{-# LANGUAGE OverloadedStrings, LambdaCase #-}

module BangState (
    BangState,
    initBangState,
    getBangsJSON,
    getBangsBrotli,
    addBang,
) where

import Codec.Compression.Brotli (compress)
import Control.Concurrent.STM.TChan
import Control.Monad (forever)
import Data.Aeson
import Data.ByteString (ByteString, toStrict, empty)
import Data.Text (Text)
import GHC.Conc
import Network.HTTP.Simple (Response, httpJSON, getResponseBody)
import System.AtomicWrite.Writer.LazyByteString (atomicWriteFile)

import Bangs

data BangState = BangState {
    ownBangs :: TVar Bangs,
    ddgBangs :: TVar Bangs,
    serializedBangs :: TVar ByteString,
    brotliBangs :: TVar ByteString,
    syncFileNotifications :: TChan ()
}

reserialize :: BangState -> STM ()
reserialize s = do
    own <- readTVar $ ownBangs s
    ddg <- readTVar $ ddgBangs s

    let jsonBs = encode $ own <> ddg -- left biased union
    writeTVar (serializedBangs s) $ toStrict $ jsonBs
    writeTVar (brotliBangs s)     $ toStrict $ compress jsonBs
    writeTChan (syncFileNotifications s) ()

-- spawns a thread for syncing the current state to disk. do *NOT* use forkIO on this
-- function, it does so internally, and using forkIO may result in a (hard to trigger)
-- race condition
spawnFileSyncThread :: BangState -> IO ()
spawnFileSyncThread s = do
    readableChan <- atomically $ dupTChan (syncFileNotifications s)

    _ <- forkIO $ forever $ do
        nextBangs <- atomically $ do
            readTChan readableChan
            readTVar (ownBangs s)
        atomicWriteFile "bangs.json" $ encode nextBangs

    atomically $ reserialize s

loadOwnBangs :: IO Bangs
loadOwnBangs = eitherDecodeFileStrict "bangs.json" >>= \case
    Left e -> error e
    Right b -> return b

-- also spawns a thread for disk synchronization
initBangState :: IO BangState
initBangState = do
    ans <- (httpJSON "https://duckduckgo.com/bang.v255.js") :: IO (Response DDGBangs)
    s <- BangState
        <$> (loadOwnBangs >>= newTVarIO)
        <*> newTVarIO (toBangs $ getResponseBody ans)
        <*> newTVarIO empty -- initially filled in by 'spawnFileSyncThread'
        <*> newTVarIO empty -- same as above
        <*> newBroadcastTChanIO

    spawnFileSyncThread s
    return s

getBangsJSON :: BangState -> IO ByteString
getBangsJSON s = readTVarIO $ serializedBangs s

getBangsBrotli :: BangState -> IO ByteString
getBangsBrotli s = readTVarIO $ brotliBangs s

addBang :: Text -> Text -> BangState -> IO ()
addBang bang url s = error "TODO"