module Cache (newInMemory, start, CacheM, getInbox) where

import Control.Concurrent.STM
  ( TVar
  , atomically
  , newTVarIO
  , readTVar
  , readTVarIO
  , writeTVar
  )
import Intro
import qualified Mail as M
import qualified Queue as Q

data Cache = Cache
  { count :: Int
  , inbox :: [M.Mail]
  }

type CacheM = TVar Cache

newInMemory :: IO CacheM
newInMemory = newTVarIO newCache

start :: Q.QueueM M.Mail -> CacheM -> IO ()
start queue cache = go
 where
  go :: IO ()
  go = do
    mail <- Q.pull queue
    updateCache cache (`addMail` mail)
    go

getInbox :: CacheM -> IO [M.Mail]
getInbox c = inbox <$> readTVarIO c

newCache :: Cache
newCache = Cache 0 []

addMail :: Cache -> M.Mail -> Cache
addMail cache mail = cache{count = count cache + 1, inbox = mail : inbox cache}

updateCache :: CacheM -> (Cache -> Cache) -> IO ()
updateCache c f = atomically $ do
  cache <- readTVar c
  writeTVar c (f cache)