/**
 * Parses a human-friendly duration string (e.g., '30m', '1h', '2d') into an ISO date string
 * representing that duration ago from now.
 *
 * @param duration - Duration string with format: <number><unit>
 *                   Supported units: m (minutes), h (hours), d (days)
 * @returns ISO date string representing the time that duration ago
 * @throws Error if the duration format is invalid
 */
export const parseTimeDuration = (duration: string): string => {
  const match = /^(\d+)([dhm])$/.exec(duration);

  if (!match) {
    throw new Error(
      'Invalid time duration format. Expected format: <number><unit>, where unit is m (minutes), h (hours), or d (days). Examples: 30m, 1h, 2d',
    );
  }

  const value = Number.parseInt(match[1], 10);
  const unit = match[2];

  if (value <= 0) {
    throw new Error('Time duration value must be greater than 0.');
  }

  let milliseconds: number;
  switch (unit) {
    case 'm':
      milliseconds = value * 60 * 1000; // minutes to ms
      break;
    case 'h':
      milliseconds = value * 60 * 60 * 1000; // hours to ms
      break;
    case 'd':
      milliseconds = value * 24 * 60 * 60 * 1000; // days to ms
      break;
    default:
      throw new Error(`Unsupported time unit: ${unit}`);
  }

  const fromDate = new Date(Date.now() - milliseconds);
  return fromDate.toISOString();
};