source: node_modules/postgres-interval/index.js

'use strict'

var extend = require('xtend/mutable')

module.exports = PostgresInterval

function PostgresInterval (raw) {
  if (!(this instanceof PostgresInterval)) {
    return new PostgresInterval(raw)
  }
  extend(this, parse(raw))
}
var properties = ['seconds', 'minutes', 'hours', 'days', 'months', 'years']
PostgresInterval.prototype.toPostgres = function () {
  var filtered = properties.filter(this.hasOwnProperty, this)

  // In addition to `properties`, we need to account for fractions of seconds.
  if (this.milliseconds && filtered.indexOf('seconds') < 0) {
    filtered.push('seconds')
  }

  if (filtered.length === 0) return '0'
  return filtered
    .map(function (property) {
      var value = this[property] || 0

      // Account for fractional part of seconds,
      // remove trailing zeroes.
      if (property === 'seconds' && this.milliseconds) {
        value = (value + this.milliseconds / 1000).toFixed(6).replace(/\.?0+$/, '')
      }

      return value + ' ' + property
    }, this)
    .join(' ')
}

var propertiesISOEquivalent = {
  years: 'Y',
  months: 'M',
  days: 'D',
  hours: 'H',
  minutes: 'M',
  seconds: 'S'
}
var dateProperties = ['years', 'months', 'days']
var timeProperties = ['hours', 'minutes', 'seconds']
// according to ISO 8601
PostgresInterval.prototype.toISOString = PostgresInterval.prototype.toISO = function () {
  var datePart = dateProperties
    .map(buildProperty, this)
    .join('')

  var timePart = timeProperties
    .map(buildProperty, this)
    .join('')

  return 'P' + datePart + 'T' + timePart

  function buildProperty (property) {
    var value = this[property] || 0

    // Account for fractional part of seconds,
    // remove trailing zeroes.
    if (property === 'seconds' && this.milliseconds) {
      value = (value + this.milliseconds / 1000).toFixed(6).replace(/0+$/, '')
    }

    return value + propertiesISOEquivalent[property]
  }
}

var NUMBER = '([+-]?\\d+)'
var YEAR = NUMBER + '\\s+years?'
var MONTH = NUMBER + '\\s+mons?'
var DAY = NUMBER + '\\s+days?'
var TIME = '([+-])?([\\d]*):(\\d\\d):(\\d\\d)\\.?(\\d{1,6})?'
var INTERVAL = new RegExp([YEAR, MONTH, DAY, TIME].map(function (regexString) {
  return '(' + regexString + ')?'
})
  .join('\\s*'))

// Positions of values in regex match
var positions = {
  years: 2,
  months: 4,
  days: 6,
  hours: 9,
  minutes: 10,
  seconds: 11,
  milliseconds: 12
}
// We can use negative time
var negatives = ['hours', 'minutes', 'seconds', 'milliseconds']

function parseMilliseconds (fraction) {
  // add omitted zeroes
  var microseconds = fraction + '000000'.slice(fraction.length)
  return parseInt(microseconds, 10) / 1000
}

function parse (interval) {
  if (!interval) return {}
  var matches = INTERVAL.exec(interval)
  var isNegative = matches[8] === '-'
  return Object.keys(positions)
    .reduce(function (parsed, property) {
      var position = positions[property]
      var value = matches[position]
      // no empty string
      if (!value) return parsed
      // milliseconds are actually microseconds (up to 6 digits)
      // with omitted trailing zeroes.
      value = property === 'milliseconds'
        ? parseMilliseconds(value)
        : parseInt(value, 10)
      // no zeros
      if (!value) return parsed
      if (isNegative && ~negatives.indexOf(property)) {
        value *= -1
      }
      parsed[property] = value
      return parsed
    }, {})
}