{-# LANGUAGE OverloadedStrings, LambdaCase #-}

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

import Codec.Compression.Brotli (compress)
import Control.Applicative ((<|>))
import Control.Concurrent.STM.TChan
import Control.Monad (forever)
import Crypto.Hash (hashlazy, Digest, SHA512)
import Data.Aeson
import Data.ByteArray.Encoding (convertToBase, Base(Base64))
import Data.ByteString (ByteString, toStrict, empty, take)
import Data.Text (Text)
import Data.Text.Encoding (decodeASCII)
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,
    serializedHash :: TVar Text,
    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
    -- hash: for now, base64 of the first 120 bits of the SHA512 of the bangs
    writeTVar (serializedHash s)  $ decodeASCII $ Data.ByteString.take 20
        $ convertToBase Base64 $ (hashlazy jsonBs :: Digest SHA512)
    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" <|> return (Left "") >>= \case
    Left _ -> return mempty
    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
        <*> newTVarIO ""    -- 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 -> Text -> BangState -> IO ()
addBang _ _ _ _ = error $ "TODO"

getBangsHash :: BangState -> IO Text
getBangsHash s = readTVarIO $ serializedHash s