import debug from 'debug';
import util from 'util';
import fetch from 'node-fetch';
import fs from 'fs';

import { WATCH_BASE } from './util.mjs';
import { retryable, exclusive } from './retry.mjs';
import { TemporaryError } from './retry.mjs';

const log = debug('youtube-maze:api');
const METADATA_REGEXES = [
    /window\["ytInitialPlayerResponse"\] = (\{.*?\});/,
    /var ytInitialPlayerResponse = (\{.*?\});/,
];

/**
 * Fetch metadata about a YouTube video.
 *
 * @async
 * @param String videoId Identifier of the video to fetch.
 * @return Object The video metadata object.
 */
const bareGetMetadata = async (videoId) =>
{
    const url = util.format(WATCH_BASE, encodeURIComponent(videoId));
    log(`Fetching ${videoId} (${url})`);
    const res = await fetch(url);

    if (res.status === 429)
    {
        throw new TemporaryError('Too many requests');
    }
    else if (res.status !== 200)
    {
        throw new Error(`Invalid YouTube HTTP status: ${res.status}`);
    }

    const body = await res.text();
    const searchResults = METADATA_REGEXES.map(regex => body.match(regex));
    const searchResult = searchResults.find(item => item !== null);

    if (searchResult === null)
    {
        throw new TemporaryError(`Incomplete YouTube response for video ${videoId}`);
    }

    const metadata = JSON.parse(searchResult[1]);

    if (metadata.playabilityStatus.status !== 'OK')
    {
        throw new Error(`Video ${videoId} is not available; \
status: ${metadata.playabilityStatus.status}; \
reason: "${metadata.playabilityStatus.reason}"`);
    }

    const actualId = metadata.videoDetails.videoId;

    if (videoId !== actualId)
    {
        throw new Error(`Video ${videoId} has actual id ${actualId}`);
    }

    log(`Done fetching ${videoId}`);
    return metadata;
};

export const getMetadata = exclusive(retryable(bareGetMetadata));

/**
 * Get video ID and title.
 *
 * @param Object metadata The video metadata object from `getMetadata`.
 * @return Object Containing the video ID and title.
 */
export const getVideoInfo = metadata => ({
    videoId: metadata.videoDetails.videoId,
    title: metadata.videoDetails.title,
});

/**
 * Find videos linked from the endscreen of a YouTube video.
 *
 * @param Object metadata The video metadata object from `getMetadata`.
 * @return List of identifiers of linked videos.
 */
export const getEndScreenVideos = metadata =>
{
    if (!('endscreen' in metadata))
    {
        return [];
    }

    return metadata.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 Object metadata The video metadata object from `getMetadata`.
 * @return List of identifiers of linked videos.
 */
export const getCardVideos = metadata =>
{
    if (!('cards' in metadata))
    {
        return [];
    }

    return metadata.cards.cardCollectionRenderer.cards
        .map(card => card.cardRenderer.content)
        .filter(content => 'videoInfoCardContentRenderer' in content)
        .map(content => content.videoInfoCardContentRenderer)
        .map(rdr => rdr.action.watchEndpoint.videoId);
};