{-# LANGUAGE GeneralizedNewtypeDeriving, TypeSynonymInstances #-}
module Hranker.Rank
( highestRank
, indexToRank
, Rank
, rankToIndex
) where

import Control.Arrow (first)

newtype Rank = Rank { getRank :: Int } deriving (Enum, Eq, Ord)

instance Read Rank where
    -- Although this may look complicated, all it does is delegates to Read for Int and then converts the result
    readsPrec i = fmap (first Rank) . readsPrec i

instance Show Rank where
    show = show . getRank

-- | The highest possible rank. Ranks count upwards from this rank.
highestRank :: Rank
highestRank = Rank 1

-- | Convert a rank to a zero-based position in the list
rankToIndex :: Rank -> Int
rankToIndex r = getRank r - getRank highestRank

-- | Inverse function of rankToIndex
indexToRank :: Int -> Rank
indexToRank = Rank . (+ getRank highestRank)