import Graph from 'graph-data-structure';
import fs from 'fs';
import path from 'path';
import util from 'util';

import * as api from './api.mjs';
import {graphToDOT} from './graph.mjs';

const YOUTUBE_WATCH = 'https://youtu.be/%s';

// Fetch the output path from command line
if (process.argv.length !== 3)
{
    console.error(`Usage: node explore [output]`);
    process.exit(1);
}

const dest = process.argv[2];

// Graph of visited videos. Each node is a video which is linked to all the
// videos to which there is a link, either through a card or an endscreen item
const videosGraph = Graph();

// Store metadata about each visited video
const videosMeta = Object.create(null);

/**
 * Recursively explore a video and the video linked from it to fill
 * the video graph.
 *
 * @param videoId Source video identifier.
 */
const exploreVideo = async videoId =>
{
    // Make sure we don’t explore the same video twice
    if (videoId in videosMeta)
    {
        return Promise.resolve();
    }

    const playerConfig = await api.getPlayerConfig(videoId);
    videosMeta[videoId] = api.getVideoMeta(playerConfig);

    const linkedVideos = [
        ...api.getEndScreenVideos(playerConfig),
        ...api.getCardVideos(playerConfig),
    ];

    // Add links between this video and the linked ones
    linkedVideos.forEach(id => videosGraph.addEdge(videoId, id));

    // Recurse on linked videos
    return Promise.all(linkedVideos.map(id => exploreVideo(id)));
};

// Metadata of the source video
const rootVideoId = 'EZGra6O8ClQ';
console.log('Starting to explore!');

exploreVideo(rootVideoId).then(() =>
{
    fs.writeFileSync(
        dest,
        graphToDOT(
            videosGraph,
            id => videosMeta[id].title,
            id => util.format(YOUTUBE_WATCH, id)
        )
    );

    console.log('Finished. Result in ' + dest);
}).catch(console.error);