{-# LANGUAGE TupleSections #-}

-- | An intentionally-leaky StatsD interface to Datadog
--
-- $usage
--
module Freckle.App.Stats
  ( StatsSettings
  , defaultStatsSettings
  , setStatsSettingsTags
  , envParseStatsSettings

  -- * Client
  , StatsClient
  , tagsL
  , withStatsClient
  , HasStatsClient(..)

  -- * Reporting
  , tagged
  , increment
  , counter
  , gauge
  , histogram
  , histogramSince
  , histogramSinceMs
  ) where

import Freckle.App.Prelude

import Blammo.Logging
import Control.Lens (Lens', lens, view, (&), (.~), (<>~))
import Control.Monad.Reader (local)
import Data.Aeson (Value(..))
import Data.String
import Data.Time (diffUTCTime)
import Freckle.App.Ecs
import qualified Freckle.App.Env as Env
import qualified Network.StatsD.Datadog as Datadog
import Yesod.Core.Lens
import Yesod.Core.Types (HandlerData)

data StatsSettings = StatsSettings
  { amsEnabled :: Bool
  , amsSettings :: Datadog.DogStatsSettings
  , amsTags :: [(Text, Text)]
  }

defaultStatsSettings :: StatsSettings
defaultStatsSettings = StatsSettings
  { amsEnabled = False
  , amsSettings = Datadog.defaultSettings
  , amsTags = []
  }

setStatsSettingsTags :: [(Text, Text)] -> StatsSettings -> StatsSettings
setStatsSettingsTags x settings = settings { amsTags = x }

envParseStatsSettings :: Env.Parser Env.Error StatsSettings
envParseStatsSettings =
  StatsSettings
    <$> Env.switch "DOGSTATSD_ENABLED" mempty
    <*> (buildSettings
        <$> optional (Env.var Env.str "DOGSTATSD_HOST" mempty)
        <*> optional (Env.var Env.auto "DOGSTATSD_PORT" mempty)
        )
    <*> (buildTags
        <$> optional (Env.var Env.nonempty "DD_ENV" mempty)
        <*> optional (Env.var Env.nonempty "DD_SERVICE" mempty)
        <*> optional (Env.var Env.nonempty "DD_VERSION" mempty)
        <*> Env.var Env.keyValues "DOGSTATSD_TAGS" (Env.def [])
        )
 where
  buildSettings mHost mPort =
    Datadog.defaultSettings
      & maybe id (Datadog.host .~) mHost
      . maybe id (Datadog.port .~) mPort

  buildTags mEnv mService mVersion tags =
    catMaybes
        [ ("env", ) <$> mEnv
        , ("environment", ) <$> mEnv -- Legacy
        , ("service", ) <$> mService
        , ("version", ) <$> mVersion
        ]
      <> tags

data StatsClient = StatsClient
  { scClient :: Datadog.StatsClient
  , scTags :: [(Text, Text)]
  }

tagsL :: Lens' StatsClient [(Text, Text)]
tagsL = lens scTags $ \x y -> x { scTags = y }

class HasStatsClient env where
  statsClientL :: Lens' env StatsClient

instance HasStatsClient StatsClient where
  statsClientL = id

instance HasStatsClient site =>  HasStatsClient (HandlerData child site) where
  statsClientL = envL . siteL . statsClientL

withStatsClient
  :: (MonadMask m, MonadUnliftIO m)
  => StatsSettings
  -> (StatsClient -> m a)
  -> m a
withStatsClient StatsSettings {..} f = do
  if amsEnabled
    then do
      tags <- (amsTags <>) <$> getEcsMetadataTags

      Datadog.withDogStatsD amsSettings $ \client ->
        -- Add the tags to the thread context so they're present in all logs
        withThreadContext (map toPair tags)
          $ f StatsClient { scClient = client, scTags = tags }
    else f $ StatsClient { scClient = Datadog.Dummy, scTags = amsTags }
  where toPair = bimap (fromString . unpack) String

-- | Include the given tags on all metrics emitted from a block
tagged
  :: (MonadReader env m, HasStatsClient env) => [(Text, Text)] -> m a -> m a
tagged tags = local $ statsClientL . tagsL <>~ tags

-- | Synonym for @'counter' 1@
increment
  :: (MonadUnliftIO m, MonadReader env m, HasStatsClient env) => Text -> m ()
increment name = counter name 1

counter
  :: (MonadUnliftIO m, MonadReader env m, HasStatsClient env)
  => Text
  -> Int
  -> m ()
counter = sendMetric Datadog.Counter

gauge
  :: (MonadUnliftIO m, MonadReader env m, HasStatsClient env)
  => Text
  -> Double
  -> m ()
gauge = sendMetric Datadog.Gauge

-- | Emit an elapsed duration (which Datadog calls a /histogram/)
--
-- The 'ToMetricValue' constraint can be satisfied by most numeric types and is
-- assumed to be seconds.
--
histogram
  :: ( MonadUnliftIO m
     , MonadReader env m
     , HasStatsClient env
     , Datadog.ToMetricValue n
     )
  => Text
  -> n
  -> m ()
histogram = sendMetric Datadog.Histogram

histogramSince
  :: (MonadUnliftIO m, MonadReader env m, HasStatsClient env)
  => Text
  -> UTCTime
  -> m ()
histogramSince = histogramSinceBy toSeconds where toSeconds = round @_ @Int

histogramSinceMs
  :: (MonadUnliftIO m, MonadReader env m, HasStatsClient env)
  => Text
  -> UTCTime
  -> m ()
histogramSinceMs = histogramSinceBy toMilliseconds
  where toMilliseconds = (* 1000) . realToFrac @_ @Double

histogramSinceBy
  :: ( MonadUnliftIO m
     , MonadReader env m
     , HasStatsClient env
     , Datadog.ToMetricValue n
     )
  => (NominalDiffTime -> n)
  -> Text
  -> UTCTime
  -> m ()
histogramSinceBy f name time = do
  now <- liftIO getCurrentTime
  let delta = f $ now `diffUTCTime` time
  sendMetric Datadog.Histogram name delta

sendMetric
  :: ( MonadUnliftIO m
     , MonadReader env m
     , HasStatsClient env
     , Datadog.ToMetricValue v
     )
  => Datadog.MetricType
  -> Text
  -> v
  -> m ()
sendMetric metricType name metricValue = do
  StatsClient {..} <- view statsClientL

  Datadog.send scClient
    $ Datadog.metric (Datadog.MetricName name) metricType metricValue
    & (Datadog.tags .~ map (uncurry Datadog.tag) scTags)

getEcsMetadataTags :: MonadIO m => m [(Text, Text)]
getEcsMetadataTags = maybe [] toTags <$> getEcsMetadata
 where
  toTags (EcsMetadata EcsContainerMetadata {..} EcsContainerTaskMetadata {..})
    = [ ("container_id", ecmDockerId)
      , ("container_name", ecmDockerName)
      , ("docker_image", ecmImage)
      , ("image_tag", ecmImageID)
      , ("cluster_name", ectmCluster)
      , ("task_arn", ectmTaskARN)
      , ("task_family", ectmFamily)
      , ("task_version", ectmRevision)
      ]

-- $usage
-- Usage:
--
-- - Use 'envParseStatsSettings' to configure things
--
--   @
--   data AppSettings = AppSettings
--    { -- ...
--    , appStatsSettings :: StatsSettings
--    }
--
--   loadSettings :: IO AppSettings
--   loadSettings = Env.parse id $ AppSettings
--     <$> -- ...
--     <*> 'envParseStatsSettings'
--   @
--
--   This will read,
--
--   - @DOGSTATSD_ENABLED=x@
--   - @DOGSTATSD_HOST=127.0.0.1@
--   - @DOGSTATSD_PORT=8125@
--   - @DOGSTATSD_TAGS=[<key>:<value>,...]@
--   - Optionally @DD_ENV@, @DD_SERVICE@, and @DD_VERSION@
--
-- - Give your @App@ a 'HasStatsClient' instance
--
--   @
--   data App = App
--     { -- ...
--     , appStatsClient :: 'StatsClient'
--     }
--
--   instance 'HasStatsClient' App where
--     'statsClientL' = lens appStatsClient $ \x y -> { appStatsClient = y }
--   @
--
-- - Use 'withStatsClient' to build and store a client on your @App@ when you
--   run it
--
--   @
--   'withStatsClient' appStatsSettings $ \client -> do
--     app <- App
--       <$> ...
--       <*> pure client
--
--     'runApp' app $ ...
--   @
--
-- - Throughout your application code, emit metrics as desired
--
--   @
--   import qualified Freckle.App.Stats as Stats
--
--   myFunction :: (MonadIO m, MonadReader env m, 'HasStatsClient' env) => m ()
--   myFunction = do
--     start <- liftIO getCurrentTime
--     result <- myAction
--
--     Stats.'increment' \"action.attempt\"
--     Stats.'histogramSinceMs' \"action.duration\" start
--
--     case result of
--       Left err -> do
--         Stats.'increment' \"action.failure\"
--         -- ...
--       Right x -. do
--         Stats.'increment' \"action.success\"
--         -- ...
--   @
--