import {useCallback, useEffect, useRef, useState} from 'react';
import {Link} from 'react-router-dom';
import {useTranslation} from 'react-i18next';
import {toast} from 'sonner';
import {Check, Loader2, Play, Shuffle, Timer} from 'lucide-react';

import {Badge} from '@/components/ui/badge';
import {Button} from '@/components/ui/button';
import {Card} from '@/components/ui/card';
import {Skeleton} from '@/components/ui/skeleton';
import GameCover from '../components/GameCover.jsx';
import FitText from '../components/FitText.jsx';
import PageContainer from '../components/PageContainer.jsx';
import {saveGameStatus} from '../utils/backlog.js';
import {formatDate} from '../utils/format.js';
import {formatPlaytime} from '../utils/games.js';
import {request} from '../utils/api.js';

// maxMinutes is IGDB's normal time to beat; a limit leaves out games without IGDB data.
const BUDGETS = [
    {key: 'SHORT', maxMinutes: 300},
    {key: 'MEDIUM', maxMinutes: 900},
    {key: 'LONG', maxMinutes: 2400},
    {key: 'ANY', maxMinutes: null},
];
// Core derives the moods from IGDB's genres, themes and game modes, and SPEEDRUN from speedrun.com; a mood leaves out
// games without that data.
const MOODS = ['ANY', 'STORY', 'COOP', 'CHILL', 'ACTION', 'SCARY', 'SPEEDRUN'];
// The rows in the order Core sends them; RANDOM is the mood row.
const ROW_ORDER = ['NEXT_UP', 'SIMILAR', 'LONGEST', 'RANDOM'];
// The backend reads only this many excludes. With a bigger backlog the oldest seen games can come back.
const MAX_EXCLUDES = 100;
const ROW_CLASS = 'flex gap-4 overflow-x-auto snap-x snap-mandatory pb-2 sm:grid sm:grid-cols-3 sm:overflow-visible';
const CARD_CLASS = 'w-64 shrink-0 snap-start sm:w-auto';

// The mood only filters the RANDOM row.
const pickerQuery = (maxMinutes, mood, exclude, category) => {
    const params = new URLSearchParams();
    if (category) params.set('category', category);
    if (maxMinutes) params.set('maxMinutes', String(maxMinutes));
    if (mood !== 'ANY' && (!category || category === 'RANDOM')) params.set('mood', mood);
    exclude.forEach((appid) => params.append('exclude', String(appid)));
    return params.toString();
};

const fetchPicker = (maxMinutes, mood, exclude, category, signal) => request(
    `${import.meta.env.VITE_CORE_API_URL}/api/library/picker?${pickerQuery(maxMinutes, mood, exclude, category)}`,
    {signal});

export default function PlayNextPage() {
    const {t} = useTranslation();
    const [budget, setBudget] = useState(BUDGETS[3]);
    const [mood, setMood] = useState('ANY');
    const [rows, setRows] = useState(null);
    const [seen, setSeen] = useState({});
    const [error, setError] = useState(null);
    // Keys ('ALL' or a row) with a request in flight.
    const [loading, setLoading] = useState(() => new Set());
    // One controller per request key ('ALL' or a row). A slow answer for an older budget, mood or reroll must not
    // replace the newer one.
    const controllers = useRef(new Map());

    useEffect(() => {
        const current = controllers.current;
        return () => current.forEach((controller) => controller.abort());
    }, []);

    const startLoading = useCallback((key) => setLoading((old) => new Set(old).add(key)), []);
    const finishLoading = useCallback((key) => setLoading((old) => {
        const next = new Set(old);
        next.delete(key);
        return next;
    }), []);

    const nextSignal = useCallback((key) => {
        controllers.current.get(key)?.abort();
        const controller = new AbortController();
        controllers.current.set(key, controller);
        return controller.signal;
    }, []);

    const loadAll = useCallback(async (maxMinutes, moodKey) => {
        controllers.current.forEach((controller) => controller.abort());
        const signal = nextSignal('ALL');
        setError(null);
        setLoading(new Set(['ALL']));
        const {ok, status, data} = await fetchPicker(maxMinutes, moodKey, [], null, signal);
        if (signal.aborted) return;
        finishLoading('ALL');
        if (status === 401) return;
        if (!ok || !data) {
            setError(status === 0 ? 'INFO.ERROR.NETWORK_FAILURE' : 'PLAY_NEXT.ERROR_LOAD');
            return;
        }
        const categories = data.categories ?? [];
        setRows(categories);
        setSeen(Object.fromEntries(categories.map((c) => [c.source, c.games.map((g) => g.appid)])));
    }, [nextSignal, finishLoading]);

    const loadRow = useCallback(async (source, exclude, maxMinutes, moodKey) => {
        const signal = nextSignal(source);
        startLoading(source);
        const {ok, status, data} = await fetchPicker(maxMinutes, moodKey, exclude, source, signal);
        if (signal.aborted) return;
        finishLoading(source);
        if (!ok || !data) {
            if (status !== 401) toast.error(t(status === 0 ? 'INFO.ERROR.NETWORK_FAILURE' : 'PLAY_NEXT.ERROR_LOAD'));
            return;
        }
        const row = (data.categories ?? []).find((c) => c.source === source);
        if (!row && exclude.length > 0) {
            // Every game that fits was shown: start the row over.
            await loadRow(source, [], maxMinutes, moodKey);
            return;
        }
        setRows((old) => ROW_ORDER
            .map((key) => (key === source ? row : old.find((r) => r.source === key)))
            .filter(Boolean));
        setSeen((old) => ({
            ...old,
            [source]: [...exclude, ...(row?.games ?? []).map((g) => g.appid)].slice(-MAX_EXCLUDES),
        }));
    }, [nextSignal, startLoading, finishLoading, t]);

    useEffect(() => {
        loadAll(BUDGETS[3].maxMinutes, 'ANY');
    }, [loadAll]);

    const chooseBudget = (next) => {
        if (next.key === budget.key) return;
        setRows(null);
        setSeen({});
        setBudget(next);
        loadAll(next.maxMinutes, mood);
    };

    const chooseMood = (next) => {
        if (next === mood) return;
        setMood(next);
        if (rows === null) loadAll(budget.maxMinutes, next);
        else loadRow('RANDOM', [], budget.maxMinutes, next);
    };

    const headingFor = (source) => (source === 'RANDOM' && mood !== 'ANY'
        ? t('PLAY_NEXT.CATEGORY.MOOD', {mood: t(`PLAY_NEXT.MOOD.${mood}`)})
        : t(`PLAY_NEXT.CATEGORY.${source}`));
    const moodRowMissing = rows !== null && mood !== 'ANY' && !loading.has('RANDOM')
        && !rows.some((r) => r.source === 'RANDOM');

    return (
        <PageContainer className="p-4 md:p-8 space-y-6">
            <div className="space-y-2">
                <h1 className="text-3xl font-bold tracking-tight">{t('PLAY_NEXT.TITLE')}</h1>
                <p className="text-muted-foreground">{t('PLAY_NEXT.SUBTITLE')}</p>
            </div>

            <div className="space-y-2">
                <div className="flex flex-wrap gap-2" role="group" aria-label={t('PLAY_NEXT.BUDGET_LABEL')}>
                    {BUDGETS.map((b) => (
                        <Button
                            key={b.key}
                            size="sm"
                            variant={budget.key === b.key ? 'default' : 'outline'}
                            aria-pressed={budget.key === b.key}
                            onClick={() => chooseBudget(b)}
                        >
                            {t(`PLAY_NEXT.BUDGET.${b.key}`)}
                        </Button>
                    ))}
                </div>
                {budget.maxMinutes && (
                    <p className="text-xs text-muted-foreground">{t('PLAY_NEXT.BUDGET_HINT')}</p>
                )}
            </div>

            <div className="space-y-2">
                <div className="flex flex-wrap gap-2" role="group" aria-label={t('PLAY_NEXT.MOOD_LABEL')}>
                    {MOODS.map((key) => (
                        <Button
                            key={key}
                            size="sm"
                            variant={mood === key ? 'default' : 'outline'}
                            aria-pressed={mood === key}
                            onClick={() => chooseMood(key)}
                        >
                            {t(`PLAY_NEXT.MOOD.${key}`)}
                        </Button>
                    ))}
                </div>
                {mood !== 'ANY' && (
                    <p className="text-xs text-muted-foreground">
                        {t(mood === 'SPEEDRUN' ? 'PLAY_NEXT.MOOD_HINT_SPEEDRUN' : 'PLAY_NEXT.MOOD_HINT')}
                    </p>
                )}
                {moodRowMissing && (
                    <p className="text-muted-foreground">
                        {t(emptyKey(budget, mood))}
                    </p>
                )}
            </div>

            {error && (
                <div className="space-y-3">
                    <p className="text-sm text-destructive">{t(error)}</p>
                    <Button variant="outline" onClick={() => loadAll(budget.maxMinutes, mood)}>
                        <Shuffle/>{t('PLAY_NEXT.REROLL')}
                    </Button>
                </div>
            )}

            {rows === null && !error && ROW_ORDER.map((source) => (
                <div key={source} className={ROW_CLASS}>
                    {Array.from({length: 3}, (_, i) => <Skeleton key={i} className={`h-56 rounded-xl ${CARD_CLASS}`}/>)}
                </div>
            ))}

            {rows?.map(({source, games}) => (
                <section key={source} aria-labelledby={`row-${source}`} className="min-w-0 space-y-3">
                    <div className="flex items-center justify-between gap-2">
                        <h2 id={`row-${source}`} className="text-xl font-semibold">{headingFor(source)}</h2>
                        <Button
                            size="sm"
                            variant="outline"
                            aria-label={t('PLAY_NEXT.REROLL_ROW', {category: headingFor(source)})}
                            onClick={() => loadRow(source, seen[source] ?? [], budget.maxMinutes, mood)}
                            disabled={loading.has(source)}
                        >
                            {loading.has(source) ? <Loader2 className="animate-spin"/> : <Shuffle/>}
                        </Button>
                    </div>
                    <div className={ROW_CLASS}>
                        {games.map((game) => (
                            <div key={game.appid} className={CARD_CLASS}><PickCard game={game}/></div>
                        ))}
                    </div>
                </section>
            ))}

            {rows?.length === 0 && !moodRowMissing && (
                <p className="text-muted-foreground">
                    {t(emptyKey(budget, 'ANY'))}
                </p>
            )}
        </PageContainer>
    );
}

// The row heading says why a NEXT_UP or RANDOM game was picked.
const reasonText = (reason, t, language) => {
    if (reason?.source === 'SIMILAR') {
        return t('PLAY_NEXT.REASON.SIMILAR', {
            name: reason.anchorName ?? `App ${reason.anchorAppid}`,
            playtime: formatPlaytime(reason.anchorPlaytimeMinutes),
        });
    }
    if (reason?.source === 'LONGEST') {
        return t('PLAY_NEXT.REASON.LONGEST', {date: formatDate(reason.firstSeenAt, language, {dateStyle: 'medium'})});
    }
    return null;
};

const emptyKey = (budget, mood) => {
    // With a length limit, waiting for the background check may never help.
    if (mood === 'SPEEDRUN' && !budget.maxMinutes) return 'PLAY_NEXT.EMPTY_SPEEDRUN';
    if (mood !== 'ANY') return 'PLAY_NEXT.EMPTY_MOOD';
    return budget.maxMinutes ? 'PLAY_NEXT.EMPTY_BUDGET' : 'PLAY_NEXT.EMPTY';
};

function PickCard({game}) {
    const {t, i18n} = useTranslation();
    const [busy, setBusy] = useState(false);
    const [started, setStarted] = useState(false);
    const reason = reasonText(game.reason, t, i18n.language);

    const startPlaying = async () => {
        setBusy(true);
        try {
            const response = await saveGameStatus(game.appid, 'PLAYING');
            if (response.status === 401) return;
            if (!response.ok) {
                toast.error(t('BACKLOG.SAVE_FAILED'));
                return;
            }
            setStarted(true);
            toast.success(t('BACKLOG.SAVED'));
        } catch (err) {
            console.error('Start playing error:', err);
            toast.error(t('INFO.ERROR.NETWORK_FAILURE'));
        } finally {
            setBusy(false);
        }
    };

    return (
        <Card className="gap-3 overflow-hidden p-0">
            <Link to={`/library/${game.appid}`} className="block">
                <GameCover appid={game.appid} imageUrl={game.imageUrl} className="w-full"/>
            </Link>
            <div className="flex flex-1 flex-col gap-3 px-4 pb-4">
                <Link to={`/library/${game.appid}`} className="@container block min-w-0 font-semibold hover:text-primary transition-colors">
                    <FitText text={game.name ?? `App ${game.appid}`}/>
                </Link>
                {reason && <p className="text-sm text-muted-foreground">{reason}</p>}
                <div className="flex flex-wrap items-center gap-2 text-sm text-muted-foreground">
                    {game.timeToBeatMinutes > 0 && (
                        <span className="flex items-center gap-1">
                            <Timer className="size-4"/>{formatPlaytime(game.timeToBeatMinutes)}
                        </span>
                    )}
                    {game.priority && (
                        <Badge variant="secondary">
                            {t('BACKLOG.PRIORITY_LABEL')}: {t(`BACKLOG.PRIORITY.${game.priority}`)}
                        </Badge>
                    )}
                </div>
                <div className="mt-auto">
                    {started ? (
                        <p className="flex items-center gap-1.5 text-sm font-medium text-primary">
                            <Check className="size-4"/>{t('PLAY_NEXT.STARTED')}
                        </p>
                    ) : (
                        <Button size="sm" className="w-full" onClick={startPlaying} disabled={busy}>
                            {busy ? <Loader2 className="animate-spin"/> : <Play/>}
                            {t('PLAY_NEXT.START_PLAYING')}
                        </Button>
                    )}
                </div>
            </div>
        </Card>
    );
}