import { defaultLocale } from "./_lib/defaultLocale.mjs";
import { getDefaultOptions } from "./_lib/defaultOptions.mjs";

/**
 * The {@link formatDuration} function options.
 */

const defaultFormat = [
  "years",
  "months",
  "weeks",
  "days",
  "hours",
  "minutes",
  "seconds",
];

/**
 * @name formatDuration
 * @category Common Helpers
 * @summary Formats a duration in human-readable format
 *
 * @description
 * Return human-readable duration string i.e. "9 months 2 days"
 *
 * @typeParam DateType - The `Date` type, the function operates on. Gets inferred from passed arguments. Allows to use extensions like [`UTCDate`](https://github.com/date-fns/utc).
 *
 * @param duration - The duration to format
 * @param options - An object with options.
 *
 * @returns The formatted date string
 *
 * @example
 * // Format full duration
 * formatDuration({
 *   years: 2,
 *   months: 9,
 *   weeks: 1,
 *   days: 7,
 *   hours: 5,
 *   minutes: 9,
 *   seconds: 30
 * })
 * //=> '2 years 9 months 1 week 7 days 5 hours 9 minutes 30 seconds'
 *
 * @example
 * // Format partial duration
 * formatDuration({ months: 9, days: 2 })
 * //=> '9 months 2 days'
 *
 * @example
 * // Customize the format
 * formatDuration(
 *   {
 *     years: 2,
 *     months: 9,
 *     weeks: 1,
 *     days: 7,
 *     hours: 5,
 *     minutes: 9,
 *     seconds: 30
 *   },
 *   { format: ['months', 'weeks'] }
 * ) === '9 months 1 week'
 *
 * @example
 * // Customize the zeros presence
 * formatDuration({ years: 0, months: 9 })
 * //=> '9 months'
 * formatDuration({ years: 0, months: 9 }, { zero: true })
 * //=> '0 years 9 months'
 *
 * @example
 * // Customize the delimiter
 * formatDuration({ years: 2, months: 9, weeks: 3 }, { delimiter: ', ' })
 * //=> '2 years, 9 months, 3 weeks'
 */
export function formatDuration(duration, options) {
  const defaultOptions = getDefaultOptions();
  const locale = options?.locale ?? defaultOptions.locale ?? defaultLocale;
  const format = options?.format ?? defaultFormat;
  const zero = options?.zero ?? false;
  const delimiter = options?.delimiter ?? " ";

  if (!locale.formatDistance) {
    return "";
  }

  const result = format
    .reduce((acc, unit) => {
      const token = `x${unit.replace(/(^.)/, (m) => m.toUpperCase())}`;
      const value = duration[unit];
      if (value !== undefined && (zero || duration[unit])) {
        return acc.concat(locale.formatDistance(token, value));
      }
      return acc;
    }, [])
    .join(delimiter);

  return result;
}

// Fallback for modularized imports:
export default formatDuration;