Population Pyramid

import { type ChartPoint, barX, defineChart, groupBy, 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 { Users } from "lucide-react";

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

interface PopulationDatum {
    ageGroup: string;
    sex: "MALE" | "FEMALE";
    count: number;
}

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

const ageGroups = ["0-14", "15-29", "30-44", "45-59", "60-74", "75+"];
const pyramidSexes: ("MALE" | "FEMALE")[] = ["MALE", "FEMALE"];

function generateDemoData(): PopulationDatum[] {
    const results: PopulationDatum[] = [];
    const maleCounts = [65, 82, 95, 88, 54, 32];
    const femaleCounts = [62, 80, 98, 92, 58, 38];

    ageGroups.forEach((age, idx) => {
        results.push({ ageGroup: age, sex: "MALE", count: maleCounts[idx] });
        results.push({ ageGroup: age, sex: "FEMALE", count: femaleCounts[idx] });
    });

    return results;
}

function shadcnTooltipContent<TDatum>(points: readonly ChartPoint<TDatum>[]) {
    if (points.length === 0) return { title: "", rows: [] };
    const d = points[0].datum as PopulationDatum;
    if (!d) return { title: "", rows: [] };
    return {
        title: `Age Group ${d.ageGroup}`,
        rows: [
            {
                label: d.sex === "MALE" ? "Male Population" : "Female Population",
                value: `${d.count}k`,
                color: d.sex === "MALE" ? "var(--chart-1)" : "var(--chart-2)",
            },
        ],
    };
}

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

    const counts = useMemo(() => {
        return groupBy(rawData, {
            by: {
                ageGroup: "ageGroup",
                sex: "sex",
            },
            outputs: { count: { value: "count", reduce: "sum" } },
        });
    }, [rawData]);

    const definition = useMemo(
        () =>
            defineChart(
                {
                    renderer: motionRenderer,
                    marks: [
                        barX(counts, {
                            id: "population-bars",
                            x: (row: PopulationDatum) => (row.sex === "MALE" ? -row.count : row.count),
                            y: "ageGroup",
                            z: "sex",
                            color: "sex",
                            layout: stack({ offset: "diverging", order: pyramidSexes }),
                            key: (row: PopulationDatum) => `${row.ageGroup}:${row.sex}`,
                            inset: 1,
                            radius: 3,
                        }),
                    ],
                    scales: {
                        x: {
                            scale: scaleLinear().domain([-120, 120]),
                            grid: true,
                            axis: {
                                ticks: {
                                    count: 7,
                                    format: (value: number) => `${Math.abs(value)}k`,
                                },
                                label: "Population (Thousands)",
                            },
                        },
                        y: {
                            scale: () => scaleBand<string>().domain(ageGroups).paddingInner(0.15).paddingOuter(0.05),
                        },
                    },
                    color: {
                        domain: pyramidSexes,
                        range: ["var(--chart-1)", "var(--chart-2)"],
                    },
                    margin: { top: 24, right: 24, bottom: 32, left: 55 },
                    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),
                    },
                },
            ),
        [counts],
    );

    return (
        <Card className="w-full max-w-xl">
            <CardHeader>
                <CardTitle>Diverging Population Demographic Pyramid</CardTitle>
                <CardDescription>
                    Bilateral horizontal bar chart displaying male vs female population distributions across age
                    brackets
                </CardDescription>
            </CardHeader>
            <CardContent>
                <div className="h-[250px] w-full">
                    <Chart
                        definition={definition}
                        renderer={motionRenderer}
                        height={250}
                        ariaLabel="Diverging Population Demographic Pyramid Chart"
                    />
                </div>
            </CardContent>
            <CardFooter className="flex-col items-start gap-2 text-sm">
                <div className="flex items-center gap-2 leading-none font-medium">
                    Peak working-age demographic concentrated in 30-44 bracket{" "}
                    <Users className="h-4 w-4 text-emerald-500" />
                </div>
                <div className="text-muted-foreground leading-none">
                    Negative male X values mirror positive female X values around zero center axis
                </div>
            </CardFooter>
        </Card>
    );
}

export default PopulationPyramid;