module Exercise01 where

import Test.QuickCheck

{-H1.1a)-}
myPair :: Integer -> Integer -> Integer
myPair x y | x >= 0 && y >= 0 = 2 ^ y * (2 * x + 1) - 1

{-H1.1b)-}
mySnd :: Integer -> Integer
mySnd p | p >= 0 && even (p + 1) = mySnd (div (p + 1) 2 - 1) + 1 
        | p >= 0 && odd (p + 1) = 0

{-H1.1c)-}
myFst :: Integer -> Integer
myFst p | p >= 0 = div (div (p + 1) (2 ^ mySnd p) - 1) 2

{-H1.1d)-}
prop_myPair :: Integer -> Integer -> Integer -> Property
prop_myPair p x y = 
    p >= 0 && x >= 0 && y >= 0 ==> p == myPair x y

{-H2-}
digitToEo :: Integer -> String
digitToEo 0 = "nul"
digitToEo 1 = "unu"
digitToEo 2 = "du"
digitToEo 3 = "tri"
digitToEo 4 = "kvar"
digitToEo 5 = "kvin"
digitToEo 6 = "ses"
digitToEo 7 = "sep"
digitToEo 8 = "ok"
digitToEo 9 = "nau"

{-WETT-}
numberToEo :: Integer -> String
numberToEo 0 = "nul"
numberToEo n = number n 0

number :: Integer -> Integer -> String
number n x  
    | x == 0 = number d0 1 ++ printIf (printIf " " d0 ++ digitToEo m0) m0 
    | x == 1 = number d0 2 ++ printIf (printIf " " d0 ++ printIf (digitToEo m0) (m0 - 1) ++ "dek") m0
    | x == 2 = (if d0 > 0 then number d0 3 else "") ++ printIf (printIf " " d0 ++ printIf (digitToEo m0) (m0 - 1)  ++ "cent") m0
    | x == 3 = number d000 6 ++ printIf (printIf " " d000 ++ printIf (number m000 0 ++ " ") (m000 - 1) ++ "mil") m000
    | x < 64 = number d000 (x + 3) ++ printIf (printIf " " d000 ++ number m000 0 ++ " " ++ ending x ++ printIf "j" (m000 - 1)) m000
    | otherwise = ""
    where   d0 = div n 10
            m0 = mod n 10
            d000 = div n 1000
            m000 = mod n 1000

ending :: Integer -> String
ending x 
    | x == 6 = "miliono"
    | x == 9 = "miliardo"
    | mod x 6 == 0 = number (div x 6) 0 ++ "iliono"
    | otherwise = number (div (x - 3) 6) 0 ++ "iliardo"

printIf :: String -> Integer -> String
printIf s c = if c > 0 then s else ""

{-TTEW-}