module HodaTime.InstantTest
(
  instantTests
)
where

import Test.Tasty
import Test.Tasty.HUnit
import Test.Tasty.QuickCheck as QC

import Data.HodaTime.Instant (Instant, fromSecondsSinceUnixEpoch, add, difference, minus)
import qualified Data.HodaTime.Duration as D
import Data.HodaTime.TimeZone (utc, timeZone)
import Data.HodaTime.ZonedDateTime (fromInstant, toLocalTime, toInstant, ZonedDateTime, year, month, day)
import Data.HodaTime.Calendar.Gregorian (Gregorian)
import Data.HodaTime.Calendar.Julian (Julian)
import Data.HodaTime.LocalTime (hour, minute, second)
import Data.Time.Clock.POSIX (getPOSIXTime, posixSecondsToUTCTime)
import Data.Time.Calendar (toGregorian)
import Data.Time.Calendar.Julian (toJulian)
import Data.Time.LocalTime (todHour, todMin, todSec, hoursToTimeZone, utcToLocalTime, LocalTime(..))

instantTests :: TestTree
instantTests = testGroup "Instant Tests" [unitTests, qcProps]

qcProps :: TestTree
qcProps = testGroup "(checked by QuickCheck)"
  [
     QC.testProperty "difference (add i d) i == d (add handles negative durations)" prop_addDifferenceRoundTrip
    ,QC.testProperty "add (minus i d) d == i (minus is the inverse of add)" prop_minusAddRoundTrip
  ]

unitTests :: TestTree
unitTests = testGroup "Unit tests"
  [
     testCase "test_fromSecondsSinceUnixEpoch" test_fromSecondsSinceUnixEpoch
    ,testCase "test_instantDate" test_instantDate
    ,testCase "test_instantRoundTrip" test_instantRoundTrip
    ,testCase "test_instantCrossCalendar" test_instantCrossCalendar
  ]

test_fromSecondsSinceUnixEpoch :: Assertion
test_fromSecondsSinceUnixEpoch = do
  posT <- getPOSIXTime
  tz <- utc
  let
    secs = round posT
    zdt :: ZonedDateTime Gregorian
    zdt = flip fromInstant tz . fromSecondsSinceUnixEpoch $ secs
    lt = toLocalTime zdt
    utcT = posixSecondsToUTCTime posT
    (LocalTime _ tod) = utcToLocalTime (hoursToTimeZone 0) utcT
    todT = (todHour tod, todMin tod, round . todSec $ tod)
    t = (hour lt, minute lt, second lt)
    str = "time(" ++ show secs ++ "): "
  assertEqual str todT t

-- | The date (year, month, day) of an 'Instant' converted through the public 'ZonedDateTime' path (in UTC) must
--   agree with Data.Time.  This exercises the cycle-based 'Instant' -> date decode ('daysToGregorian').
test_instantDate :: Assertion
test_instantDate = do
  posT <- getPOSIXTime
  tz <- utc
  let
    secs = round posT
    zdt :: ZonedDateTime Gregorian
    zdt = flip fromInstant tz . fromSecondsSinceUnixEpoch $ secs
    utcT = posixSecondsToUTCTime posT
    (LocalTime dayGreg _) = utcToLocalTime (hoursToTimeZone 0) utcT
    (ty, tm, td) = toGregorian dayGreg
    expected = (fromIntegral ty, tm, td)
    actual = (year zdt, succ . fromEnum $ month zdt, day zdt)
    str = "date(" ++ show secs ++ "): "
  assertEqual str expected actual

-- | 'Instant' -> 'ZonedDateTime' -> 'Instant' (via 'toInstant') must round-trip exactly.  Tested in UTC and in a
--   zone with a non-zero UTC offset (so a sign error in the offset arithmetic would be caught).  A 'ZonedDateTime'
--   maps to exactly one 'Instant', so this conversion is always unambiguous (the ambiguity is on the reverse,
--   CalendarDateTime -> ZonedDateTime, direction).
test_instantRoundTrip :: Assertion
test_instantRoundTrip = mapM_ check ["UTC", euZone]
  where
    euZone = "Europe/Zurich"
    check zoneName = do
      tz <- timeZone zoneName
      let
        inst = fromSecondsSinceUnixEpoch 1700000000
        zdt :: ZonedDateTime Gregorian
        zdt = fromInstant inst tz
      assertEqual ("Instant -> ZonedDateTime -> Instant round-trips in " ++ zoneName) inst (toInstant zdt)

-- | The SAME 'Instant' decoded into two different calendars must land on the same absolute day: its Gregorian and
--   Julian labels must each match Data.Time, and both 'ZonedDateTime's must convert back (via 'toInstant') to the
--   original 'Instant'.  This locks in the Julian epoch alignment \- Julian must be 13 days behind Gregorian in the
--   modern era, not identical to it.
test_instantCrossCalendar :: Assertion
test_instantCrossCalendar = do
  tz <- utc
  let
    inst = fromSecondsSinceUnixEpoch 1592352000     -- 2020-06-17T00:00:00Z
    zdtG :: ZonedDateTime Gregorian
    zdtG = fromInstant inst tz
    zdtJ :: ZonedDateTime Julian
    zdtJ = fromInstant inst tz
    utcT = posixSecondsToUTCTime 1592352000
    (LocalTime dayGreg _) = utcToLocalTime (hoursToTimeZone 0) utcT
    (gy, gm, gd) = toGregorian dayGreg
    (jy, jm, jd) = toJulian dayGreg
    actualG = (year zdtG, succ . fromEnum $ month zdtG, day zdtG)
    actualJ = (year zdtJ, succ . fromEnum $ month zdtJ, day zdtJ)
  assertEqual "Gregorian date" (fromIntegral gy, gm, gd) actualG
  assertEqual "Julian date (13 days behind Gregorian in 2020)" (fromIntegral jy, jm, jd) actualJ
  assertEqual "Gregorian round-trips to the same Instant" inst (toInstant zdtG)
  assertEqual "Julian round-trips to the same Instant" inst (toInstant zdtJ)

-- | Adding a 'Duration' and then taking the 'difference' back out must return the original 'Duration', for any
--   duration including negative ones.  This locks in that 'add' handles negative durations (i.e. it is not limited
--   to future instants).
prop_addDifferenceRoundTrip :: Int -> Int -> Int -> Bool
prop_addDifferenceRoundTrip base s ns = difference (add i d) i == d
  where (i, d) = instantAndDuration base s ns

-- | 'minus' is the exact inverse of 'add': shifting an 'Instant' back by a 'Duration' and then forward again by the
--   same 'Duration' returns the original 'Instant', for any duration including negative ones.
prop_minusAddRoundTrip :: Int -> Int -> Int -> Bool
prop_minusAddRoundTrip base s ns = add (minus i d) d == i
  where (i, d) = instantAndDuration base s ns

-- | Build an 'Instant' / 'Duration' pair from raw generated 'Int's, bounding the magnitudes so the (Int32) day
--   field cannot overflow while still exercising the full sign range (negative seconds and nanoseconds included).
instantAndDuration :: Int -> Int -> Int -> (Instant, D.Duration)
instantAndDuration base s ns = (i, d)
  where
    i = fromSecondsSinceUnixEpoch (base `rem` secBound)
    d = D.fromSeconds (s `rem` secBound) `D.add` D.fromNanoseconds (ns `rem` nsBound)
    secBound = 100000000000
    nsBound  = 1000000000000