Virtualized React Charts: Load Data on Zoom/Pan

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import { Subject, debounceTime } from "rxjs";

import {
    easing,
    EAutoRange,
    EAxisAlignment,
    EHorizontalAnchorPoint,
    EVerticalAnchorPoint,
    EWrapTo,
    EXyDirection,
    FastLineRenderableSeries,
    MouseWheelZoomModifier,
    NativeTextAnnotation,
    NumberRange,
    NumericAxis,
    SciChartOverview,
    SciChartSurface,
    XAxisDragModifier,
    XyDataSeries,
    YAxisDragModifier,
    ZoomExtentsModifier,
    ZoomPanModifier,
    ECoordinateMode,
    AxisBase2D,
} from "scichart";
import { appTheme } from "./appTheme";

export const getChartsInitializationApi = () => {
    let mainSurface: SciChartSurface;
    let mainXAxis: AxisBase2D;
    let mainDataSeries: XyDataSeries;

    const createMainChart = async (rootElement: string | HTMLDivElement) => {
        const { wasmContext, sciChartSurface } = await SciChartSurface.create(rootElement, {
            theme: appTheme.SciChartJsTheme,
        });
        const xAxis = new NumericAxis(wasmContext, {
            axisAlignment: EAxisAlignment.Bottom,
            visibleRange: new NumberRange(4000000, 5000000),
            autoRange: EAutoRange.Never,
            labelPrecision: 0,
            useNativeText: true,
        });

        sciChartSurface.xAxes.add(xAxis);
        const yAxis = new NumericAxis(wasmContext, {
            axisAlignment: EAxisAlignment.Right,
            visibleRange: new NumberRange(-5000, 5000),
            autoRange: EAutoRange.Never,
            labelPrecision: 0,
            useNativeText: true,
        });
        sciChartSurface.yAxes.add(yAxis);

        const dataSeries = new XyDataSeries(wasmContext, { containsNaN: false, isSorted: true });
        const rendSeries = new FastLineRenderableSeries(wasmContext, {
            dataSeries,
            strokeThickness: 2,
            stroke: appTheme.VividOrange,
        });
        sciChartSurface.renderableSeries.add(rendSeries);
        rendSeries.rolloverModifierProps.tooltipTextColor = "black";
        rendSeries.rolloverModifierProps.showRollover = true;

        sciChartSurface.chartModifiers.add(
            new ZoomExtentsModifier({ xyDirection: EXyDirection.YDirection }),
            new XAxisDragModifier(),
            new YAxisDragModifier(),
            new ZoomPanModifier({ enableZoom: true }),
            new MouseWheelZoomModifier()
        );

        // Create an observable stream
        const subject = new Subject<NumberRange>();

        // Push visible range changes into the observable
        xAxis.visibleRangeChanged.subscribe(async (args) => {
            subject.next(args.visibleRange);
        });

        // subscribe to the observable with a debounce
        subject.pipe(debounceTime(250)).subscribe((r: NumberRange) => {
            // Fetch data and update the dataSeries
            loadPoints(r.min, r.max, sciChartSurface.domCanvas2D.width, dataSeries)
                .then(() => {
                    // Update the y axis
                    const yRange = yAxis.getWindowedYRange(null);
                    yAxis.animateVisibleRange(yRange, 250, easing.outExpo);
                })
                .catch((err) =>
                    showError(
                        sciChartSurface,
                        "Server data is unavailable.  Please do npm run build, then npm start and access the site at localhost:3000"
                    )
                );
        });

        mainSurface = sciChartSurface;
        mainXAxis = xAxis;
        mainDataSeries = dataSeries;

        return { sciChartSurface };
    };

    const createOverview = async (rootElement: string | HTMLDivElement) => {
        const overview = await SciChartOverview.create(mainSurface, rootElement, { theme: appTheme.SciChartJsTheme });
        const overviewData = new XyDataSeries(mainSurface.webAssemblyContext2D, { containsNaN: false, isSorted: true });
        // Load the full dataSet
        loadPoints(0, 10000000, overview.overviewSciChartSurface.domCanvas2D.width, overviewData).catch((err) => {});

        const overviewSeries = overview.overviewSciChartSurface.renderableSeries.get(0);
        overviewSeries.dataSeries = overviewData;
        overview.overviewSciChartSurface.zoomExtents();

        return { sciChartSurface: overview.overviewSciChartSurface };
    };

    const afterOverviewInit = () => {
        // Load initial data
        loadPoints(
            mainXAxis.visibleRange.min,
            mainXAxis.visibleRange.max,
            mainSurface.domCanvas2D.width,
            mainDataSeries
        )
            .then(() => {
                mainSurface.zoomExtents();
            })
            .catch((err) =>
                showError(
                    mainSurface,
                    "Server data is unavailable.  Please do npm run build, then npm start and access the site at localhost:3000"
                )
            );
    };

    return { createMainChart, createOverview, afterOverviewInit };
};

const loadPoints = async (xFrom: number, xTo: number, chartWidth: number, dataSeries: XyDataSeries) => {
    chartWidth = Math.floor(chartWidth);

    const response = await fetch(`api/data/${xFrom}-${xTo}/${chartWidth}`);
    const data: { x: number[]; y: number[] } = await response.json();
    console.log(`Loaded ${data.x.length} points`);
    dataSeries.clear();
    dataSeries.appendRange(data.x, data.y);
};

const showError = (sciChartSurface: SciChartSurface, message: string) => {
    if (!sciChartSurface.annotations.getById("error")) {
        sciChartSurface.annotations.add(
            new NativeTextAnnotation({
                id: "error",
                text: message,
                x1: 0.5,
                y1: 0.5,
                textColor: "red",
                fontSize: 24,
                horizontalAnchorPoint: EHorizontalAnchorPoint.Center,
                verticalAnchorPoint: EVerticalAnchorPoint.Center,
                xCoordinateMode: ECoordinateMode.Relative,
                yCoordinateMode: ECoordinateMode.Relative,
                lineSpacing: 5,
                wrapTo: EWrapTo.ViewRect,
            })
        );
    }
};