module Exercise01 where

import Test.QuickCheck

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

{-H1.1b)-}
mySnd :: Integer -> Integer
mySnd z
    | mod z 2 == 1    = 1 + mySnd ((z - 1) `div` 2)
    | otherwise       = 0

{-H1.1c)-}
myFst :: Integer -> Integer
myFst z
    | mod z 2 == 1    = myFst ((z - 1) `div` 2)
    | otherwise       = z `div` 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-}
digToEo :: Integer -> String
digToEo 0 = ""
digToEo 10 = " dek"
digToEo n = " " ++ digitToEo n

digToEoOne :: Integer -> String
digToEoOne 1 = " "
digToEoOne n = digToEo n

numberToEo :: Integer -> String
numberToEo 0 = "nul"
numberToEo n = tail $ helper n 0

helper :: Integer -> Integer -> String
helper 0 _ = ""
helper n e = div n 1000 `helper` (e+1) ++ mod n 1000 `trippletToEo` e

trippletToEo :: Integer -> Integer -> String
trippletToEo 0 _            = ""
trippletToEo 1 1            = " mil"
trippletToEo n exponent     = hundretsToEo n 0 ++ suffix n exponent

hundretsToEo :: Integer -> Integer -> String
hundretsToEo 0 _    = ""
hundretsToEo n e    
    | e==0              = rest ++ digToEo digit
    | digit /= 0        = rest ++ digToEoOne digit ++ hundretsSuffix e
    | otherwise         = rest
    where rest = div n 10 `hundretsToEo` (e+1)
          digit = n `mod` 10

hundretsSuffix :: Integer -> String
hundretsSuffix 1 = "dek"
hundretsSuffix 2 = "cent"

suffix :: Integer -> Integer -> String
suffix n 0     = ""
suffix n 1     = " mil"
suffix 1 e = suffixBig e
suffix n e = suffixBig e ++ "j"

suffixBig :: Integer -> String
suffixBig 2 = " miliono"
suffixBig 3 = " miliardo"
suffixBig e
    | even e            = prefix ++ "iliono"
    | otherwise         = prefix ++ "iliardo"
    where prefix = digToEo $ div e 2
{-TTEW-}