Guitar.hs

-- cf. Haskore/Guitar
module Sound.MIDI.ALSA.Guitar where

import qualified Sound.MIDI.ALSA.Common as Common
import Sound.MIDI.Message.Channel.Voice (Pitch, toPitch, fromPitch, )
import Data.Maybe (mapMaybe, )


class Transpose pitch where
   getPitch :: pitch -> Int
   transpose :: Int -> pitch -> Maybe pitch

instance Transpose Pitch where
   getPitch = fromPitch
   transpose = Common.increasePitch


mapChordToString ::
   (Transpose pitch, Ord pitch) =>
   [Pitch] -> [pitch] -> [pitch]
mapChordToString strings chord =
   mapMaybe (choosePitchForString chord) strings

choosePitchForString ::
   (Transpose pitch, Ord pitch) =>
   [pitch] -> Pitch -> Maybe pitch
choosePitchForString chord string =
   let roundDown x d = x - mod x d
       minAbove x =
          transpose
             (- roundDown (getPitch x - fromPitch string) 12) x
   in  maximum (map minAbove chord)

stringPitches :: [Pitch]
stringPitches =
   reverse $ map toPitch [40, 45, 50, 55, 59, 64]
--   reverse [(-2,E), (-2,A), (-1,D), (-1,G), (-1,B), (0,E)]