/**
 * Vaaditaan riippuvuudet: node-fetch sekä node-html-parser
 * Käyttöesimerkki:

const FORUM_URL = ""; // esim. "https://www.punkinfinland.net/forum/"
const TOPIC_ID  = ""; // esim. "769221" (kts. https://www.punkinfinland.net/forum/viewtopic.php?t=769221)

const crawler = require( "./phpbb_crawler" )({
    logger: false,
    fetch_timeout: 1000,
    forum_url: FORUM_URL
});

crawler.fetchTopicPosts( TOPIC_ID ).then( posts => {
    console.log( posts );
});

*/

const fetch = (...args) => import( "node-fetch" ).then(({ default: fetch }) => fetch( ...args ));

const HTMLParser = require( "node-html-parser" );

module.exports = (() => {

    const assets = {};

    return opts => {

        const FORUM_BASE_URL = opts.forum_url;

        const FETCH_TIMEOUT = opts.fetch_timeout == null ? 100 : opts.fetch_timeout;

        const logger = opts.logger == false ? { info: ()=>{}, error: ()=>{} } : opts.logger || console;

        if (!FORUM_BASE_URL) throw new Error( "Missing FORUM_BASE_URL" );

        return { fetchTopicPosts, fetchTopicviewStats, fetchTopicviewPagePosts };

        async function fetchDOM( url, force ) {

            if (force || !assets[ url ]) {

                // Koska ei haluta rasittaa palvelinta turhan paljoa, odotellaan kutsujen välillä
                await new Promise( cb => setTimeout( cb, FETCH_TIMEOUT ));

                var response = await fetch( url );

                assets[ url ] = await response.text();
            }

            return HTMLParser.parse( assets[ url ] );
        }

        async function fetchTopicPosts( TOPIC_ID, force ) {

            var stats = await fetchTopicviewStats( TOPIC_ID, force );

            logger.info(  `Topic ${ TOPIC_ID } stats:`, stats );

            var all_posts = [];

            for (var page_n = 1; page_n <= stats.pages_count; page_n++) {

                var posts = await fetchTopicviewPagePosts( TOPIC_ID, stats.posts_per_page * (page_n - 1), force );

                logger.info(  `Got ${ posts.length } post from page ${ page_n }` );

                for (var post of posts) all_posts.push( post );
            }

            logger.info( `Ready! Fetched ${ all_posts.length } posts from topic ${ TOPIC_ID }!` );

            return all_posts;
        }

        async function fetchTopicviewStats( topic_id, force ) {

            var DOM = await fetchDOM( `${ FORUM_BASE_URL }viewtopic.php?t=${ topic_id }&start=0` );

            var _pagination_elem = DOM.querySelector( "#page-body .action-bar.bar-top > .pagination" );

            var posts_count, pages_count = 1, posts_per_page;

            try {
                // Ei toimi aina kirjautuneelle käyttäjälle (mahdollinen "Lukemattomia viestejä"-ilmoitus)
                // "12 345 posts <ul><li class=....." -> "12345"
                posts_count = parseInt( _pagination_elem.innerHTML.trim().match( /^[\d\s]+/ )[0].replace( /\s/g, "" ));
            } catch (error) { logger.error( error ); }

            try {
                var _last_page_btn_elem;
                for (var elem of _pagination_elem.querySelectorAll( "ul > li:not(.arrow)" )) _last_page_btn_elem = elem;
                pages_count = parseInt( _last_page_btn_elem.text );
            } catch (error) { logger.error( error ); }

            try {
                posts_per_page = DOM.querySelectorAll( "#page-body > .post" ).length;
            } catch (error) { logger.error( error ); }

            return { posts_count, pages_count, posts_per_page };
        }

        async function fetchTopicviewPagePosts( topic_id, offset, force ) {

            var DOM = await fetchDOM( `${ FORUM_BASE_URL }viewtopic.php?t=${ topic_id }&start=${ offset }` );

            var posts = DOM.querySelectorAll( "#page-body > .post" ).map( elem => {

                var post = { }

                try { // id="pXXXX" -> XXXX
                    post.id = elem.id.substr( 1 );
                } catch (error) { logger.error( error ); }

                try {
                    post.username = elem.querySelector( ".postprofile .username, .postprofile .username-coloured" ).textContent;
                } catch (error) { logger.error( error ); }

                try { // p.author esim.: <span class="posti">... .&raquo; </span>12 Aug 2021, 15:17\n
                    var post_header = elem.querySelector( ".postbody .author" ).innerHTML.trim();
                    post.published_at = post_header.substr( post_header.lastIndexOf(">") + 1 );
                    post.published_at = datetime_to_timestamp( post.published_at );
                } catch (error) { logger.error( error ); }

                try {
                    post.content = elem.querySelector( ".postbody .content" ).innerHTML;
                } catch (error) { logger.error( error ); }

                return post;
            });

            return posts;
        }
    }
})();

// @see https://github.com/widop/phpbb3/blob/master/language/en/common.php
const datetime_matchers = [{
    pattern: /Yesterday, (?<hours>\d+):(?<minutes>\d+)/,
    _parse: (match, now) => (now = new Date( now.getTime() - 24 * 60 * 60 * 1000 ), now.setHours(match.groups.hours), now.setMinutes(match.groups.minutes), now )
}, {
    pattern: /Today, (?<hours>\d+):(?<minutes>\d+)/,
    _parse: (match, now) => (now.setHours(match.groups.hours), now.setMinutes(match.groups.minutes), now )
}, {
    pattern: /1 hour ago/,
    _parse: (match, now) => new Date( now.getTime() - 60 * 60 * 1000 )
}, {
    pattern: /(?<minutes>\d+) minutes? ago/,
    _parse: (match, now) => new Date( now.getTime() - match.groups.minutes * 60 * 1000 )
}, {
    pattern: /less than a minute ago/,
    _parse: (match, now) => now
}];

function datetime_to_timestamp( string ) {

    var now = new Date();
    now.setSeconds(0);

    for (var matcher of datetime_matchers) {
        var match = string.match( matcher.pattern );
        if (match) return matcher._parse ? matcher._parse( match, now ) : match;
    }

    return new Date( string ) || string;
}