{-# LANGUAGE OverloadedStrings, DeriveGeneric #-}

-- https://www.schoolofhaskell.com/school/starting-with-haskell/libraries-and-frameworks/text-manipulation/json

module GMPDP where

import Data.Aeson
import Data.Text
import Control.Applicative
import qualified Data.ByteString.Lazy as B
import Network.HTTP.Conduit (simpleHttp)
import GHC.Generics

import Xmobar

import Control.Monad (when, guard)
import Control.Concurrent.STM
import Control.Exception (SomeException (..), handle, evaluate)

import System.INotify (Event(..), EventVariety(..), initINotify, addWatch)

import qualified Data.ByteString.Char8 as BS (ByteString, pack)


-- | Type of each JSON entry in record syntax.
data Song =
  Song { title :: !String
       , artist :: !String
       , album :: !String
       } deriving (Eq,Show,Generic)

data PlayTime =
  PlayTime { current :: !Int
           , total :: !Int
           } deriving (Eq,Show,Generic)

data GMPDPStatus =
  GMPDPStatus { song :: Song
              , time :: PlayTime
              } deriving (Eq,Show,Generic)

-- Instances to convert our type to/from JSON.

instance FromJSON Song
instance FromJSON PlayTime
instance FromJSON GMPDPStatus

-- | Location of the local copy, in case you have it,
--   of the JSON file.
jsonFile :: FilePath
jsonFile = "/home/jao/.config/Google Play Music Desktop Player/json_store/playback.json"

getJSON :: IO B.ByteString
getJSON = B.readFile jsonFile

getGMPDPStatus :: IO (Maybe GMPDPStatus)
getGMPDPStatus = do
    s <- (eitherDecode <$> getJSON) :: IO (Either String GMPDPStatus)
    case s of
      Left _ -> return Nothing
      Right r -> return $ Just r

newtype GMPDP = GMPDP String deriving (Show,Read,Generic)

handleNotification :: TVar (Maybe GMPDPStatus) -> Event -> IO ()
handleNotification v _ =
  getGMPDPStatus >>= \s -> atomically $ writeTVar v s

formatStatus Nothing = ""
formatStatus (Just s) =
  fmtt (current $ time s) ++ "/" ++ fmtt (total $ time s) ++
  " " ++ title (song s) ++ " <fc=sienna4>" ++ album (song s) ++ "</fc>" ++
  " " ++ artist (song s)
  where fmtt ms = let s = ms `div` 1000
                      sr x = if x < 10 then "0" ++ show x else show x
                  in sr (s `div` 60) ++ ":" ++ sr (s `mod` 60)

changeLoop :: Eq a => STM a -> (a -> IO ()) -> IO ()
changeLoop s f = atomically s >>= go
 where
    go old = do
        f old
        go =<< atomically (do
            new <- s
            guard (new /= old)
            return new)

instance Exec GMPDP where
  alias (GMPDP a) = a
  start (GMPDP _) cb = do
    i <- initINotify
    s <- getGMPDPStatus
    v <- newTVarIO s
    addWatch i [CloseWrite] (BS.pack jsonFile) (handleNotification v)
    changeLoop (readTVar v) $ \s -> cb (formatStatus s)