
        dir.and_then(|n| {
            let state = app.session.world_state();
            let plane = match d.inputs.first()?.items.first()? {
                Sel::Profile { sketch, .. } => profile_plane(app, *sketch)?,
                _ => solidcraft_engine::geom::Plane::from_normal(base, n)?,
            };
            let targets: Vec<String> = d
                .extra
                .get("targets")
                .and_then(serde_json::Value::as_array)
                .map(|a| a.iter().filter_map(|v| v.as_str().map(str::to_owned)).collect())
                .unwrap_or_default();
            solidcraft_engine::doc::through_all_distance(&state, &plane, &targets).ok()
        })
    } else {
        None
    };
    let sign = match (to_span, &d.kind) {
        (Some(span), _) => {
            if span < 0.0 {
                -1.0
            } else {
                1.0
            }
        }
        (_, Kind::Extrude { direction: 1, .. }) => -1.0,
        _ => 1.0,
    };
    let symmetric = to_span.is_none() && matches!(d.kind, Kind::Extrude { direction: 2, .. });
    // Extrudes and moves go either way; radii and thicknesses stay positive.
    let signed = matches!(
        d.kind,
        Kind::Extrude { .. }
            | Kind::Move { .. }
            | Kind::Section { .. }
            | Kind::OffsetPlane { .. }
            | Kind::OffsetFaces { .. }
            | Kind::SketchModify(crate::sketch_modify_ui::Mod::Move { .. })
    );
    let focus = std::mem::take(&mut d.focus);
    let half_height = app.cam.half_height();
    let axis = revolve_axis(app, d);
    if matches!(d.kind, Kind::Revolve { .. }) {
        if let Some(axis) = axis {
            draw_revolve(app, ui, painter, proj, d, base, bs, axis, focus);
        }
        return;
    }
    // Two sides: the second distance gets its own arrow the other way.
    if let (Kind::Extrude { direction: crate::dialogs::TWO_SIDES, distance2, .. }, Some(n)) = (&mut d.kind, dir)
        && let Some(l2) = app.session.doc.eval(distance2, ValueKind::Length).ok().filter(|v| v.is_finite())
    {
        drag_arrow(ui, painter, proj, base, bs, -n, l2, true, egui::Id::new("sc_manipulator2"), half_height, distance2);
    }
    // An offset plane shows where it will be.
    if let (Kind::OffsetPlane { offset }, Some(n)) = (&d.kind, dir)
        && let Ok(off) = app.session.doc.eval(offset, ValueKind::Length)
        && let Some(q) = offset_plane_quad(proj, base + n * off, n, half_height * 0.25)
    {
        painter.extend(projected_polygon(&q, t.construction_plane, Stroke::new(1.2, t.origin_plane_edge)));
    }
    // Holes: the depth arrow points into the material (empty depth: through all); the
    // diameter is typed in the box.
    let mut dir = dir;
    // Extrude taper: a handle beside the arrow tip; dragging it sideways tilts the walls.
    let cam_right = app.cam.basis().0;
    if let (Kind::Extrude { direction: 0 | 1, distance, taper, taper_present, to_offset, .. }, Some(n)) = (&mut d.kind, dir) {
        let n = n * sign;
        let span = to_span.map(|span| span.abs() + app.session.doc.eval(to_offset, ValueKind::Length).unwrap_or(0.0)).or(all_span);
        if let Ok(l) = span.map(Ok).unwrap_or_else(|| app.session.doc.eval(distance, ValueKind::Length))
            && l.is_finite()
            && l.abs() > 1e-9
            && let Some(e) = (cam_right - n * cam_right.dot(n)).normalized()
        {
            let px = 2.0 * half_height / f64::from(proj.rect.height().max(1.0));
            let ang = app.session.doc.eval(taper, ValueKind::Angle).ok().filter(|v| v.is_finite()).unwrap_or(0.0);
            let before = taper.clone();
            taper_handle(ui, painter, proj, base - e * (40.0 * px), n * l, -e, ang, taper);
            if *taper != before {
                *taper_present = true;
            }
        }
    }
    if let (Kind::Hole { depth, opts, .. }, Some(n)) = (&mut d.kind, dir) {
        let l = if opts.all { 0.0 } else { app.session.doc.eval(depth, ValueKind::Length).ok().filter(|v| v.is_finite()).unwrap_or(0.0) };
        let before = depth.clone();
        drag_arrow(ui, painter, proj, base, bs, -n, l, false, egui::Id::new("sc_manipulator_depth"), half_height, depth);
        // Dragging the depth turns "through all" into a distance.
        if *depth != before {
            opts.all = false;
        }
        dir = None;
    }
    // A fillet with a radius spline is shaped by its handles along the edge; the arrow would sit
    // on one of them.
    if radius_spline_handles(app, ui, painter, proj, d) {
        dir = None;
    }
    let Some((label, kind, value)) = d.primary() else { return };
    let len = all_span.or_else(|| {
        if to_span.is_some() && value.trim().is_empty() { Some(0.0) } else { app.session.doc.eval(value, kind).ok().filter(|v| v.is_finite()) }
    });
    let before = value.clone();
    let mut box_at = bs + vec2(16.0, -30.0);
    if let (Some(n), Some(l)) = (dir, len.filter(|_| kind == ValueKind::Length)) {
        let n = n * sign;
        let baseline = to_span.map(f64::abs).unwrap_or(0.0);
        let mut shown_value = format_len(l + baseline);
        let original_shown = shown_value.clone();
        let dragged = if to_span.is_some() { &mut shown_value } else { &mut *value };
        if let Some(ts) = drag_arrow(ui, painter, proj, base, bs, n, l + baseline, signed, egui::Id::new("sc_manipulator"), half_height, dragged) {
            if to_span.is_some()
                && shown_value != original_shown
                && let Ok(v) = app.session.doc.eval(&shown_value, ValueKind::Length)
            {
                *value = format_len(v - baseline);
            }
            if symmetric && let Some(bt) = proj.to_screen(base - n * l) {
                arrow(painter, bs, bt, t.manipulator);
            }
            painter.circle(bs, 3.5, t.manipulator, Stroke::new(1.0, Color32::WHITE));
            box_at = ts + vec2(14.0, -12.0);
        }
    }
    value_box(ui, label, value, box_at, focus || *value != before);
    if *value != before
        && let Kind::Extrude { all, .. } = &mut d.kind
    {
        *all = false;
    }
}

/// The command's main value in the viewport, next to the geometry: the keyboard goes here while
/// the window is open, so a number typed straight after a pick sets the value. `at` is its
/// top-left corner. `select_all` re-selects the whole field, both right after a pick and on every
/// frame a drag is changing the value underneath it: without the latter, a drag that grows the
/// text (e.g. "4 mm" -> "15 mm") would leave the stale, shorter selection from the pick in place,
/// covering only part of the new text.
fn value_box(ui: &mut egui::Ui, label: &str, value: &mut String, at: Pos2, select_all: bool) {
    let t = Tokens::get();
    let id = egui::Id::new("sc_canvas_value");
    crate::frame::area(egui::Id::new("sc_canvas_area")).fixed_pos(at).order(egui::Order::Foreground).show(ui.ctx(), |ui| {
        egui::Frame::popup(ui.style()).inner_margin(egui::Margin::symmetric(6, 3)).show(ui, |ui| {
            ui.horizontal(|ui| {
                ui.label(egui::RichText::new(label).color(t.text_dim).size(11.5));
                let r = ui.add(egui::TextEdit::singleline(value).id(id).desired_width(72.0));
                crate::params_dialog::complete(ui, &r, value);
                if select_all {
                    r.request_focus();
                    let n = value.chars().count();
                    let mut st = egui::text_edit::TextEditState::load(ui.ctx(), id).unwrap_or_default();
                    st.cursor.set_char_range(Some(egui::text_selection::CCursorRange::two(egui::text::CCursor::new(0), egui::text::CCursor::new(n))));
                    st.store(ui.ctx(), id);
                }
            });
        });
    });
}

/// A draggable arrow from `base` along `n` showing `l` (at least a short stub); dragging writes
/// the snapped length into `value`. Returns the tip's screen position.
#[allow(clippy::too_many_arguments)]
fn drag_arrow(
    ui: &mut egui::Ui,
    painter: &egui::Painter,
    proj: &Proj,
    base: Vec3,
    bs: Pos2,
    n: Vec3,
    l: f64,
    signed: bool,
    id: egui::Id,
    half_height: f64,
    value: &mut String,
) -> Option<Pos2> {
    let t = Tokens::get();
    let min = 40.0 * 2.0 * half_height / f64::from(proj.rect.height().max(1.0));
    let shown = if l.abs() < min { min * if l < 0.0 { -1.0 } else { 1.0 } } else { l };
    let ts = proj.to_screen(base + n * shown)?;
    crate::scenario::publish_handle(if id == egui::Id::new("sc_manipulator") { "arrow" } else { "arrow2" }, ts);
    let r = ui.interact(egui::Rect::from_center_size(ts, vec2(20.0, 20.0)), id, egui::Sense::drag());
    let hot = r.hovered() || r.dragged();
    let col = if hot { t.accent } else { t.manipulator };
    arrow(painter, bs, ts, col);
    if hot {
        painter.circle_stroke(ts, 8.0, Stroke::new(1.5, col));
        ui.ctx().set_cursor_icon(egui::CursorIcon::Grab);
    }
    if r.dragged()
        && let Some(p) = r.interact_pointer_pos()
        && let Some(v) = along(proj, p, base, n)
    {
        let free = ui.input(|i| i.modifiers.alt || i.modifiers.ctrl || i.modifiers.command);
        let step = snap_step(half_height);
        let mut v = if free { v } else { (v / step).round() * step };
        if !signed {
            v = v.max(if free { 1e-3 } else { step });
        }
        *value = format_len(v);
    }
    Some(ts)
}

/// A fillet's radius spline on each of its edges (a spline fillet, or the splines a taper gave
/// them): the radius curve drawn into the body from the edge, and a handle per control radius at
/// its Greville position, that far from the edge. Dragging a handle sets its control radius
/// (snapped unless Alt/Ctrl); double-clicking the curve adds a control radius there without
/// changing it, double-clicking a handle between the ends removes it. A spline fillet's edges
/// share one spline, so every edge's handles edit it. A taper's handles show on a single edge
/// only: the first edit makes the fillet a spline fillet starting from that edge's taper, which
/// would put the same radius on every other edge. Whether the handles are shown.
fn radius_spline_handles(app: &SolveApp, ui: &mut egui::Ui, painter: &egui::Painter, proj: &Proj, d: &mut Dialog) -> bool {
    use serde_json::{Value, json};
    use solidcraft_engine::doc::kernel::RadiusSpline;
    enum Edit {
        Set(usize, f64),
        Insert(f64),
        Remove(usize),
    }
    let t = Tokens::get();
    let Kind::Fillet { chamfer: false, .. } = d.kind else { return false };
    let st = app.session.world_state();
    let edges: Vec<(std::sync::Arc<Mesh>, usize, Vec3, Vec3)> = d
        .inputs
        .first()
        .into_iter()
        .flat_map(|i| &i.items)
        .filter_map(|x| match x {
            Sel::Edge { body, index, .. } => {
                let m = st.body(body)?.mesh();
                let (a, b) = m.edges.get(*index).and_then(|e| Some((*e.first()?, *e.last()?)))?;
                Some((m, *index, a, b))
            }
            _ => None,
        })
        .collect();
    let Some(&(_, _, a0, b0)) = edges.first() else { return false };
    let eval = |e: &str| app.session.doc.eval(e, ValueKind::Length).ok().filter(|v| v.is_finite());
    let style = d.extra.get("type").and_then(Value::as_str).unwrap_or("constant").to_string();
    // Each edge's spline with the end its positions start from; the spline the handles edit,
    // whether it starts at the first edge's far end, and whether it is still the taper's.
    let (laws, base, swap, taper): (Vec<Option<(RadiusSpline, Vec3)>>, Option<RadiusSpline>, bool, bool) = if style == "spline" {
        let Kind::Fillet { radius, .. } = &d.kind else { return false };
        let knots: Vec<f64> = d.extra.get("knots").and_then(Value::as_array).into_iter().flatten().filter_map(Value::as_f64).collect();
        let exprs: Vec<String> =
            d.extra.get("radii").and_then(Value::as_array).into_iter().flatten().filter_map(Value::as_str).map(str::to_owned).collect();
        let Some(radii) = std::iter::once(radius.as_str()).chain(exprs.iter().map(String::as_str)).map(eval).collect::<Option<Vec<f64>>>() else {
            return false;
        };
        let spline = solidcraft_engine::doc::FilletStyle::spline(&knots, radii);
        let swap = d.extra.get("swap_ends").and_then(Value::as_bool).unwrap_or(false);
        let start = if swap { b0 } else { a0 };
        // Each edge runs from its end nearest the start, as the fillet builds it.
        let laws = edges.iter().map(|(_, _, a, b)| Some((spline.clone(), if start.dist(*a) <= start.dist(*b) { *a } else { *b }))).collect();
        (laws, Some(spline), swap, false)
    } else if style == "constant" && d.extra.get("fit").and_then(Value::as_str) == Some("taper") {
        // The taper of an edge: its point lies on the edge's chord. An edge that fits has none.
        let on_edge = |a: Vec3, b: Vec3, p: Vec3| {
            let ab = b - a;
            let s = ((p - a).dot(ab) / ab.dot(ab).max(1e-300)).clamp(0.0, 1.0);
            (a + ab * s).dist(p) <= 1e-6 * (1.0 + ab.len())
        };
        let laws: Vec<Option<(RadiusSpline, Vec3)>> = edges
            .iter()
            .map(|(_, _, a, b)| app.preview.tapered.iter().find(|(p, _)| on_edge(*a, *b, *p)).map(|(_, tp)| (tp.spline.clone(), tp.start)))
            .collect();
        let base = laws.first().cloned().flatten().filter(|_| edges.len() == 1);
        let swap = base.as_ref().is_some_and(|(_, s)| s.dist(b0) < s.dist(a0));
        (laws, base.map(|(l, _)| l), swap, true)
    } else {
        return false;
    };
    // Each drawn edge: its spline, the ends its positions run between, the direction into the
    // body, and the curve on screen with its positions.
    struct Drawn<'a> {
        spline: &'a RadiusSpline,
        start: Vec3,
        other: Vec3,
        n: Vec3,
        curve: Vec<(f64, Pos2)>,
    }
    let drawn: Vec<Drawn> = edges
        .iter()
        .zip(&laws)
        .filter_map(|((mesh, index, a, b), law)| {
            let (spline, start) = law.as_ref()?;
            let other = if start.dist(*a) <= start.dist(*b) { *b } else { *a };
            let mid = *start + (other - *start) * 0.5;
            // Into the body, between the two faces (the edge is straight between planar faces).
            let n = -edge_bisector(mesh, *index, mid)?;
            let curve = (0..=48)
                .filter_map(|k| {
                    let u = f64::from(k) / 48.0;
                    Some((u, proj.to_screen(*start + (other - *start) * u + n * spline.eval(u))?))
                })
                .collect();
            Some(Drawn { spline, start: *start, other, n, curve })
        })
        .collect();
    for e in &drawn {
        painter.add(egui::Shape::line(e.curve.iter().map(|c| c.1).collect(), Stroke::new(1.5, t.manipulator)));
    }
    let Some(base) = base.filter(|_| !drawn.is_empty()) else { return false };
    let mut edit = None;
    // Double-clicking the curve adds a control radius at the nearest position along it. Under
    // the handles, which are registered after it and so take the pointer first.
    let near = ui.input(|i| i.pointer.hover_pos()).and_then(|p| {
        drawn
            .iter()
            .flat_map(|e| e.curve.windows(2))
            .map(|w| {
                let ((u0, p0), (u1, p1)) = (w[0], w[1]);
                let seg = p1 - p0;
                let s = ((p - p0).dot(seg) / seg.length_sq().max(1e-6)).clamp(0.0, 1.0);
                (p0.lerp(p1, s).distance(p), u0 + (u1 - u0) * f64::from(s))
            })
            .min_by(|x, y| x.0.total_cmp(&y.0))
            .filter(|(dist, _)| *dist < 6.0)
            .map(|(_, u)| (p, u))
    });
    if let Some((p, u)) = near {
        crate::scenario::publish_handle("fillet_curve", p);
        if ui.interact(egui::Rect::from_center_size(p, vec2(12.0, 12.0)), egui::Id::new("sc_fillet_curve"), egui::Sense::click()).double_clicked() {
            edit = Some(Edit::Insert(u));
        }
    }
    let half_height = app.cam.half_height();
    let last = base.radii.len().saturating_sub(1);
    for (i, e) in drawn.iter().enumerate() {
        let at = |u: f64| e.start + (e.other - e.start) * u;
        let g = e.spline.greville();
        let tips: Vec<Option<Pos2>> = g.iter().zip(&e.spline.radii).map(|(u, r)| proj.to_screen(at(*u) + e.n * *r)).collect();
        painter.add(egui::Shape::dashed_line(&tips.iter().flatten().copied().collect::<Vec<_>>(), Stroke::new(1.0, t.manipulator), 4.0, 3.0));
        for (k, (u, ts)) in g.iter().zip(&tips).enumerate() {
            let Some(ts) = *ts else { continue };
            crate::scenario::publish_handle(&if i == 0 { format!("fillet_r{k}") } else { format!("fillet_e{i}_r{k}") }, ts);
            let r =
                ui.interact(egui::Rect::from_center_size(ts, vec2(16.0, 16.0)), egui::Id::new(("sc_fillet_r", i, k)), egui::Sense::click_and_drag());
            let hot = r.hovered() || r.dragged();
            let col = if hot { t.accent } else { t.manipulator };
            if let Some(fs) = proj.to_screen(at(*u)) {
                painter.line_segment([fs, ts], Stroke::new(1.0, col));
            }
            painter.circle(ts, if hot { 6.5 } else { 5.0 }, t.overlay, Stroke::new(2.0, col));
            if hot {
                ui.ctx().set_cursor_icon(egui::CursorIcon::Grab);
            }
            if r.double_clicked() {
                edit = Some(Edit::Remove(k));
            } else if r.dragged()
                && let Some(p) = r.interact_pointer_pos()
                && let Some(v) = along(proj, p, at(*u), e.n)
            {
                let free = ui.input(|i| i.modifiers.alt || i.modifiers.ctrl || i.modifiers.command);
                let step = snap_step(half_height);
                let v = if free { v } else { (v / step).round() * step };
                // Zero only at an end, where the round closes to a point.
                let floor = if k == 0 || k == last {
                    0.0
                } else if free {
                    1e-3
                } else {
                    step
                };
                edit = Some(Edit::Set(k, v.max(floor)));
            }
        }
    }
    // A dragged radius on a spline fillet changes its own expression; anything else writes the
    // whole spline (inserting or removing a knot moves its neighbours too).
    let whole = match edit {
        Some(Edit::Set(k, v)) if !taper => {
            if k == 0 {
                if let Kind::Fillet { radius, .. } = &mut d.kind {
                    *radius = format_len(v);
                }
            } else if let Some(Value::Array(rs)) = d.extra.get_mut("radii")
                && let Some(slot) = rs.get_mut(k - 1)
            {
                *slot = json!(format_len(v));
            }
            None
        }
        Some(Edit::Set(k, v)) => {
            let mut law = base.clone();
            if let Some(r) = law.radii.get_mut(k) {
                *r = v;
            }
            Some(law)
        }
        Some(Edit::Insert(u)) => base.insert(u),
        Some(Edit::Remove(k)) => base.remove(k),
        None => None,
    };
    if let Some(law) = whole {
        d.extra.insert("type".into(), json!("spline"));
        d.extra.remove("fit");
        d.extra.insert("knots".into(), json!(law.knots));
        d.extra.insert("swap_ends".into(), json!(swap));
        d.extra.insert("radii".into(), json!(law.radii.iter().skip(1).map(|r| format_len(*r)).collect::<Vec<_>>()));
        if let Kind::Fillet { radius, .. } = &mut d.kind {
            *radius = format_len(law.radii.first().copied().unwrap_or(0.0));
        }
    }
    true
}

/// The measured distance: a line between the closest points with its length.
fn measure_line(app: &SolveApp, painter: &egui::Painter, proj: &Proj, r: &serde_json::Value) {
    let t = Tokens::get();
    let p = |k: &str| -> Option<Vec3> {
        let a = r.get(k)?.as_array()?;
        Some(Vec3::new(a.first()?.as_f64()?, a.get(1)?.as_f64()?, a.get(2)?.as_f64()?))
    };
    let (Some(a), Some(b), Some(d)) = (p("from"), p("to"), r.get("distance_mm").and_then(|v| v.as_f64())) else { return };
    let (Some(sa), Some(sb)) = (proj.to_screen(a), proj.to_screen(b)) else { return };
    painter.line_segment([sa, sb], Stroke::new(2.0, t.manipulator));
    for s in [sa, sb] {
        painter.circle(s, 3.5, t.manipulator, Stroke::new(1.0, Color32::WHITE));
    }
    let mid = sa + (sb - sa) * 0.5 + vec2(10.0, -14.0);
    let galley = painter.layout_no_wrap(crate::prefs::show_mm(app, d, 1), egui::FontId::proportional(12.5), t.text);
    let rect = egui::Rect::from_min_size(mid, galley.size() + vec2(10.0, 6.0));
    painter.rect(rect, 3.0, t.overlay, Stroke::new(1.0, t.border), egui::StrokeKind::Inside);
    painter.galley(rect.min + vec2(5.0, 3.0), galley, t.text);
}

/// The taper handle: a line from `foot` along the extrude (`span`) leaning by `angle` towards
/// `e`, with a ring at its end; dragging the ring sideways sets the angle (1° steps, Alt/Ctrl:
/// free).
#[allow(clippy::too_many_arguments)]
fn taper_handle(ui: &mut egui::Ui, painter: &egui::Painter, proj: &Proj, foot: Vec3, span: Vec3, e: Vec3, angle: f64, value: &mut String) {
    let t = Tokens::get();
    let l = span.len();
    let end = foot + span + e * (l * angle.tan().clamp(-10.0, 10.0));
    let (Some(fs), Some(es)) = (proj.to_screen(foot), proj.to_screen(end)) else { return };
    let r = ui.interact(egui::Rect::from_center_size(es, vec2(16.0, 16.0)), egui::Id::new("sc_taper"), egui::Sense::drag());
    let hot = r.hovered() || r.dragged();
    let col = if hot { t.accent } else { t.manipulator };
    painter.add(egui::Shape::dashed_line(&[fs, es], Stroke::new(1.2, col), 5.0, 3.0));
    painter.circle(es, if hot { 6.5 } else { 5.0 }, t.overlay, Stroke::new(2.0, col));
    if hot {
        ui.ctx().set_cursor_icon(egui::CursorIcon::Grab);
    }
    if r.dragged()
        && let Some(p) = r.interact_pointer_pos()
        && let Some(s) = along(proj, p, foot + span, e)
    {
        let mut deg = s.atan2(l).to_degrees();
        if !ui.input(|i| i.modifiers.alt || i.modifiers.ctrl || i.modifiers.command) {
            deg = deg.round();
        }
        let txt = format!("{deg:.1}");
        *value = format!("{} deg", txt.trim_end_matches('0').trim_end_matches('.'));
    }
}

/// The revolve axis (a point on it and its unit direction).
pub(crate) fn revolve_axis(app: &SolveApp, d: &Dialog) -> Option<(Vec3, Vec3)> {
    if !matches!(d.kind, Kind::Revolve { .. }) {
        return None;
    }
    if let Some(selected) = d.inputs.get(1)?.items.first() {
        if let Sel::Axis { name } = selected
            && matches!(name.as_str(), "X" | "Y" | "Z")
            && let Sel::Profile { sketch, .. } = d.inputs.first()?.items.first()?
        {
            let component = app.session.doc.feature(*sketch)?.component;
            let frame = crate::dialogs::feature_frame(&app.session, component);
            let dir = match name.as_str() {
                "X" => Vec3::X,
                "Y" => Vec3::Y,
                _ => Vec3::Z,
            };
            return Some((solidcraft_engine::doc::apply_point(&frame, Vec3::ZERO), solidcraft_engine::doc::apply_vector(&frame, dir)));
        }
        if let Sel::Axis { name } = selected
            && matches!(name.as_str(), "x" | "y")
            && let Sel::Profile { sketch, .. } = d.inputs.first()?.items.first()?
        {
            let plane = profile_plane(app, *sketch)?;
            return Some((plane.origin, if name == "x" { plane.x } else { plane.y }));
        }
        return crate::dialogs::axis_of(app, selected);
    }
    let Kind::Revolve { axis: Some(axis), .. } = &d.kind else { return None };
    let vector = |key: &str| -> Option<Vec3> {
        let p = axis.get(key)?.as_array()?;
        Some(Vec3::new(p.first()?.as_f64()?, p.get(1)?.as_f64()?, p.get(2)?.as_f64()?))
    };
    Some((vector("origin")?, vector("dir")?.normalized()?))
}

/// Draw angular extents in the same clockwise sense as the modeled solid.
#[allow(clippy::too_many_arguments)]
fn draw_revolve(
    app: &SolveApp,
    ui: &mut egui::Ui,
    painter: &egui::Painter,
    proj: &Proj,
    d: &mut Dialog,
    base: Vec3,
    bs: Pos2,
    axis: (Vec3, Vec3),
    focus: bool,
) {
    let to_mode = d.inputs.iter().any(|input| input.label == "To Object");
    let extent = revolve_display_extent(app, d, axis).unwrap_or(solidcraft_engine::doc::RevolveExtent {
        start: 0.0,
        sweep: f64::NAN,
        rotation_axis: axis.1,
        display_start: 0.0,
        curved_to: false,
    });
    let mut box_at = bs + vec2(16.0, -30.0);
    let angle_before = if let Kind::Revolve { angle, .. } = &d.kind { angle.clone() } else { String::new() };
    if !extent.curved_to && extent.sweep.is_finite() {
        let (origin, direction) = axis;
        let centre = origin + direction * (base - origin).dot(direction);
        let radius = (base - centre).len();
        if radius > 1e-9 {
            let e1 = (base - centre) / radius;
            let e2 = extent.rotation_axis.cross(e1);
            let handed = match revolve_convention(d) {
                solidcraft_engine::doc::RevolveConvention::LegacyAxisStart => -direction.dot(extent.rotation_axis),
                solidcraft_engine::doc::RevolveConvention::SketchNormal => 1.0,
            };
            let at = |angle: f64| centre + (e1 * angle.cos() + e2 * angle.sin()) * radius;
            let points: Vec<_> = (0..=48).filter_map(|i| proj.to_screen(at(extent.display_start + extent.sweep * i as f64 / 48.0))).collect();
            painter.add(egui::Shape::line(points, Stroke::new(2.0, Tokens::get().manipulator)));
            if let Some(end) = proj.to_screen(at(extent.display_start + extent.sweep)) {
                box_at = end + vec2(14.0, -12.0);
            }
            if !to_mode {
                let symmetric = !d.extra.contains_key("angle2") && d.extra.get("direction").and_then(serde_json::Value::as_str) == Some("symmetric");
                let other_angle = d
                    .extra
                    .get("angle2")
                    .and_then(|value| value.as_str())
                    .and_then(|value| app.session.doc.eval(value, ValueKind::Angle).ok())
                    .unwrap_or(0.0);
                let range = if extent.sweep < 0.0 { (-std::f64::consts::TAU, 0.0) } else { (0.0, std::f64::consts::TAU) };
                if let Kind::Revolve { angle, .. } = &mut d.kind {
                    let boundary = extent.display_start + extent.sweep;
                    if let Some(end) = rotation_handle(
                        ui,
                        painter,
                        proj,
                        centre,
                        e1,
                        e2,
                        direction,
                        radius,
                        boundary,
                        if symmetric { 1.0 / (1.0 - handed * 0.5) } else { 1.0 },
                        if symmetric { 0.0 } else { -other_angle * (1.0 - handed) },
                        (range.0 - other_angle, range.1 - other_angle),
                        "revolve",
                        angle,
                    ) {
                        box_at = end + vec2(14.0, -12.0);
                    }
                    if symmetric {
                        rotation_handle(
                            ui,
                            painter,
                            proj,
                            centre,
                            e1,
                            e2,
                            direction,
                            radius,
                            extent.display_start,
                            -2.0 * handed,
                            0.0,
                            range,
                            "revolve2",
                            angle,
                        );
                    }
                }
                if let Some(other) = d.extra.get_mut("angle2") {
                    let mut value = other.as_str().map(str::to_owned).unwrap_or_else(|| other.to_string());
                    let before = value.clone();
                    let first_angle = extent.sweep - other_angle;
                    rotation_handle(
                        ui,
                        painter,
                        proj,
                        centre,
                        e1,
                        e2,
                        direction,
                        radius,
                        extent.display_start,
                        -handed,
                        0.0,
                        (range.0 - first_angle, range.1 - first_angle),
                        "revolve2",
                        &mut value,
                    );
                    if value != before {
                        *other = serde_json::Value::String(value);
                    }
                }
            }
        }
    }
    if to_mode {
        crate::frame::area(egui::Id::new("sc_canvas_area")).fixed_pos(box_at).order(egui::Order::Foreground).show(ui.ctx(), |ui| {
            egui::Frame::popup(ui.style()).inner_margin(egui::Margin::symmetric(6, 3)).show(ui, |ui| {
                let text = if extent.curved_to {
                    "To surface".into()
                } else if extent.sweep.is_finite() {
                    format!("Sweep {:.1}°", extent.sweep.to_degrees())
                } else {
                    "Choose target".into()
                };
                ui.label(text).on_hover_text(crate::i18n::tr_label("Determined by To Object. Choose Angle to edit the angular extent."));
            });
        });
    } else if let Kind::Revolve { angle, .. } = &mut d.kind {
        let dragging = *angle != angle_before;
        value_box(ui, crate::i18n::tr_label("Angle"), angle, box_at, focus || dragging);
    }
}

fn revolve_convention(d: &Dialog) -> solidcraft_engine::doc::RevolveConvention {
    d.extra
        .get("convention")
        .and_then(|value| serde_json::from_value(value.clone()).ok())
        .unwrap_or(solidcraft_engine::doc::RevolveConvention::SketchNormal)
}

fn revolve_display_extent(app: &SolveApp, d: &Dialog, axis: (Vec3, Vec3)) -> Option<solidcraft_engine::doc::RevolveExtent> {
    let Sel::Profile { sketch, .. } = d.inputs.first()?.items.first()? else { return None };
    let state = app.session.world_state();
    let ss = state.sketch(*sketch)?;
    let regions: Vec<_> = d
        .inputs
        .first()?
        .items
        .iter()
        .filter_map(|item| match item {
            Sel::Profile { sketch: id, index } if id == sketch => ss.profiles.get(*index).map(|profile| profile.region.clone()),
            _ => None,
        })
        .collect();
    let regions = solidcraft_engine::sketch::merge_regions(&regions);
    let plane = profile_plane(app, *sketch)?;
    let to_mode = d.inputs.iter().any(|input| input.label == "To Object");
    let to = if to_mode {
        let point = crate::dialogs::object_point(&d.inputs, "To Object")?;
        Some(Vec3::new(point.get(0)?.as_f64()?, point.get(1)?.as_f64()?, point.get(2)?.as_f64()?))
    } else {
        None
    };
    let Kind::Revolve { angle, .. } = &d.kind else { return None };
    let angles = if to_mode {
        (0.0, None)
    } else {
        let angle = app.session.doc.eval(angle, ValueKind::Angle).ok()?;
        let other = d.extra.get("angle2").map(|value| app.session.doc.eval(value.as_str().unwrap_or_default(), ValueKind::Angle)).transpose().ok()?;
        (angle, other)
    };
    solidcraft_engine::doc::revolve_extent_with_convention(
        &state,
        &plane,
        &regions,
        axis,
        angles,
        d.extra.get("direction").and_then(serde_json::Value::as_str) == Some("symmetric"),
        to,
        revolve_convention(d),
    )
    .ok()
}

#[allow(clippy::too_many_arguments)]
fn rotation_handle(
    ui: &mut egui::Ui,
    painter: &egui::Painter,
    proj: &Proj,
    centre: Vec3,
    e1: Vec3,
    e2: Vec3,
    axis: Vec3,
    radius: f64,
    boundary: f64,
    scale: f64,
    offset: f64,
    range: (f64, f64),
    name: &str,
    value: &mut String,
) -> Option<Pos2> {
    let end = proj.to_screen(centre + (e1 * boundary.cos() + e2 * boundary.sin()) * radius)?;
    crate::scenario::publish_handle(name, end);
    let response = ui.interact(egui::Rect::from_center_size(end, vec2(20.0, 20.0)), egui::Id::new(("sc_rotator", name)), egui::Sense::drag());
    let hot = response.hovered() || response.dragged();
    let color = if hot { Tokens::get().accent } else { Tokens::get().manipulator };
    painter.circle(end, if hot { 7.0 } else { 5.5 }, color, Stroke::new(1.5, Color32::WHITE));
    if hot {
        ui.ctx().set_cursor_icon(egui::CursorIcon::Grab);
    }
    if response.dragged()
        && let Some(pointer) = response.interact_pointer_pos()
    {
        let (origin, direction) = proj.ray(pointer);
        let den = direction.dot(axis);
        let (a, b) = ((range.0 - offset) / scale, (range.1 - offset) / scale);
        let bounds = (a.min(b), a.max(b));
        // Near edge-on, a plane intersection magnifies subpixel pointer error.
        let raw = if den.abs() > 0.05 {
            let point = origin + direction * ((centre - origin).dot(axis) / den) - centre;
            Some(point.dot(e2).atan2(point.dot(e1)))
        } else {
            projected_rotation_angle(proj, pointer, centre, e1, e2, radius, boundary, bounds)
        };
        if let Some(raw) = raw {
            let boundary_angle = (-4..=4)
                .map(|k| raw + k as f64 * std::f64::consts::TAU)
                .filter(|angle| *angle >= bounds.0 - 1e-4 && *angle <= bounds.1 + 1e-4)
                .min_by(|a, b| (a - boundary).abs().total_cmp(&(b - boundary).abs()))
                .unwrap_or_else(|| raw.clamp(bounds.0, bounds.1));
            let mut angle = (boundary_angle.clamp(bounds.0, bounds.1) * scale + offset).to_degrees();
            if !ui.input(|input| input.modifiers.alt || input.modifiers.ctrl || input.modifiers.command) {
                angle = (angle / 5.0).round() * 5.0;
            }
            if angle.abs() < 0.05 {
                angle = 0.0;
            }
            let text = format!("{angle:.1}");
            *value = format!("{} deg", text.trim_end_matches('0').trim_end_matches('.'));
        }
    }
    Some(end)
}

/// An edge-on ring has two equally valid depths; retain the branch nearest the current handle.
#[allow(clippy::too_many_arguments)]
fn projected_rotation_angle(
    proj: &Proj,
    pointer: Pos2,
    centre: Vec3,
    e1: Vec3,
    e2: Vec3,
    radius: f64,
    current: f64,
    (lo, hi): (f64, f64),
) -> Option<f64> {
    let distance = |angle: f64| {
        proj.to_screen(centre + (e1 * angle.cos() + e2 * angle.sin()) * radius)
            .map(|point| f64::from(point.distance_sq(pointer)))
            .unwrap_or(f64::INFINITY)
    };
    let step = (hi - lo) / 720.0;
    let mut best = None;
    for i in 0..=720 {
        let angle = lo + step * i as f64;
        let score = distance(angle);
        if !score.is_finite() {
            continue;
        }
        if best.is_none_or(|(old_angle, old_score): (f64, f64)| {
            score < old_score - 1e-4 || (score - old_score).abs() <= 1e-4 && (angle - current).abs() < (old_angle - current).abs()
        }) {
            best = Some((angle, score));
        }
    }
    let (angle, _) = best?;
    let (mut a, mut b) = ((angle - step).max(lo), (angle + step).min(hi));
    for _ in 0..24 {
        let (left, right) = (a + (b - a) / 3.0, b - (b - a) / 3.0);
        if distance(left) <= distance(right) {
            b = right;
        } else {
            a = left;
        }
    }
    Some((a + b) / 2.0)
}
fn arrow(painter: &egui::Painter, a: Pos2, b: Pos2, col: Color32) {
    let v = b - a;
    let l = v.length();
    if l < 1.0 {
        return;
    }
    let u = v / l;
    let n = vec2(-u.y, u.x);
    painter.line_segment([a, b], Stroke::new(2.0, col));
    let head = 11.0f32.min(l * 0.6);
    painter.add(egui::Shape::convex_polygon(vec![b, b - u * head + n * head * 0.45, b - u * head - n * head * 0.45], col, Stroke::NONE));
}

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

    #[test]
    fn offset_plane_preview_stays_within_its_square() {
        let rect = egui::Rect::from_min_size(Pos2::ZERO, vec2(800.0, 600.0));
        let mut worst = f32::NEG_INFINITY;
        for n in [Vec3::X, Vec3::Y, Vec3::Z] {
            for dir in crate::viewport::orbit_directions() {
                let cam = solidcraft_engine::render::Camera::default().looking_from(dir);
                let proj = Proj { cam, vp: cam.view_proj(4.0 / 3.0, 100.0), rect };
                let h = cam.half_height() * 0.25;
                let (Some(q), Some(c), Some(side)) =
                    (offset_plane_quad(&proj, Vec3::ZERO, n, h), proj.to_screen(Vec3::ZERO), proj.to_screen(cam.basis().0 * h))
                else {
                    continue;
                };
                // The square's half diagonal on screen (an orthographic view), plus stroke and feathering.
                let limit = c.distance(side) * 2f32.sqrt() + 3.0;
                for p in crate::viewport::drawn_points(projected_polygon(&q, Color32::GRAY, Stroke::new(1.2, Color32::BLACK))) {
                    worst = worst.max(p.distance(c) - limit);
                }
            }
        }
        assert!(worst <= 0.0, "a vertex {worst} px past the square");
    }

    #[test]
    fn snapping_steps_and_formatting() {
        assert_eq!(snap_step(40.0), 1.0);
        assert_eq!(snap_step(100.0), 2.0);
        assert_eq!(snap_step(4.0), 0.1);
        assert_eq!(format_len(12.0), "12 mm");
        assert_eq!(format_len(-2.5), "-2.5 mm");
        assert_eq!(format_len(-0.0001), "0 mm");
    }
}