// - render the proxy (act-as) session duration the server now sends as a real number.
//
// Before this the duration lived only inside the human description ("...(duration 252000ms)"), so the
// feed could print that sentence verbatim but never reformat or sort by it without regexing prose.
//
// UNDEFINED IS NOT ZERO, and that distinction is the whole reason the structured field exists.
// Virtually every row in this feed - reads, changes, sign-ins - has NO duration; only a proxy access-end
// does. A `?? 0` anywhere in this path would stamp "0s" onto all of them. Zero itself is a legitimate
// value (a session opened and closed inside one millisecond), so it must render, which is exactly why
// "absent" cannot be represented as 0.
//
// Anything nonsensical - NaN, Infinity, negative (a clock problem, not a fact about the session) -
// degrades to undefined so the caller shows nothing. A patient's own access log is the last place to
// display "NaN" or assert a negative duration.
export function formatSessionDuration(durationMs: number | undefined): string | undefined {
    if (durationMs === undefined || !Number.isFinite(durationMs) || durationMs < 0) {
        return undefined;
    }

    const totalSeconds = Math.round(durationMs / 1000);
    const hours = Math.floor(totalSeconds / 3600);
    const minutes = Math.floor((totalSeconds % 3600) / 60);
    const seconds = totalSeconds % 60;

    // Two units at most: "1h 1m" and "4m 12s" read cleanly, "1h 1m 12s" is noise on a feed row.
    if (hours > 0) {
        return minutes > 0 ? `${hours}h ${minutes}m` : `${hours}h`;
    }
    if (minutes > 0) {
        return seconds > 0 ? `${minutes}m ${seconds}s` : `${minutes}m`;
    }
    return `${seconds}s`;
}