Holiday calculation for iOS

holiday.swift

// Playground - noun: a place where people can play

// This is free and unencumbered software released into the public domain.
// Anyone is free to copy, modify, publish, use, compile, sell, or
// distribute this software, either in source code form or as a compiled
// binary, for any purpose, commercial or non-commercial, and by any
// means.

// This playground calculates a set of opening hours keys, such as "every friday",
// "2. day in month friday", "easter sunday" etc, which can be used to figure out
// when something is open or closed, taking holidays etc into account

import Foundation

// The Anonymous Gregorian algorithm
func easter(Y : Int) -> NSDateComponents {
  let a = Y % 19
  let b = Int(floor(Double(Y) / 100))
  let c = Y % 100
  let d = Int(floor(Double(b) / 4))
  let e = b % 4
  let f = Int(floor(Double(b+8) / 25))
  let g = Int(floor(Double(b-f+1) / 3))
  let h = (19*a + b - d - g + 15) % 30
  let i = Int(floor(Double(c) / 4))
  let k = c % 4
  let L = (32 + 2*e + 2*i - h - k) % 7
  let m = Int(floor(Double(a + 11*h + 22*L) / 451))
  let components = NSDateComponents()
  components.year = Y
  components.month = Int(floor(Double(h + L - 7*m + 114) / 31))
  components.day = ((h + L - 7*m + 114) % 31) + 1
  components.timeZone = NSTimeZone(forSecondsFromGMT: 0)
  return components
}

// Compare two date components
func compareDate(a : NSDateComponents, b : NSDateComponents) -> Bool {
  return a.day == b.day && a.month == b.month && a.year == b.year
}

// Calculate which date keys a date belongs to
func dateKey(date: NSDate) -> Array<String> {
  var keys = Array<String>()
  let cal = NSCalendar(calendarIdentifier: NSGregorianCalendar)!
  let dateflags: NSCalendarUnit = .DayCalendarUnit | .MonthCalendarUnit | .YearCalendarUnit
  let com = cal.components(dateflags, fromDate: date)
  if com.day == 1 && com.month == 1 {
    keys.append("Hver 1. januar")
  } else if com.day == 31 && com.month == 12 {
    keys.append("Hver 31. december")
  } else if com.day == 26 && com.month == 12 {
    keys.append("Hver 26. december")
  } else if com.day == 25 && com.month == 12 {
    keys.append("Hver 25. december")
  } else if com.day == 24 && com.month == 12 {
    keys.append("Hver 24. december")
  } else {  // continue to easter calculations
    // Calculate all the danish holidays that depend on easter
    let easterSunday = easter(com.year)
    let easterDate = cal.dateFromComponents(easterSunday)!
    let a = NSDateComponents()
    a.day = -3
    let maundyThursday = cal.components(dateflags, fromDate: cal.dateByAddingComponents(a, toDate: easterDate, options: nil)!)
    a.day = -2
    let goodFriday = cal.components(dateflags, fromDate: cal.dateByAddingComponents(a, toDate: easterDate, options: nil)!)
    a.day = 1
    let easterMonday = cal.components(dateflags, fromDate: cal.dateByAddingComponents(a, toDate: easterDate, options: nil)!)
    a.day = 3*7+5
    let greatPrayerDay = cal.components(dateflags, fromDate: cal.dateByAddingComponents(a, toDate: easterDate, options: nil)!)
    a.day = 5*7+4
    let ascensionThursday = cal.components(dateflags, fromDate: cal.dateByAddingComponents(a, toDate: easterDate, options: nil)!)
    a.day = 7*7
    let pentecostDate = cal.dateByAddingComponents(a, toDate: easterDate, options: nil)!
    let pentecostDay = cal.components(dateflags, fromDate: pentecostDate)
    a.day = 1
    let whitMonday = cal.components(dateflags, fromDate: cal.dateByAddingComponents(a, toDate: pentecostDate, options: nil)!)
    
    if compareDate(easterSunday, com) {
      keys.append("Hver Påskedag")
    } else if compareDate(maundyThursday, com) {
      keys.append("Hver Skærtorsdag")
    } else if compareDate(goodFriday, com) {
      keys.append("Hver Langfredag")
    } else if compareDate(easterMonday, com) {
      keys.append("Hver 2. påskedag")
    } else if compareDate(greatPrayerDay, com) {
      keys.append("Hver St. Bededag")
    } else if compareDate(ascensionThursday, com) {
      keys.append("Hver Kr. Himmelfartsdag")
    } else if compareDate(pentecostDay, com) {
      keys.append("Hver Pinsedag")
    } else if compareDate(whitMonday, com) {
      keys.append("Hver 2. pinsedag")
    } else if com.day == 5 && com.month == 6 {
      keys.append("Hver Grundlovsdag (5/6)")
    } else if com.day == 1 && com.month == 5 {
      // make sure easter based holidays are checked first
      // this may collide, ie. in 2015
      keys.append("Hver 1. maj")
    } else {  // continue to normal weekdays
      let danishweekdays = [ "", "Søndag", "Mandag", "Tirsdag", "Onsdag", "Torsdag", "Fredag", "Lørdag" ]  // 1 indexed, sunday first
      let ordinals = [ "", "1. i måneden", "2. i måneden", "3. i måneden", "4. i måneden", "5. i måneden" ]
      
      let weekdayflags: NSCalendarUnit = .WeekdayCalendarUnit | .WeekdayOrdinalCalendarUnit
      let weekday = cal.components(weekdayflags, fromDate: date)
      keys.append("Hver \(danishweekdays[weekday.weekday])")
      keys.append("\(ordinals[weekday.weekdayOrdinal]) \(danishweekdays[weekday.weekday])")
      
      // Calculate the every other weekday of this year
      let newyear = NSDateComponents()
      newyear.day = 1
      newyear.month = 1
      newyear.year = com.year
      newyear.timeZone = NSTimeZone(forSecondsFromGMT: 0)
      let newyearDate = cal.dateFromComponents(newyear)!
      let newyearWeekday = cal.components(weekdayflags, fromDate: newyearDate)
      let weekdayOffset = weekday.weekday-newyearWeekday.weekday
      
      let a = NSDateComponents()
      for i in 0..<27 {
        a.day = 14*i+weekdayOffset
        let t = cal.dateByAddingComponents(a, toDate: newyearDate, options: nil)
        let datecom = cal.components(dateflags, fromDate: t!)
        if compareDate(datecom, com) {
          keys.append("Hver anden \(danishweekdays[weekday.weekday])")
          break
        }
      }
    }
  }
  return keys
}

func dateFrom(year: Int, month: Int, date: Int) -> NSDate {
  let a = NSDateComponents()
  a.day = date
  a.month = month
  a.year = year
  a.timeZone = NSTimeZone(forSecondsFromGMT: 0)
  let cal = NSCalendar(calendarIdentifier: NSGregorianCalendar)!
  return cal.dateFromComponents(a)!
}

println(dateKey(dateFrom(2015, 1, 2)))
println(dateKey(dateFrom(2015, 1, 9)))
println(dateKey(dateFrom(2015, 5, 1)))
// Expected output:
//[Hver Fredag, 1. i måneden Fredag, Hver anden Fredag]
//[Hver Fredag, 2. i måneden Fredag]
//[Hver St. Bededag]

println(dateKey(NSDate()))