Count down cards left while asking

Cards/Card.hs

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+module Cards.Card
+  ( Tier -- Tier stuff
+  , tierDiff
+  , tierName
+  , Card -- Card stuff
+  , sides
+  , tier
+  , lastChecked
+  , offset
+  , isDue
+  , reset
+  , update
+  , createCard
+  ) where
+
+import Data.Time
+
+data Card = Card
+  { sides :: [String]
+  , tier :: Tier
+  , lastChecked :: UTCTime
+  , offset :: NominalDiffTime
+  } deriving (Show)
+
+data Tier = Unrevised
+          | TenMin | TwentyMin | FortyMin
+          | OneDay | TwoDays | FourDays | EightDays
+          | SixteenDays | ThirtyTwoDays | SixtyFourDays
+  deriving (Show, Eq, Ord, Enum, Bounded)
+
+{-
+ - Tier stuff
+ -}
+
+tierDiff :: Tier -> NominalDiffTime
+tierDiff Unrevised     = 0
+tierDiff TenMin        = 60 * 10
+tierDiff TwentyMin     = 60 * 20
+tierDiff FortyMin      = 60 * 40
+tierDiff OneDay        = 3600 * ( 1 * 24 - 8)
+tierDiff TwoDays       = 3600 * ( 2 * 24 - 8)
+tierDiff FourDays      = 3600 * ( 4 * 24 - 8)
+tierDiff EightDays     = 3600 * ( 8 * 24 - 8)
+tierDiff SixteenDays   = 3600 * (16 * 24 - 8)
+tierDiff ThirtyTwoDays = 3600 * (32 * 24 - 8)
+tierDiff SixtyFourDays = 3600 * (64 * 24 - 8)
+
+tierName :: Tier -> String
+tierName Unrevised     = "unrevised"
+tierName TenMin        = "10min"
+tierName TwentyMin     = "20min"
+tierName FortyMin      = "40min"
+tierName OneDay        =  "1d"
+tierName TwoDays       =  "2d"
+tierName FourDays      =  "4d"
+tierName EightDays     =  "8d"
+tierName SixteenDays   = "16d"
+tierName ThirtyTwoDays = "32d"
+tierName SixtyFourDays = "64d"
+
+{-
+ - Card stuff
+ -}
+
+isDue :: UTCTime -> Card -> Bool
+isDue time Card{tier=t, lastChecked=lc, offset=o} =
+  diffUTCTime time lc >= o + tierDiff t
+
+-- These functions use the IO monad for generating random offsets.
+-- TODO: actually implement random offset
+updateOffset :: Card -> IO Card
+updateOffset Card{sides=s, tier=t, lastChecked=lc} = do
+  return Card{sides=s, tier=t, lastChecked=lc, offset=0}
+
+reset :: UTCTime -> Card -> Card
+reset time Card{sides=s} =
+  Card{sides=s, tier=minBound, lastChecked=time, offset=0}
+
+update :: UTCTime -> Card -> IO Card
+update time Card{sides=s, tier=t} =
+  updateOffset $ Card {sides=s, tier=boundedSucc t, lastChecked=time, offset=0}
+
+-- helper function
+boundedSucc :: (Eq a, Bounded a, Enum a) => a -> a
+boundedSucc a
+  | a == maxBound = a
+  | otherwise     = succ a
+
+createCard :: UTCTime -> [String] -> Card
+createCard time s =
+  Card{sides=s, tier=minBound, lastChecked=time, offset=0}
+
+{-
+ - Parsing Cards
+ -}
+
+-- TODO