WeekdayOfMonth.hs

{-# LANGUAGE CPP #-}
{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE ViewPatterns #-}

#include "thyme.h"

module Data.Thyme.Calendar.WeekdayOfMonth where

import Prelude
import Control.Applicative
import Control.DeepSeq
import Control.Lens
import Control.Monad
import Data.AffineSpace
import Data.Data
import Data.Thyme.Calendar
import Data.Thyme.Calendar.Internal
import Data.Thyme.TH
import System.Random
import Test.QuickCheck

data WeekdayOfMonth = WeekdayOfMonth
    { womYear :: {-# UNPACK #-}!Year
    , womMonth :: {-# UNPACK #-}!Month
    , womNth :: {-# UNPACK #-}!Int -- ^ ±1–5, negative means n-th last
    , womDayOfWeek :: {-# UNPACK #-}!DayOfWeek
    } deriving (INSTANCES_USUAL, Show)

instance NFData WeekdayOfMonth

instance Bounded WeekdayOfMonth where
    minBound = minBound ^. weekdayOfMonth
    maxBound = maxBound ^. weekdayOfMonth

instance Random WeekdayOfMonth where
    randomR = randomIsoR weekdayOfMonth
    random = over _1 (^. weekdayOfMonth) . random

instance Arbitrary WeekdayOfMonth where
    arbitrary = view weekdayOfMonth <$> arbitrary

{-# INLINE weekdayOfMonth #-}
weekdayOfMonth :: Iso' Day WeekdayOfMonth
weekdayOfMonth = iso toWeekday fromWeekday where

    {-# INLINEABLE toWeekday #-}
    toWeekday :: Day -> WeekdayOfMonth
    toWeekday day@(view ordinalDate -> ord) = WeekdayOfMonth y m n wd where
        YearMonthDay y m d = ord ^. yearMonthDay
        WeekDate _ _ wd = toWeekOrdinal ord day
        n = div (d - 1) 7

    {-# INLINEABLE fromWeekday #-}
    fromWeekday :: WeekdayOfMonth -> Day
    fromWeekday (WeekdayOfMonth y m n wd) = refDay .+^ s * offset where
        refOrd = yearMonthDay # YearMonthDay y m
            (if n < 0 then monthLength (isLeapYear y) m else 1)
        refDay = ordinalDate # refOrd
        WeekDate _ _ wd1 = toWeekOrdinal refOrd refDay
        s = signum n
        wo = s * (wd - wd1)
        offset = (abs n - 1) * 7 + if wo < 0 then wo + 7 else wo

{-# INLINEABLE weekdayOfMonthValid #-}
weekdayOfMonthValid :: WeekdayOfMonth -> Maybe Day
weekdayOfMonthValid (WeekdayOfMonth y m n wd) = (refDay .+^ s * offset)
        <$ guard (n /= 0 && 1 <= wd && wd <= 7 && offset < len) where
    len = monthLength (isLeapYear y) m
    refOrd = yearMonthDay # YearMonthDay y m (if n < 0 then len else 1)
    refDay = ordinalDate # refOrd
    WeekDate _ _ wd1 = toWeekOrdinal refOrd refDay
    s = signum n
    wo = s * (wd - wd1)
    offset = (abs n - 1) * 7 + if wo < 0 then wo + 7 else wo

-- * Lenses
thymeLenses ''WeekdayOfMonth