module.exports = parseFormat

var dayNames = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday']
var abbreviatedDayNames = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat']
var shortestDayNames = ['Su', 'Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa']
var monthNames = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December']
var abbreviatedMonthNames = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']

var regexDayNames = new RegExp(dayNames.join('|'), 'i')
var regexAbbreviatedDayNames = new RegExp(abbreviatedDayNames.join('|'), 'i')
var regexShortestDayNames = new RegExp('\\b(' + shortestDayNames.join('|') + ')\\b', 'i')
var regexMonthNames = new RegExp(monthNames.join('|'), 'i')
var regexAbbreviatedMonthNames = new RegExp(abbreviatedMonthNames.join('|'), 'i')

var regexFirstSecondThirdFourth = /(\d+)(st|nd|rd|th)\b/i
var regexEndian = /(\d{1,4})([/.-])(\d{1,2})[/.-](\d{1,4})/

var regexTimezone = /((\+|-)\d\d:?\d\d)$/
var amOrPm = '(' + ['AM?', 'PM?'].join('|') + ')'
var regexHoursWithLeadingZeroDigitMinutesSecondsAmPm = new RegExp('0\\d\\:\\d{1,2}\\:\\d{1,2}(\\s*)' + amOrPm, 'i')
var regexHoursWithLeadingZeroDigitMinutesAmPm = new RegExp('0\\d\\:\\d{1,2}(\\s*)' + amOrPm, 'i')
var regexHoursWithLeadingZeroDigitAmPm = new RegExp('0\\d(\\s*)' + amOrPm, 'i')
var regexHoursMinutesSecondsAmPm = new RegExp('\\d{1,2}\\:\\d{1,2}\\:\\d{1,2}(\\s*)' + amOrPm, 'i')
var regexHoursMinutesAmPm = new RegExp('\\d{1,2}\\:\\d{1,2}(\\s*)' + amOrPm, 'i')
var regexHoursAmPm = new RegExp('\\d{1,2}(\\s*)' + amOrPm, 'i')

var regexISO8601HoursWithLeadingZeroMinutesSecondsMilliseconds = /\d{2}:\d{2}:\d{2}\.\d{3}/
var regexISO8601HoursWithLeadingZeroMinutesSecondsCentiSeconds = /\d{2}:\d{2}:\d{2}\.\d{2}/
var regexISO8601HoursWithLeadingZeroMinutesSecondsDeciSeconds = /\d{2}:\d{2}:\d{2}\.\d{1}/
var regexHoursWithLeadingZeroMinutesSeconds = /0\d:\d{2}:\d{2}/
var regexHoursWithLeadingZeroMinutes = /0\d:\d{2}/
var regexHoursMinutesSeconds = /\d{1,2}:\d{2}:\d{2}/
var regexHoursMinutesSecondsMilliseconds = /\d{1,2}:\d{2}:\d{2}\.\d{3}/
var regexHoursMinutesSecondsCentiSeconds = /\d{1,2}:\d{2}:\d{2}\.\d{2}/
var regexHoursMinutesSecondsDeciSeconds = /\d{1,2}:\d{2}:\d{2}\.\d{1}/
var regexHoursMinutes = /\d{1,2}:\d{2}/
var regexYearLong = /\d{4}/
var regexDayLeadingZero = /0\d/
var regexDay = /\d{1,2}/
var regexYearShort = /\d{2}/

var regexDayShortMonthShort = /^([1-9])\/([1-9]|0[1-9])$/
var regexDayShortMonth = /^([1-9])\/(1[012])$/
var regexDayMonthShort = /^(0[1-9]|[12][0-9]|3[01])\/([1-9])$/
var regexDayMonth = /^(0[1-9]|[12][0-9]|3[01])\/(1[012]|0[1-9])$/

var regexMonthShortYearShort = /^([1-9])\/([1-9][0-9])$/
var regexMonthYearShort = /^(0[1-9]|1[012])\/([1-9][0-9])$/

var formatIncludesMonth = /([/][M]|[M][/]|[MM]|[MMMM])/

var regexFillingWords = /\b(at)\b/i

var regexUnixMillisecondTimestamp = /\d{13}/
var regexUnixTimestamp = /\d{10}/

// option defaults
var defaultOrder = {
  '/': 'MDY',
  '.': 'DMY',
  '-': 'YMD'
}

function parseFormat (dateString, options) {
  var format = dateString.toString()

  // default options
  options = options || {}
  options.preferredOrder = options.preferredOrder || defaultOrder

  // Unix Millisecond Timestamp ☛ x
  format = format.replace(regexUnixMillisecondTimestamp, 'x')
  // Unix Timestamp ☛ X
  format = format.replace(regexUnixTimestamp, 'X')

  // escape filling words
  format = format.replace(regexFillingWords, '[$1]')

  //  DAYS

  // Monday ☛ dddd
  format = format.replace(regexDayNames, 'dddd')
  // Mon ☛ ddd
  format = format.replace(regexAbbreviatedDayNames, 'ddd')
  // Mo ☛ dd
  format = format.replace(regexShortestDayNames, 'dd')

  // 1st, 2nd, 23rd ☛ do
  format = format.replace(regexFirstSecondThirdFourth, 'Do')

  // MONTHS

  // January ☛ MMMM
  format = format.replace(regexMonthNames, 'MMMM')
  // Jan ☛ MMM
  format = format.replace(regexAbbreviatedMonthNames, 'MMM')

  // replace endians, like 8/20/2010, 20.8.2010 or 2010-8-20
  format = format.replace(regexEndian, replaceEndian.bind(null, options))

  // TIME

  // timezone +02:00 ☛ Z
  format = format.replace(regexTimezone, 'Z')
  // 23:39:43.331 ☛ 'HH:mm:ss.SSS'
  format = format.replace(regexISO8601HoursWithLeadingZeroMinutesSecondsMilliseconds, 'HH:mm:ss.SSS')
  // 23:39:43.33 ☛ 'HH:mm:ss.SS'
  format = format.replace(regexISO8601HoursWithLeadingZeroMinutesSecondsCentiSeconds, 'HH:mm:ss.SS')
  // 23:39:43.3 ☛ 'HH:mm:ss.S'
  format = format.replace(regexISO8601HoursWithLeadingZeroMinutesSecondsDeciSeconds, 'HH:mm:ss.S')
  function replaceWithAmPm (timeFormat) {
    return function (match, whitespace, amPm) {
      return timeFormat + whitespace + (amPm[0].toUpperCase() === amPm[0] ? 'A' : 'a')
    }
  }
  // 05:30:20pm ☛ hh:mm:ssa
  format = format.replace(regexHoursWithLeadingZeroDigitMinutesSecondsAmPm, replaceWithAmPm('hh:mm:ss'))
  // 10:30:20pm ☛ h:mm:ssa
  format = format.replace(regexHoursMinutesSecondsAmPm, replaceWithAmPm('h:mm:ss'))
  // 05:30pm ☛ hh:mma
  format = format.replace(regexHoursWithLeadingZeroDigitMinutesAmPm, replaceWithAmPm('hh:mm'))
  // 10:30pm ☛ h:mma
  format = format.replace(regexHoursMinutesAmPm, replaceWithAmPm('h:mm'))
  // 05pm ☛ hha
  format = format.replace(regexHoursWithLeadingZeroDigitAmPm, replaceWithAmPm('hh'))
  // 10pm ☛ ha
  format = format.replace(regexHoursAmPm, replaceWithAmPm('h'))
  // 05:30:20 ☛ HH:mm:ss
  format = format.replace(regexHoursWithLeadingZeroMinutesSeconds, 'HH:mm:ss')
  // 5:30:20.222 ☛ H:mm:ss.SSS
  format = format.replace(regexHoursMinutesSecondsMilliseconds, 'H:mm:ss.SSS')
  // 5:30:20.22 ☛ H:mm:ss.SS
  format = format.replace(regexHoursMinutesSecondsCentiSeconds, 'H:mm:ss.SS')
  // 5:30:20.2 ☛ H:mm:ss.S
  format = format.replace(regexHoursMinutesSecondsDeciSeconds, 'H:mm:ss.S')
  // 10:30:20 ☛ H:mm:ss
  format = format.replace(regexHoursMinutesSeconds, 'H:mm:ss')
  // 05:30 ☛ H:mm
  format = format.replace(regexHoursWithLeadingZeroMinutes, 'HH:mm')
  // 10:30 ☛ HH:mm
  format = format.replace(regexHoursMinutes, 'H:mm')

  // do we still have numbers left?

  // Lets check for 4 digits first, these are years for sure
  format = format.replace(regexYearLong, 'YYYY')

  // check if both numbers are < 13, then it must be D/M
  format = format.replace(regexDayShortMonthShort, 'D/M')

  // check if first number is < 10 && last < 13, then it must be D/MM
  format = format.replace(regexDayShortMonth, 'D/MM')

  // check if last number is < 32 && last < 10, then it must be DD/M
  format = format.replace(regexDayMonthShort, 'DD/M')

  // check if both numbers are > 10, but first < 32 && last < 13, then it must be DD/MM
  format = format.replace(regexDayMonth, 'DD/MM')

  // check if first < 10 && last > 12, then it must be M/YY
  format = format.replace(regexMonthShortYearShort, 'M/YY')

  // check if first < 13 && last > 12, then it must be MM/YY
  format = format.replace(regexMonthYearShort, 'MM/YY')

  // to prevent 9.20 gets formated to D.Y, we format the complete date first, then go for the time
  if (format.match(formatIncludesMonth)) {
    var regexHoursDotWithLeadingZeroOrDoubleDigitMinutes = /0\d.\d{2}|\d{2}.\d{2}/
    var regexHoursDotMinutes = /\d{1}.\d{2}/

    format = format.replace(regexHoursDotWithLeadingZeroOrDoubleDigitMinutes, 'H.mm')
    format = format.replace(regexHoursDotMinutes, 'h.mm')
  }

  // now, the next number, if existing, must be a day
  format = format.replace(regexDayLeadingZero, 'DD')
  format = format.replace(regexDay, 'D')

  // last but not least, there could still be a year left
  format = format.replace(regexYearShort, 'YY')

  if (format.length < 1) {
    format = undefined
  }

  return format
}

// if we can't find an endian based on the separator, but
// there still is a short date with day, month & year,
// we try to make a smart decision to identify the order
function replaceEndian (options, matchedPart, first, separator, second, third) {
  var parts
  var hasSingleDigit = Math.min(first.length, second.length, third.length) === 1
  var hasQuadDigit = Math.max(first.length, second.length, third.length) === 4
  var preferredOrder = typeof options.preferredOrder === 'string' ? options.preferredOrder : options.preferredOrder[separator]

  first = parseInt(first, 10)
  second = parseInt(second, 10)
  third = parseInt(third, 10)
  parts = [first, second, third]
  preferredOrder = preferredOrder.toUpperCase()

  // If first is a year, order will always be Year-Month-Day
  if (first > 31) {
    parts[0] = hasQuadDigit ? 'YYYY' : 'YY'
    parts[1] = hasSingleDigit ? 'M' : 'MM'
    parts[2] = hasSingleDigit ? 'D' : 'DD'
    return parts.join(separator)
  }

  // Second will never be the year. And if it is a day,
  // the order will always be Month-Day-Year
  if (second > 12) {
    parts[0] = hasSingleDigit ? 'M' : 'MM'
    parts[1] = hasSingleDigit ? 'D' : 'DD'
    parts[2] = hasQuadDigit ? 'YYYY' : 'YY'
    return parts.join(separator)
  }

  // if third is a year ...
  if (third > 31) {
    parts[2] = hasQuadDigit ? 'YYYY' : 'YY'

    // ... try to find day in first and second.
    // If found, the remaining part is the month.
    if (preferredOrder[0] === 'M' && first < 13) {
      parts[0] = hasSingleDigit ? 'M' : 'MM'
      parts[1] = hasSingleDigit ? 'D' : 'DD'
      return parts.join(separator)
    }
    parts[0] = hasSingleDigit ? 'D' : 'DD'
    parts[1] = hasSingleDigit ? 'M' : 'MM'
    return parts.join(separator)
  }

  // if we had no luck until here, we use the preferred order
  parts[preferredOrder.indexOf('D')] = hasSingleDigit ? 'D' : 'DD'
  parts[preferredOrder.indexOf('M')] = hasSingleDigit ? 'M' : 'MM'
  parts[preferredOrder.indexOf('Y')] = hasQuadDigit ? 'YYYY' : 'YY'

  return parts.join(separator)
}