import util from 'util';
import request from 'request';

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

/**
 * Fetch the `ytplayer.config` object for a YouTube video.
 *
 * @async
 * @param videoId Identifier of the video to fetch.
 * @return The player configuration object.
 */
export const getPlayerConfig = videoId =>
{
    const url = util.format(WATCH_BASE, videoId);

    return new Promise((resolve, reject) =>
    {
        request(url, (err, _, body) =>
        {
            if (err)
            {
                reject(err);
                return;
            }

            // Look for the definition of ytplayer.config and unserialize it
            // and the player_response subobject
            try
            {
                const playerConfig = JSON.parse(body.match(PLAYER_REGEX)[1]);
                playerConfig.args.player_response
                    = JSON.parse(playerConfig.args.player_response);
                resolve(playerConfig);
            }
            catch (err)
            {
                reject(err);
            }
        });
    });
};

/**
 * 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);
};