/**
 * ECharts Download Utilities
 *
 * Provides programmatic chart export functionality for downloading
 * charts as PNG or SVG images. These utilities wrap ECharts' built-in
 * export capabilities with a convenient API and sensible defaults.
 */

import type * as echarts from 'echarts';

// ─── Types ───────────────────────────────────────────────────────────────────

export type ExportFormat = 'png' | 'svg';

export interface DownloadOptions {
	/** The file name (without extension) */
	fileName?: string;
	/** Export format: 'png' or 'svg' */
	format?: ExportFormat;
	/** Pixel ratio for PNG exports (default: 2 for retina quality) */
	pixelRatio?: number;
	/** Background color (default: '#ffffff' for PNG, 'none' for SVG) */
	backgroundColor?: string;
	/** Components to exclude from the export (e.g. ['toolbox']) */
	excludeComponents?: string[];
}

// ─── Defaults ────────────────────────────────────────────────────────────────

const DEFAULT_FILE_NAME = 'open-meteo-chart';
const DEFAULT_PIXEL_RATIO = 2;

// ─── Download Functions ──────────────────────────────────────────────────────

/**
 * Downloads a single ECharts instance as an image file.
 *
 * @param chart  - The ECharts instance to export
 * @param options - Download configuration options
 */
export function downloadChart(chart: echarts.ECharts, options: DownloadOptions = {}): void {
	const {
		fileName = DEFAULT_FILE_NAME,
		format = 'png',
		pixelRatio = DEFAULT_PIXEL_RATIO,
		backgroundColor,
		excludeComponents = ['toolbox']
	} = options;

	const resolvedBg = backgroundColor ?? (format === 'svg' ? 'none' : '#ffffff');

	// Use ECharts' getDataURL for PNG, getConnectedDataURL for SVG
	const dataUrl = chart.getDataURL({
		type: format === 'svg' ? 'svg' : 'png',
		pixelRatio: format === 'png' ? pixelRatio : 1,
		backgroundColor: resolvedBg,
		excludeComponents
	});

	triggerDownload(dataUrl, `${fileName}.${format}`);
}

/**
 * Downloads all provided ECharts instances as separate image files.
 * Each file is named with an incrementing suffix (e.g. chart-1.png, chart-2.png).
 *
 * @param charts  - Array of ECharts instances to export
 * @param options - Download configuration options (fileName is used as prefix)
 */
export function downloadAllCharts(
	charts: echarts.ECharts[],
	options: DownloadOptions = {}
): void {
	const { fileName = DEFAULT_FILE_NAME, ...rest } = options;

	charts.forEach((chart, index) => {
		if (chart && !chart.isDisposed()) {
			downloadChart(chart, {
				...rest,
				fileName: charts.length === 1 ? fileName : `${fileName}-${index + 1}`
			});
		}
	});
}

/**
 * Returns the data URL of a chart without triggering a download.
 * Useful for previewing or embedding chart images programmatically.
 *
 * @param chart   - The ECharts instance to export
 * @param options - Export configuration options
 * @returns A base64-encoded data URL string
 */
export function getChartDataUrl(
	chart: echarts.ECharts,
	options: DownloadOptions = {}
): string {
	const {
		format = 'png',
		pixelRatio = DEFAULT_PIXEL_RATIO,
		backgroundColor,
		excludeComponents = ['toolbox']
	} = options;

	const resolvedBg = backgroundColor ?? (format === 'svg' ? 'none' : '#ffffff');

	return chart.getDataURL({
		type: format === 'svg' ? 'svg' : 'png',
		pixelRatio: format === 'png' ? pixelRatio : 1,
		backgroundColor: resolvedBg,
		excludeComponents
	});
}

// ─── Internal Helpers ────────────────────────────────────────────────────────

/**
 * Triggers a browser file download from a data URL.
 * Creates a temporary anchor element, clicks it, and removes it.
 */
function triggerDownload(dataUrl: string, fileName: string): void {
	const link = document.createElement('a');
	link.href = dataUrl;
	link.download = fileName;
	link.style.display = 'none';

	document.body.appendChild(link);
	link.click();

	// Clean up the DOM after a brief delay to ensure the download starts
	requestAnimationFrame(() => {
		document.body.removeChild(link);
	});
}