Difference Chart

import { type ChartPoint, defineChart, differenceY, rollingWindow } 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 { scaleLinear, scaleUtc } from "d3-scale";
import { ArrowUpRight } from "lucide-react";

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

interface StockDiffDatum {
    Date: Date;
    Close: number;
}

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

function generateDemoData(): StockDiffDatum[] {
    const baseDate = new Date(2025, 0, 1);
    return Array.from({ length: 30 }, (_, i) => {
        const d = new Date(baseDate);
        d.setDate(baseDate.getDate() + i);
        const close = 150 + Math.sin(i * 0.4) * 20 + (i % 2 === 0 ? 5 : -5);
        return { Date: d, Close: close };
    });
}

function shadcnTooltipContent<TDatum>(points: readonly ChartPoint<TDatum>[]) {
    if (points.length === 0) return { title: "", rows: [] };
    const d = points[0].datum as any;
    if (!d) return { title: "", rows: [] };
    const dateStr = d.Date.toLocaleDateString("en-US", { month: "short", day: "numeric" });
    const diff = d.Close - d.average;
    return {
        title: dateStr,
        rows: [
            { label: "Close Price", value: `$${d.Close.toFixed(2)}`, color: "var(--chart-1)" },
            { label: "20-day Average", value: `$${d.average.toFixed(2)}`, color: "var(--muted-foreground)" },
            {
                label: "Net Surplus",
                value: `${diff >= 0 ? "+" : ""}$${diff.toFixed(2)}`,
                color: diff >= 0 ? "var(--chart-1)" : "var(--chart-2)",
            },
        ],
    };
}

export function DifferenceChart() {
    const rawData = useMemo(() => generateDemoData(), []);

    const data = useMemo(() => {
        return rollingWindow(rawData, {
            size: 10,
            orderBy: "Date",
            anchor: "end",
            partial: false,
            outputs: {
                average: { value: "Close", reduce: "mean" },
            },
        });
    }, [rawData]);

    const definition = useMemo(
        () =>
            defineChart(
                {
                    renderer: motionRenderer,
                    marks: [
                        differenceY(data, {
                            id: "price-difference",
                            x: "Date",
                            y1: "average",
                            y2: "Close",
                            positiveFill: "var(--chart-1)",
                            negativeFill: "var(--chart-2)",
                            fillOpacity: 0.3,
                            stroke: "var(--chart-1)",
                            strokeWidth: 2,
                            comparisonStroke: "var(--border)",
                            comparisonStrokeWidth: 2,
                        }),
                    ],
                    scales: {
                        x: {
                            scale: scaleUtc,
                            axis: {
                                line: false,
                                label: "Date",
                                ticks: {
                                    size: 0,
                                    padding: 10,
                                    format: (d: Date) =>
                                        d.toLocaleDateString("en-US", { month: "short", day: "numeric" }),
                                },
                            },
                        },
                        y: {
                            scale: scaleLinear().domain([120, 185]),
                            grid: true,
                            axis: {
                                line: false,
                                label: "Price ($)",
                                ticks: { size: 0 },
                            },
                        },
                    },
                    margin: { top: 24, right: 24, bottom: 32, left: 45 },
                    theme: {
                        foreground: "var(--muted-foreground)",
                        grid: "var(--border)",
                        background: "transparent",
                    },
                },
                {
                    focus: "group-x",
                    tooltip: {
                        use: tooltip,
                        className:
                            "font-sans shadow-none rounded-md bg-popover text-popover-foreground border p-2 text-xs",
                        anchor: "group-center",
                        placement: "auto",
                        content: (points) => shadcnTooltipContent(points),
                    },
                },
            ),
        [data],
    );

    return (
        <Card className="w-full max-w-xl">
            <CardHeader>
                <CardTitle>Price vs Moving Average Difference</CardTitle>
                <CardDescription>
                    Dual-color difference area chart tracking price premium vs discount to moving mean
                </CardDescription>
            </CardHeader>
            <CardContent>
                <div className="h-[250px] w-full">
                    <Chart
                        definition={definition}
                        renderer={motionRenderer}
                        height={250}
                        ariaLabel="Price vs Moving Average Difference Chart"
                    />
                </div>
            </CardContent>
            <CardFooter className="flex-col items-start gap-2 text-sm">
                <div className="flex items-center gap-2 leading-none font-medium">
                    Positive difference fill (green) reflects asset trading premium{" "}
                    <ArrowUpRight className="h-4 w-4 text-emerald-500" />
                </div>
                <div className="text-muted-foreground leading-none">
                    Green area highlights periods above baseline mean; Red area highlights discount dips below baseline
                </div>
            </CardFooter>
        </Card>
    );
}

export default DifferenceChart;