module Pai where

import Data.Char (toUpper)
import Data.List (sort)
import Data.Maybe
import Control.Monad

data MCol = Man | Pin | Sou | Cha
    deriving (Eq,Ord)
data MCard = MCard MCol Int
    deriving (Eq,Ord)

charMcol = [(Man,'M'),(Pin,'P'),(Sou,'S'),(Cha,'C')]
instance Show MCol where
    show x = [snd a | a <-charMcol, fst a == x]

instance Read MCol where
    readsPrec p r = [(fst a,t)|(c,t) <- lex r, a <- charMcol, map toUpper c == [snd a]]

instance Show MCard where
    show (MCard a b) = show b ++ show a

instance Read MCard where
    readsPrec p r = [ (MCard col n,u) | (c1,t)<- lex r, 
                                        let n = (read c1)::Int, 
                                        (c2,u) <-lex t, 
                                        let col=(read c2)::MCol]

isCha c@(MCard col n) = (col == Cha)
isLaoTou c@(MCard col n) = ((n == 1) || (n == 9)) && (not $ isCha c)
is19 c@(MCard col n) = (isCha c) || (isLaoTou c)

orderedPai = sort $ [MCard c n | c<-[Man,Pin,Sou], n <-[1..9]] ++ (map (MCard Cha) [1..7])

nextPai p = if xs /= [] then Just $ head xs
            else Nothing
    where (x:xs) = dropWhile (/= p) orderedPai

nextPai' p@(MCard c n) = do
    nx <- nextPai p
    guard ((c /= Cha) && (n /= 9))
    return nx