bpm.hs

module Main where

import Data.Time.Clock.POSIX
import System.IO

avgNum :: Int
avgNum = 4

main :: IO ()
main = do
  putStrLn "Tap to the beat of a song to determine its BPM."
  hSetEcho stdin False
  hSetBuffering stdin NoBuffering
  loop [1]

average :: (Foldable t, Integral a, Show a) => t a -> a
average n = sum n `div` fromIntegral (length n)

diff :: Num t => [t] -> [t]
diff [] = []
diff ls = zipWith (flip (-)) (tail ls) ls

loop :: [Integer] -> IO a
loop lst = do
  getChar
  t <- getPOSIXTime
  let lastFew = round (t * 1000) : take avgNum lst
  let avg = average (diff lastFew)
  print (60000 `div` if avg > 0 then avg else 1)
  loop lastFew