Synchronized Dual-Grid X-Axis Crosshair

import { type ChartPoint, defineChart, dot, lineY } from "@tanstack/charts";
import { focusGuideX } from "@tanstack/charts/focus/guide";
import { motion } from "@tanstack/charts/motion";
import { tooltip } from "@tanstack/charts/tooltip";
import { viewGrid } from "@tanstack/charts/view";
import { Chart } from "@tanstack/react-charts/core";
import { useMemo } from "react";

import { scaleLinear, scaleUtc } from "d3-scale";
import { Link2 } from "lucide-react";

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

interface TravelerDatum {
    date: Date;
    current: number;
    previous: number;
}

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

function generateDemoData(): TravelerDatum[] {
    const results: TravelerDatum[] = [];
    for (let m = 0; m < 12; m++) {
        const date = new Date(Date.UTC(2024, m, 1));
        results.push({
            date,
            current: Math.round(180 + Math.sin(m * 0.5) * 60 + Math.random() * 20),
            previous: Math.round(240 + Math.cos(m * 0.5) * 50 + Math.random() * 20),
        });
    }
    return results;
}

function shadcnTooltipContent<TDatum>(points: readonly ChartPoint<TDatum>[]) {
    if (points.length === 0) return { title: "", rows: [] };
    const d = points[0].datum as TravelerDatum;
    if (!d) return { title: "", rows: [] };
    return {
        title: d.date.toLocaleDateString("en-US", { month: "short", year: "numeric", timeZone: "UTC" }),
        rows: [
            { label: "2024 Travelers", value: `${d.current}k`, color: "var(--chart-1)" },
            { label: "2023 Travelers", value: `${d.previous}k`, color: "var(--chart-2)" },
        ],
    };
}

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

    const subViewCurrent = useMemo(
        () =>
            defineChart({
                renderer: motionRenderer,
                marks: [
                    lineY(data, {
                        id: "current-line",
                        x: "date",
                        y: "current",
                        stroke: "var(--chart-1)",
                        strokeWidth: 2,
                    }),
                    dot(data, {
                        id: "current-points",
                        x: "date",
                        y: "current",
                        fill: "var(--chart-1)",
                        r: 3,
                    }),
                    focusGuideX(data, {
                        id: "current-guide",
                        x: "date",
                        y: "current",
                        xRule: { stroke: "var(--muted-foreground)", strokeWidth: 1, strokeDasharray: "4 4" },
                    }),
                ],
                scales: {
                    x: {
                        scale: scaleUtc,
                        axis: false,
                    },
                    y: {
                        scale: scaleLinear,
                        grid: true,
                        axis: { label: "2024 (k)" },
                    },
                },
                margin: { top: 12, right: 24, bottom: 12, left: 45 },
            }),
        [data],
    );

    const subViewPrevious = useMemo(
        () =>
            defineChart({
                renderer: motionRenderer,
                marks: [
                    lineY(data, {
                        id: "previous-line",
                        x: "date",
                        y: "previous",
                        stroke: "var(--chart-2)",
                        strokeWidth: 2,
                    }),
                    dot(data, {
                        id: "previous-points",
                        x: "date",
                        y: "previous",
                        fill: "var(--chart-2)",
                        r: 3,
                    }),
                    focusGuideX(data, {
                        id: "previous-guide",
                        x: "date",
                        y: "previous",
                        xRule: { stroke: "var(--muted-foreground)", strokeWidth: 1, strokeDasharray: "4 4" },
                    }),
                ],
                scales: {
                    x: {
                        scale: scaleUtc,
                        axis: {
                            ticks: {
                                format: (v: Date) => v.toLocaleDateString("en-US", { month: "short", timeZone: "UTC" }),
                            },
                        },
                    },
                    y: {
                        scale: scaleLinear,
                        grid: true,
                        axis: { label: "2023 (k)" },
                    },
                },
                margin: { top: 12, right: 24, bottom: 28, left: 45 },
            }),
        [data],
    );

    const definition = useMemo(
        () =>
            defineChart(
                viewGrid({
                    id: "synchronized-cursors",
                    rows: [
                        { id: "current", grow: 1 },
                        { id: "previous", grow: 1 },
                    ],
                    columns: [{ id: "main", grow: 1 }],
                    rowGap: 8,
                    views: [
                        { id: "current", row: "current", column: "main", chart: subViewCurrent },
                        {
                            id: "previous",
                            row: "previous",
                            column: "main",
                            share: { x: "current" },
                            chart: subViewPrevious,
                        },
                    ],
                }),
                {
                    scales: {
                        x: { scale: scaleUtc },
                        y: { scale: scaleLinear },
                    },
                    keyboard: true,
                    focus: "group-x",
                    focusRing: false,
                    maxFocusDistance: Number.POSITIVE_INFINITY,
                    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),
                    },
                },
            ),
        [subViewCurrent, subViewPrevious],
    );

    return (
        <Card className="w-full max-w-xl">
            <CardHeader>
                <CardTitle>Synchronized Dual-Grid X-Axis Crosshair Cursors</CardTitle>
                <CardDescription>
                    Multi-panel vertically synchronized charts sharing pointer cursor alignment across separate Y scales
                </CardDescription>
            </CardHeader>
            <CardContent>
                <div className="h-[270px] w-full">
                    <Chart
                        definition={definition}
                        renderer={motionRenderer}
                        height={270}
                        ariaLabel="Synchronized Dual-Grid X-Axis Crosshair Cursors Chart"
                    />
                </div>
            </CardContent>
            <CardFooter className="flex-col items-start gap-2 text-sm">
                <div className="flex items-center gap-2 leading-none font-medium">
                    Moving cursor over top grid synchronizes crosshair on bottom grid{" "}
                    <Link2 className="h-4 w-4 text-emerald-500" />
                </div>
                <div className="text-muted-foreground leading-none">
                    `viewGrid` shares identical `x` scales to align dates perfectly across stacked panels
                </div>
            </CardFooter>
        </Card>
    );
}

export default EchartsSynchronizedCursors;