'use strict';

const Promise = require('bluebird');
const moment = require('moment');

const argv = require('./argv');
const logger = require('./logger')(__filename);
const knex = require('./knex');
const include = require('./utils/argv-include')(argv);
const scrapers = require('./scrapers/scrapers');
const { fetchSitesFromArgv, fetchSitesFromConfig } = require('./sites');

const afterDate = (() => {
    if (/\d{2,4}-\d{2}-\d{2,4}/.test(argv.after)) {
        // using date
        return moment
            .utc(argv.after, ['YYYY-MM-DD', 'DD-MM-YYYY'])
            .toDate();
    }

    // using time distance (e.g. "1 month")
    return moment
        .utc()
        .subtract(...argv.after.split(' '))
        .toDate();
})();

async function extractUniqueReleases(latestReleases, accReleases) {
    const latestReleaseIdentifiers = latestReleases
        .map(release => [release.site.id, release.entryId]);

    const duplicateReleases = await knex('releases')
        .whereIn(['site_id', 'entry_id'], latestReleaseIdentifiers);

    // add entry IDs of accumulated releases to prevent an infinite scrape loop
    // when one page contains the same release as the previous
    const duplicateReleasesSiteIdAndEntryIds = duplicateReleases
        .concat(accReleases)
        .reduce((acc, release) => {
            const siteId = release.site_id || release.site.id;
            const entryId = release.entry_id || release.entryId;

            if (!acc[siteId]) acc[siteId] = {};
            acc[siteId][entryId] = true;

            return acc;
        }, {});

    const uniqueReleases = latestReleases
        .filter(release => !duplicateReleasesSiteIdAndEntryIds[release.site.id]?.[release.entryId]);

    return uniqueReleases;
}

function needNextPage(uniqueReleases, pageAccReleases) {
    if (uniqueReleases === 0) {
        return false;
    }

    if (argv.last && pageAccReleases.length < argv.last) {
        // request for last N releases not yet satisfied
        return true;
    }

    const oldestReleaseOnPage = uniqueReleases
        .sort((releaseA, releaseB) => releaseB.date - releaseA.date)
        .slice(-1)[0];

    if (oldestReleaseOnPage && moment(oldestReleaseOnPage.date).isAfter(afterDate)) {
        // oldest release on page is newer than the specified date cut-off
        return true;
    }

    // dates missing, and limit for scenes without dates not yet reached
    return pageAccReleases.length <= argv.nullDateLimit;
}

async function scrapeLatestReleases(scraper, site, preData) {
    if (!scraper.fetchLatest) {
        return [];
    }

    const scrapePage = async (page = 1, accReleases = []) => {
        const latestReleases = await scraper.fetchLatest(site, page, preData, include);

        if (!Array.isArray(latestReleases)) {
            // scraper is unable to fetch the releases and returned a HTTP code or null
            logger.warn(`Scraper returned ${latestReleases} when fetching latest from '${site.name}' (${site.network.name})`);
            return accReleases;
        }

        if (latestReleases.length === 0) {
            // scraper successfully requested releases, but found none
            return accReleases;
        }

        const latestReleasesWithSite = latestReleases.map(release => ({ ...release, site: release.site || site })); // attach site release is assigned to when stored

        const uniqueReleases = argv.redownload
            ? latestReleasesWithSite
            : await extractUniqueReleases(latestReleasesWithSite, accReleases);

        const pageAccReleases = accReleases.concat(uniqueReleases);

        logger.verbose(`Scraped '${site.name}' (${site.network.name}) page ${page}, found ${uniqueReleases.length} unique releases`);

        if (needNextPage(uniqueReleases, pageAccReleases)) {
            return scrapePage(page + 1, pageAccReleases);
        }

        return pageAccReleases;
    };

    const releases = await scrapePage(1, []);

    if (argv.last) {
        return releases.slice(0, argv.last);
    }

    if (releases.every(release => release.date)) {
        return releases
            .filter(release => moment(release.date).isAfter(afterDate));
    }

    return releases.slice(0, argv.nullDateLimit);
}

async function scrapeUpcomingReleases(scraper, site, preData) {
    if (!scraper.fetchUpcoming) {
        return [];
    }

    try {
        const upcomingReleases = await scraper.fetchUpcoming(site, 1, preData, include);

        if (upcomingReleases) {
            return upcomingReleases.map(release => ({
                ...release,
                site,
                upcoming: true,
            }));
        }
    } catch (error) {
        logger.warn(`Failed to scrape upcoming releases for '${site.slug}' (${site.network.slug})`);
    }

    return [];
}

async function scrapeSiteReleases(scraper, site, preData) {
    const [latestReleases, upcomingReleases] = await Promise.all([
        argv.latest
            ? scrapeLatestReleases(scraper, site, preData)
            : [],
        argv.upcoming
            ? scrapeUpcomingReleases(scraper, site, preData)
            : [],
    ]);

    return [...latestReleases, ...upcomingReleases];
}

async function scrapeSite(site, accSiteReleases) {
    const scraper = scrapers.releases[site.slug]
        || scrapers.releases[site.network.slug]
        || scrapers.releases[site.network.parent?.slug];

    if (!scraper) {
        logger.warn(`No scraper found for '${site.name}' (${site.network.name})`);
        return [];
    }

    try {
        const beforeFetchLatest = await scraper.beforeFetchLatest?.(site);

        const siteReleases = await scrapeSiteReleases(scraper, site, {
            accSiteReleases,
            beforeFetchLatest,
        });

        return siteReleases.map(release => ({ ...release, site }));
    } catch (error) {
        logger.error(`Failed to scrape releases from ${site.name} using ${scraper.slug}: ${error.message}`);

        return [];
    }
}

async function scrapeNetworkSequential(network) {
    return Promise.reduce(
        network.sites,
        async (chain, site) => {
            const accSiteReleases = await chain;
            const siteReleases = await scrapeSite(site, network, accSiteReleases);

            return accSiteReleases.concat(siteReleases);
        },
        Promise.resolve([]),
    );
}

async function scrapeNetworkParallel(network) {
    return Promise.map(
        network.sites,
        async site => scrapeSite(site, network),
        { concurrency: 3 },
    );
}

async function fetchUpdates() {
    const includedNetworks = argv.sites || argv.networks
        ? await fetchSitesFromArgv()
        : await fetchSitesFromConfig();

    const scrapedNetworks = await Promise.map(
        includedNetworks,
        async network => (network.parameters?.sequential
            ? scrapeNetworkSequential(network)
            : scrapeNetworkParallel(network)),
        { concurrency: 5 },
    );

    const releases = scrapedNetworks.flat(2);

    return releases;
}

module.exports = fetchUpdates;