Stacked Bar Chart with Dynamic Focus Band

import { type ChartPoint, barY, colorLegend, crosshair, defineChart, stack } from "@tanstack/charts";
import { motion } from "@tanstack/charts/motion";
import { tooltip } from "@tanstack/charts/tooltip";
import { Chart } from "@tanstack/react-charts/core";
import { useMemo } from "react";

import { scaleBand, scaleLinear } from "d3-scale";
import { Layers } from "lucide-react";

import { Card, CardContent, CardDescription, CardFooter, CardHeader, CardTitle } from "@/components/ui/card";

interface StackedCauseDatum {
    id: string;
    period: string;
    cause: string;
    deaths: number;
}

const motionRenderer = motion({
    initial: "always",
    transition: { type: "spring", stiffness: 170, damping: 18, mass: 1 },
});

const periods = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug"];
const causes = ["Zymotic", "Wounds", "Other"];
const colors = ["var(--chart-1)", "var(--chart-2)", "var(--chart-3)"];

function generateDemoData(): StackedCauseDatum[] {
    const results: StackedCauseDatum[] = [];
    periods.forEach((p) => {
        causes.forEach((c) => {
            const val = Math.floor(20 + Math.random() * 80);
            results.push({
                id: `${p}-${c}`,
                period: p,
                cause: c,
                deaths: val,
            });
        });
    });
    return results;
}

function shadcnTooltipContent<TDatum>(points: readonly ChartPoint<TDatum>[]) {
    if (points.length === 0) return { title: "", rows: [] };
    const d = points[0].datum as StackedCauseDatum;
    if (!d) return { title: "", rows: [] };
    return {
        title: `${d.period} - ${d.cause}`,
        rows: [{ label: "Count", value: `${d.deaths} cases`, color: "var(--chart-1)" }],
    };
}

export function StackedBarBandCursor() {
    const data = useMemo(() => generateDemoData(), []);

    const definition = useMemo(
        () =>
            defineChart(
                {
                    renderer: motionRenderer,
                    marks: [
                        crosshair<string, number>({
                            id: "stacked-cursor-band",
                            x: {
                                band: {
                                    fill: "var(--muted-foreground)",
                                    fillOpacity: 0.15,
                                    radius: 3,
                                },
                            },
                            y: false,
                        }),
                        barY(data, {
                            id: "stacked-cursor-bars",
                            x: "period",
                            y: "deaths",
                            z: "cause",
                            color: "cause",
                            key: "id",
                            layout: stack({ order: causes }),
                            radius: 2,
                        }),
                        crosshair<string, number>({
                            id: "stacked-cursor-rule",
                            x: false,
                            y: {
                                stroke: "var(--foreground)",
                                strokeOpacity: 0.7,
                                strokeWidth: 1,
                                strokeDasharray: "4 4",
                            },
                        }),
                    ],
                    scales: {
                        x: {
                            scale: scaleBand<string>().domain(periods).padding(0.2),
                        },
                        y: {
                            scale: scaleLinear().domain([0, 300]),
                            grid: true,
                            axis: { label: "Total Cases" },
                        },
                    },
                    color: {
                        domain: causes,
                        range: colors,
                        legend: colorLegend({ label: "Cause Category" }),
                    },
                    focus: "group-x",
                    maxFocusDistance: Number.POSITIVE_INFINITY,
                    margin: { top: 24, right: 24, bottom: 32, left: 45 },
                    theme: {
                        foreground: "var(--muted-foreground)",
                        grid: "var(--border)",
                        background: "transparent",
                    },
                },
                {
                    keyboard: true,
                    tooltip: {
                        use: tooltip,
                        className:
                            "font-sans shadow-none rounded-md bg-popover text-popover-foreground border p-2 text-xs",
                        anchor: "pointer",
                        placement: "auto",
                        content: (points) => shadcnTooltipContent(points),
                    },
                },
            ),
        [data],
    );

    return (
        <Card className="w-full max-w-xl">
            <CardHeader>
                <CardTitle>Stacked Bar Chart with Dynamic Focus X-Band Cursor</CardTitle>
                <CardDescription>
                    Hover crosshairs highlight full column bands and project horizontal segment rules
                </CardDescription>
            </CardHeader>
            <CardContent>
                <div className="h-[250px] w-full">
                    <Chart
                        definition={definition}
                        renderer={motionRenderer}
                        height={250}
                        ariaLabel="Stacked Bar Chart with Dynamic Focus X-Band Cursor Chart"
                    />
                </div>
            </CardContent>
            <CardFooter className="flex-col items-start gap-2 text-sm">
                <div className="flex items-center gap-2 leading-none font-medium">
                    Crosshair band highlights active period column <Layers className="h-4 w-4 text-emerald-500" />
                </div>
                <div className="text-muted-foreground leading-none">
                    `crosshair` with `band` fill parameter tracks discrete band scale columns
                </div>
            </CardFooter>
        </Card>
    );
}

export default StackedBarBandCursor;