Calculates a diagram of average usage per day from timestamp/value pairs

year_average.hs

import qualified Data.ByteString.Char8 as C8
import Data.UnixTime

csvTableToTuple :: String -> (Int, Int)
csvTableToTuple line =
        let date = takeWhile (/= ';') line
            val = tail $ dropWhile (/= ';') line
        in (fromEnum (utSeconds (parseUnixTime (C8.pack "%Y-%m-%d") (C8.pack date))), read val)

secondsInDay :: Int
secondsInDay = 60 * 60 * 24

valDiff :: (Int, Int) -> (Int, Int) -> (Int, Int)
valDiff (a,b) (c,d) =
        let dd = (a-c) `div` secondsInDay
        in
        (dd,(b-d) `div` dd)

outputM :: Int -> Int -> Int -> IO()
outputM _ 0 _ = return()
outputM act repeat diff = do
        putStrLn $ (show ts) ++ ", " ++ (show diff)
        outputM ts (repeat - 1) diff
        where ts = act + secondsInDay

perDay :: (Int, Int) -> [ (Int, Int) ] -> IO()
perDay _ [] = return ()
perDay last remain = do 
        let next = head remain
            (days, diffv) = valDiff next last
        outputM (fst last) days diffv
        perDay next (tail remain)

main = do 
        l <- fmap lines getContents 
        let dat = map csvTableToTuple l
        perDay (head dat) (tail dat)
        return ()