const ytdl = require('ytdl-core');
const prism = require('prism-media');

function filter(format) {
	return format.codecs === 'opus' &&
		format.container === 'webm' &&
		format.audioSampleRate == 48000;
}

/**
 * Tries to find the highest bitrate audio-only format. Failing that, will use any available audio format.
 * @private
 * @param {Object[]} formats The formats to select from
 */
function nextBestFormat(formats) {
	formats = formats
		.filter(format => format.audioBitrate)
		.sort((a, b) => b.audioBitrate - a.audioBitrate);
	return formats.find(format => !format.bitrate) || formats[0];
}

function download(url, options = {}) {
	return new Promise((resolve, reject) => {
		ytdl.getInfo(url, (err, info) => {
			if (err) return reject(err);
			// Prefer opus
			const format = info.formats.find(filter);
			const canDemux = format && info.length_seconds != 0;
			if (canDemux) options = { ...options, filter };
			else if (info.length_seconds != 0) options = { ...options, filter: 'audioonly' };
			if (canDemux) {
				const demuxer = new prism.opus.WebmDemuxer();
				return resolve(ytdl.downloadFromInfo(info, options).pipe(demuxer).on('end', () => demuxer.destroy()));
			} else {
				const transcoder = new prism.FFmpeg({
					args: [
						'-reconnect', '1',
						'-reconnect_streamed', '1',
						'-reconnect_delay_max', '5',
						'-i', nextBestFormat(info.formats).url,
						'-analyzeduration', '0',
						'-loglevel', '0',
						'-f', 's16le',
						'-ar', '48000',
						'-ac', '2',
					],
				});
				const opus = new prism.opus.Encoder({ rate: 48000, channels: 2, frameSize: 960 });
				const stream = transcoder.pipe(opus);
				stream.on('close', () => {
					transcoder.destroy();
					opus.destroy();
				});
				return resolve(stream);
			}
		});
	});
}

module.exports = Object.assign(download, ytdl);