import express from 'express';
import { exploreVideos, toGraphviz } from '../lib/explore.mjs';
import { toSVG } from '../lib/graphviz.mjs';

const router = express.Router();
export default router;

const statusPending = Symbol('PENDING');
const statusError = Symbol('ERROR');
const cache = Object.create(null);

router.get('/:videoId', async (req, res) => {
    const {videoId} = req.params;

    if (videoId in cache)
    {
        if (cache[videoId] === statusPending)
        {
            res.header('Refresh', '5');
            res.send('Exploration in progress… Please wait.');
        }
        else if (cache[videoId] === statusError)
        {
            res.status(500).send('Error');
        }
        else
        {
            res.send(cache[videoId]);
        }
    }
    else
    {
        cache[videoId] = statusPending;
        res.header('Refresh', '1');
        res.send('Exploration in progress… Please wait.');

        try
        {
            const graph = await exploreVideos(req.params.videoId);
            const graphviz = toGraphviz(...graph);
            const svg = await toSVG(graphviz);
            cache[videoId] = svg;
        }
        catch (err)
        {
            console.error(err);
            cache[videoId] = statusError;
        }
    }
});