export type DateLike = string | number | Date | null | undefined;

const hasTimezoneDesignator = (value: string): boolean => {
  return /[zZ]$/.test(value) || /[+-]\d{2}:?\d{2}$/.test(value);
};

const truncateExcessFraction = (value: string): string => {
  // Keep at most 3 fractional digits for milliseconds
  return value.replace(/(\.\d{3})\d+/, '$1');
};

export const parseUtcDate = (input: DateLike): Date => {
  if (input == null) return new Date(Number.NaN);
  if (input instanceof Date) return new Date(input.getTime());
  if (typeof input === 'number') {
    const millis = input < 1e12 ? input * 1000 : input;
    return new Date(millis);
  }

  const raw = String(input).trim();
  if (!raw) return new Date(Number.NaN);

  // Numeric strings (epoch seconds or millis)
  if (/^\d{10}$/.test(raw)) return new Date(Number(raw) * 1000);
  if (/^\d{13}$/.test(raw)) return new Date(Number(raw));

  // Already has timezone; trust the browser parser
  if (hasTimezoneDesignator(raw)) return new Date(raw);

  // Normalize common forms: "YYYY-MM-DD HH:MM:SS[.fff...]" -> ISO-like
  let norm = raw.replace(' ', 'T');
  norm = truncateExcessFraction(norm);

  // Date-only string -> treat as UTC midnight
  if (/^\d{4}-\d{2}-\d{2}$/.test(norm)) {
    return new Date(`${norm}T00:00:00Z`);
  }

  // If ISO-like without timezone, explicitly mark as UTC
  if (/^\d{4}-\d{2}-\d{2}T/.test(norm) && !hasTimezoneDesignator(norm)) {
    return new Date(`${norm}Z`);
  }

  // Fallback to native parsing
  return new Date(norm);
};

export const formatLocalDate = (value: DateLike, options?: Intl.DateTimeFormatOptions): string => {
  const d = value instanceof Date ? value : parseUtcDate(value);
  if (Number.isNaN(d.getTime())) return 'N/A';
  return d.toLocaleDateString(undefined, options);
};

export const formatLocalDateTime = (value: DateLike, options?: Intl.DateTimeFormatOptions): string => {
  const d = value instanceof Date ? value : parseUtcDate(value);
  if (Number.isNaN(d.getTime())) return 'N/A';
  const base: Intl.DateTimeFormatOptions = {
    year: 'numeric',
    month: 'long',
    day: 'numeric',
    hour: 'numeric',
    minute: '2-digit',
    timeZoneName: 'short',
  };
  return d.toLocaleString(undefined, { ...base, ...(options || {}) });
};