Charts: Add TimeSeriesForecastChart component

projects/js-packages/charts/changelog/add-area-chart-component

@@ -0,0 +1,4 @@
+Significance: minor
+Type: added
+
+TimeSeriesForecastChart: add compound composition pattern and full legend prop parity

projects/js-packages/charts/changelog/add-time-series-forecast-chart

@@ -0,0 +1,4 @@
+Significance: minor
+Type: added
+
+Add TimeSeriesForecastChart component for visualizing time series data with forecast periods.

projects/js-packages/charts/package.json

@@ -95,6 +95,12 @@
 		},
 		"./sparkline/style.css": "./dist/components/sparkline/index.css",
 		"./style.css": "./dist/index.css",
+		"./time-series-forecast-chart": {
+			"jetpack:src": "./src/charts/time-series-forecast-chart/index.ts",
+			"import": "./dist/charts/time-series-forecast-chart/index.js",
+			"require": "./dist/charts/time-series-forecast-chart/index.cjs"
+		},
+		"./time-series-forecast-chart/style.css": "./dist/charts/time-series-forecast-chart/index.css",
 		"./tooltip": {
 			"jetpack:src": "./src/components/tooltip/index.ts",
 			"import": "./dist/components/tooltip/index.js",
@@ -171,6 +177,9 @@
 			"sparkline": [
 				"./dist/components/sparkline/index.d.ts"
 			],
+			"time-series-forecast-chart": [
+				"./dist/charts/time-series-forecast-chart/index.d.ts"
+			],
 			"tooltip": [
 				"./dist/components/tooltip/index.d.ts"
 			],

projects/js-packages/charts/src/charts/time-series-forecast-chart/index.ts

@@ -0,0 +1,12 @@
+export {
+	default as TimeSeriesForecastChart,
+	TimeSeriesForecastChartUnresponsive,
+} from './time-series-forecast-chart';
+
+export type {
+	TimeSeriesForecastChartProps,
+	TimeSeriesForecastAccessors,
+	SeriesKeys,
+	Accessor,
+	ForecastTooltipParams,
+} from './types';

projects/js-packages/charts/src/charts/time-series-forecast-chart/private/forecast-divider.tsx

@@ -0,0 +1,57 @@
+import { DataContext } from '@visx/xychart';
+import { useContext } from 'react';
+import type { FC } from 'react';
+
+interface ForecastDividerProps {
+	/**
+	 * The date at which the forecast begins
+	 */
+	forecastStart: Date;
+	/**
+	 * Color of the divider line. Default: '#888888'
+	 */
+	color?: string;
+}
+
+/**
+ * Renders a vertical dashed line at the forecast start position.
+ * Uses DataContext from visx/xychart to access scales.
+ *
+ * @param root0               - Props object
+ * @param root0.forecastStart - The date at which the forecast begins
+ * @param root0.color         - Color of the divider line
+ * @return SVG line element or null if scales are not available
+ */
+export const ForecastDivider: FC< ForecastDividerProps > = ( {
+	forecastStart,
+	color = '#888888',
+} ) => {
+	const context = useContext( DataContext );
+
+	if ( ! context?.xScale || ! context?.yScale ) {
+		return null;
+	}
+
+	const { xScale, innerHeight } = context;
+
+	// Get x position from scale
+	const xScaleFn = xScale as ( value: Date ) => number | undefined;
+	const x = xScaleFn( forecastStart );
+
+	if ( x === undefined || ! Number.isFinite( x ) ) {
+		return null;
+	}
+
+	return (
+		<line
+			x1={ x }
+			x2={ x }
+			y1={ 0 }
+			y2={ innerHeight }
+			stroke={ color }
+			strokeDasharray="4 4"
+			strokeWidth={ 1 }
+			data-testid="forecast-divider"
+		/>
+	);
+};

projects/js-packages/charts/src/charts/time-series-forecast-chart/private/index.ts

@@ -0,0 +1,2 @@
+export { useForecastData } from './use-forecast-data';
+export { ForecastDivider } from './forecast-divider';

projects/js-packages/charts/src/charts/time-series-forecast-chart/private/use-forecast-data.ts

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+import { useMemo } from 'react';
+import type { TimeSeriesForecastAccessors, TransformedForecastPoint, BandPoint } from '../types';
+
+interface UseForecastDataOptions< D > {
+	data: readonly D[];
+	accessors: TimeSeriesForecastAccessors< D >;
+	forecastStart: Date;
+}
+
+interface UseForecastDataResult {
+	historical: TransformedForecastPoint[];
+	forecast: TransformedForecastPoint[];
+	bandData: BandPoint[];
+	yDomain: [ number, number ];
+	xDomain: [ Date, Date ];
+}
+
+/**
+ * Safe number extraction - returns null for non-finite numbers
+ *
+ * @param n - The value to extract as a number
+ * @return The number if valid and finite, otherwise null
+ */
+const asNumber = ( n: number | null | undefined ): number | null => {
+	return typeof n === 'number' && Number.isFinite( n ) ? n : null;
+};
+
+/**
+ * Hook to transform and split forecast data for rendering
+ *
+ * Handles:
+ * - Transforming generic data via accessors
+ * - Splitting data into historical and forecast portions
+ * - Creating band data for uncertainty regions
+ * - Computing x and y domains
+ *
+ * @param root0               - Options object
+ * @param root0.data          - Array of data points
+ * @param root0.accessors     - Accessor functions to extract values from data
+ * @param root0.forecastStart - Date at which forecast begins
+ * @return Transformed data split into historical and forecast portions
+ */
+export function useForecastData< D >( {
+	data,
+	accessors,
+	forecastStart,
+}: UseForecastDataOptions< D > ): UseForecastDataResult {
+	return useMemo( () => {
+		if ( data.length === 0 ) {
+			const now = new Date();
+			return {
+				historical: [],
+				forecast: [],
+				bandData: [],
+				yDomain: [ 0, 100 ] as [ number, number ],
+				xDomain: [ now, now ] as [ Date, Date ],
+			};
+		}
+
+		// 1. Transform all points via accessors
+		const transformed: TransformedForecastPoint[] = data.map( ( d, i ) => ( {
+			date: accessors.x( d, i ),
+			value: accessors.y( d, i ),
+			lower: accessors.yLower ? asNumber( accessors.yLower( d, i ) ) : null,
+			upper: accessors.yUpper ? asNumber( accessors.yUpper( d, i ) ) : null,
+			originalIndex: i,
+		} ) );
+
+		// 2. Sort by date for rendering stability
+		transformed.sort( ( a, b ) => a.date.getTime() - b.date.getTime() );
+
+		// 3. Split by forecastStart
+		// Both series include the transition point so the lines connect seamlessly
+		const forecastStartTime = forecastStart.getTime();
+		const historical = transformed.filter( p => p.date.getTime() <= forecastStartTime );
+		const forecast = transformed.filter( p => p.date.getTime() >= forecastStartTime );
+
+		// 4. Band data: only points with BOTH valid lower AND upper
+		const bandData: BandPoint[] = forecast
+			.filter(
+				( p ): p is TransformedForecastPoint & { lower: number; upper: number } =>
+					p.lower !== null && p.upper !== null
+			)
+			.map( p => ( { date: p.date, lower: p.lower, upper: p.upper } ) );
+
+		// 5. Compute y domain including bounds
+		const allValues = transformed.map( p => p.value );
+		const allLowers = transformed.map( p => p.lower ).filter( ( v ): v is number => v !== null );
+		const allUppers = transformed.map( p => p.upper ).filter( ( v ): v is number => v !== null );
+
+		const allYValues = [ ...allValues, ...allLowers, ...allUppers ];
+		const minY = Math.min( ...allYValues );
+		const maxY = Math.max( ...allYValues );
+
+		// Add some padding to y domain
+		const yPadding = ( maxY - minY ) * 0.1;
+		const yDomain: [ number, number ] = [ Math.max( 0, minY - yPadding ), maxY + yPadding ];
+
+		// 6. Compute x domain
+		const allDates = transformed.map( p => p.date );
+		const xDomain: [ Date, Date ] = [
+			new Date( Math.min( ...allDates.map( d => d.getTime() ) ) ),
+			new Date( Math.max( ...allDates.map( d => d.getTime() ) ) ),
+		];
+
+		return { historical, forecast, bandData, yDomain, xDomain };
+	}, [ data, accessors, forecastStart ] );
+}

projects/js-packages/charts/src/charts/time-series-forecast-chart/stories/config.tsx

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+import {
+	chartDecorator,
+	sharedChartArgTypes,
+	ChartStoryArgs,
+} from '../../../stories/chart-decorator';
+import { legendArgTypes } from '../../../stories/legend-config';
+import { sharedThemeArgs, themeArgTypes } from '../../../stories/theme-config';
+import TimeSeriesForecastChart from '../time-series-forecast-chart';
+import type { TimeSeriesForecastChartProps } from '../types';
+import type { Meta } from '@storybook/react';
+
+/**
+ * Sample forecast data point type
+ */
+export type SampleForecastDatum = {
+	date: Date;
+	value: number;
+	lower?: number;
+	upper?: number;
+};
+
+/**
+ * Generate sample forecast data for storybook demonstrations.
+ *
+ * @param historicalDays - Number of historical days to generate
+ * @param forecastDays   - Number of forecast days to generate
+ * @param baseValue      - Starting value for the data
+ * @param trend          - Daily trend increment
+ * @param volatility     - Random noise amplitude
+ * @return Array of sample forecast data points
+ */
+export const generateForecastData = (
+	historicalDays: number = 30,
+	forecastDays: number = 14,
+	baseValue: number = 100,
+	trend: number = 0.5,
+	volatility: number = 10
+): SampleForecastDatum[] => {
+	const data: SampleForecastDatum[] = [];
+	const startDate = new Date();
+	startDate.setDate( startDate.getDate() - historicalDays );
+
+	// Generate historical data (no bounds)
+	for ( let i = 0; i < historicalDays; i++ ) {
+		const date = new Date( startDate );
+		date.setDate( date.getDate() + i );
+		const noise = ( Math.random() - 0.5 ) * volatility * 2;
+		const value = baseValue + trend * i + noise;
+		data.push( { date, value: Math.max( 0, value ) } );
+	}
+
+	// Generate forecast data (with bounds)
+	const lastHistoricalValue = data[ data.length - 1 ].value;
+	for ( let i = 0; i < forecastDays; i++ ) {
+		const date = new Date( startDate );
+		date.setDate( date.getDate() + historicalDays + i );
+		const projectedValue = lastHistoricalValue + trend * ( i + 1 );
+
+		// Uncertainty grows with time
+		const uncertaintySpread = volatility * ( 1 + i * 0.2 );
+		const lower = projectedValue - uncertaintySpread;
+		const upper = projectedValue + uncertaintySpread;
+
+		data.push( {
+			date,
+			value: projectedValue,
+			lower: Math.max( 0, lower ),
+			upper,
+		} );
+	}
+
+	return data;
+};
+
+/**
+ * Fixed sample data for consistent story rendering
+ * Note: The last historical point (2024-02-19) is also the first forecast point
+ * to ensure the lines connect seamlessly at the transition.
+ */
+export const sampleForecastData: SampleForecastDatum[] = [
+	// Historical data (no bounds)
+	{ date: new Date( '2024-01-01' ), value: 100 },
+	{ date: new Date( '2024-01-08' ), value: 108 },
+	{ date: new Date( '2024-01-15' ), value: 115 },
+	{ date: new Date( '2024-01-22' ), value: 112 },
+	{ date: new Date( '2024-01-29' ), value: 125 },
+	{ date: new Date( '2024-02-05' ), value: 130 },
+	{ date: new Date( '2024-02-12' ), value: 128 },
+	// Forecast data (with bounds) - starts at last historical point for seamless connection
+	{ date: new Date( '2024-02-19' ), value: 135, lower: 135, upper: 135 }, // Transition point (no spread yet)
+	{ date: new Date( '2024-02-26' ), value: 142, lower: 132, upper: 152 },
+	{ date: new Date( '2024-03-04' ), value: 148, lower: 135, upper: 161 },
+	{ date: new Date( '2024-03-11' ), value: 155, lower: 138, upper: 172 },
+	{ date: new Date( '2024-03-18' ), value: 162, lower: 140, upper: 184 },
+];
+
+/**
+ * Sample accessors for the default data type
+ */
+export const sampleAccessors = {
+	x: ( d: SampleForecastDatum ) => d.date,
+	y: ( d: SampleForecastDatum ) => d.value,
+	yLower: ( d: SampleForecastDatum ) => d.lower,
+	yUpper: ( d: SampleForecastDatum ) => d.upper,
+};
+
+/**
+ * Forecast start date - the transition point where forecast begins
+ */
+export const sampleForecastStart = new Date( '2024-02-19' );
+
+type StoryArgs = ChartStoryArgs< TimeSeriesForecastChartProps< SampleForecastDatum > >;
+
+export const timeSeriesForecastChartMetaArgs: Meta< StoryArgs > = {
+	title: 'JS Packages/Charts Library/Charts/Time Series Forecast Chart',
+	component: TimeSeriesForecastChart,
+	parameters: {
+		layout: 'centered',
+	},
+	decorators: [ chartDecorator ],
+	argTypes: {
+		...legendArgTypes,
+		...themeArgTypes,
+		...sharedChartArgTypes,
+		showTooltip: {
+			control: 'boolean',
+			description: 'Show tooltips on hover',
+			table: { category: 'Tooltip' },
+		},
+		animation: {
+			control: 'boolean',
+			description: 'Enable chart animation',
+			table: { category: 'Visual Style' },
+		},
+		gridVisibility: {
+			control: { type: 'select' },
+			options: [ 'x', 'y', 'xy', 'none' ],
+			description: 'Grid visibility',
+			table: { category: 'Visual Style' },
+		},
+	},
+};
+
+export const timeSeriesForecastChartStoryArgs = {
+	...sharedThemeArgs,
+	data: sampleForecastData,
+	accessors: sampleAccessors,
+	forecastStart: sampleForecastStart,
+	showTooltip: true,
+	showLegend: false,
+	animation: false,
+	gridVisibility: 'y' as const,
+	maxWidth: 800,
+	aspectRatio: 0.5,
+	resizeDebounceTime: 300,
+};