/* global self ReadableStream Response */

self.addEventListener('install', () => {
	self.skipWaiting()
})

self.addEventListener('activate', event => {
	event.waitUntil(self.clients.claim())
})

const map = new Map()

// This should be called once per download
// Each event has a dataChannel that the data will be piped through
self.onmessage = event => {
	// We send a heartbeat every x secound to keep the
	// service worker alive if a transferable stream is not sent
	if (event.data === 'ping') {
		return
	}

	const data = event.data
	const downloadUrl = data.url || self.registration.scope + Math.random() + '/' + (typeof data === 'string' ? data : data.filename)
	const port = event.ports[0]
	const metadata = new Array(3) // [stream, data, port]

	metadata[1] = data
	metadata[2] = port

	// Note to self:
	// old streamsaver v1.2.0 might still use `readableStream`...
	// but v2.0.0 will always transfer the stream throught MessageChannel #94
	if (event.data.readableStream) {
		metadata[0] = event.data.readableStream
	} else if (event.data.transferringReadable) {
		port.onmessage = evt => {
			port.onmessage = null
			metadata[0] = evt.data.readableStream
		}
	} else {
		metadata[0] = createStream(port)
	}

	map.set(downloadUrl, metadata)
	port.postMessage({
		download: downloadUrl
	})
}

function createStream(port) {
	// ReadableStream is only supported by chrome 52
	return new ReadableStream({
		start(controller) {
			// When we receive data on the messageChannel, we write
			port.onmessage = ({
				data
			}) => {
				if (data === 'end') {
					return controller.close()
				}

				if (data === 'abort') {
					controller.error('Aborted the download')
					return
				}

				controller.enqueue(data)
			}
		},
		cancel() {
			console.log('user aborted')
		}
	})
}

self.onfetch = event => {
	const url = event.request.url

	// this only works for Firefox
	if (url.endsWith('/ping')) {
		return event.respondWith(new Response('pong'))
	}

	const hijacke = map.get(url)

	if (!hijacke) return null

	const [stream, data, port] = hijacke

	map.delete(url)

	// Not comfortable letting any user control all headers
	// so we only copy over the length & disposition
	const responseHeaders = new Headers({
		'Content-Type': 'application/octet-stream; charset=utf-8',

		// To be on the safe side, The link can be opened in a iframe.
		// but octet-stream should stop it.
		'Content-Security-Policy': "default-src 'none'",
		'X-Content-Security-Policy': "default-src 'none'",
		'X-WebKit-CSP': "default-src 'none'",
		'X-XSS-Protection': '1; mode=block'
	})

	let headers = new Headers(data.headers || {})

	if (headers.has('Content-Length')) {
		responseHeaders.set('Content-Length', headers.get('Content-Length'))
	}

	if (headers.has('Content-Disposition')) {
		responseHeaders.set('Content-Disposition', headers.get('Content-Disposition'))
	}

	// data, data.filename and size should not be used anymore
	if (data.size) {
		console.warn('Depricated')
		responseHeaders.set('Content-Length', data.size)
	}

	let fileName = typeof data === 'string' ? data : data.filename
	if (fileName) {
		console.warn('Depricated')
		// Make filename RFC5987 compatible
		fileName = encodeURIComponent(fileName).replace(/['()]/g, escape).replace(/\*/g, '%2A')
		responseHeaders.set('Content-Disposition', "attachment; filename*=UTF-8''" + fileName)
	}

	event.respondWith(new Response(stream, {
		headers: responseHeaders
	}))

	port.postMessage({
		debug: 'Download started'
	})
}