import { createMemo, createSignal, For, Show, onMount, onCleanup, JSXElement } from "solid-js";

// A dependency-free, reactive chart. It draws SVG — nothing is vendored, nothing is
// registered on a global, and there is no <canvas>.
//
// Being SVG is what makes it small. The picture IS the reactive tree: change
// props.series and Solid re-renders it, so there is no imperative update() to call and
// no mount-time construction pushing data into a canvas the reactive system cannot see.
// Marks name CSS variables (`fill: var(--color-chart-1)`), so the palette themes and
// inverts for dark mode for free — a canvas paints pixels and cannot read a variable.
//
// The marks are assembled as an SVG STRING and set with innerHTML, not written as JSX
// <path>/<line> elements. The Go-native Solid compiler namespaces an element as SVG only
// when it is written literally inside an <svg> in the same template; a <path> produced by
// control flow (<For>, a callback) is created in the HTML namespace and never paints.
// Setting innerHTML on an <svg> parses the string in the SVG namespace — the same trick
// uikit/Icons.tsx uses. Pointer handlers ride the <svg> element (a real Solid node), and
// which bar/slice the pointer is over is computed from geometry, not per-element listeners.
//
// Layout is measured, not scaled: a ResizeObserver reports the container's pixel width
// and the SVG is drawn at that width (viewBox === pixel box, 1:1), so text stays crisp
// at any size and pointer coordinates map straight onto the drawing. On the server (no
// ResizeObserver) it renders once at a sane default width and re-measures on mount.

export type ChartKind = "line" | "area" | "bar" | "pie" | "donut";

export interface ChartSeries {
    name: string;
    data: number[];
    // Override this series' palette slot. Any CSS colour; a var(--color-chart-n) keeps
    // it theme-aware. Leave unset to take the Nth slot of the categorical palette.
    color?: string;
}

export interface ChartProps {
    kind: ChartKind;
    // The x categories (line/area/bar) or the slice names (pie/donut). Optional only
    // because a bare numeric series can fall back to 1..n; supply them for real charts.
    labels?: string[];
    series: ChartSeries[];

    // bar / area: stack the series instead of grouping them side by side.
    stacked?: boolean;
    // bar only: lay the bars horizontally — categories run down the y-axis, values along x.
    horizontal?: boolean;
    // line / area: "smooth" draws a Catmull-Rom spline through the points.
    curve?: "linear" | "smooth";
    // donut only: inner-radius fraction of the outer radius (0.6 by default).
    donutRatio?: number;

    // Give the chart depth: bars extrude, pie/donut tilt and gain a rim (line/area ignore
    // it). An embellishment — flat reads more precisely — but sometimes wanted.
    threeD?: boolean;
    depth?: number; // 3D extrusion depth in px (default 16).

    height?: number; // px of the plot area (default 300). The legend adds its own height.
    width?: number;  // fix the width instead of measuring the container.
    class?: string;
    title?: string;  // a caption centred above the plot.

    // Override the whole categorical palette (else the --color-chart-1..8 tokens).
    palette?: string[];
    // Format a value for the value-axis ticks and the tooltip. Defaults to en-US grouping.
    valueFormat?: (v: number) => string;

    legend?: boolean;  // default: true when there is more than one series (or a pie).
    grid?: boolean;    // cartesian only; default true.
    axes?: boolean;    // cartesian only; default true.
    tooltip?: boolean; // default true.
    yMin?: number;     // pin the value domain instead of deriving it from the data.
    yMax?: number;
}

// The palette a component IS allowed to name — the tokens carry the theming. Referenced
// by index; a ninth series is the caller's problem (fold it into "Other"), never a
// synthesised ninth hue.
const CHART_TOKENS = [
    "var(--color-chart-1)", "var(--color-chart-2)", "var(--color-chart-3)", "var(--color-chart-4)",
    "var(--color-chart-5)", "var(--color-chart-6)", "var(--color-chart-7)", "var(--color-chart-8)",
];

const DEFAULT_HEIGHT = 300;
const DEFAULT_WIDTH = 640;   // used only until the container is measured (and on the server)
const BAR_MAX_W = 24;        // cap a bar's thickness; the band's leftover is deliberate air
const BAR_RADIUS = 4;        // rounded data-end
const SEG_GAP = 2;           // the surface gap between touching marks (stacked segments)
const MARK_R = 4;            // hover marker radius (8px mark)
const DEFAULT_DEPTH = 16;    // 3D extrusion depth

// ── number + geometry helpers ───────────────────────────────────────────────────

// A value or label can carry markup-breaking characters (a series name from a CSV
// header, a "<"), and it goes into an innerHTML string — escape everything untrusted.
const esc = (s: unknown) =>
    String(s).replace(/[&<>"]/g, (c) => (c === "&" ? "&amp;" : c === "<" ? "&lt;" : c === ">" ? "&gt;" : "&quot;"));

// Constructed lazily, not at module load: the SSR runtime (goja) may import this file
// while baking a page, and building the formatter at import time would run there too.
let _intl: Intl.NumberFormat | null = null;
const defaultFormat = (v: number) => {
    if (!Number.isFinite(v)) return String(v);
    _intl ??= new Intl.NumberFormat("en-US", { maximumFractionDigits: 2 });
    return _intl.format(v);
};

// "Nice" axis bounds: rounded min/max plus tick values a reader recognises (0, 20, 40 …)
// rather than the raw data extent.
function niceScale(min: number, max: number, maxTicks = 5): { min: number; max: number; ticks: number[] } {
    if (!Number.isFinite(min) || !Number.isFinite(max) || min === max) {
        // A flat or empty series still needs a drawable axis.
        const v = Number.isFinite(max) ? max : 0;
        min = Math.min(0, v);
        max = v === min ? min + 1 : Math.max(0, v);
    }
    const niceNum = (range: number, round: boolean) => {
        const exp = Math.floor(Math.log10(range));
        const frac = range / Math.pow(10, exp);
        const nf = round
            ? frac < 1.5 ? 1 : frac < 3 ? 2 : frac < 7 ? 5 : 10
            : frac <= 1 ? 1 : frac <= 2 ? 2 : frac <= 5 ? 5 : 10;
        return nf * Math.pow(10, exp);
    };
    const step = niceNum((max - min) / Math.max(1, maxTicks - 1), true);
    const niceMin = Math.floor(min / step) * step;
    const niceMax = Math.ceil(max / step) * step;
    const ticks: number[] = [];
    const decimals = Math.max(0, -Math.floor(Math.log10(step)));
    for (let v = niceMin; v <= niceMax + step * 0.5; v += step) {
        ticks.push(Number(v.toFixed(decimals + 2)));
    }
    return { min: niceMin, max: niceMax, ticks };
}

// A rectangle with a chosen subset of corners rounded — the data-end of a bar rounds,
// the baseline end stays square, and which end that is depends on orientation and sign.
function roundRectPath(x: number, y: number, w: number, h: number, r: number, side: BarSide): string {
    const rr = Math.max(0, Math.min(r, w / 2, h / 2));
    const tl = side === "top" || side === "left" ? rr : 0;
    const tr = side === "top" || side === "right" ? rr : 0;
    const br = side === "bottom" || side === "right" ? rr : 0;
    const bl = side === "bottom" || side === "left" ? rr : 0;
    return `M${x + tl},${y} L${x + w - tr},${y} Q${x + w},${y} ${x + w},${y + tr}` +
        ` L${x + w},${y + h - br} Q${x + w},${y + h} ${x + w - br},${y + h}` +
        ` L${x + bl},${y + h} Q${x},${y + h} ${x},${y + h - bl}` +
        ` L${x},${y + tl} Q${x},${y} ${x + tl},${y} Z`;
}

// A bar extruded up-and-right by (dx, dy): a right side face (darkened), a top face
// (lightened) and the front face. The overlays are flat black/white washes so the shading
// needs no colour maths on a CSS variable it cannot read at build time.
function bar3D(x: number, y: number, w: number, h: number, color: string, op: number, dx: number, dy: number): string {
    const top = `M${x},${y} L${x + dx},${y - dy} L${x + w + dx},${y - dy} L${x + w},${y} Z`;
    const right = `M${x + w},${y} L${x + w + dx},${y - dy} L${x + w + dx},${y + h - dy} L${x + w},${y + h} Z`;
    return `<path d="${right}" fill="${color}" fill-opacity="${op}"/><path d="${right}" fill="#000" fill-opacity="${0.24 * op}"/>` +
        `<path d="${top}" fill="${color}" fill-opacity="${op}"/><path d="${top}" fill="#fff" fill-opacity="${0.2 * op}"/>` +
        `<rect x="${x}" y="${y}" width="${w}" height="${h}" fill="${color}" fill-opacity="${op}"/>`;
}

function linePathD(pts: [number, number][]): string {
    if (!pts.length) return "";
    return pts.map((p, i) => `${i ? "L" : "M"}${p[0]},${p[1]}`).join(" ");
}

const sign = (x: number) => (x < 0 ? -1 : 1);

// Interior tangent for monotone-cubic interpolation (d3's curveMonotoneX): the lesser of
// the two neighbouring secant slopes, and zero at a local extremum. This is the whole
// point of the monotone curve — the tangent is capped so a segment can never bulge past
// its endpoints, so an area fill can't dip below a value-0 point into negative space the
// way a Catmull-Rom overshoot does.
function monoTangent(x0: number, y0: number, x1: number, y1: number, x2: number, y2: number): number {
    const h0 = x1 - x0, h1 = x2 - x1;
    const s0 = h0 !== 0 ? (y1 - y0) / h0 : 0;
    const s1 = h1 !== 0 ? (y2 - y1) / h1 : 0;
    const p = (s0 * h1 + s1 * h0) / (h0 + h1);
    return (sign(s0) + sign(s1)) * Math.min(Math.abs(s0), Math.abs(s1), 0.5 * Math.abs(p)) || 0;
}

// Endpoint tangent (d3 slope2): a parabola-end estimate constrained by the adjacent
// interior tangent t, so the boundary segments don't overshoot either.
function endTangent(x0: number, y0: number, x1: number, y1: number, t: number): number {
    const h = x1 - x0;
    return h !== 0 ? (3 * (y1 - y0) / h - t) / 2 : t;
}

// Monotone cubic through every point, emitted as cubic beziers. A monotone interpolant
// never overshoots its data, so the smoothed curve stays within the value range of each
// pair of adjacent points.
function smoothPathD(pts: [number, number][]): string {
    const n = pts.length;
    if (n < 3) return linePathD(pts);
    const m: number[] = new Array(n);
    for (let i = 1; i < n - 1; i++) {
        m[i] = monoTangent(pts[i - 1][0], pts[i - 1][1], pts[i][0], pts[i][1], pts[i + 1][0], pts[i + 1][1]);
    }
    m[0] = endTangent(pts[0][0], pts[0][1], pts[1][0], pts[1][1], m[1]);
    m[n - 1] = endTangent(pts[n - 2][0], pts[n - 2][1], pts[n - 1][0], pts[n - 1][1], m[n - 2]);
    let d = `M${pts[0][0]},${pts[0][1]}`;
    for (let i = 0; i < n - 1; i++) {
        const dx = (pts[i + 1][0] - pts[i][0]) / 3;
        const c1x = pts[i][0] + dx, c1y = pts[i][1] + dx * m[i];
        const c2x = pts[i + 1][0] - dx, c2y = pts[i + 1][1] - dx * m[i + 1];
        d += ` C${c1x},${c1y} ${c2x},${c2y} ${pts[i + 1][0]},${pts[i + 1][1]}`;
    }
    return d;
}

// A point on a circle tilted about its horizontal axis by factor k (k=1 is upright): the
// vertical radius shrinks to k·r, so the circle reads as an ellipse seen at an angle.
function tiltPoint(cx: number, cy: number, r: number, deg: number, k: number): [number, number] {
    const a = (deg - 90) * Math.PI / 180; // 0° at 12 o'clock, clockwise
    return [cx + r * Math.cos(a), cy + k * r * Math.sin(a)];
}

// One pie/donut slice from a0 to a1 degrees, tilted by k (k=1 upright). rIn === 0 gives a
// pie wedge. Uses elliptical arcs so the tilt is exact, not a polygon approximation.
function slicePathD(cx: number, cy: number, rOut: number, rIn: number, a0: number, a1: number, k = 1): string {
    const large = a1 - a0 > 180 ? 1 : 0;
    const [ox0, oy0] = tiltPoint(cx, cy, rOut, a0, k);
    const [ox1, oy1] = tiltPoint(cx, cy, rOut, a1, k);
    if (rIn <= 0) {
        return `M${cx},${cy} L${ox0},${oy0} A${rOut},${k * rOut} 0 ${large} 1 ${ox1},${oy1} Z`;
    }
    const [ix1, iy1] = tiltPoint(cx, cy, rIn, a1, k);
    const [ix0, iy0] = tiltPoint(cx, cy, rIn, a0, k);
    return `M${ox0},${oy0} A${rOut},${k * rOut} 0 ${large} 1 ${ox1},${oy1} L${ix1},${iy1} A${rIn},${k * rIn} 0 ${large} 0 ${ix0},${iy0} Z`;
}

const clamp = (v: number, lo: number, hi: number) => Math.min(hi, Math.max(lo, v));

// ── the component ────────────────────────────────────────────────────────────────

export function Chart(props: ChartProps): JSXElement {
    let wrap: HTMLDivElement | undefined;
    const [measured, setMeasured] = createSignal(props.width ?? DEFAULT_WIDTH);
    const width = () => props.width ?? measured();
    const height = () => props.height ?? DEFAULT_HEIGHT;

    onMount(() => {
        if (props.width != null || !wrap) return;
        const read = () => { if (wrap && wrap.clientWidth > 0) setMeasured(wrap.clientWidth); };
        read();
        if (typeof ResizeObserver === "undefined") return;
        const ro = new ResizeObserver(read);
        ro.observe(wrap);
        onCleanup(() => ro.disconnect());
    });

    const isRadial = () => props.kind === "pie" || props.kind === "donut";
    const colorOf = (i: number) =>
        props.series[i]?.color ?? props.palette?.[i % (props.palette.length || 1)] ?? CHART_TOKENS[i % CHART_TOKENS.length];
    const fmt = (v: number) => (props.valueFormat ?? defaultFormat)(v);
    const showLegend = () => props.legend ?? (isRadial() || props.series.length > 1);

    // Clicking a legend key hides its series (cartesian) or slice (radial); the domain,
    // layout and marks recompute from what's left. A Set of the hidden indices — the index
    // is the series index for a cartesian chart, the slice index for a pie/donut.
    const [hidden, setHidden] = createSignal<Set<number>>(new Set());
    const toggle = (i: number) => setHidden((prev) => {
        const next = new Set(prev);
        next.has(i) ? next.delete(i) : next.add(i);
        return next;
    });

    return (
        <div ref={wrap} class={"w-full" + (props.class ? " " + props.class : "")}>
            <Show when={props.title}>
                <div class="mb-2 text-center text-sm font-medium text-ink">{props.title}</div>
            </Show>
            {/* the plot + its absolutely-positioned tooltip share this relative box, so the
                tooltip's pointer coordinates aren't thrown off by a title or legend outside it. */}
            <div class="relative w-full">
                <Show when={isRadial()} fallback={
                    <CartesianChart props={props} width={width()} height={height()} colorOf={colorOf} fmt={fmt} hidden={hidden} />
                }>
                    <RadialChart props={props} width={width()} height={height()} colorOf={colorOf} fmt={fmt} hidden={hidden} />
                </Show>
            </div>
            <Show when={showLegend()}>
                <Legend props={props} colorOf={colorOf} hidden={hidden()} onToggle={toggle} />
            </Show>
        </div>
    );
}

interface SubProps {
    props: ChartProps;
    width: number;
    height: number;
    colorOf: (i: number) => string;
    fmt: (v: number) => string;
    hidden: () => Set<number>; // series/slice indices the legend has toggled off
}

type BarSide = "top" | "bottom" | "left" | "right";
interface BarMark { x: number; y: number; w: number; h: number; side: BarSide; seriesIdx: number; catIdx: number; value: number; round: boolean; }
interface LineMark { seriesIdx: number; line: string; area: string; pts: [number, number][]; }

// ── cartesian (line / area / bar) ─────────────────────────────────────────────────

function CartesianChart(p: SubProps): JSXElement {
    const [hover, setHover] = createSignal<number | null>(null);
    const [pointer, setPointer] = createSignal<[number, number]>([0, 0]);

    const horiz = () => p.props.kind === "bar" && !!p.props.horizontal;
    // 3D extrudes bars only; on a line/area it reads as noise, so it is a no-op there.
    const threeD = () => !!p.props.threeD && p.props.kind === "bar";
    const depth = () => p.props.depth ?? DEFAULT_DEPTH;
    const dx = () => (threeD() ? depth() * 0.7 : 0);
    const dy = () => (threeD() ? depth() * 0.55 : 0);

    const labels = () => p.props.labels ?? p.props.series[0]?.data.map((_, i) => String(i + 1)) ?? [];
    const n = () => Math.max(labels().length, ...p.props.series.map((s) => s.data.length), 0);

    // The value domain. Stacked bars/areas reach the tallest STACK, not the tallest single
    // value; bars and areas always include zero so the baseline is honest.
    const shown = (i: number) => !p.hidden().has(i);
    const domain = createMemo(() => {
        const series = p.props.series;
        const count = n();
        const includeZero = p.props.kind === "bar" || p.props.kind === "area";
        let lo = Infinity, hi = -Infinity;
        if (p.props.stacked) {
            for (let i = 0; i < count; i++) {
                let pos = 0, neg = 0;
                for (let s = 0; s < series.length; s++) {
                    if (!shown(s)) continue;
                    const v = series[s].data[i] ?? 0;
                    if (v >= 0) pos += v; else neg += v;
                }
                hi = Math.max(hi, pos); lo = Math.min(lo, neg);
            }
        } else {
            for (let s = 0; s < series.length; s++) {
                if (!shown(s)) continue;
                for (const v of series[s].data) { hi = Math.max(hi, v); lo = Math.min(lo, v); }
            }
        }
        if (includeZero) { lo = Math.min(lo, 0); hi = Math.max(hi, 0); }
        const scale = niceScale(p.props.yMin ?? lo, p.props.yMax ?? hi);
        if (p.props.yMin != null) scale.min = p.props.yMin;
        if (p.props.yMax != null) scale.max = p.props.yMax;
        return scale;
    });

    // Margins: the value axis wants room for its ticks, the category axis for its labels —
    // which sides those are on flips with orientation. 3D adds depth to the top and right,
    // where bars extrude, so nothing clips.
    const layout = createMemo(() => {
        const d = domain();
        const showAxes = p.props.axes ?? true;
        const valTickW = Math.max(...d.ticks.map((t) => p.fmt(t).length), 1) * 7 + 12;
        const catLabelW = Math.max(...labels().map((s) => s.length), 1) * 7 + 12;
        let left: number, bottom: number;
        if (horiz()) {
            left = showAxes ? Math.max(28, catLabelW) : 8;   // category labels on the left
            bottom = showAxes ? 28 : 8;                       // value ticks on the bottom
        } else {
            left = showAxes ? Math.max(28, valTickW) : 8;    // value ticks on the left
            bottom = showAxes ? 28 : 8;                       // category labels on the bottom
        }
        const top = 12 + dy();
        const right = 12 + dx();
        return {
            left, top, right, bottom,
            plotW: Math.max(0, p.width - left - right),
            plotH: Math.max(0, p.height - top - bottom),
        };
    });

    // valuePos: pixel along the VALUE axis (y for vertical, x for horizontal).
    // catCenter: pixel of category i along the CATEGORY axis (x for vertical, y for horizontal).
    const valuePos = (v: number) => {
        const d = domain(), l = layout();
        const t = (v - d.min) / (d.max - d.min || 1);
        return horiz() ? l.left + l.plotW * t : l.top + l.plotH * (1 - t);
    };
    const bandFull = () => (horiz() ? layout().plotH : layout().plotW) / Math.max(1, n());
    const catStart = () => (horiz() ? layout().top : layout().left);
    const catCenter = (i: number) => catStart() + bandFull() * (i + 0.5);
    const baseValue = () => valuePos(clamp(0, domain().min, domain().max));

    // Bars resolved to plain rectangles + which side is the (rounded) data-end, so the
    // renderer draws vertical and horizontal bars the same way.
    const bars = createMemo(() => {
        if (p.props.kind !== "bar") return [] as BarMark[];
        const out: BarMark[] = [];
        const count = n(), bf = bandFull(), base = baseValue(), h = horiz();
        const series = p.props.series;
        // rect(bandOffset, thickness, valueA, valueB) → a rectangle in the right orientation.
        const rect = (off: number, thick: number, va: number, vb: number): { x: number; y: number; w: number; h: number } =>
            h ? { x: Math.min(va, vb), y: off, w: Math.abs(vb - va), h: thick }
              : { x: off, y: Math.min(va, vb), w: thick, h: Math.abs(vb - va) };
        if (p.props.stacked) {
            const thick = Math.min(BAR_MAX_W, bf * 0.72);
            for (let i = 0; i < count; i++) {
                const off = catStart() + bf * i + (bf - thick) / 2;
                let lastPos = -1, lastNeg = -1;
                for (let s = 0; s < series.length; s++) {
                    if (!shown(s)) continue;
                    const v = series[s].data[i] ?? 0;
                    if (v > 0) lastPos = s; else if (v < 0) lastNeg = s;
                }
                let accPos = 0, accNeg = 0;
                for (let s = 0; s < series.length; s++) {
                    if (!shown(s)) continue;
                    const v = series[s].data[i] ?? 0;
                    if (v === 0) continue;
                    const from = v >= 0 ? accPos : accNeg;
                    const to = from + v;
                    if (v >= 0) accPos = to; else accNeg = to;
                    const isEnd = (v > 0 && s === lastPos) || (v < 0 && s === lastNeg);
                    const inset = isEnd ? 0 : SEG_GAP; // 2px surface gap between segments
                    const vFrom = valuePos(from);
                    // pull the value end toward the baseline by the gap (except the outer end)
                    const vTo = valuePos(to) + (h ? (v >= 0 ? -inset : inset) : (v >= 0 ? inset : -inset));
                    const r = rect(off, thick, vFrom, vTo);
                    out.push({ ...r, side: barSide(h, v), seriesIdx: s, catIdx: i, value: v, round: isEnd });
                }
            }
        } else {
            // Grouped bars re-flow around hidden series: only the shown ones take a slot, so
            // the group re-centres instead of leaving a gap. Colour still keys off the
            // original series index.
            const vis = series.map((_, s) => s).filter(shown);
            const nS = Math.max(1, vis.length);
            const groupSize = Math.min(bf * 0.72, (BAR_MAX_W + SEG_GAP) * nS);
            const each = Math.max(1, Math.min(BAR_MAX_W, groupSize / nS - SEG_GAP));
            for (let i = 0; i < count; i++) {
                const g = catStart() + bf * i + (bf - groupSize) / 2;
                vis.forEach((s, j) => {
                    const v = series[s].data[i] ?? 0;
                    const off = g + j * (groupSize / nS) + (groupSize / nS - each) / 2;
                    const r = rect(off, each, base, valuePos(v));
                    out.push({ ...r, side: barSide(h, v), seriesIdx: s, catIdx: i, value: v, round: true });
                });
            }
        }
        return out;
    });

    // Line/area paths, one per series. Stacked areas ride on the running total below.
    const paths = createMemo(() => {
        if (p.props.kind !== "line" && p.props.kind !== "area") return [] as LineMark[];
        const count = n(), base = baseValue();
        const smooth = p.props.curve === "smooth";
        const stackAcc = new Array(count).fill(0);
        const out: LineMark[] = [];
        p.props.series.forEach((s, si) => {
            if (!shown(si)) return; // a hidden series draws nothing and doesn't lift the stack
            const pts: [number, number][] = [];
            const lowerPts: [number, number][] = [];
            for (let i = 0; i < count; i++) {
                const v = s.data[i] ?? 0;
                const yTop = p.props.stacked ? stackAcc[i] + v : v;
                const yBot = p.props.stacked ? stackAcc[i] : 0;
                pts.push([catCenter(i), valuePos(yTop)]);
                lowerPts.push([catCenter(i), p.props.stacked ? valuePos(yBot) : base]);
                if (p.props.stacked) stackAcc[i] = yTop;
            }
            const line = smooth ? smoothPathD(pts) : linePathD(pts);
            const rev = [...lowerPts].reverse();
            const area = line + " L" + linePathD(rev).slice(1) + " Z";
            out.push({ seriesIdx: si, line, area, pts });
        });
        return out;
    });

    const showAxes = () => p.props.axes ?? true;
    const showGrid = () => p.props.grid ?? true;
    const isBar = () => p.props.kind === "bar";

    // The whole SVG interior, as a string (see the file header for why innerHTML and not
    // JSX marks). Recomputed when the data, the size, or the hovered index changes.
    const body = createMemo(() => {
        const l = layout(), d = domain(), hv = hover(), h = horiz();
        const out: string[] = [];

        // gridlines + value ticks (perpendicular to the value axis)
        for (const t of d.ticks) {
            const vp = valuePos(t);
            if (showGrid()) {
                out.push(h
                    ? `<line x1="${vp}" x2="${vp}" y1="${l.top}" y2="${l.top + l.plotH}" stroke="var(--color-line)" stroke-width="1"/>`
                    : `<line x1="${l.left}" x2="${l.left + l.plotW}" y1="${vp}" y2="${vp}" stroke="var(--color-line)" stroke-width="1"/>`);
            }
            if (showAxes()) {
                out.push(h
                    ? `<text x="${vp}" y="${p.height - 8}" text-anchor="middle" fill="var(--color-ink-faint)" style="font-size:11px;font-variant-numeric:tabular-nums">${esc(p.fmt(t))}</text>`
                    : `<text x="${l.left - 8}" y="${vp}" text-anchor="end" dominant-baseline="middle" fill="var(--color-ink-faint)" style="font-size:11px;font-variant-numeric:tabular-nums">${esc(p.fmt(t))}</text>`);
            }
        }

        // baseline (the value-0 line), a touch stronger than the grid
        const bv = baseValue();
        out.push(h
            ? `<line x1="${bv}" x2="${bv}" y1="${l.top}" y2="${l.top + l.plotH}" stroke="var(--color-line-strong)" stroke-width="1"/>`
            : `<line x1="${l.left}" x2="${l.left + l.plotW}" y1="${bv}" y2="${bv}" stroke="var(--color-line-strong)" stroke-width="1"/>`);

        // category labels (along the category axis)
        if (showAxes()) {
            labels().forEach((lab, i) =>
                out.push(h
                    ? `<text x="${l.left - 8}" y="${catCenter(i)}" text-anchor="end" dominant-baseline="middle" fill="var(--color-ink-faint)" style="font-size:11px">${esc(lab)}</text>`
                    : `<text x="${catCenter(i)}" y="${p.height - 8}" text-anchor="middle" fill="var(--color-ink-faint)" style="font-size:11px">${esc(lab)}</text>`));
        }

        // crosshair (line/area only — a bar reader aims at a bar, not a hairline)
        if (p.props.tooltip !== false && hv !== null && !isBar()) {
            const c = catCenter(hv);
            out.push(`<line x1="${c}" x2="${c}" y1="${l.top}" y2="${l.top + l.plotH}" stroke="var(--color-line-strong)" stroke-width="1"/>`);
        }

        // bars — flat or extruded. 3D draws back-to-front so nearer bars overlap farther ones.
        const bs = bars();
        if (threeD()) {
            for (const b of bs) {
                const op = hv === null || hv === b.catIdx ? 1 : 0.5;
                out.push(bar3D(b.x, b.y, b.w, b.h, esc(p.colorOf(b.seriesIdx)), op, dx(), dy()));
            }
        } else {
            for (const b of bs) {
                const op = hv === null || hv === b.catIdx ? 1 : 0.5;
                out.push(`<path d="${roundRectPath(b.x, b.y, b.w, b.h, b.round ? BAR_RADIUS : 0, b.side)}" fill="${esc(p.colorOf(b.seriesIdx))}" fill-opacity="${op}"/>`);
            }
        }

        // areas then lines (3D does not apply — depth reads as noise on a line).
        for (const pth of paths()) {
            if (p.props.kind === "area") out.push(`<path d="${pth.area}" fill="${esc(p.colorOf(pth.seriesIdx))}" fill-opacity="0.1"/>`);
        }
        for (const pth of paths()) {
            out.push(`<path d="${pth.line}" fill="none" stroke="${esc(p.colorOf(pth.seriesIdx))}" stroke-width="2" stroke-linejoin="round" stroke-linecap="round"/>`);
        }

        // hover markers on line/area, at the snapped index
        if (p.props.tooltip !== false && hv !== null && !isBar()) {
            for (const pth of paths()) {
                const pt = pth.pts[hv];
                if (pt) out.push(`<circle cx="${pt[0]}" cy="${pt[1]}" r="${MARK_R}" fill="${esc(p.colorOf(pth.seriesIdx))}" stroke="var(--color-surface)" stroke-width="2"/>`);
            }
        }

        return out.join("");
    });

    const onMove = (e: PointerEvent) => {
        if (p.props.tooltip === false) return;
        const rect = (e.currentTarget as SVGElement).getBoundingClientRect();
        const px = e.clientX - rect.left, py = e.clientY - rect.top;
        const along = horiz() ? py - layout().top : px - layout().left;
        setHover(clamp(Math.floor(along / bandFull()), 0, Math.max(0, n() - 1)));
        setPointer([px, py]);
    };

    const anchorX = () => (horiz() ? pointer()[0] : catCenter(hover()!));
    const anchorY = () => (horiz() ? catCenter(hover()!) : pointer()[1]);

    return (
        <>
            <svg width={p.width} height={p.height} viewBox={`0 0 ${p.width} ${p.height}`} class="block overflow-visible"
                role="img" innerHTML={body()} onpointermove={onMove} onpointerleave={() => setHover(null)} />
            <Show when={p.props.tooltip !== false && hover() !== null}>
                <CartesianTooltip
                    props={p.props} colorOf={p.colorOf} fmt={p.fmt} hidden={p.hidden()}
                    index={hover()!} label={labels()[hover()!] ?? ""}
                    anchorX={anchorX()} anchorY={anchorY()} width={p.width} height={p.height} />
            </Show>
        </>
    );
}

function barSide(horiz: boolean, v: number): BarSide {
    return horiz ? (v >= 0 ? "right" : "left") : (v >= 0 ? "top" : "bottom");
}

function CartesianTooltip(p: {
    props: ChartProps; colorOf: (i: number) => string; fmt: (v: number) => string; hidden: Set<number>;
    index: number; label: string; anchorX: number; anchorY: number; width: number; height: number;
}): JSXElement {
    const flipLeft = () => p.anchorX > p.width / 2;
    const style = () => ({
        left: `${p.anchorX}px`,
        top: `${clamp(p.anchorY, 8, p.height - 8)}px`,
        transform: `translate(${flipLeft() ? "calc(-100% - 12px)" : "12px"}, -50%)`,
    });
    const rows = () => p.props.series.map((s, i) => ({ s, i })).filter(({ i }) => !p.hidden.has(i));
    return (
        <div class="pointer-events-none absolute z-10 min-w-32 max-w-64 rounded-default border border-line bg-surface px-3 py-2 text-ss shadow-lg"
            style={style()}>
            <div class="mb-1 font-medium text-ink">{p.label}</div>
            <For each={rows()}>{(row) => (
                <div class="flex items-center gap-2 leading-relaxed">
                    <span class="inline-block h-2.5 w-2.5 shrink-0 rounded-xs" style={{ "background-color": p.colorOf(row.i) }} />
                    <span class="text-ink-muted">{row.s.name}</span>
                    <span class="ml-auto font-semibold text-ink" style={{ "font-variant-numeric": "tabular-nums" }}>
                        {p.fmt(row.s.data[p.index] ?? 0)}
                    </span>
                </div>
            )}</For>
        </div>
    );
}

// ── radial (pie / donut) ──────────────────────────────────────────────────────────

function RadialChart(p: SubProps): JSXElement {
    const [hover, setHover] = createSignal<number | null>(null);
    const [pointer, setPointer] = createSignal<[number, number]>([0, 0]);

    const threeD = () => !!p.props.threeD;
    const depth = () => p.props.depth ?? DEFAULT_DEPTH;
    const tilt = () => (threeD() ? 0.62 : 1); // vertical squash of the disc when tilted

    const values = () => p.props.series[0]?.data ?? [];
    const labels = () => p.props.labels ?? values().map((_, i) => String(i + 1));
    const shown = (i: number) => !p.hidden().has(i);
    const total = () => values().reduce((a, v, i) => a + (shown(i) ? Math.max(0, v) : 0), 0);

    const geo = () => {
        const k = tilt();
        const cx = p.width / 2;
        // tilting shrinks the disc's height to k·2r and adds `depth` below; keep it centred.
        const rOut = Math.max(0, Math.min(p.width, p.height - (threeD() ? depth() : 0)) / 2 - 8);
        const cy = p.height / 2 - (threeD() ? depth() / 2 : 0);
        const rIn = p.props.kind === "donut" ? rOut * (p.props.donutRatio ?? 0.6) : 0;
        return { cx, cy, rOut, rIn, k };
    };

    // Slices with their angular spans. A lone value becomes a full ring (drawn as a
    // circle/ellipse, since an arc from 0° to 360° collapses).
    const slices = createMemo(() => {
        const t = total();
        const out: { idx: number; a0: number; a1: number; value: number }[] = [];
        let a = 0;
        values().forEach((v, i) => {
            const val = shown(i) ? Math.max(0, v) : 0; // a hidden slice takes no arc
            const sweep = t > 0 ? (val / t) * 360 : 0;
            out.push({ idx: i, a0: a, a1: a + sweep, value: val });
            a += sweep;
        });
        return out;
    });

    // The extruded rim under one slice: the front-facing part of its outer arc (angles
    // 90°–270°, where the ellipse edge dips below centre) swept down by `depth`.
    const wall = (g: ReturnType<typeof geo>, a0: number, a1: number): string => {
        const w0 = Math.max(a0, 90), w1 = Math.min(a1, 270);
        if (w1 <= w0) return "";
        const [x0, y0] = tiltPoint(g.cx, g.cy, g.rOut, w0, g.k);
        const [x1, y1] = tiltPoint(g.cx, g.cy, g.rOut, w1, g.k);
        const large = w1 - w0 > 180 ? 1 : 0;
        return `M${x0},${y0} A${g.rOut},${g.k * g.rOut} 0 ${large} 1 ${x1},${y1}` +
            ` L${x1},${y1 + depth()} A${g.rOut},${g.k * g.rOut} 0 ${large} 0 ${x0},${y0 + depth()} Z`;
    };

    const body = createMemo(() => {
        const g = geo(), hv = hover();
        const out: string[] = [];
        const positive = slices().filter((s) => s.value > 0);
        const single = positive.length === 1;

        // 3D: draw every slice's rim first (the disc's thickness), then the top faces on top.
        if (threeD()) {
            for (const s of single ? positive : slices()) {
                if (s.a1 <= s.a0) continue;
                const d = single ? wall(g, 90, 270) : wall(g, s.a0, s.a1);
                if (!d) continue;
                const c = esc(p.colorOf(s.idx));
                out.push(`<path d="${d}" fill="${c}"/><path d="${d}" fill="#000" fill-opacity="0.3"/>`);
            }
        }

        if (single) {
            const s = positive[0];
            out.push(`<path d="${slicePathD(g.cx, g.cy, g.rOut, 0, 0, 359.999, g.k)}" fill="${esc(p.colorOf(s.idx))}"/>`);
            if (g.rIn > 0) out.push(`<ellipse cx="${g.cx}" cy="${g.cy}" rx="${g.rIn}" ry="${g.k * g.rIn}" fill="var(--color-surface)"/>`);
        } else {
            for (const s of slices()) {
                if (s.a1 <= s.a0) continue;
                const op = hv === null || hv === s.idx ? 1 : 0.55;
                out.push(`<path d="${slicePathD(g.cx, g.cy, g.rOut, g.rIn, s.a0, s.a1, g.k)}" fill="${esc(p.colorOf(s.idx))}" fill-opacity="${op}" stroke="var(--color-surface)" stroke-width="${SEG_GAP}"/>`);
            }
        }
        return out.join("");
    });

    const onMove = (e: PointerEvent) => {
        if (p.props.tooltip === false) return;
        const rect = (e.currentTarget as SVGElement).getBoundingClientRect();
        const g = geo();
        const px = e.clientX - rect.left, py = e.clientY - rect.top;
        const dx = px - g.cx, dy = (py - g.cy) / g.k; // undo the tilt to test against a circle
        const dist = Math.hypot(dx, dy);
        if (dist > g.rOut || (g.rIn > 0 && dist < g.rIn)) { setHover(null); return; }
        let deg = (Math.atan2(dy, dx) * 180 / Math.PI + 90 + 360) % 360;
        const s = slices().find((s) => s.value > 0 && deg >= s.a0 && deg < s.a1);
        setHover(s ? s.idx : null);
        setPointer([px, py]);
    };

    return (
        <>
            <svg width={p.width} height={p.height} viewBox={`0 0 ${p.width} ${p.height}`} class="block" role="img"
                innerHTML={body()} onpointermove={onMove} onpointerleave={() => setHover(null)} />
            <Show when={p.props.tooltip !== false && hover() !== null}>
                <div class="pointer-events-none absolute z-10 min-w-28 max-w-64 rounded-default border border-line bg-surface px-3 py-2 text-ss shadow-lg"
                    style={{
                        left: `${clamp(pointer()[0], 8, p.width - 8)}px`,
                        top: `${clamp(pointer()[1], 8, p.height - 8)}px`,
                        transform: "translate(-50%, calc(-100% - 12px))",
                    }}>
                    <div class="flex items-center gap-2">
                        <span class="inline-block h-2.5 w-2.5 shrink-0 rounded-xs" style={{ "background-color": p.colorOf(hover()!) }} />
                        <span class="text-ink-muted">{labels()[hover()!] ?? ""}</span>
                    </div>
                    <div class="mt-1 flex items-baseline gap-2">
                        <span class="font-semibold text-ink" style={{ "font-variant-numeric": "tabular-nums" }}>
                            {p.fmt(values()[hover()!] ?? 0)}
                        </span>
                        <span class="text-ink-faint">
                            {total() > 0 ? ((Math.max(0, values()[hover()!] ?? 0) / total()) * 100).toFixed(1) + "%" : ""}
                        </span>
                    </div>
                </div>
            </Show>
        </>
    );
}

// ── legend ─────────────────────────────────────────────────────────────────────

function Legend(p: { props: ChartProps; colorOf: (i: number) => string; hidden: Set<number>; onToggle: (i: number) => void }): JSXElement {
    // Pie/donut identity is the SLICE; cartesian identity is the SERIES. A line keys with
    // a short stroke, a fill (bar/area/slice) with a swatch — the legend mirrors the mark.
    // Each key is a button: click it to toggle that series/slice, which greys the key and
    // strikes its label while the chart recomputes without it.
    const isRadial = p.props.kind === "pie" || p.props.kind === "donut";
    const isLine = p.props.kind === "line";
    const items = () => isRadial
        ? (p.props.labels ?? p.props.series[0]?.data.map((_, i) => String(i + 1)) ?? []).map((name, i) => ({ name, i }))
        : p.props.series.map((s, i) => ({ name: s.name, i }));
    return (
        <div class="mt-3 flex flex-wrap items-center gap-x-4 gap-y-1.5">
            <For each={items()}>{(it) => {
                const off = () => p.hidden.has(it.i);
                return (
                    <button type="button" onclick={() => p.onToggle(it.i)} aria-pressed={!off()}
                        class="flex cursor-pointer select-none items-center gap-1.5">
                        <Show when={isLine} fallback={
                            <span class="inline-block h-2.5 w-2.5 rounded-xs" style={{ "background-color": p.colorOf(it.i), opacity: off() ? 0.35 : 1 }} />
                        }>
                            <span class="inline-block h-0.5 w-4 rounded-full" style={{ "background-color": p.colorOf(it.i), opacity: off() ? 0.35 : 1 }} />
                        </Show>
                        <span class={"text-ss " + (off() ? "text-ink-faint line-through" : "text-ink-soft")}>{it.name}</span>
                    </button>
                );
            }}</For>
        </div>
    );
}
