import util from 'util';
import * as api from './api.mjs';
import { WATCH_BASE, escapeQuotes } from './util.mjs';

const GRAPH_NODE = '    "%s" [label="%s", URL="%s", fontcolor=blue]';
const GRAPH_LINK = '    "%s" -> "%s"';

/**
 * Explore the video graph starting from the given root.
 *
 * @async
 * @param string videoId Source video identifier.
 * @param function onUpdate Callback run every time a new video is explored.
 * @return Array.<Object, Object> Nodes and set of neighbors of each node.
 */
export const exploreVideos = async (videoId, onUpdate) =>
{
    // Store metadata about each visited video
    const videosNodes = Object.create(null);

    // List of videos linked from each video either through a card or an
    // endscreen item
    const nextVideos = Object.create(null);

    // Videos that still need to be explored
    const queue = [videoId];

    while (queue.length > 0)
    {
        const currentId = queue.shift();

        if (!(currentId in videosNodes))
        {
            const metadata = await api.getMetadata(currentId);
            const info = api.getVideoInfo(metadata);

            videosNodes[currentId] = info;
            nextVideos[currentId] = new Set();

            // Add links between this video and the linked ones
            api.getEndScreenVideos(metadata)
                .forEach(nextId => nextVideos[info.videoId].add(nextId));
            api.getCardVideos(metadata)
                .forEach(nextId => nextVideos[info.videoId].add(nextId));

            for (let nextId of nextVideos[info.videoId])
            {
                queue.push(nextId);
            }
        }

        onUpdate(Object.keys(videosNodes).length, queue.length);
    }

    return [videosNodes, nextVideos];
};

/**
 * Convert a video graph to the GraphViz format.
 *
 * @param Object videosNodes Videos of the graph.
 * @param Object nextVideos For each video, list of next videos.
 * @return string GraphViz representation of the graph.
 */
export const toGraphviz = (videosNodes, nextVideos) =>
{
    // Convert videosNodes
    const nodesStr = Object.entries(videosNodes).map(([id, {title}]) =>
    {
        const url = util.format(WATCH_BASE, id);
        return util.format(GRAPH_NODE, id, escapeQuotes(title), url);
    }).join('\n');

    // Convert edges
    const nextStr = Object.entries(nextVideos).map(([id, neighbors]) =>
        Array.from(neighbors)
            .map(neighbor => util.format(GRAPH_LINK, id, neighbor))
            .join('\n')
    ).join('\n');

    return `digraph "" {
${nodesStr}

${nextStr}}`;
};