import * as https from 'https'

import * as jsdom from 'jsdom'
import * as $ from 'jquery'


function getDocument(url: URL|string): Promise<Document> {
	return new Promise((resolve, reject) => {
		https.get(url, (res) => {
			// if failing to load page, reject
			if (!res.statusCode || res.statusCode < 200 || 300 <= res.statusCode) {
				reject(new Error(`
Failed to load.
Status Code: ${res.statusCode || 'no status code found'}
				`))
				res.resume()
				return;
			}
			res.setEncoding('utf8')
			const body: string[] = []
			res.on('data', (chunk) => { body.push(chunk) })
			res.on('end', () => {
				let data: Document;
				// if failing to parse contents as Document, reject
				try {
					data = new jsdom.JSDOM(body.join('')).window.document
				} catch (err) {
					reject(err)
					return;
				}
				resolve(data)
			})
		}).on('error', (err) => { reject(err) }) // if failing to get url, reject
	})
}


function related(document: Document): Promise<Document[]> {
	return Promise.all(
		[...$('h2 > span#See_also', document).parent().nextUntil('h2').find('ul').addBack('ul')]
			.filter((ul) => [...ul.children].every((li) => li.children.length === 1 && li.children[0].matches('a[href]')))
			.map((ul) => [...$(ul).find('a')])
			.reduce((x, y) => x.concat(y)) // COMBAK `Array#flat`
			.map((a) => getDocument((a as HTMLAnchorElement).href))
	)
}