-- | Module containing ratelimit stuff
module Calamity.HTTP.Internal.Ratelimit (
    newRateLimitState,
    doRequest,
) where

import Calamity.Client.Types (BotC)
import Calamity.HTTP.Internal.Route
import Calamity.HTTP.Internal.Types
import Calamity.Internal.Utils
import Control.Applicative
import Control.Concurrent
import Control.Concurrent.Event (Event)
import qualified Control.Concurrent.Event as E
import Control.Concurrent.STM
import qualified Control.Exception.Safe as Ex
import Control.Lens
import Control.Monad
import Data.Aeson
import Data.Aeson.Lens
import qualified Data.ByteString as B
import qualified Data.ByteString.Lazy as LB
import Data.Maybe
import qualified Data.Text.Lazy as LT
import Data.Time
import Data.Time.Clock.POSIX
import Network.HTTP.Client (responseStatus)
import Network.HTTP.Req
import Network.HTTP.Types
import Polysemy (Sem)
import qualified Polysemy as P
import PyF
import qualified StmContainers.Map as SC
import Prelude hiding (error)
import qualified Prelude

newRateLimitState :: IO RateLimitState
newRateLimitState = RateLimitState <$> SC.newIO <*> SC.newIO <*> E.newSet

data Ratelimit
  = KnownRatelimit Bucket
  | UnknownRatelimit RouteKey

getRateLimit :: RateLimitState -> RouteKey -> STM Ratelimit
getRateLimit s h = do
  bucketKey <- SC.lookup h $ bucketKeys s
  bucket <- join <$> sequenceA (flip SC.lookup (buckets s) <$> bucketKey)
  case bucket of
    Just bucket' ->
      pure $ KnownRatelimit bucket'
    Nothing ->
      pure $ UnknownRatelimit h

{- | Knowing the bucket for a route, and the ratelimit info, map the route to
 the bucket key and retrieve the bucket
-}
updateBucket :: RateLimitState -> RouteKey -> B.ByteString -> BucketState -> STM Bucket
updateBucket s h b bucketState = do
  bucketKey <- SC.lookup h $ bucketKeys s
  case bucketKey of
    Just bucketKey' -> do
      -- if we know the bucket key here, then the bucket has already been made
      -- if the given bucket key is different than the known bucket key then oops
      bucket <- SC.lookup bucketKey' $ buckets s
      case bucket of
        Just bucket' -> do
          modifyTVar' (bucket' ^. #state) (`mergeStates` bucketState)
          pure bucket'
        Nothing -> Prelude.error "Not possible"
    Nothing -> do
      -- the bucket key wasn't known, make a new bucket and insert it
      bs <- Bucket <$> newTVar bucketState
      SC.insert bs b $ buckets s
      SC.insert b h $ bucketKeys s
      pure bs
 where
  mergeStates :: BucketState -> BucketState -> BucketState
  mergeStates old new =
    new
      { ongoing = old ^. #ongoing
      , -- we only ignore the previous 'remaining' if we've not reset yet and the
        -- reset time has changed
        remaining =
          if isJust (old ^. #resetTime) && (old ^. #resetKey /= new ^. #resetKey)
            then min (old ^. #remaining) (new ^. #remaining)
            else new ^. #remaining
      , -- only take the new resetTime if it actually changed
        resetTime =
          if old ^. #resetKey /= new ^. #resetKey
            then new ^. #resetTime
            else old ^. #resetTime
      }

resetBucket :: Bucket -> STM ()
resetBucket bucket =
  modifyTVar'
    (bucket ^. #state)
    ( \bs ->
        bs & #remaining .~ bs ^. #limit
          & #resetTime .~ Nothing
    )

canResetBucketNow :: UTCTime -> BucketState -> Bool
canResetBucketNow _ BucketState{ongoing} | ongoing > 0 = False
-- don't allow resetting the bucket if there's ongoing requests, we'll wait
-- until another request finishes and updates the counter
canResetBucketNow now bs = case bs ^. #resetTime of
  Just rt -> now > rt
  Nothing -> False

-- canResetBucket :: BucketState -> Bool
-- canResetBucket bs = isNothing $ bs ^. #startedWaitingTime

shouldWaitForUnlock :: BucketState -> Bool
shouldWaitForUnlock BucketState{remaining = 0, ongoing} = ongoing > 0
shouldWaitForUnlock _ = False

data WaitDelay
  = WaitUntil UTCTime
  | WaitRetrySoon
  | GoNow
  deriving (Show)

intoWaitDelay :: Maybe UTCTime -> WaitDelay
intoWaitDelay (Just t) = WaitUntil t
intoWaitDelay Nothing = WaitRetrySoon

-- | Maybe wait for a bucket, updating its state to say we used it
useBucketOnce :: Bucket -> IO ()
useBucketOnce bucket = go 0
 where
  go :: Int -> IO ()
  go tries = do
    now <- getCurrentTime
    mWaitDelay <- atomically $ do
      s <- readTVar $ bucket ^. #state

      -- -- [0]
      -- -- if there are ongoing requests, wait for them to finish and deliver
      -- -- truth on the current ratelimit state
      when
        (shouldWaitForUnlock s)
        retry

      -- if there are no ongoing requests, and the bucket reset time has lapsed,
      -- we can just reset the bucket.
      --
      -- if we've already reset the bucket then there should be an ongoing
      -- request so we'll just end up waiting for that to finish
      when
        (canResetBucketNow now s)
        (resetBucket bucket)

      s <- readTVar $ bucket ^. #state

      if s ^. #remaining - s ^. #ongoing > 0
        then do
          -- there are tokens remaining for us to use
          modifyTVar'
            (bucket ^. #state)
            ( (#remaining -~ 1)
                . (#ongoing +~ 1)
            )
          pure GoNow
        else do
          -- the bucket has expired, there are no ongoing requests because of
          -- [0] wait and then retry after we can unlock the bucket
          pure (intoWaitDelay $ s ^. #resetTime)

    -- putStrLn (show now <> ": Using bucket, waiting until: " <> show mWaitDelay <> ", uses: " <> show s <> ", " <> inf)

    case mWaitDelay of
      WaitUntil waitUntil -> do
        if waitUntil < now
          then threadDelayMS 20
          else -- if the reset is in the past, we're fucked
            threadDelayUntil waitUntil
        -- if we needed to sleep, go again so that multiple concurrent requests
        -- don't exceed the bucket, to ensure we don't sit in a loop if a
        -- request dies on us, bail out after 50 loops
        if tries < 50
          then go (tries + 1)
          else pure () -- print "bailing after number of retries"
      WaitRetrySoon -> do
        threadDelayMS 20
        if tries < 50
          then go (tries + 1)
          else pure () -- print "bailing after number of retries"
      GoNow -> do
        -- print "ok going forward with request"
        pure ()

doDiscordRequest :: BotC r => IO LbsResponse -> Sem r DiscordResponseType
doDiscordRequest r = do
  r'' <- P.embed $ Ex.catchAny (Right <$> r) (pure . Left . Ex.displayException)
  case r'' of
    Right r' -> do
      let status = responseStatus . toVanillaResponse $ r'
      if
          | statusIsSuccessful status -> do
            let resp = responseBody r'
            debug [fmt|Got good response from discord: {status:s}|]
            now <- P.embed getCurrentTime
            let rlHeaders = buildBucketState now r'
            pure $ Good resp rlHeaders
          | status == status429 -> do
            now <- P.embed getCurrentTime
            let resp = responseBody r'
            case (resp ^? _Value, buildBucketState now r') of
              (Just !rv, bs) ->
                pure $ Ratelimited (parseRetryAfter now rv) (isGlobal rv) bs
              _ ->
                pure $ ServerError (statusCode status)
          | statusIsClientError status -> do
            let err = responseBody r'
            error [fmt|Something went wrong: {err:s}, response: {r':s}|]
            pure $ ClientError (statusCode status) err
          | otherwise -> do
            debug [fmt|Got server error from discord: {statusCode status}|]
            pure $ ServerError (statusCode status)
    Left e -> do
      error [fmt|Something went wrong with the http client: {e}|]
      pure . InternalResponseError $ LT.pack e

-- | Parse a ratelimit header returning when it unlocks
parseRateLimitHeader :: HttpResponse r => UTCTime -> r -> Maybe UTCTime
parseRateLimitHeader now r = computedEnd <|> end
 where
  computedEnd :: Maybe UTCTime
  computedEnd = flip addUTCTime now <$> resetAfter

  resetAfter :: Maybe NominalDiffTime
  resetAfter = realToFrac <$> responseHeader r "X-Ratelimit-Reset-After" ^? _Just . _Double

  end :: Maybe UTCTime
  end =
    posixSecondsToUTCTime . realToFrac
      <$> responseHeader r "X-Ratelimit-Reset" ^? _Just . _Double

buildBucketState :: HttpResponse r => UTCTime -> r -> Maybe (BucketState, B.ByteString)
buildBucketState now r = (,) <$> bs <*> bucketKey
 where
  remaining = responseHeader r "X-RateLimit-Remaining" ^? _Just . _Integral
  limit = responseHeader r "X-RateLimit-Limit" ^? _Just . _Integral
  resetKey = ceiling <$> responseHeader r "X-RateLimit-Reset" ^? _Just . _Double
  resetTime = parseRateLimitHeader now r
  bs = BucketState resetTime <$> resetKey <*> remaining <*> limit <*> pure 0
  bucketKey = responseHeader r "X-RateLimit-Bucket"

-- | Parse the retry after field, returning when to retry
parseRetryAfter :: UTCTime -> Value -> UTCTime
parseRetryAfter now r = addUTCTime retryAfter now
 where
  retryAfter = realToFrac $ r ^?! key "retry_after" . _Double

isGlobal :: Value -> Bool
isGlobal r = r ^? key "global" . _Bool == Just True

-- Either (Either a a) b
data ShouldRetry a b
  = Retry a
  | RFail a
  | RGood b

retryRequest ::
  BotC r =>
  -- | number of retries
  Int ->
  -- | action to perform
  Sem r (ShouldRetry a b) ->
  Sem r (Either a b)
retryRequest maxRetries action = retryInner 0
 where
  retryInner numRetries = do
    res <- action
    case res of
      Retry r | numRetries > maxRetries -> do
        debug [fmt|Request failed after {maxRetries} retries|]
        pure $ Left r
      Retry _ ->
        retryInner (numRetries + 1)
      RFail r -> do
        debug "Request failed due to error response"
        pure $ Left r
      RGood r ->
        pure $ Right r

threadDelayMS :: Int -> IO ()
threadDelayMS ms = threadDelay (1000 * ms)

tenMS :: NominalDiffTime
tenMS = 0.01

threadDelayUntil :: UTCTime -> IO ()
threadDelayUntil when = do
  let when' = addUTCTime tenMS when -- lol
  now <- getCurrentTime
  let msUntil = ceiling . (* 1000) . realToFrac @_ @Double $ diffUTCTime when' now
  threadDelayMS msUntil

-- Run a single request
doSingleRequest ::
  BotC r =>
  RateLimitState ->
  Route ->
  -- | Global lock
  Event ->
  -- | Request action
  IO LbsResponse ->
  Sem r (ShouldRetry RestError LB.ByteString)
doSingleRequest rlstate route gl r = do
  P.embed $ E.wait (globalLock rlstate)

  rl <- P.embed . atomically $ getRateLimit rlstate (routeKey route)

  case rl of
    KnownRatelimit bucket ->
      P.embed $ useBucketOnce bucket
    _ -> debug "unknown ratelimit"

  r' <- doDiscordRequest r

  case r' of
    Good v rlHeaders -> do
      void . P.embed . atomically $ do
        case rl of
          KnownRatelimit bucket ->
            modifyTVar' (bucket ^. #state) (#ongoing -~ 1)
          _ -> pure ()
        case rlHeaders of
          Just (bs, bk) ->
            void $ updateBucket rlstate (routeKey route) bk bs
          Nothing -> pure ()
      pure $ RGood v
    Ratelimited unlockWhen False (Just (bs, bk)) -> do
      debug [fmt|429 ratelimited on route, retrying at {unlockWhen:s}|]

      P.embed . atomically $ do
        case rl of
          KnownRatelimit bucket ->
            modifyTVar' (bucket ^. #state) (#ongoing -~ 1)
          _ -> pure ()
        void $ updateBucket rlstate (routeKey route) bk bs

      P.embed $ do
        threadDelayUntil unlockWhen

      pure $ Retry (HTTPError 429 Nothing)
    Ratelimited unlockWhen False _ -> do
      debug "Internal error (ratelimited but no headers), retrying"
      case rl of
        KnownRatelimit bucket ->
          void . P.embed . atomically $ modifyTVar' (bucket ^. #state) (#ongoing -~ 1)
        _ -> pure ()

      P.embed $ threadDelayUntil unlockWhen
      pure $ Retry (HTTPError 429 Nothing)
    Ratelimited unlockWhen True bs -> do
      debug "429 ratelimited globally"

      P.embed $ do
        atomically $ do
          case rl of
            KnownRatelimit bucket ->
              modifyTVar' (bucket ^. #state) (#ongoing -~ 1)
            _ -> pure ()
          case bs of
            Just (bs', bk) ->
              void $ updateBucket rlstate (routeKey route) bk bs'
            Nothing ->
              pure ()

        E.clear gl
        threadDelayUntil unlockWhen
        E.set gl
      pure $ Retry (HTTPError 429 Nothing)
    ServerError c -> do
      debug "Server failed, retrying"
      case rl of
        KnownRatelimit bucket ->
          P.embed $ useBucketOnce bucket
        _ -> debug "unknown ratelimit"
      pure $ Retry (HTTPError c Nothing)
    InternalResponseError c -> do
      debug "Internal error, retrying"
      case rl of
        KnownRatelimit bucket ->
          P.embed $ useBucketOnce bucket
        _ -> debug "unknown ratelimit"
      pure $ Retry (InternalClientError c)
    ClientError c v -> do
      case rl of
        KnownRatelimit bucket ->
          P.embed $ useBucketOnce bucket
        _ -> debug "unknown ratelimit"
      pure $ RFail (HTTPError c $ decode v)

doRequest :: BotC r => RateLimitState -> Route -> IO LbsResponse -> Sem r (Either RestError LB.ByteString)
doRequest rlstate route action =
  retryRequest
    5
    (doSingleRequest rlstate route (globalLock rlstate) action)