/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License;
 * you may not use this file except in compliance with the Elastic License.
 */

import moment from 'moment';

const d = moment.duration;
const roundingRules = [
  [ d(500, 'ms'), d(100, 'ms') ],
  [ d(5, 'second'), d(1, 'second') ],
  [ d(7.5, 'second'), d(5, 'second') ],
  [ d(15, 'second'), d(10, 'second') ],
  [ d(45, 'second'), d(30, 'second') ],
  [ d(3, 'minute'), d(1, 'minute') ],
  [ d(9, 'minute'), d(5, 'minute') ],
  [ d(20, 'minute'), d(10, 'minute') ],
  [ d(45, 'minute'), d(30, 'minute') ],
  [ d(2, 'hour'), d(1, 'hour') ],
  [ d(6, 'hour'), d(3, 'hour') ],
  [ d(24, 'hour'), d(12, 'hour') ],
  [ d(1, 'week'), d(1, 'd') ],
  [ d(3, 'week'), d(1, 'week') ],
  [ d(1, 'year'), d(1, 'month') ],
  [ Infinity, d(1, 'year') ]
];

function find(rules, check) {
  function pick(buckets, duration) {
    const target = duration / buckets;
    let lastResp;

    for (let i = 0; i < rules.length; i++) {
      const rule = rules[i];
      const resp = check(rule[0], rule[1], target);

      if (resp == null) {
        if (lastResp) { return lastResp; }
        break;
      }

      lastResp = resp;
    }

    // fallback to just a number of milliseconds, ensure ms is >= 1
    const ms = Math.max(Math.floor(target), 1);
    return moment.duration(ms, 'ms');
  }

  return function (buckets, duration) {
    const interval = pick(buckets, duration);
    if (interval) { return moment.duration(interval._data); }
  };
}

const revRoundingRules = roundingRules.slice(0).reverse();

/*
 * 24 hours: 600 seconds
 * 12 hours: 300 seconds
 * 4 hours: 60 seconds
 * 1 hour: 30 seconds
 * 15 minutes: 10 seconds
 */
export const calculateAuto = find(revRoundingRules, (bound, interval, target) => {
  if (bound > target) {
    return interval;
  }
});