import { useEffect, useState } from 'react';
import { useHttpService } from '../../services';
import { readLifecycle } from '../SandboxMode/sandboxLifecycle';

const MINUTE = 60_000;
const HOUR = 60 * MINUTE;
const DAY = 24 * HOUR;
const plural = (n: number, unit: string) => `${n} ${unit}${n === 1 ? '' : 's'}`;

/** "Resets in 2 days, 4 hours", or nothing once the instant has passed. */
export function resetCountdownLabel(scheduledAt: string, now: number): string | null {
    const left = Date.parse(scheduledAt) - now;
    if (!Number.isFinite(left) || left <= 0) return null;
    const days = Math.floor(left / DAY);
    const hours = Math.floor((left % DAY) / HOUR);
    if (days > 0) return `Resets in ${plural(days, 'day')}${hours > 0 ? `, ${plural(hours, 'hour')}` : ''}`;
    if (hours > 0) return `Resets in ${plural(hours, 'hour')}`;
    return 'Resets in less than an hour';
}

/**
 * The countdown to the sandbox's next scheduled recreation, only when the server has one recorded. Without
 * one, or if the read fails, there is nothing to count down to and nothing is shown.
 */
export function useSandboxResetCountdown(enabled: boolean): string | null {
    const { get } = useHttpService();
    const [scheduledAt, setScheduledAt] = useState<string | null>(null);
    const [now, setNow] = useState(() => Date.now());

    useEffect(() => {
        if (!enabled) return;
        let live = true;
        readLifecycle((url) => get(url))
            .then((lifecycle) => { if (live) setScheduledAt(lifecycle.recreation?.scheduledAt ?? null); })
            .catch(() => { if (live) setScheduledAt(null); });
        return () => { live = false; };
        // eslint-disable-next-line react-hooks/exhaustive-deps
    }, [enabled]);

    useEffect(() => {
        if (!scheduledAt) return;
        const timer = setInterval(() => setNow(Date.now()), MINUTE);
        return () => clearInterval(timer);
    }, [scheduledAt]);

    return scheduledAt ? resetCountdownLabel(scheduledAt, now) : null;
}