import moment, { duration as d } from 'moment';

export function TimeBucketsCalcAutoIntervalProvider() {
  // these are the rounding rules used by roundInterval()

  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') ]
  ];

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

  function find(rules, check, last) {
    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 (!last) continue;
          if (lastResp) return lastResp;
          break;
        }

        if (!last) return resp;
        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);
    };
  }

  return {
    near: find(revRoundingRules, function near(bound, interval, target) {
      if (bound > target) return interval;
    }, true),

    lessThan: find(revRoundingRules, function (bound, interval, target) {
      if (interval < target) return interval;
    }),

    atLeast: find(revRoundingRules, function atLeast(bound, interval, target) {
      if (interval <= target) return interval;
    }),
  };
}
