/** SRS §9.4.5 — business hours 09:00–18:00, Mon–Fri (local server timezone). */

const BUSINESS_START_HOUR = 9;
const BUSINESS_END_HOUR = 18;

export function isBusinessHoursEnabled(): boolean {
    if (process.env.DEBUG_SLA_FAST_MODE === 'true') return false;
    return process.env.SLA_BUSINESS_HOURS !== 'false';
}

export function businessMsBetween(start: Date, end: Date): number {
    if (end.getTime() <= start.getTime()) return 0;

    let total = 0;
    const cursor = new Date(start);

    while (cursor.getTime() < end.getTime()) {
        const day = cursor.getDay();
        if (day !== 0 && day !== 6) {
            const windowStart = new Date(cursor);
            windowStart.setHours(BUSINESS_START_HOUR, 0, 0, 0);
            const windowEnd = new Date(cursor);
            windowEnd.setHours(BUSINESS_END_HOUR, 0, 0, 0);

            const sliceStart = Math.max(cursor.getTime(), windowStart.getTime(), start.getTime());
            const sliceEnd = Math.min(end.getTime(), windowEnd.getTime());
            if (sliceEnd > sliceStart) {
                total += sliceEnd - sliceStart;
            }
        }
        cursor.setDate(cursor.getDate() + 1);
        cursor.setHours(0, 0, 0, 0);
    }

    return total;
}

export function effectiveElapsedMs(
    track: { startTime: Date | string; metadata?: Record<string, unknown> | null },
    nowMs: number
): number {
    const meta = track.metadata || {};
    const start = new Date(track.startTime).getTime();
    const pausedAt = meta.pausedAt ? new Date(String(meta.pausedAt)).getTime() : null;
    const effectiveEnd = pausedAt ? Math.min(nowMs, pausedAt) : nowMs;

    let elapsed = isBusinessHoursEnabled()
        ? businessMsBetween(new Date(start), new Date(effectiveEnd))
        : effectiveEnd - start;

    const accumulatedPause = Number(meta.accumulatedPauseMs || 0);
    elapsed = Math.max(0, elapsed - accumulatedPause);
    return elapsed;
}