const numberFormat = new Intl.NumberFormat('en-US', { maximumFractionDigits: 1 });

/** Separate SVG paths at unavailable periods, including isolated recorded points. */
export function metricPlayerPaths(values: readonly (number | null)[], ceiling: number) {
    const segments: { x: number; y: number }[][] = [];
    let segment: { x: number; y: number }[] = [];
    for (let index = 0; index < values.length; index++) {
        const value = values[index];
        if (value === null) {
            segment = [];
            continue;
        }
        if (!segment.length) segments.push(segment);
        segment.push({
            x: ((index + 0.5) / values.length) * 100,
            y: 100 - (value / ceiling) * 100
        });
    }
    const line = (points: typeof segment) =>
        points.map(({ x, y }, index) => `${index ? 'L' : 'M'}${x},${y}`).join(' ');
    return {
        line: segments.map(line).join(' '),
        area: segments
            .map((points) => `${line(points)} L${points.at(-1)!.x},100 L${points[0].x},100 Z`)
            .join(' ')
    };
}

/** Label the actual bucket start in the chosen timezone; never imply local calendar-day buckets. */
export function metricPeriodLabels(
    points: readonly { startAt: number }[],
    days: 1 | 7 | 30,
    timeZone: string
) {
    const stride = days === 7 ? 1 : Math.max(1, Math.ceil(points.length / 6));
    const weekday = new Intl.DateTimeFormat('en-US', { timeZone, weekday: 'short' });
    const date = new Intl.DateTimeFormat('en-US', { timeZone, day: 'numeric' });
    const clock = new Intl.DateTimeFormat('en-US', { timeZone, hour: 'numeric' });
    return points.flatMap((point, index) =>
        index % stride
            ? []
            : [
                  {
                      index,
                      position: ((index + 0.5) / points.length) * 100,
                      label:
                          days === 1 ? clock.format(point.startAt) : weekday.format(point.startAt),
                      date: days === 30 ? date.format(point.startAt) : ''
                  }
              ]
    );
}

export function metricNumber(value: number): string {
    if (!Number.isFinite(value)) return '—';
    if (value > 0 && value < 0.1) return '<0.1';
    return numberFormat.format(value);
}

/** Normalize lobby-hours by captured wall time so partial buckets remain comparable. */
export function metricAverageLobbies(lobbyHours: number, capturedHours: number): number | null {
    if (!Number.isFinite(lobbyHours) || !Number.isFinite(capturedHours) || capturedHours <= 0)
        return null;
    return lobbyHours / capturedHours;
}

/** Use up to four whole-lobby intervals while retaining fractional averages in the data. */
export function metricLobbyAxis(maximumLobbies: number) {
    const maximum = Number.isFinite(maximumLobbies) ? Math.max(1, maximumLobbies) : 1;
    const targetStep = Math.max(1, maximum / 4);
    const magnitude = 10 ** Math.floor(Math.log10(targetStep));
    const step =
        [1, 2, 5, 10]
            .map((multiple) => multiple * magnitude)
            .find((value) => value >= targetStep) ?? 10 * magnitude;
    const intervals = Math.ceil(maximum / step);
    return {
        ceiling: intervals * step,
        ticks: Array.from({ length: intervals + 1 }, (_, index) => (intervals - index) * step)
    };
}

export function metricPercent(value: number, total: number): string {
    if (!Number.isFinite(value) || !Number.isFinite(total) || total <= 0) return '—';
    const percent = (100 * value) / total;
    return percent > 0 && percent < 0.1 ? '<0.1%' : `${percent.toFixed(1)}%`;
}

/** Input is hours; retain short, real observations instead of rounding them to zero. */
export function metricDuration(hours: number): string {
    if (!Number.isFinite(hours) || hours < 0) return '—';
    if (hours === 0) return '0 h';
    const seconds = hours * 3600;
    if (seconds < 1) return '<1 s';
    if (seconds < 60) return `${numberFormat.format(seconds)} s`;
    if (hours < 0.1) return `${numberFormat.format(seconds / 60)} min`;
    return `${numberFormat.format(hours)} h`;
}

/** Missing evidence always sorts last, in either direction. */
export function compareMetricValues(
    left: number | null,
    right: number | null,
    direction: 'asc' | 'desc'
): number {
    const a = left !== null && Number.isFinite(left) ? left : null;
    const b = right !== null && Number.isFinite(right) ? right : null;
    if (a === null || b === null) return a === b ? 0 : a === null ? 1 : -1;
    return (a - b) * (direction === 'asc' ? 1 : -1);
}

/** Clamp saved pages after filtering or polling changes the result count. */
export function metricPage<T>(rows: T[], requested: string | null, size = 15) {
    const parsed = Number(requested);
    const pages = Math.max(1, Math.ceil(rows.length / size));
    const page = Math.min(pages, Number.isSafeInteger(parsed) && parsed > 0 ? parsed : 1);
    const start = (page - 1) * size;
    return {
        page,
        pages,
        rows: rows.slice(start, start + size),
        start: rows.length ? start + 1 : 0,
        end: Math.min(rows.length, start + size),
        total: rows.length
    };
}