import { EMPTY } from "./placeholder";

/**
 * Extract the date portion (YYYY-MM-DD) of an ISO date/datetime string in
 * the user's local timezone — the same calendar day that `formatDate` would
 * render. Use this to prefill date-field form state (the YYYY-MM-DD strings
 * `parseDate` accepts) so the prefill matches what the detail page is
 * displaying.
 *
 * If the value is already a `YYYY-MM-DD` string (no time), it's returned
 * verbatim. For ISO datetimes, the local-tz extraction prevents the
 * "midnight-UTC stored, displays as previous day" off-by-one we otherwise hit
 * for dates west of UTC.
 */
export function toDateInputValue(value: string | null | undefined): string {
  if (!value) return "";
  if (/^\d{4}-\d{2}-\d{2}$/.test(value)) return value;
  const date = new Date(value);
  if (isNaN(date.getTime())) return value;
  const yyyy = date.getFullYear();
  const mm = String(date.getMonth() + 1).padStart(2, "0");
  const dd = String(date.getDate()).padStart(2, "0");
  return `${yyyy}-${mm}-${dd}`;
}

/**
 * Format a date string consistently across the app.
 *
 * Uses the same formatting logic as the app-shell DescriptionCard `type: "date"`
 * field so that dates look identical in both detail views and tables.
 */
export function formatDate(
  value: string | Date | null | undefined,
  style: "short" | "medium" | "long" | "datetime" = "medium",
): string {
  if (!value) return EMPTY;

  // Date-only "YYYY-MM-DD" values must be parsed as a local-tz date.
  // `new Date("YYYY-MM-DD")` interprets the string as UTC midnight, which then
  // shifts ±1 day when fed through `toLocaleDateString` in non-UTC locales —
  // e.g. a stored date "2026-05-03" displays as "May 2" in PST. Constructing
  // the Date from year/month/day pins it to local midnight so the display
  // matches the underlying calendar day in any timezone.
  let date: Date;
  if (value instanceof Date) {
    // Preserve the original instant (incl. milliseconds); re-parsing via
    // `new Date(value)` would round-trip through `Date#toString()`.
    date = value;
  } else if (/^\d{4}-\d{2}-\d{2}$/.test(value)) {
    const [y, m, d] = value.split("-").map(Number);
    date = new Date(y, m - 1, d);
  } else {
    date = new Date(value);
  }
  if (isNaN(date.getTime())) return typeof value === "string" ? value : EMPTY;

  const options: Record<string, Intl.DateTimeFormatOptions> = {
    short: { month: "numeric", day: "numeric", year: "2-digit" },
    medium: { month: "short", day: "numeric", year: "numeric" },
    long: { weekday: "long", month: "long", day: "numeric", year: "numeric" },
    datetime: {
      month: "short",
      day: "numeric",
      year: "numeric",
      hour: "numeric",
      minute: "2-digit",
    },
  };

  if (style === "datetime") {
    return date.toLocaleString(undefined, options[style]);
  }

  return date.toLocaleDateString(undefined, options[style]);
}