// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.
import { DAY, HOUR, MINUTE, SECOND, WEEK } from "./constants.ts";
function calculateMonthsDifference(from, to) {
  let months = (to.getFullYear() - from.getFullYear()) * 12 + (to.getMonth() - from.getMonth());
  if (to.getDate() < from.getDate()) {
    months--;
  }
  return months;
}
/**
 * Calculates the difference of the 2 given dates in various units. If the units
 * are omitted, it returns the difference in the all available units.
 *
 * @param from Year to calculate difference from.
 * @param to Year to calculate difference to.
 * @param options Options such as units to calculate difference in.
 * @returns The difference of the 2 given dates in various units.
 *
 * @example Basic usage
 * ```ts
 * import { difference } from "@std/datetime/difference";
 * import { assertEquals } from "@std/assert";
 *
 * const date0 = new Date("2018-05-14");
 * const date1 = new Date("2020-05-13");
 *
 * assertEquals(difference(date0, date1), {
 *   milliseconds: 63072000000,
 *   seconds: 63072000,
 *   minutes: 1051200,
 *   hours: 17520,
 *   days: 730,
 *   weeks: 104,
 *   months: 23,
 *   quarters: 7,
 *   years: 1
 * });
 * ```
 *
 * @example Calculate difference in specific units
 *
 * The `units` option defines which units to calculate the difference in.
 *
 * ```ts
 * import { difference } from "@std/datetime/difference";
 * import { assertEquals } from "@std/assert";
 *
 * const date0 = new Date("2018-05-14");
 * const date1 = new Date("2020-05-13");
 *
 * const result = difference(date0, date1, { units: ["days", "months", "years"] });
 *
 * assertEquals(result, {
 *   days: 730,
 *   months: 23,
 *   years: 1
 * });
 * ```
 */ export function difference(from, to, options) {
  [from, to] = from < to ? [
    from,
    to
  ] : [
    to,
    from
  ];
  const uniqueUnits = options?.units ? [
    ...new Set(options?.units)
  ] : [
    "milliseconds",
    "seconds",
    "minutes",
    "hours",
    "days",
    "weeks",
    "months",
    "quarters",
    "years"
  ];
  const differenceInMs = Math.abs(from.getTime() - to.getTime());
  const differences = {};
  for (const uniqueUnit of uniqueUnits){
    switch(uniqueUnit){
      case "milliseconds":
        differences.milliseconds = differenceInMs;
        break;
      case "seconds":
        differences.seconds = Math.floor(differenceInMs / SECOND);
        break;
      case "minutes":
        differences.minutes = Math.floor(differenceInMs / MINUTE);
        break;
      case "hours":
        differences.hours = Math.floor(differenceInMs / HOUR);
        break;
      case "days":
        differences.days = Math.floor(differenceInMs / DAY);
        break;
      case "weeks":
        differences.weeks = Math.floor(differenceInMs / WEEK);
        break;
      case "months":
        differences.months = calculateMonthsDifference(from, to);
        break;
      case "quarters":
        differences.quarters = Math.floor(differences.months !== undefined && differences.months / 3 || calculateMonthsDifference(from, to) / 3);
        break;
      case "years":
        differences.years = Math.floor(differences.months !== undefined && differences.months / 12 || calculateMonthsDifference(from, to) / 12);
        break;
    }
  }
  return differences;
}
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