// Shared date parsing for Stampli M/D/YY and MM/DD/YYYY formats.
// Stampli exports switched from MM/DD/YYYY to M/D/YY in 2026-06/07; both
// formats must parse, and anything else must be rejected (null), never
// passed through as a malformed string (payments-dashboard#65).

// Parse "M/D/YY" or "MM/DD/YYYY" into { year, month, day }, or null.
// Two-digit years are 2000-based. Validates the date is real (no 2/30).
export function parseMDY(value) {
  const match = /^(\d{1,2})\/(\d{1,2})\/(\d{2}|\d{4})$/.exec(String(value ?? "").trim());
  if (!match) return null;
  const month = parseInt(match[1], 10);
  const day = parseInt(match[2], 10);
  let year = parseInt(match[3], 10);
  if (match[3].length === 2) year += 2000;
  const dt = new Date(year, month - 1, day);
  if (dt.getFullYear() !== year || dt.getMonth() !== month - 1 || dt.getDate() !== day) {
    return null;
  }
  return { year, month, day };
}

// "YYYY-MM-DD" or null.
export function toISODate(value) {
  const p = parseMDY(value);
  if (!p) return null;
  return `${p.year}-${String(p.month).padStart(2, "0")}-${String(p.day).padStart(2, "0")}`;
}

// Canonical "MM/DD/YYYY" or null. Stored form for send_payment_on.
export function toCanonicalMDY(value) {
  const p = parseMDY(value);
  if (!p) return null;
  return `${String(p.month).padStart(2, "0")}/${String(p.day).padStart(2, "0")}/${p.year}`;
}

// Local-midnight Date or null. Replaces slackAppHome's parseMDYLocal, which
// built year-1926 dates from 2-digit years via new Date(26, ...).
export function parseMDYLocal(value) {
  const p = parseMDY(value);
  if (!p) return null;
  return new Date(p.year, p.month - 1, p.day);
}

// Local-midnight Date from a stored ISO "YYYY-MM-DD" (returned_date,
// paid_date), or null. new Date("YYYY-MM-DD") parses as UTC midnight and
// renders a day early in US-local display; this stays local like
// parseMDYLocal. Validates the date is real (no 2026-02-30).
export function parseISOLocal(value) {
  const match = /^(\d{4})-(\d{2})-(\d{2})$/.exec(String(value ?? "").trim());
  if (!match) return null;
  const year = parseInt(match[1], 10);
  const month = parseInt(match[2], 10);
  const day = parseInt(match[3], 10);
  const dt = new Date(year, month - 1, day);
  if (dt.getFullYear() !== year || dt.getMonth() !== month - 1 || dt.getDate() !== day) {
    return null;
  }
  return dt;
}

// Plausibility window for ingested send dates. Anything outside is treated
// as parser garbage and the row is rejected loudly rather than stored.
// Relative to the current year so it never expires (7 years back covers
// historical re-ingests; 2 years forward covers future-scheduled checks).
export function isPlausibleSendYear(value) {
  const p = parseMDY(value);
  if (p === null) return false;
  const now = new Date().getFullYear();
  return p.year >= now - 7 && p.year <= now + 2;
}