import { ArrayBuffers } from './ArrayBuffers';

export interface ParsedDataUri {
	type: string;
	params: Record<string, string | boolean>;
	content: string;
	base64: boolean;

	getData(enc: 'utf-8' | 'base64'): Promise<string>;

	getData(): Promise<ArrayBuffer>;
}

export function parseDataUri(data: string): undefined | ParsedDataUri {
	if (!data || !data.startsWith('data:')) {
		return;
	}
	// https://en.wikipedia.org/wiki/Data_URI_scheme
	// data:content/type;base64,
	// data:content/type;a=b,content
	const [header, body] = data.split(',');
	const [type, ...paramsStr] = header.slice('data:'.length).split(';');
	const content = body;
	const params: Record<string, string | boolean> = Object.fromEntries(
		paramsStr.map((s) => {
			const [k, v] = s.trim().split('=');
			return [k, v ?? true];
		}),
	);
	// params charset=utf-8
	// params base64
	// params a=b
	let base64 = Boolean(params.base64);
	return {
		type,
		params,
		content,
		base64,
		getData: async (enc?: 'utf-8' | 'base64') => {
			if (!enc) {
				return await fetch(data).then((v) => v.arrayBuffer());
			}
			//
			let buf: BufferSource;
			if (base64) {
				if (enc === 'base64') {
					return content;
				}
				buf = await fetch(data).then((v) => v.arrayBuffer());
			} else {
				let raw = decodeURIComponent(content);
				if (enc === 'utf-8') {
					return raw;
				}
				buf = ArrayBuffers.from(raw, 'utf-8') as BufferSource;
			}
			if (enc === 'utf-8') {
				return new TextDecoder(enc).decode(buf);
			}
			if (enc === 'base64') {
				return ArrayBuffers.toString(buf, 'base64');
			}
			return buf;
		},
	} as ParsedDataUri;
}