export type Unit =
  | 'second'
  | 'minute'
  | 'hour'
  | 'day'
  | 'week'
  | 'month'
  | 'quarter'
  | 'year';

const MS_PER_SECOND = 1e3;
const SECS_PER_MIN = 60;
const SECS_PER_HOUR = SECS_PER_MIN * 60;
const SECS_PER_DAY = SECS_PER_HOUR * 24;
const SECS_PER_WEEK = SECS_PER_DAY * 7;

export function selectUnit(
  from: Date | number,
  to: Date | number = Date.now(),
  thresholds: Partial<Thresholds> = {}
): {value: number; unit: Unit} {
  const resolvedThresholds: Thresholds = {
    ...DEFAULT_THRESHOLDS,
    ...(thresholds || {}),
  };
  const secs = (+from - +to) / MS_PER_SECOND;
  if (Math.abs(secs) < resolvedThresholds.second) {
    return {
      value: Math.round(secs),
      unit: 'second',
    };
  }
  const mins = secs / SECS_PER_MIN;
  if (Math.abs(mins) < resolvedThresholds.minute) {
    return {
      value: Math.round(mins),
      unit: 'minute',
    };
  }
  const hours = secs / SECS_PER_HOUR;
  if (Math.abs(hours) < resolvedThresholds.hour) {
    return {
      value: Math.round(hours),
      unit: 'hour',
    };
  }

  const days = secs / SECS_PER_DAY;
  if (Math.abs(days) < resolvedThresholds.day) {
    return {
      value: Math.round(days),
      unit: 'day',
    };
  }
  const fromDate = new Date(from);
  const toDate = new Date(to);

  const years = fromDate.getFullYear() - toDate.getFullYear();
  if (Math.round(Math.abs(years)) > 0) {
    return {
      value: Math.round(years),
      unit: 'year',
    };
  }

  const months = years * 12 + fromDate.getMonth() - toDate.getMonth();
  if (Math.round(Math.abs(months)) > 0) {
    return {
      value: Math.round(months),
      unit: 'month',
    };
  }
  const weeks = secs / SECS_PER_WEEK;

  return {
    value: Math.round(weeks),
    unit: 'week',
  };
}

type Thresholds = Record<'second' | 'minute' | 'hour' | 'day', number>;

export const DEFAULT_THRESHOLDS: Thresholds = {
  second: 45, // seconds to minute
  minute: 45, // minutes to hour
  hour: 22, // hour to day
  day: 5, // day to week
};