import util from 'util';
import fetch from 'node-fetch';

const YOUTUBE_BASE = 'https://www.youtube.com/%s';
const WATCH_BASE = util.format(YOUTUBE_BASE, 'watch?v=%s');
const PLAYER_CONFIG_REGEX = /ytplayer\.config = (\{.*?\});/;

/**
 * Make a promise that is resolved in a point in the future.
 *
 * @param Number time Time to wait before resolving the promise (ms).
 * @return null
 */
const sleep = time => new Promise(resolve => setTimeout(resolve, time));

/**
 * Fetch the `ytplayer.config` object for a YouTube video.
 *
 * @async
 * @param String videoId Identifier of the video to fetch.
 * @param Number retries Allowed number of retries after fetch errors.
 * @param Number cooldown Time to wait before retrying (ms).
 * @return Object The player configuration object.
 */
export const getPlayerConfig = async (videoId, retries = 3, cooldown = 1000) =>
{
    const url = util.format(WATCH_BASE, videoId);
    const res = await fetch(url);
    const body = await res.text();

    // Look for the definition of ytplayer.config and unserialize it
    const configSearch = body.match(PLAYER_CONFIG_REGEX);

    if (configSearch === null)
    {
        if (retries > 0)
        {
            console.info(`Error while fetching ${videoId}, retrying in ${cooldown} ms`);
            await sleep(cooldown);
            return getPlayerConfig(videoId, retries - 1, cooldown * 2);
        }
        else
        {
            throw new Error('Unable to find player configuration');
        }
    }

    const config = JSON.parse(configSearch[1]);
    config.args.player_response = JSON.parse(config.args.player_response);
    return config;
};

/**
 * Get metadata about a YouTube video.
 *
 * @param playerConfig The `ytplayer.config` object corresponding to the source
 * YouTube video, as obtained from `getPlayerConfig`.
 * @return Object containing the video metadata.
 */
export const getVideoMeta = playerConfig => ({
    videoId: playerConfig.args.player_response.videoDetails.videoId,
    title: playerConfig.args.player_response.videoDetails.title,
});

/**
 * Find videos linked from the endscreen of a YouTube video.
 *
 * @param playerConfig The `ytplayer.config` object corresponding to the source
 * YouTube video, as obtained from `getPlayerConfig`.
 * @return List of identifiers of linked videos.
 */
export const getEndScreenVideos = playerConfig =>
{
    const response = playerConfig.args.player_response;

    if (!('endscreen' in response))
    {
        return [];
    }

    return response.endscreen.endscreenRenderer.elements
        .map(elt => elt.endscreenElementRenderer)
        .filter(rdr => 'watchEndpoint' in rdr.endpoint)
        .map(rdr => rdr.endpoint.watchEndpoint.videoId);
};

/**
 * Find videos linked from as cards from a YouTube video.
 *
 * @param playerConfig The `ytplayer.config` object corresponding to the source
 * YouTube video, as obtained from `getPlayerConfig`.
 * @return List of identifiers of linked videos.
 */
export const getCardVideos = playerConfig =>
{
    const response = playerConfig.args.player_response;

    if (!('cards' in response))
    {
        return [];
    }

    return response.cards.cardCollectionRenderer.cards
        .map(card => card.cardRenderer.content)
        .filter(content => 'videoInfoCardContentRenderer' in content)
        .map(content => content.videoInfoCardContentRenderer)
        .map(rdr => rdr.action.watchEndpoint.videoId);
};