// @flow

export type Interval = {
  years: number,
  months: number,
  days: number,
  hours: number,
  minutes: number,
  seconds: number,
};

// Regexp construction enhanced from `postgres-interval`, which is licensed
// under the MIT license and is copyright (c) Ben Drucker <bvdrucker@gmail.com>
// (bendrucker.me).

const NUMBER = "([+-]?\\d+)";
const YEAR = `${NUMBER}\\s+years?`;
const MONTH = `${NUMBER}\\s+mons?`;
const DAY = `${NUMBER}\\s+days?`;
// NOTE: PostgreSQL automatically overflows seconds into minutes and minutes
// into hours, so we can rely on minutes and seconds always being 2 digits
// (plus decimal for seconds). The overflow stops at hours - hours do not
// overflow into days, so could be arbitrarily long.
const TIME = "([+-])?(\\d+):(\\d\\d):(\\d\\d(?:\\.\\d{1,6})?)";

const INTERVAL = new RegExp(
  "^" +
    // All parts of an interval are optional
    [YEAR, MONTH, DAY, TIME].map(str => "(?:" + str + ")?").join("\\s*") +
    "$"
);

export function parseInterval(interval: string): Interval {
  const [, years, months, days, plusMinusTime, hours, minutes, seconds] =
    INTERVAL.exec(interval || "") || [];

  const timeMultiplier = plusMinusTime === "-" ? -1 : 1;

  return {
    years: years ? parseInt(years, 10) : 0,
    months: months ? parseInt(months, 10) : 0,
    days: days ? parseInt(days, 10) : 0,
    hours: hours ? timeMultiplier * parseInt(hours, 10) : 0,
    minutes: minutes ? timeMultiplier * parseInt(minutes, 10) : 0,
    // Seconds can be decimal; all other values are integer
    seconds: seconds ? timeMultiplier * parseFloat(seconds) : 0,
  };
}