M

anus.hs

-- | Look for player state changes over time
candidate :: Wire Error Y.MPD Int64 Change
candidate = mkStateM NotPlaying $ \_dt (t, s) ->
  Y.stState `fmap` Y.status >>= \s' -> case (s, s') of
    -- If we were not playing and are not playing now there is no candidate to send
    (NotPlaying, Y.Stopped) -> return (Left NoCandidate, NotPlaying)
    (NotPlaying, Y.Paused)  -> return (Left NoCandidate, NotPlaying)
    -- If we started playing just now there is a candidate to send
    (NotPlaying, Y.Playing) -> do
      Just song <- Y.currentSong
      return (Right (Just (fetchTrackData song & timestamp .~ t)), Playing song t)
    -- If we were playing and are not playing now we send that change
    (Playing _ _,    Y.Stopped) -> return (Right Nothing, NotPlaying)
    (Playing _ _,    Y.Paused)  -> return (Right Nothing, NotPlaying)
    -- If we were playing and are playing everything become complicated
    (Playing song ts, Y.Playing) -> do
      Just song' <- Y.currentSong
      -- If the songs are different, then new song is a candidate to send
      if song /= song' then
        return (Right (Just (fetchTrackData song' & timestamp .~ t)), Playing song' t)
      else
        -- Otherwise, if song has been played more then its duration
        -- it means that its looped, so we send it as candidate once again
        let ts' = ts + fromIntegral (Y.sgLength song)
        in if ts + fromIntegral (Y.sgLength song) < t
          then return (Right (Just (fetchTrackData song' & timestamp .~ ts')), Playing song' ts')
          -- Otherwise, there is no candidate to send
          else return (Left NoCandidate, s)