import dayjs from 'dayjs';

/**
 * Doormile timestamps are IST (Asia/Kolkata) wall-clock stored in Postgres
 * `timestamp without time zone` columns. Some responses come back with a
 * trailing Z/offset anyway — a known Go+pgx footgun where a naive DB timestamp
 * loads into `time.Time` under the UTC location and gets marshalled with a
 * false "Z" suffix. dayjs reads a Z-suffixed string as a real UTC instant and
 * converts it to the browser's local time, adding a spurious +5:30 on top of
 * digits that were already correct IST.
 *
 * Stripping any trailing zone marker before parsing makes both cases — truly
 * naive, or naive-with-false-Z — render and bucket identically as the raw
 * wall-clock digits. Every page that displays or buckets a Doormile timestamp
 * must go through here, or two pages will disagree about which day a row is on.
 */
export const parseDoormileTimestamp = (raw) => {
  if (!raw) return dayjs(null);
  const stripped = String(raw).replace(/(Z|[+-]\d{2}:?\d{2})$/, '');
  return dayjs(stripped);
};

/** `raw` rendered in `format`, or `fallback` when the timestamp is unusable. */
export const formatDoormileTimestamp = (raw, format = 'DD MMM YYYY, hh:mm A', fallback = '—') => {
  const parsed = parseDoormileTimestamp(raw);
  return parsed.isValid() ? parsed.format(format) : fallback;
};

/** The calendar day (`YYYY-MM-DD`) a Doormile timestamp falls on. */
export const doormileDay = (raw) => {
  const parsed = parseDoormileTimestamp(raw);
  return parsed.isValid() ? parsed.format('YYYY-MM-DD') : undefined;
};