'use strict';

import util from 'util';

const YOUTUBE_WATCH = 'https://youtu.be/%s';
const GRAPH_NODE = '    "%s" [label="%s", URL="%s", fontcolor=blue]';
const GRAPH_LINK = '    "%s" -> "%s"';

/**
 * Escape double quotes in a string.
 */
const escapeQuotes = str => str.replace(/"/g, '\\"');

/**
 * Convert a graph of videos to the DOT format.
 *
 * @param nodes Nodes of the graph.
 * @param next For each node, list of next neighbors.
 * @param [title=identity] Function giving the name of each node.
 * @param [url=none] Function given the URL of each node, or an empty string
 * if a node has no URL.
 * @return DOT representation of the graph.
 */
export const graphToDOT = (nodes, next) =>
{
    // Convert nodes
    const nodesStr = Object.entries(nodes).map(([id, {title}]) =>
    {
        const url = util.format(YOUTUBE_WATCH, id);
        return util.format(GRAPH_NODE, id, escapeQuotes(title), url);
    }).join('\n');

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

    return `digraph youtube {
        ${nodesStr}
        ${nextStr}
    }`;
};