/**
 * Day-breaker: assigns a calendar workDate to a raw instant, in a given IANA
 * timezone (defaulting to UTC when the caller has none available, e.g. an
 * Assignment whose Position isn't bound to a physical Site). ReportedTimeBlock's
 * `workDate` is a pure calendar-date value (no time/tz component once stored),
 * so this always normalizes to a UTC-midnight Date representing that calendar day.
 */
export function toWorkDate(instant: Date, timezone = "UTC"): Date {
  const partsIn = (tz: string) =>
    new Intl.DateTimeFormat("en-CA", {
      timeZone: tz,
      year: "numeric",
      month: "2-digit",
      day: "2-digit",
    }).formatToParts(instant);

  let parts: Intl.DateTimeFormatPart[];
  try {
    parts = partsIn(timezone);
  } catch {
    // Intl.DateTimeFormat throws RangeError for an unknown/misconfigured IANA timezone, and
    // the timezone ultimately comes from DB (Site.timezone). Fall back to UTC so day-breaking
    // stays best-effort and a single bad value can't crash the triggering punch/void/unvoid
    // transaction (ADR-024).
    parts = partsIn("UTC");
  }

  const value = (type: string) => parts.find((p) => p.type === type)?.value;
  const year = value("year") ?? "1970";
  const month = value("month") ?? "01";
  const day = value("day") ?? "01";
  return new Date(`${year}-${month}-${day}T00:00:00.000Z`);
}

export function addDays(date: Date, days: number): Date {
  return new Date(date.getTime() + days * 24 * 60 * 60 * 1000);
}

/**
 * Public day-breaker API. `formReportedBlocks` requires the caller to pass the `workDate` it
 * computes, which must use exactly these semantics — so consumers resolving that input reach for the
 * same helpers rather than reimplementing them. Bundled into one object to keep the module registry
 * namespace clean (mirrors the `jpTimeClassificationStrategy` export precedent).
 */
export const dayBreaker = { toWorkDate, addDays };